Toally stumped on this lean spike and bucking. Need you guys to help me please

[Firechicken5.3]

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


G8 3.0 DCFCO disabled LS7 MAF+Timing+LS9 cam O2 B1S2 off PE 12.5afr.hptlean spike problem 4-17-17.hpl

[AJK13]

To me that looks like a lot of timing. I'd try pulling like 5 degree across the board and see where it gets you

[Firechicken5.3]

I loaded my stock timing tables to see if that would affect anything and it didn't. I basically reverted my tune back to stock except for the things I had to keep modified. It made no difference in the lean spike or the bucking. It's almost like it just dies for a spit second and comes back.

Do the idle tables come into play anywhere in deceleration?

[AJK13]

can you screen shot your log where you see it going lean?

[Firechicken5.3]

lean screen shot.PNG


lean screen shot 2.PNG


lean screen shot 3.PNG


Here are some screen shots (I hope) of when it went lean. I am watching the wideband, yellow line, spike. it went to 18.0 afr. when this happens it bucks a little bit until it either goes into fuel cut mode or straightens back out, or I give it a little gas. Like I said it doesn't do it every time and it will do it with or without fuel cut enabled. Any gear doesn't matter.

[Firechicken5.3]

No body? It's a very annoying problem. Car runs pretty good except on decel and idle sounds like it has a miss.

[Niemer]

It doesn't look like it shows up in your narrowbands, which is odd.

[Firechicken5.3]

Yeah kinda. Narrow band is moving rapidly but you can see it in the wideband. It's not the gauge because I can feel the car reacting. The wideband is where the bank 1 rear o2 usually is.

[Niemer]

It should really be closer to your NBs. You don't have cats, right? Positive there are no leaks? Post your tune.

[Firechicken5.3]

I do still have cats. I have a stock exhaust system except for mufflers. I thought it might be an exhaust leak pre o2 so I got new manifold gaskets And flattened the flange and used some copper spray on it. The manifold flange where connect to the downpipe to the cat does not have a gasket. It's still may be a leak but I'm not so sure. The spike didn't change after I replaced the gaskets and it's not every time I decelerate it's only when it wants to.

My tune is posted in the original post.

[Niemer]

Your wideband needs to be before the cat.

[Firechicken5.3]

While that is technically true, it won't fix the issue. My wideband has been installed there since I got the car. I have only had this problem since the cam install and dod delete.

I only use the wideband for wot tuning

[GHuggins]

Just looks like an O2 switching issue from the posted screenshots... The majority of the time your O2 is lean... Your wideband is worthless for anything other than wot tuning and even then can't be used for anything like transients due to their locations... Cat's will do burnoffs and everything else, so completely worthless for drivability...

[Firechicken5.3]

O2 switching? Like bad or worn out sensor? Why did this problem just present itself now after the cam swap?

I know the wideband can't be used for anything other than WOT.

My AFR is set for 14.68 like stock. My fuel trims are pretty good so it must be close.

What do you suggest I do to fix the problem?

[Firechicken5.3]

Here is a scan from today. This is basically a stock tune again minus the MAF table and IAT corrections for the LS7 maf. I did mess with idle to try and fix the lean spike but it didn't work. Lots of slow cruising lean spikes in this one.

lean spike problem 4-22-17 stock tune modified idle.hpl

[GHuggins]

Increase proportional airflow mode 10% and see if there's any difference... Think your cam just slowed down airflow in the lower rpms...

[Firechicken5.3]

Thanks. I will give this a try. Sounds like it may work from the description. I'll report back soon I hope.

[GHuggins]

If you can get just a log of this issue - in other words get it to act up then stop and restart the log while it's acting up then stop making a short log of only this issue happening... Will help us all to see what's going on I just want to make sure it's not cutting timing or something like that too...

[Firechicken5.3]

Ok. I'll try and get that which may almost be impossible since there is no way to predict on which deceleration it will decide to lean spike.

I also tried the closed loop proportional airflow mode adjustment. I multiplied the entire thing by 1.10. I only had a little bit of drive time with it but I think it helped slightly. There is still a Lean spike but it doesn't go quite as lean as usual. I'll do more driving later and verify. Maybe add another 5%

[GHuggins]

Change your min O2 setting to 400mv too instead of the 250mv's setting that it currently is...