Really need some tuning help with a spike while decelerating
So, I recently removed the Displacement on demand from my G8 and added a LS9 cam in preparation for a supercharger later this summer.
While tuning for the new cam and DoD delete I can't seem to find out why I am having a lean spike only while cruising with slight deceleration. I have tuned the MAF and disabled VE but no change. I then disabled MAF and checked VE. No change with VE only and the trims looked good. I re-enabled both MAF and VE but the spike remains. It seems to be a random occurrence. It does not happen every time I decelerate and its unpredictable but it only happens during deceleration while cruising. I disabled DFCO to try and eliminate that and there was no change. Sometimes the spike will be accompanied by some slight bucking. I thought it might be something to do with the Torque converter engaging. I used the VCM scanner to lock the converter and that kind of made a change but the lean spike turned to a rich spike. So then I unlocked it but that didn't make a change.
I have a scan from today. its about 20 minutes long and the spike occurs multiple times during the scan. I just cant figure out what is causing my problem. Is it a mechanical issue or a tuning issue? I thought it was an exhaust leak at first so I got new manifold gaskets and resealed the manifold to the cat. Maybe it is timing chain slack? Idk guys, I need help.
2009.5 Pontiac G8 GT 6.0 L76 A6
Mods: Vararam OTR intake, LS7 MAF, DoD delete, LS9 Cam, .660 Valve springs, HD chain, melling Oil pump, Pypes axle back mufflers
It is your MAF sensor signal going bonkers. This is common at low flow and when the MAF is close to the TB like you have with your vararam. Are you sure you fully disabled the MAF when driving it in VE? Try unplugging the yellow wire on the maf to be sure you are truly in VE. Also, log Dynamic Airflow.
I am fairly certain I disabled the maf. I followed a guide I found on here. I will try unplugging the wire like you suggest.
I did not have any problems before the cam swap/DOD delete and I was running the Vararam with the same maf setup. It was suggested that the cam has low flow numbers down low so maybe that coupled with the unstable low flow numbers in the maf have now caused a problem??
Is it torque management pulling insane amounts of timing? I had this problem when I swapped to my cam. Had to eliminate limit tq management under trans settings.
Is it torque management pulling insane amounts of timing? I had this problem when I swapped to my cam. Had to eliminate limit tq management under trans settings.
Torque management is gone. Plus I'm still seeing roughly 20 degrees timing when this happens and timing doesn't spike when my wideband does.
It could possibly be an exhaust leak still maybe? It doesn't always do it on every deceleration though.
It's the maf signal. Plot the maf frequency and you will see how bad it is when it goes lean. Its jumping from 2500 to 750hz between frames. Also plot dynamic airflow. This is the air calc the ecm uses for fueling after blending the maf with the ve. Also log VE airflow and compare them. It should be much steadier.
If you cant clean up the maf signal, look into the ve correction factor table. You will want to change it to favor the ve calc more at the low flows.
Hmmmm interesting. Why do you think the maf signal is jumping all around. Is it the big LSA of the LS9 cam? I also don't have any sort of screen or flow straightener on the maf.
I'll set up maf frequency in my graph and check that out.
Hmmmm interesting. Why do you think the maf signal is jumping all around. Is it the big LSA of the LS9 cam? I also don't have any sort of screen or flow straightener on the maf.
I'll set up maf frequency in my graph and check that out.
Don't recall there being much difference in LSA between stock and LS9
From what I read a while back, there are certain LS7 mafs that give a weak signal and certain versions that give a stronger signal. May want to do some research, could be your problem.
I've run LS7 maf only in all my recent cammed cars with no problems.
Really need some tuning help with a spike while decelerating
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Originally Posted by gr8g8
