Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

You run it to Closed Loop?

Got a data log program?

Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

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

Re: Thoughts on backfire?
 

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

Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

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...

Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

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?

Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

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!

Re: Thoughts on backfire?
 

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!

Re: Thoughts on backfire?
 

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?

Re: Thoughts on backfire?
 

I agree, Marc is the man

Re: Thoughts on backfire?
 

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!

Re: Thoughts on backfire?
 

Smooth cars are fast cars.

Re: Thoughts on backfire?
 

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

Re: Thoughts on backfire?
 

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.

Re: Thoughts on backfire?
 

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.