Thoughts on backfire?

[secondchance]

Originally Posted by Karl

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]

Originally Posted by KILLSHOTS

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]

Originally Posted by KILLSHOTS

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.

Originally Posted by Schrade

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:



then all the way rearward:



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)

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]

Originally Posted by 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.

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

That should be an easy fix...

[KILLSHOTS]

Originally Posted by Schrade

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.