Thoughts on backfire?

[KILLSHOTS]

As many of you know, I just went from stock catted manifolds and straight pipes to coated OBX headers (no cats) and Corsa. Sent the PROM to Marc and he removed the DFCO. Yet, this thing is backfiring like an SOB!!! It backfires loudly on nearly every upshift. Frigging embarrassing!

Bill Boudreau data-scanned the car and it is running unusually lean on deceleration. Marc says this is common with FIC injectors and says Accel are better about this. I spent enough cash installing the new FIC and I'm not changing to Accel just to "see what happens". Marc says he can add fuel on decel but isn't sure if this will fix it.

What am I missing? Do I have an exhaust leak? And if so, can an exhaust leak really cause such raucous backfiring? Can I really be the ONLY guy running headers and Corsa without cats whose mufflers are about to blow clean off the car?

TIA!

[mike100]

two things that helped mine-
1) disable the air injection when running catless (I kept my tubes). The air injection leans the post combustion pipe mixture.
2) add catalysts to muffle the pop.

I have the FIC Lucas type injectors. Turning off DFCO worked for me, but there is the possibility of a backfire during the warm up event when the air injection pump is still running...otherwise only goes off once in a blue moon. Cats help a lot.

[Karl]

The consensus says FIC injectors are not very good. I am about to replace mine with the accell 150821 units. I do not have any backfiring but I am in need of new injectors.

When I purchased the car last year the prior owner had FIC injectors installed. I guess they didn't last long with the ethanol in todays fuel.

[XfireZ51]

I would absolutely make certain there are no exhaust leaks. Decel produces high vacuum and improper exhaust system sealing will suck fresh air into the exhaust. And it does not need to be at the collector. Could be further back and it would still cause a popping.

A few questions:

1. Did Bill note if the BLMs are leaner in one bank versus the other during decel?

2. The datalog should show the injector pulse width. Does it look like injectors are shutting off?

3. What about the O2 sensor voltages on both banks? What are they during decel? Are they different from each other?

4. Can you tell where in the exhaust the popping is happening? At the header or further downstream?

[KILLSHOTS]

I would absolutely make certain there are no exhaust leaks. Decel produces high vacuum and improper exhaust system sealing will suck fresh air into the exhaust. And it does not need to be at the collector. Could be further back and it would still cause a popping.

A few questions:

1. Did Bill note if the BLMs are leaner in one bank versus the other during decel?

2. The datalog should show the injector pulse width. Does it look like injectors are shutting off?

3. What about the O2 sensor voltages on both banks? What are they during decel? Are they different from each other?

4. Can you tell where in the exhaust the popping is happening? At the header or further downstream?
The backfiring is definitely happening at the mufflers. Marc mentioned the injectors and asked about the O2 sensors, as well. But the more I think about this, the more it seems like it must be exhaust leaks. 3 weeks ago, the car had straight pipes (except for cats) and was EXTREMELY loud. Also, the DFCO had not been disabled at that point, yet there was virtually no backfire. The injectors were changed in February, so they're not the problem. Bill drove the car thoroughly several times after install and probably would have noted loud backfiring if it was happening then, which tells me the situation is worsening over time. I'm thinking exhaust clamps are loosening with heat cycling. What do you think?

[XfireZ51]

The backfiring is definitely happening at the mufflers. Marc mentioned the injectors and asked about the O2 sensors, as well. But the more I think about this, the more it seems like it must be exhaust leaks. 3 weeks ago, the car had straight pipes (except for cats) and was EXTREMELY loud. Also, the DFCO had not been disabled at that point, yet there was virtually no backfire. The injectors were changed in February, so they're not the problem. Bill drove the car thoroughly several times after install and probably would have noted loud backfiring if it was happening then, which tells me the situation is worsening over time. I'm thinking exhaust clamps are loosening with heat cycling. What do you think?

Chris,

That's an important observation. Leak is the first thing I would suspect and inspect for. Decel would cause fresh air to be drawn into hot exhaust. Would also explain lean mixture. Which side is it or is it both? Yes I've had clamps stretch.
First time I ran into this was after putting MagnaFlow muffs on my 84 Xfire. Doing some tuning, and I was constantly needing to add fuel in the "decel region" of the VE table. That's around 20-30kPa. Until one day I walked up behind the car and noticed the left muffler hanging low. Fixed that, and then I needed to take a ton of fuel out. So the O2 sensor can be affected even by a leak quite a bit downstream of it basically making the situation worse.

[Karl]

I had a few noticable exhaust leaks where the collector and the exhaust meet up. I used red high temp silicone RTV sealant to fix it.

[KILLSHOTS]

Chris,

That's an important observation. Leak is the first thing I would suspect and inspect for. Decel would cause fresh air to be drawn into hot exhaust. Would also explain lean mixture. Which side is it or is it both? Yes I've had clamps stretch.
First time I ran into this was after putting MagnaFlow muffs on my 84 Xfire. Doing some tuning, and I was constantly needing to add fuel in the "decel region" of the VE table. That's around 20-30kPa. Until one day I walked up behind the car and noticed the left muffler hanging low. Fixed that, and then I needed to take a ton of fuel out. So the O2 sensor can be affected even by a leak quite a bit downstream of it basically making the situation worse.
Thanks Dom. Not sure on which side, or whether it's isolated to one side or the other; I wasn't able to discern that on my drive. I'll just need to get under there and start wrenching to see if that works.

[Kevin]

The consensus says FIC injectors are not very good. I am about to replace mine with the accell 150821 units. I do not have any backfiring but I am in need of new injectors.

When I purchased the car last year the prior owner had FIC injectors installed. I guess they didn't last long with the ethanol in todays fuel.

I haven't heard this consensus....

[Z06scentair]

I haven't heard this consensus....

I'm with Kevin, always had good luck with them!

At least a half dozen sets installed over the years.

Brad

[Karl]

I haven't heard this consensus....

That's what I have been told up here in FBI land.

I had a 1992 Nissan Maxima and the injectors on that car were well know for failing due to ethanol in the fuel.

If I knew about the failing injectors on the LT-5 before I purchased I would have purchased a 1993 or later model year.

[Kevin]

That's what I have been told up here in FBI land.

I had a 1992 Nissan Maxima and the injectors on that car were well know for failing due to ethanol in the fuel.

If I knew about the failing injectors on the LT-5 before I purchased I would have purchased a 1993 or later model year.

no zr-1 is immune from failing injectors

[Karl]

I suppose you are correct but I have never heard of a failing injector on a 1993 to 1995 LT-5.

[KILLSHOTS]

Reached under the car and managed to tighten 6 of the 8 clamps (didn't jack it up yet, figured I'd try what I could reach quickly and see if it helped at all.) The 6 I hit felt pretty darn tight but I made them a little tighter; don't know how far I can go before shearing a bolt. Took it out for a quick spin and the backfire seemed less frequent but just as intense. To answer Dom's question, seems like it's primarily driver's side. If it isn't one of those other 2 clamps, I'm stumped. Marc says, "I would guess that we have a 50% chance that we could cover-up what ever is wrong by adding fuel during engine deceleration."

[mike100]

Headers, no catalysts, and a Corsa (no)catback is basically straight pipes with a couple of chambers for standing wave acoustical tricks.

I thought the Corsa was too loud with the factory manifolds and factory cats- I doubt there is much to be done about the intense popping. Usually conventional mufflers and cats muffle the lean pops to a common burble.

[Kevin]

I suppose you are correct but I have never heard of a failing injector on a 1993 to 1995 LT-5.

you must have missed the work we did on lance millers yellow car.

[Karl]

you must have missed the work we did on lance millers yellow car.

Sure did!

[XfireZ51]

I have had my Accel injectors since 08. Never a hiccup.

[Schrade]

The consensus says FIC injectors are not very good. I am about to replace mine with the accell 150821 units. I do not have any backfiring but I am in need of new injectors.

When I purchased the car last year the prior owner had FIC injectors installed. I guess they didn't last long with the ethanol in todays fuel.

I've never heard ANYone say ANYthing that could be construed as ANYthing but +, about Jon, or FIC. I've talked with him, AND his help, and seen his address to customers on forum boards, with issues that customer THOUGHT would be fixed by new INJ's install, but were failed customer diagnosis, and I don't know too many business entities that are better, when it comes to CS.

If you had a bad experience, I think you should contact him, and allow him to address the issue. And he's done so in the past, ON FORUM BOARDS FOR ALL TO SEE.

============================

KS; looks like you might have a couple of issues here; a little FSM reading (never fun, but highly informative) might lead to a common root issue solution, such as a shaky ground on an important / multi-ground connector...

[Schrade]

Will an exhaust leak cause backfire, when he's got a good burn in the cylinders?

If so, what burns? HC's? Will HC's light up SES?

Got SES there KS?

[Karl]

I don't want to turn this thread into battle of the fuel injector manufactures/retailers.

Bottom line is I am going with the Accell units. There are at least two well respected LT-5 tuners not saying the best things about them. One is mentioned in this thread.

I am holding the receipt from FIC, purchase date 06/07/2010 "delphi new 92 zr1 2nd day." I did not technically have a bad experience with anyone at FIC. I just have a product of theirs that I am not happy with.

This is not a job I want to do twice, let alone once.

Later!

[KILLSHOTS]

Will an exhaust leak cause backfire, when he's got a good burn in the cylinders?

If so, what burns? HC's? Will HC's light up SES?

Got SES there KS?
No sir, nothing out of the ordinary, other than the backfire. When I'm shifting somewhat slowly, it actually backfires when I depress the clutch during full-throttle acceleration runs. Marc says he's seen maybe 1 car in the past 15 years backfire at such high RPM.

2 changes occurred: the new exhaust and Marc reprogrammed the PROM to add fuel and disable the DFCO. I'm baffled and even Marc doesn't really have an answer.

Start watching the "ZR-1s FOR SALE" section, guys...

[GOLDCYLON]

I have had my Accel injectors since 08. Never a hiccup.

Same as my RC injectors since 07 never a hiccup

[secondchance]

I suppose you are correct but I have never heard of a failing injector on a 1993 to 1995 LT-5.

Karl,

I have a 94 and my injectors went bad.

[Karl]

Karl,

I have a 94 and my injectors went bad.

When and what did you replace them with?

[Schrade]

Looks like an injector debate thread is in order.

OP probably isn't too concerned with that debate ATM.

==========================================
KS; you do static FP tests? Leakdown time?

--------------------------------------------------------------------------

The fuse circuit overload is a concrete clue. Maybe start there, to that thread...

[KILLSHOTS]

Looks like an injector debate thread is in order.

OP probably isn't too concerned with that debate ATM.

==========================================
KS; you do static FP tests? Leakdown time?

--------------------------------------------------------------------------

The fuse circuit overload is a concrete clue. Maybe start there, to that thread...
Thanks Schrade, you're spot-on there! Frankly, I'm amazed with the track these threads often take. Anybody remember the exercise in 3rd grade where the teacher whispers to the 1st kid a topic and each kid then whispers to the next his take on said topic? What comes out of the mouth of the 30th kid is a million miles from what the teacher originally said. Good example: go check out my 4.10 gear thread. I'm still sorry I posted that thing.

Nope, the tests you mention are Greek to me. I let Bill handle all that, as I really just want to drive and enjoy the car. The fuse deal isn't related, though; that started when I got the engine compartment wet on Tuesday.

[PhillipsLT5]

header bolts loose?, manufacture of header gasket?
You were not enjoying the no cat smell, maybe cats will eliminate back fire?

[KILLSHOTS]

header bolts loose?, manufacture of header gasket?
You were not enjoying the no cat smell, maybe cats will eliminate back fire?
Hey Phil, yeah no indication that it's an exhaust leak at this point. Adding fuel or cats would only mask the problem; there's something else that's causing it. Marc suggested injectors and I just talked to Bill and he did, too. But my point is that the injectors seemed fine a few weeks ago, there was no backfiring with my old straight-pipe exhaust system. This is very frustrating, to say the least.

[Pete]

Hey Phil, yeah no indication that it's an exhaust leak at this point. Adding fuel or cats would only mask the problem; there's something else that's causing it. Marc suggested injectors and I just talked to Bill and he did, too. But my point is that the injectors seemed fine a few weeks ago, there was no backfiring with my old straight-pipe exhaust system. This is very frustrating, to say the least.

Bingo you will mask the issue.
If all is good,meaning you don't have other issues, I'm with Marc about injectors.

Here's an idea buy/install Accel injectors if it fixes your issue then return the FIC's for a refund if it does not fix the issue I'm sure Karl will buy them from you, at a discounted price :-D jk.
Let us know the outcome.

I like to do injectors once since it's so involved to change injectors in our Z's plus gaskets.

Myself and all the fast Z's here in FBI land run Accels for the past 5-10 years no issues and they all run like Bat out of H@ll :cheers:

I don't see battle of posts just exchanging ideas.
Agree to Disagree
Pete

[secondchance]

When and what did you replace them with?

They were replaced in April 2009 with FIC rebuilt (cleaned?) Bosch units. A couple of days ago I suspected leaking injector but seemed fine yesterday. We shall see...

[Hog]

No sir, nothing out of the ordinary, other than the backfire. When I'm shifting somewhat slowly, it actually backfires when I depress the clutch during full-throttle acceleration runs. Marc says he's seen maybe 1 car in the past 15 years backfire at such high RPM.

2 changes occurred: the new exhaust and Marc reprogrammed the PROM to add fuel and disable the DFCO. I'm baffled and even Marc doesn't really have an answer.

Start watching the "ZR-1s FOR SALE" section, guys...

Chris, I can see adding some fuel in specific areas helping, but I dont see DFCO changes helping a normal driving upshift "backfire'. DFCO could be an issue if you were having an ingear off idle coast down backfire.

Is you exhaust 2 seperate pipes from the headers back?
No sort of cross over correct?

You are accelerating at WOT, then shift time comes, does it pop when you press the clutch, or pop when you let off the throttle.

You get a pop during slow shifting, this would assume a closed throttle, but if you get a pop as the engine is unloaded while still in WOT fueling mode, thats another.

Sounds like a powershift test is in order.

Any reports of flaming out the pipes during shifts or if you wind her up in 2nd gear and let off the throttle without touching the clutch and let the engine slow you down. If there is substantial nastyness happening during teh pulldown, couldbe pulling atmosphere when teh entire t-body back plenum is in extreme vacuum conditions, injectors and their sealing could have effects here as well.

If adding a touch of fuel via calibration isnt masking anything, its correcting an instability that you introduced from a non-OEM exhaust.

I dont see injectors magically failing before during a header install, esp. non OEM 90-92 injectors, but weirder things have happened.

Sorry to be so wordy, just trying to talk it out.

Not trying to put anyone down, but when you have a customer asking Why? Why? Why? And you dont have an answer supported by your own diagnostics, it's easier to start down the customer down the "common issues-tree" to try an appease said customer.
Sometimes the answer should be "I dont know?" bring it in and I'll go through it", this is human nature to some, again not directed at anyone, of necessarily even applies to your issues.
I've had to do this with people personally, and some people get nasty when you say "I dont know what your issue is, but after I do a diagnosis I'll have a better idea" When in my head I'm sometimes thinking "Sorry I cant fix your vehicle over the phone, I'm not a mind reader".

[XfireZ51]

How soon after the header install was the calibration changed or was it concurrent? Any chance we can see Bill's datalog?

[KILLSHOTS]

Gentlemen,

Thanks so much for all the input; it is GREATLY appreciated!

I think the mystery may be solved. I just heard from Marc. He double-checked my file and discovered that anti-backfire did not get enabled on my calibration. I'll ship it to him today and will hopefully be a little less noisy by next weekend.

Thanks again! Stay tuned...

[PhillipsLT5]

I thought you liked it loud, hopefully that works

[Schrade]

No sweat, we're all friends here...

I had hoped it was a hardware issue, too. But tightening most of the already-tight clamps didn't change much. And I haven't heard many guys complaining that Corsa clamps suck. I'm hoping the backfire fairy comes tonight and takes the backfire and leaves me a dollar. That's how it works, right?

If you think you have exhaust leak causing backfire (personally, I DON'T, because exhaust shouldn't burn, unless there's unburned fuel in it, but I never got paid for wrenchin'), but anyway, spray the slip-fits with WD, then loosen them, and re-tighten them.

I did that with mine after a few days final torque-down, just to make sure that they were seated. Maybe do it while they're still warm.

Got it; the connector @ the '?', is NOT the connector to DIS-connect for AIR pump dis-able. There's 25A a fuse UNDERNEATH it, on the impellor housing, out of sight and access of course. Pulled it.

Then finish centering the slack in the slip-fit pipes (and getting a little oil in the clamps, and female + male sections of pipe REALLY makes this part easier). With binding pipe sections, it's gonna' tough to slide the sections forward and backward, to get travel.

(process repeated from header-to-first section juncture, and proceeded back)

Last section slid forward and marked:

https://lh3.googleusercontent.com/-VylJZJRqMEo/U4DrGewl2-I/AAAAAAAAEUE/kG8Vh9_mC9g/s1024/IMG_6543.JPG

then all the way rearward:

https://lh6.googleusercontent.com/-CpwZ1Owf5bw/U4Drh592eHI/AAAAAAAAEUQ/vJD3FOjpEFc/s1024/IMG_6544.JPG

and locked in halfway (with the clamps turned up sideways, to not catch speedbumps, etc. Believe it or not, was already there - all pipes and clamps were lubed for adjustment, and hung down freely)

https://lh6.googleusercontent.com/-lU-Rp4a5xXg/U4Dr2JihMzI/AAAAAAAAEUc/fJ3Zy7lD_sw/s1024/IMG_6545.JPG

Some FP snappics here:

http://www.zr1.net/forum/showthread.php?t=23485



FP test is just like checking air in your tire.

[XfireZ51]

My experience has been that slip fits do exactly that. They slip. Mine are tack welded because they have a tendency to twist from the torquing of the motor.

[KILLSHOTS]

Should have the PROM back from Marc by tomorrow. If the "anti-backfire" feature lives up to its name, then all will be well in my garage.

As long as I can fix my fuse issue, anyway.

[Schrade]

Should have the PROM back from Marc by tomorrow. If the "anti-backfire" feature lives up to its name, then all will be well in my garage.

As long as I can fix my fuse issue, anyway.

Sounds good; find that stray ground on the fuse circuit?

That should be an easy fix...

[KILLSHOTS]

Sounds good; find that stray ground on the fuse circuit?

That should be an easy fix...
Not yet. I'm sure I just got something wet under the hood. Dave suggested that I remove the battery and use a hair dryer on the bundle of wires that go through the firewall under there, which I intend to do but haven't yet. Just haven't made it a priority yet since the car has no PROM in it anyway.

[KILLSHOTS]

The modified PROM is back in the car. Backfire problem is solved. Which leaves me with an entirely new issue...

The fuel that is now being added on deceleration is manifesting itself as a huge puff of gray smoke being blown out of the tailpipes. It is most evident a moment or two after an acceleration run, when I have mostly or completely lifted off the throttle. Can't decide yet which is more embarrassing: the backfiring or the smoke. The challenges of modifying this car are really starting to wear on me.

[Schrade]

You run it to Closed Loop?

Got a data log program?

[Hog]

DFCO could clear this up, if you get it enabled quickly enough.

Glad you got the backfire fixed, reducing backpressure/scavenging characteristics can affect a lot. Glad Mark got your fueling correct to eliminate the issue.

[KILLSHOTS]

You run it to Closed Loop?

Got a data log program?
Yep, I went out and ran it hard for 15 minutes or so. It was definitely warm. No data logging program, unfortunately. I just emailed Marc to ask whether he just disabled the DFCO, or if he may have also added more fuel on top of that.

[KILLSHOTS]

DFCO could clear this up, if you get it enabled quickly enough.

Glad you got the backfire fixed, reducing backpressure/scavenging characteristics can affect a lot. Glad Mark got your fueling correct to eliminate the issue.
Marc just disabled the DFCO, which is what stopped the backfire and started the gray haze.

[Hog]

Marc just disabled the DFCO, which is what stopped the backfire and started the gray haze.

I though DFCO was already disabled on your last backfiring calibration?

[KILLSHOTS]

I though DFCO was already disabled on your last backfiring calibration?
We thought it was. Marc couldn't figure it out. Then I got an email from him on Monday AM telling me that he had been going over my file trying to find an answer, and found that he hadn't disabled it. So I sent it to him and got it back today. Which puts me where I am right now.

[XfireZ51]

The modified PROM is back in the car. Backfire problem is solved. Which leaves me with an entirely new issue...

The fuel that is now being added on deceleration is manifesting itself as a huge puff of gray smoke being blown out of the tailpipes. It is most evident a moment or two after an acceleration run, when I have mostly or completely lifted off the throttle. Can't decide yet which is more embarrassing: the backfiring or the smoke. The challenges of modifying this car are really starting to wear on me.

Forgive me, but challenges like this are minor. And they've been solved by any number of others before. I wouldn't get discouraged. You'll be glad you didn't.

[Hog]

We thought it was. Marc couldn't figure it out. Then I got an email from him on Monday AM telling me that he had been going over my file trying to find an answer, and found that he hadn't disabled it. So I sent it to him and got it back today. Which puts me where I am right now.
Sorry, I thought that his Anti-backfire changes were seperate from from DFCO.

On my experiences with DFCO. On stock calibrations that a work with, there is a delay timer that starts counting the moment the PCM/ECM detects a closed throttle. On my trucks its set by GM to 4 seconds, so 4 seconds after I let off the throttle, DFCO kicks in cutting the injector pulsewidth essentially cutting fuel to the engine. When DFCO does engage, there is a marked increase the rate of deceleration, compared to when the engine is idling with the throttle closed. I was running LT headers and 4" sidepipes at the time, and after the computer entered DFCO, I could hit throttle and a loud "CRACK" would be heard as the fueling recommenced as DFCO was dropped.

Here are a few DFCO parameters from an LT5 ECM
DFCO RPM Enable Threshold
DFCO RPM Disable Threshold
DFCO MAP Enable Threshold
DFCO MAP Disable Threshold
DFCO RPM Decrease Disable Threshold
DFCO Enable Delay
DFCO Enable TPS Threshold Hysteresis
DFCO Enable Coolant Temp Threshold
DFCO Enable Vehicle Speed Threshold

My question is, can anyone tell us what the DFCO Enable Delay is in a stock calibration?

What I am wondering about is that you were getting a backfire as soon as you depressed the clutch. Unless the DFCO Enable Delay is set to "Zero" seconds, DFCO engagement "shouldnt" be the source of your push clutch then immediate backfire issue. I could see DFCO being an issue during coast down from high rpm, but my suspicion is that the part of the "anti-back fire" calibration mods that you received today were mostly fueling, possibly spark, but not DFCO. I can 100% understand a DFCO engagement causing a crackle, but not as soon as the clutch pedal is pushed.(again unless the DFCO enable is set to zero seconds)

Knowing the stock enable times would help. If mu suspicions are correct and DFCO is not the primary issue here, you should be able to have a non-backfiring ZR-1 that also doesnt spew gray smoke. This would be accomplished by using whatever cal. changes were used that stopped the backfire, in addition to a more thorough calibration of the DFCO settings. This however, may be beyond the capabilities of mail order tuning. DFCO recalibration is very trying at best, as aposed to Enabling or Disabling its function entirely.

On GM trucks with the tow/haul switches, I can take have the truck shift normally when the tow/haul button is off. But when you press the T/H button, I change a whole slew of ECM/TCM tables and make the same truck accelerate harder, shift harder(bark tires if that is desired) all with the flick of the T/H button. Many tuners, call this collective group of numerous transmission parameter changes their "Tow/Haul *** Mod", rather than describe each and every change that was made to the entire calibration. My point here is that it is much easier to decsribe a group of calibration changes as "Tow/Haul ***" or "Anti-BAckfire" modes to a customer, than it is to list the 10's or even hundreds of changes you made, esp. when it really wont make a difference.
This may, or may not be the case with Mr Haibeck's marketing of his excellent ECM calibrations and the hard work and dedication he puts into all the work he does for his customers.. But if I were in his shoes, it's what I would do. It simply keeps phonetime, and internet time to a minimum. It would be different if these professionals got paid for their question/answer sessions, but usually they dont. (eg. It almost took me an hour to formulate and type this post, but theres a difference between business and pleasure)

Sorry for the book, but its a complicated issue IMO.

[XfireZ51]

Stock is 250ms for Delay, 3 sec for a repeat. But Hog, DFCO has been disabled. So now there's fuel continuing to flow even while throttle is closed. Don't forget that when you hit the throttle, you are invoking Acceleration Enrichment. Too big a pump shot and...

[Hog]

Stock is 250ms for Delay, 3 sec for a repeat. But Hog, DFCO has been disabled. So now there's fuel continuing to flow even while throttle is closed. Don't forget that when you hit the throttle, you are invoking Acceleration Enrichment. Too big a pump shot and...
Yes I understand that, but yesterday it wasnt, and the car backfired, today with DFCO and whatever else changed in the cal., it doesnt backfire, but spews gray smoke.

I shouldnt have included my example of stock 4 second DFCO delay, the "Crack" I described has nothing to do with the OP's backfire, I was trying to illustrate the delay itself.

In my own instance, Accleration Enrichment also has its own timer delay. Normal fueling when the throttle is touched. The PCM I was referring to doesnt have a "pump shot" like the older ECM's do, but thats either here nor their.

Wow, 250ms, thats pretty close enough to zero to be the cause of a backfire, 1/4 of a second. But the 2nd touch has me interested, 3 seconds.
Could you rev up, let off, get a crack, touch throttle, then get another crack 3 seconds later? Oh one could spend days on stuff like this.

[KILLSHOTS]

Sorry, I thought that his Anti-backfire changes were seperate from from DFCO.

On my experiences with DFCO. On stock calibrations that a work with, there is a delay timer that starts counting the moment the PCM/ECM detects a closed throttle. On my trucks its set by GM to 4 seconds, so 4 seconds after I let off the throttle, DFCO kicks in cutting the injector pulsewidth essentially cutting fuel to the engine. When DFCO does engage, there is a marked increase the rate of deceleration, compared to when the engine is idling with the throttle closed. I was running LT headers and 4" sidepipes at the time, and after the computer entered DFCO, I could hit throttle and a loud "CRACK" would be heard as the fueling recommenced as DFCO was dropped.

Here are a few DFCO parameters from an LT5 ECM
DFCO RPM Enable Threshold
DFCO RPM Disable Threshold
DFCO MAP Enable Threshold
DFCO MAP Disable Threshold
DFCO RPM Decrease Disable Threshold
DFCO Enable Delay
DFCO Enable TPS Threshold Hysteresis
DFCO Enable Coolant Temp Threshold
DFCO Enable Vehicle Speed Threshold

My question is, can anyone tell us what the DFCO Enable Delay is in a stock calibration?

What I am wondering about is that you were getting a backfire as soon as you depressed the clutch. Unless the DFCO Enable Delay is set to "Zero" seconds, DFCO engagement "shouldnt" be the source of your push clutch then immediate backfire issue. I could see DFCO being an issue during coast down from high rpm, but my suspicion is that the part of the "anti-back fire" calibration mods that you received today were mostly fueling, possibly spark, but not DFCO. I can 100% understand a DFCO engagement causing a crackle, but not as soon as the clutch pedal is pushed.(again unless the DFCO enable is set to zero seconds)

Knowing the stock enable times would help. If mu suspicions are correct and DFCO is not the primary issue here, you should be able to have a non-backfiring ZR-1 that also doesnt spew gray smoke. This would be accomplished by using whatever cal. changes were used that stopped the backfire, in addition to a more thorough calibration of the DFCO settings. This however, may be beyond the capabilities of mail order tuning. DFCO recalibration is very trying at best, as aposed to Enabling or Disabling its function entirely.

On GM trucks with the tow/haul switches, I can take have the truck shift normally when the tow/haul button is off. But when you press the T/H button, I change a whole slew of ECM/TCM tables and make the same truck accelerate harder, shift harder(bark tires if that is desired) all with the flick of the T/H button. Many tuners, call this collective group of numerous transmission parameter changes their "Tow/Haul *** Mod", rather than describe each and every change that was made to the entire calibration. My point here is that it is much easier to decsribe a group of calibration changes as "Tow/Haul ***" or "Anti-BAckfire" modes to a customer, than it is to list the 10's or even hundreds of changes you made, esp. when it really wont make a difference.
This may, or may not be the case with Mr Haibeck's marketing of his excellent ECM calibrations and the hard work and dedication he puts into all the work he does for his customers.. But if I were in his shoes, it's what I would do. It simply keeps phonetime, and internet time to a minimum. It would be different if these professionals got paid for their question/answer sessions, but usually they dont. (eg. It almost took me an hour to formulate and type this post, but theres a difference between business and pleasure)

Sorry for the book, but its a complicated issue IMO.
Most of this is Greek to me, Hog, but I certainly do appreciate you taking the time to write the thoughtful post. Prior to the DFCO being disabled, the backfire wasn't happening the very instant I depressed the clutch, but very shortly thereafter as the revs began to drop slightly. I noticed it because I was granny-shifting the car, being that I was still getting used to Bill's shifter. If I remember correctly, the timing of the backfire was quite consistent, leading credence to the idea that this DFCO delay was controlling it somehow.

One thing I noticed today with the gray smokescreen that seemed odd to me is that it didn't appear for maybe 2-3 seconds or so after I let up on the throttle. Strange, as I would have expected it to appear immediately upon lift-throttle. Something having to do with this delay of which you speak?

[KILLSHOTS]

Forgive me, but challenges like this are minor. And they've been solved by any number of others before. I wouldn't get discouraged. You'll be glad you didn't.
I get your point, Dom. The issue is that unlike most guys on here, I haven't the time, the tools, the know-how or the inclination to wrench on my Z by myself. I've always wanted one because they're so damn cool, but had I fully realized how unique and complicated the LT-5 was and how averse almost all mechanics are to working on them, my decision to purchase one may have been different. This is simply the latest in a long list of mishaps associated with trying to get my car right. And given the long-distance nature (remove, package, ship, wait, reinstall, hope it's right this time) of tune-adjustment after tune-adjustment, it gets a little tedious. (Of course, this has NOTHING to do with Marc; he's awesome and goes out of his way to help me.)

Imagine trying to get the water temperature in your shower just right, and then imagine the faucet handle is in some guy's house 3 miles down the road, and you can sorta get the picture.

[XfireZ51]

Killshot,

You went from a situation that shutoff fuel creating a lean mixture which lit once it hit fresh air by the mufflers. Now you have a mixture where the fuel continues to be injected w a closed throttle creating a rich mixture. So the fuel tables need to be modded to reduce that amount of fuel in the decel area. I guess that's the point of being involved in a community. Nobody has ALL the answers.

[KILLSHOTS]

Killshot,

You went from a situation that shutoff fuel creating a lean mixture which lit once it hit fresh air by the mufflers. Now you have a mixture where the fuel continues to be injected w a closed throttle creating a rich mixture. So the fuel tables need to be modded to reduce that amount of fuel in the decel area. I guess that's the point of being involved in a community. Nobody has ALL the answers.
You're 100% correct. No disagreement. We're absolutely on the same page. I understand fully that there is experimental adjustment required. The mild frustration I expressed has only to do with the fact that I cannot handle said experimental adjustment myself; rather, the person I need to handle it for me is 1800 miles away, and there is no answer other than trial and error until we hit the sweet spot. My point, relative to the complexity and uniqueness of the ZR-1, was that if it was a small-block Chevy having the same issues, there would be 437 guys within a half-mile radius of me who could tune it instantly.

I still love my Z. I'm just looking forward to the experimentation ending and the enjoyment beginning.

[PhillipsLT5]

Talk to GC, FBI was tuning his car long distance, also Corey is in TX, a bit closer, hope you get it figured out, the good news the weather here is still HOT!

[KILLSHOTS]

Talk to GC, FBI was tuning his car long distance, also Corey is in TX, a bit closer, hope you get it figured out, the good news the weather here is still HOT!
Hey Phil! I have total confidence in Marc; primary frustration is that it doesn't seem like something that can be done without a bunch of trial and error. I thought disabling DFCO would be the end of it. I was elated today when there was no backfire. I was equally deflated when I saw this new smokescreen from the tailpipes. If anybody can get it right, Marc can. I'm sure before C&C in October!

[Hog]

Most of this is Greek to me, Hog, but I certainly do appreciate you taking the time to write the thoughtful post. Prior to the DFCO being disabled, the backfire wasn't happening the very instant I depressed the clutch, but very shortly thereafter as the revs began to drop slightly. I noticed it because I was granny-shifting the car, being that I was still getting used to Bill's shifter. If I remember correctly, the timing of the backfire was quite consistent, leading credence to the idea that this DFCO delay was controlling it somehow.



Yes I agree, the consistency of the timing of the backfire certainly does support DFCO being a large part, or the entire issue.



One thing I noticed today with the gray smokescreen that seemed odd to me is that it didn't appear for maybe 2-3 seconds or so after I let up on the throttle. Strange, as I would have expected it to appear immediately upon lift-throttle. Something having to do with this delay of which you speak?

The 2-3 second delay of the smokescreen is puzzling.

The delay I was talking about, was dealing with the Deceleration Fuel Cut Off(DFCO). Now that DFCO has been "turned off", the time delays associated with the DFCO function, should also be turned off.

There are AE(Acceleration Enrichment) and PE(Power Enrichment) modes. With PE Mode is used to add extra fuel when the engine requires it. It is akin to power valves and/or other parts of a carburater that enrich or increase theratio of fuel to air under periods of increased load such as WOT operation. This is what causes the wideband to read more fuel rich than, when the car is being cruised around under lighter loads. When the car is at WOT, the ECM enters PE Mode which is an Open Loop state, which means the ECM is no longer using the O2 sensors to fuel the engine. This is because teh stock Narrowband O2 sensors dont accurately measuer a/f ratios when getting far from Stoichimetric. Whereas a Wideband O2 sensor can read a "wide-range" of a/f ratios.
So as you are crusing down the road with your car up to temp, the ECM is reading the amount of oxygen in the exhaust, also known as "Closed Loop". The loop of ECM and o2 sensors is "Closed" to other fueling inputs. Then you require a does of Permagrin, pull back to 2nd or 3rd and go to WOT. Now the engines requires more fuel, the ECM stops using the O2 sensors for fueling inputs exlusively and looks to the PE Mode tables for how to fuel the engine, thus the feedback loop of the O2 sensors and ECM is "OPEN" while the PE mode lookup tables are used for fueling.

On some systems, there is also some Decelleration Enleanment tables, which effectively lean out the a/f ratio as the vehicle decelerates. View it as the opposite of the PE Mode I described above.
This is seperate and distinct from DFCO which shuts off injector activity. I am optimistic that there are some parameters/tables in the LT5 ECM that can be adjusted to at least minimize.

Some terms are used interchangibly, like PE Mode and AE mode in my experience have been used interchangibly. But then sometimes AE can be used to decsribe the act of extra or less fuel being added/subtracted as the throttle opens and closes. Some systems call this AE, Pumpshot. This is exactly what "pumpshot" implies, more fuel being added as the throttle opens, just like is done in a carb's pump shot as the throttle open. In EFI the injectopr pulsewidth is momentarily increased to prevent a lean bog/miss as manifold vacuum drops as the throttle opens.


If all else fails here, I think we should install some igniters in the tailpipes and put this extra fuel to use. It will be quiet with no backfire, and will look cool with flames coming out of the pipes.(sorry, an attempt at levity to lighten the situation, but if my long psosts are irritating, perhaps I should post with some BREVITY instead)j/k

Hang in there, someone out there has experienced the exact same issues you are experiencing. And yes, I agree with you because of the special circumstances caused by a low production run, and an even lower percentage of modified ZR-1's, finding the answers you seek can take more time than other platforms. J
Hang in there, keep thinking "Permagrin, Permagrin, Permagrin", it will be worth it in the end.

BTW: Hows the SOTP (Seat Of The Pants aka-butt dyno) acceleration with the new exhaust?

[PhillipsLT5]

Hey Phil! I have total confidence in Marc; primary frustration is that it doesn't seem like something that can be done without a bunch of trial and error. I thought disabling DFCO would be the end of it. I was elated today when there was no backfire. I was equally deflated when I saw this new smokescreen from the tailpipes. If anybody can get it right, Marc can. I'm sure before C&C in October!

I agree, Marc is the man

[KILLSHOTS]

Yes I agree, the consistency of the timing of the backfire certainly does support DFCO being a large part, or the entire issue.




The 2-3 second delay of the smokescreen is puzzling.

The delay I was talking about, was dealing with the Deceleration Fuel Cut Off(DFCO). Now that DFCO has been "turned off", the time delays associated with the DFCO function, should also be turned off.

There are AE(Acceleration Enrichment) and PE(Power Enrichment) modes. With PE Mode is used to add extra fuel when the engine requires it. It is akin to power valves and/or other parts of a carburater that enrich or increase theratio of fuel to air under periods of increased load such as WOT operation. This is what causes the wideband to read more fuel rich than, when the car is being cruised around under lighter loads. When the car is at WOT, the ECM enters PE Mode which is an Open Loop state, which means the ECM is no longer using the O2 sensors to fuel the engine. This is because teh stock Narrowband O2 sensors dont accurately measuer a/f ratios when getting far from Stoichimetric. Whereas a Wideband O2 sensor can read a "wide-range" of a/f ratios.
So as you are crusing down the road with your car up to temp, the ECM is reading the amount of oxygen in the exhaust, also known as "Closed Loop". The loop of ECM and o2 sensors is "Closed" to other fueling inputs. Then you require a does of Permagrin, pull back to 2nd or 3rd and go to WOT. Now the engines requires more fuel, the ECM stops using the O2 sensors for fueling inputs exlusively and looks to the PE Mode tables for how to fuel the engine, thus the feedback loop of the O2 sensors and ECM is "OPEN" while the PE mode lookup tables are used for fueling.

On some systems, there is also some Decelleration Enleanment tables, which effectively lean out the a/f ratio as the vehicle decelerates. View it as the opposite of the PE Mode I described above.
This is seperate and distinct from DFCO which shuts off injector activity. I am optimistic that there are some parameters/tables in the LT5 ECM that can be adjusted to at least minimize.

Some terms are used interchangibly, like PE Mode and AE mode in my experience have been used interchangibly. But then sometimes AE can be used to decsribe the act of extra or less fuel being added/subtracted as the throttle opens and closes. Some systems call this AE, Pumpshot. This is exactly what "pumpshot" implies, more fuel being added as the throttle opens, just like is done in a carb's pump shot as the throttle open. In EFI the injectopr pulsewidth is momentarily increased to prevent a lean bog/miss as manifold vacuum drops as the throttle opens.


If all else fails here, I think we should install some igniters in the tailpipes and put this extra fuel to use. It will be quiet with no backfire, and will look cool with flames coming out of the pipes.(sorry, an attempt at levity to lighten the situation, but if my long psosts are irritating, perhaps I should post with some BREVITY instead)j/k

Hang in there, someone out there has experienced the exact same issues you are experiencing. And yes, I agree with you because of the special circumstances caused by a low production run, and an even lower percentage of modified ZR-1's, finding the answers you seek can take more time than other platforms. J
Hang in there, keep thinking "Permagrin, Permagrin, Permagrin", it will be worth it in the end.

BTW: Hows the SOTP (Seat Of The Pants aka-butt dyno) acceleration with the new exhaust?
Hey Hog,

I talked to Marc and he says he can remove some fuel on decel, which will hopefully help. I'm going to try to get it up to Bill's next weekend; hopefully he can take a ride in it and datalog it for me so I'll have some fuel ratio info to send back to Marc with the PROM. If that doesn't work, I'm definitely going with your idea of installing some remotely-operated spark plugs in the tailpipes!

On your SOTP question, I honestly don't feel it. In fact, my experience with this car seems very strange to me overall, as for some reason, I'm having a hard time actually "feeling" any of the mods. I have added at least 35HP, plus new injectors/coils/plugs, switched to 4.10 gears, and switched to tires that DO NOT slip at all. Yet, for some reason, it doesn't "feel" any faster to me than it did the first time I drove it back in February, when it was 100% stock and had faulty injectors. It's not because it's running poorly; this thing pulls hard and revs to 7000 so fast that I HAVE to keep an eye on the tach or risk hitting the limiter. I've never become jaded to the power of any car so quickly. My butt-dyno must be faulty!

[XfireZ51]

Hey Hog,

I talked to Marc and he says he can remove some fuel on decel, which will hopefully help. I'm going to try to get it up to Bill's next weekend; hopefully he can take a ride in it and datalog it for me so I'll have some fuel ratio info to send back to Marc with the PROM. If that doesn't work, I'm definitely going with your idea of installing some remotely-operated spark plugs in the tailpipes!

On your SOTP question, I honestly don't feel it. In fact, my experience with this car seems very strange to me overall, as for some reason, I'm having a hard time actually "feeling" any of the mods. I have added at least 35HP, plus new injectors/coils/plugs, switched to 4.10 gears, and switched to tires that DO NOT slip at all. Yet, for some reason, it doesn't "feel" any faster to me than it did the first time I drove it back in February, when it was 100% stock and had faulty injectors. It's not because it's running poorly; this thing pulls hard and revs to 7000 so fast that I HAVE to keep an eye on the tach or risk hitting the limiter. I've never become jaded to the power of any car so quickly. My butt-dyno must be faulty!

Smooth cars are fast cars.

[mike100]

roam the streets and find a stock zr-1 or even a C5-Z06 and you'll see what you got.

[Hog]

I had some time, so I pulled the mufflers off of one of my rigs, leaving the LT headers and about 3" of pipe after each collector.

I flash the PC with a calibration with the stock 4 seconds of DFCO engage timing. While driving I would release the throttle and count 4 seconds then "CRACK" a severe snap as the DFCO shut the injectors off.

Then I reflashed with the DFCO timer set to 0.250ms(1/4 of a second) and it was almost comical, lift throttle "CRACK" on throttle, off throttle "CRACK".

that lean snap as the fuel shuts off sure is loud.

KS: I went from a stock 3.08 gear to a 4.10 gear and added a locker at the same time. After a short break in, I went out and romped on it and I was disappointed. I thought even with the 325/50/15 BFG drag radials I would have some traction issue, but no.
Wit the 3.08's and 28" tire, trans in OD with the cruise control engaged, at 70mph climbing a mild grade on the highway would cause the throttle to open, torque converter to unlock, and sometimes a down shift to drive. After gear swap, same hill, speed etc. the cruise control would barely open the throttle while climping TC stayed locked, and trans stayed in OD. My trans OD is 0.70:1 vs the ZF's 0.75:1. I noticed the gears more during light driving than I did during performance street driving.
The dragstrip is where I noticed both my gear swap, and subsequently my calibration/header/exhaust mods. The ET drop was substantial.
My "butt-dyno" was also miscalibrated.

I'm sure Marc will set you up. Goodluck.

[KILLSHOTS]

I had some time, so I pulled the mufflers off of one of my rigs, leaving the LT headers and about 3" of pipe after each collector.

I flash the PC with a calibration with the stock 4 seconds of DFCO engage timing. While driving I would release the throttle and count 4 seconds then "CRACK" a severe snap as the DFCO shut the injectors off.

Then I reflashed with the DFCO timer set to 0.250ms(1/4 of a second) and it was almost comical, lift throttle "CRACK" on throttle, off throttle "CRACK".

that lean snap as the fuel shuts off sure is loud.

KS: I went from a stock 3.08 gear to a 4.10 gear and added a locker at the same time. After a short break in, I went out and romped on it and I was disappointed. I thought even with the 325/50/15 BFG drag radials I would have some traction issue, but no.
Wit the 3.08's and 28" tire, trans in OD with the cruise control engaged, at 70mph climbing a mild grade on the highway would cause the throttle to open, torque converter to unlock, and sometimes a down shift to drive. After gear swap, same hill, speed etc. the cruise control would barely open the throttle while climping TC stayed locked, and trans stayed in OD. My trans OD is 0.70:1 vs the ZF's 0.75:1. I noticed the gears more during light driving than I did during performance street driving.
The dragstrip is where I noticed both my gear swap, and subsequently my calibration/header/exhaust mods. The ET drop was substantial.
My "butt-dyno" was also miscalibrated.

I'm sure Marc will set you up. Goodluck.
Hey Hog,

That's what I figured, too. I know the car is quicker, just can't "feel" it for some reason. Marc is great and I know we'll get this figured out sooner or later.