Thoughts on backfire?

[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".