Backfire issues - Tuning Forum

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Backfire issues
Tuesday, January 10, 2012 9:05 PM
When at WOT and full boost (turbo, currently 11psi), when I get to about 6,000 rpm, it starts backfiring rapidly and sounds like its bouncing off the rev limiter. It doesn't seem to want to shift into the next gear (automatic 4t40e with B&M Shiftplus). I have the rev limiter set to 6600 when in drive and have all gears set to shift at 5900 (this low in hopes it would solve the problem, but still hasn't) I have to do some data logging yet once I get the wideband tapped into HTP, but I doubt I'm getting much if any knock. AFR is 11.8ish using 93 octane and 50/50 water/meth injection. I'm starting to wonder if perhaps its the torque management causing my issues (supercharger reflash with torque management still fully enabled). Maybe its causing too much of a timing retard. IDK, any thoughts or suggestions?



12.6 @ 114.6 MPH


Re: Backfire issues
Wednesday, January 11, 2012 3:00 AM
Without datalogs no telling.

Whats the injector duty cycle?



FU Tuning



Re: Backfire issues
Wednesday, January 11, 2012 9:07 AM
Again, no data logs yet, so this whole this will prob be hard to figure out before getting some. I would imagine deff under 80% though. They are 835cc and boost is only at 11psi on a T3/T04E 57 trim.



12.6 @ 114.6 MPH

Re: Backfire issues
Wednesday, January 11, 2012 1:32 PM
Alright, got the wideband working with HTP and did a quick run (started to rain). I have no knock in light boost. I did notice one of the times it started backfiring, boost went up to 20psi. Then my wastegate stuck open (open vent so you hear when its open). I'm thinking I have a wastegate issue since it should only be 10psi with the spring in it plus the fact it then stuck open. Anyways, when it did this, looking at the log, I see that my injectors were still only at 63% duty cycle, but it started to lean out from about 14.4-16.0. The 2bar MAP sensor was maxed out at 206Kpa, so not sure what boost it really was at or how to tune more fuel in that area since A: its more boost than the MAP can read and B: it is only suppose to be at 10psi. Knock did hit 4.3 degrees when it leaned out, but that's it. Timing was still advanced from 14-19.5 degrees in that time. By the way this all is within about a 1 second range. Another time during this run that it did it, same thing with the MAP maxing out and it starting to lean out of course. This time with 2.1 degrees knock and -10 degrees timing. A third time, same deal. So it seems that the issue is from leaning out due to overboost. AFRs are perfect when under the 206kpa (so the MAP sensor can still read boost) Now how do you tune (SC reflash and 2 BAR MAP with HTP) for anything over 14.5ish lbs of boost? I'll have to figure out the wastegate issue, but the ultimate goal was to be around 15-20psl, so after fixing that issue, I'll still need figure out how to tune for anything over 15. Thoughts?



12.6 @ 114.6 MPH

Re: Backfire issues
Thursday, January 12, 2012 9:36 AM
wait you started to lean out from 14.4 to 16 while in boost? As in you are just at 14.4 normally in boost? Check your compression I bet you melted something running for an extended period at 14.4 in boost. Drop that down to something super safe like 11.4 until you get everything else sorted out.

Also those trans shift tables, there is also the MPH table for shifting, IRRC it has to meet both the rpm and mph setting before it will shift. Get a log, want to see if your spark advance drops off to nothing when it backfires.


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Re: Backfire issues
Thursday, January 12, 2012 12:34 PM
Leafy (Club Jeffie FEA man) wrote:

wait you started to lean out from 14.4 to 16 while in boost? As in you are just at 14.4 normally in boost?

Nooo. I'm normally 11.8 or richer in boost. When the MAP sensor maxed out at 206kpa, thats when the afr leaned out to anwhere from 14.4 to 16. All other times in boost the AFR was fine as long as boost was under the 206kpa so the sensor still knew what boost was there. AFR was only in the 14.4-16 range while in boost for a fraction of a second a few diff times. My last log showed that sometimes there was still a spark advance of anywhere between 14 and 19.5 degrees sometimes it backfired and other times it was retarded by -10 degrees and other times it dropped off to 0. It varied. All in all though, theres pretty much no doubt that the backfires were from being too lean due to overboost.



12.6 @ 114.6 MPH

Re: Backfire issues
Thursday, January 12, 2012 2:44 PM
fuel pressure? sounds like knock? spark blow out?



Re: Backfire issues
Thursday, January 12, 2012 4:44 PM
Fuel pressure at idle is currently set at 35psi. Not sure about while driving since my fuel pressure gauge is on my rail. The most knock I had during the entire log was 4.3 degrees. I doubt it would be spark blow out since they're gapped at .032 if I remember right. Plus if they blew out, wouldn't it show rich rather than lean? It's deff too lean when it happens, so I'm pretty sure thats the issue from overboosting. What I need to figure out is how to tune it for more boost than the 2 bar MAP can read. I know its possible since a few on here have done it...Anyone?



12.6 @ 114.6 MPH

Re: Backfire issues
Thursday, January 12, 2012 9:53 PM
What is your fuel pressure with the key on but the car off? Thats the base pressure and thats what most people talk and think about when setting a car up.

Rather than trying to tune out the boost spike, fix your damn wastegate so that you stop over boosting.


1994 Saturn SL2 Home Coming Edition: backup car
2002 Chevy Cavalier LS Sport Coupe: In a Junk Yard
1995 Mazda Miata R-package Class=STR
Sponsored by: Kronos Performance

WPI Class of '12 Mechanical Engineering
WPI SAE Risk and Sustainability Management Officer
Re: Backfire issues
Friday, January 13, 2012 4:40 AM
Leafy (Club Jeffie FEA man) wrote:

Rather than trying to tune out the boost spike, fix your damn wastegate so that you stop over boosting.

Yeah I know. I haven't ran the car since I discovered the issue. Either way though, I still need to tune it for more than 14psi since I'll be running more than that once its all set and done. I'm not tying to tune to compensate for the overboost, I'm trying to tune in more fuel near that boost level since thats what it will be running (after wategate is fixed and boost controller is on)



12.6 @ 114.6 MPH

Re: Backfire issues
Friday, January 13, 2012 3:43 PM
Ya, untimately my guess would be fuel , or spark blowout. Whta plugs are you running on this set up and what are they gapped at? I would tend to think more spark here than fuel.... imo.




Re: Backfire issues
Friday, January 13, 2012 5:19 PM
NGK Iradium IX's gapped at .032 or .028...don't remember which.

I traced the wastegate issue to a blow off vac line going to it. Unfortunately though the snow is here now, so I doubt I'll get it out running again for a few weeks or so to test everything.





12.6 @ 114.6 MPH

Re: Backfire issues
Friday, January 13, 2012 8:56 PM
You still on the stock fuel pump?





i find it amusing that SHOoff has nothing better to do but follow me around & be an unhelpful dick in even cross-forum. - Jon Mick
Re: Backfire issues
Saturday, January 14, 2012 9:27 AM
At that time, yes. Remember, I was only suppose to be at 10psi, which I know the stock pump can do fine. It obviously prob can't keep up with 20psi though. Racetronix pump just got here and is going in in later today.



12.6 @ 114.6 MPH

Re: Backfire issues
Friday, January 27, 2012 3:05 PM
So I thought I fixed the wastegate issue, but still haven't. I did however change the tune a round a bit so it won't lean out if it overboosts. I did a few runs and it still did the loud poping/backfire thing. I pulled the plugs and all looked good. Gap was set at .034, so I bumped them all down to .025 thinking maybe it is just spark blow out. I'm still running the stock ignition and coils. Went for a run and still getting the poping/backfires. It only seems to do it at WOT at higher RPMs and boost. Its automatic and doesn't seem to shift (I don't think at least) when it should at those times. I also have a shift kit that was on. Heres the latest log: http://www.filehosting.org/file/details/306150/2012-1-27n2.hpl Its a pretty quick one, but the main times it did it are right around 5:29.3ish and 6:06ish. If I remember right, I think it also was around 0:52.8. I notice the injector duty drops to 0 for some reason on some of those which sometimes cause a lean spike. DFCO was off as was closed loop. Anything jump out at you as to what it may be? Any help is appreciated.




12.6 @ 114.6 MPH

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