Please help tune out backfire

[LS1-450]

Have made changes to DFCO, VE, timing, base timing, cold commanded fueling...everything I could think of.

Have checked for collapsed lifter, droped valve, valve sealing, plugs, wires, gaps. No codes.

Here is current tune including mods to try & eliminate backfires. It is not where I'd like it to be in terms of spark. Please comment, thanks

[gmperformancecentre]

try this

[LS1-450]

Thanks, I see that you richened the open loop cold fueling (VE, spark as well). The OL fueling is one area that I didn't modify because didn't think that it would help. After seeing the changes that you've made + comments from others regarding the OL fueling, am optamistic that there will be an improvement.

Will post again after testing the tune. Thank-you again, your assistance is appreciated :)

[LS1-450]

OK, there is an improvement. Backfires immediately upon lifting. So, is the next modification to the VE, OL or other?

[gmperformancecentre]

post a log of a run with the tune i posted

[LS1-450]

I will later. Just got back from my garage. False alarm, it's doing the exact same thing.
Seems like once it warmed up, it got worse. So, am thinking ECT timing related.

[mistermike]

Just to be clear, it's not a backfire. An engine using ported injection is virtually impossible to induce a backfire unless you have introduced a flammable material prior to the intake port of the heads i.e. wet nitrous or alcohol spray.

The noise you're hearing is unburned fuel igniting in the exhaust manifold or header, once the correct combination of air, fuel, and temperature is achieved. Try THESE (http://forum.efilive.com/showpost.php?p=48176&postcount=25) DFCO settings. DFE1 is our resident DFCO guru.

[LS1-450]

^^^ Thanks for the settings. Haven't loaded them yet, but will.

Here is the current tune & a log. Car now POPS or BANGS during idle. Will idle for a while & then BANG, idle some more & then BANG. Problem has improved w/ a combination of the gmperformancecentre information + some additional timing, DFCO & airflow mods. Can now get it to rev & lift without POP or BANG until around 2k & under. Will try the above table settings tomorrow. Also, if anyone sees something in the tune or log, please comment.

[Baldric]

if its poping and banging. it sounds like your over fuling the intakes and thus the extra fuel is burning in the headers...

maybe drop some fuel back

your using a WB 02 ??

[LS1-450]

^^
Yes, that is the case & is what we are trying to resolve here.

Along w/DFCO & the other mods, it seems to need more timing restriction & possibly an injector flow reduction. In my log you will see that 0.89 is mapped as the wideband feedback for VE. However, regardless of how many times the VE table is changed, the mapped data remains 0.89 or 0.90. Was gonna tackle this issue next, but if it's related, what should my 30# Accels flow be?

[LS1-450]

Here's the most recent tune & log. Reducing the inj flow from 0-45kPa has improved the VE.

Problem persists. Off throttle is now OK until it is idling. While idling it Pops. Noticed bank 2 LTFT is dumping fuel & will correct this, but otherwise am stumped.

Anymore suggestions?

[LS1-450]

I am thinking that it's a mechanical problem, not a tuninng problem. Am in the process of tearing her down to have a look. There is a lifter tick & the fuel trims are adding fuel due to a lean condition. Am not sure how a lifter could cause the issue, but everything else has checked out OK...........& there's the lifter tick.

Thanks for the help & I will note any mechanical trouble if confirmed.

[LS1-450]

She's fixed!


There was a wire inside the weather seal of one of the injectors that had come loose. This caused the lean condition & the fuel trims to add fuel. Confirmed the issue by looking @ the current & previous plug. Both had signs of heat. Fixed the wiring & she now runs great again. Also, I got a better DFCO & idle as a result of member feedback here on EFILive.

Thanks guys, I appreciate the help. :)

[gmperformancecentre]

great to hear you have got her fixed :rockon::rockon: