I have a 2008 tahoe with an e38 pcm. It was originally equipped with a 4.8 which I put a turbo on. Ever since I went over 6lbs of boost it had a random misfire. Maf tune / sd tune / rich / lean / tons of timing / no timing. It didn't matter, it kept doing it. New plugs heat range 6 heat range 7, a bunch of different gaps. Hundreds of dollars in plug wires.... it kept doing it. Well it finally blew up 4 months ago.

So to start new I bought a brand new LME built 408 longblock. New plugs (tr6 gapped at 25 thousanths) new cam sensor / new crank sensor / new coil wires. Finally got it installed and running on the old 4.8 tune a few days ago. My tuner drove down today (2 hours) to get it driving for me so I could get it back up to his dyno for WOT tuning after break in.

We battled the thing for hours.... bank 1 adding 15% bank 2 removing 15% wideband saying 12.5 and going to 16.0 without so much as a change in rpms. Was this due to oil being run through them when the last motor blew up? Who knows.... they started getting closer and closer the more the engine ran. And were within 10% before we gave up.

So now that you have a small idea of the background on the problems ive had with this truck here is how it stands....

The truck is still not idling by itself even after adding 35 lbs of air on the IAC table. This was a 100 percent gain from the boosted 4.8 tune. The truck also had to be started with carb cleaner after every flash, until it re learned the fuel trims but would start on its on after that (with the gas petal being pressed). With 35 lbs of air on this table the tuner said the truck should be idling at 2000 rpm, but showed absolutely no response.

So what do I do? New e38? If so where can I get one already programmed with my stock tune for my truck and mailed to my door? New wiring harness? What else is there? I am pretty confident this is not a tuning issue at this point because the truck appeared to be non responsive to changes being made.

We are using efi live to tune, and this is my second tuner. My original tuner (MIKE @ VENGEANCE) Will not return any of my calls or send me my bone stock tune he pulled in when I first put the turbo on the 4.8.

Please help. I am willing to ship this truck anywhere in the continental us to anyone willing to fix the problem.

Thanks

 

I am not the best tuner by any means, but I am sure someone on here can help you. Please explain your setup in detail. What injectors do you have, and are you certain that you have accurate data for them? If you want the stock tune, go to holdencrazy.com and download your stock tune for your OS. Do you have an EFILive flashscan to flash in the tune? What exactly went wrong with the old engine when it blew up? Do you have the tune that it blew up with?

The most important thing in my book is accurate info. If you have wrong injector data it will never be right.

 

I have fic 60lb injectors. Injector data was provided by them. There is no 2008 tahoe with a 4.8 stock tune on that website. My tuner uses efi live for tuning. My tuner has done over a hundred e38 cars and mine seems to be the only one giving him fits. I'm trying to figure out what I need to replace or check on. He is very aggravated and does not know what the problem is.

 

Vacuum leak somewhere??

 

I am using the holley hi rise intake. The injectors o rings fit tightly, and the only vacuum hose is going to the brake booster. Maybe if it would idle properly I could spray carb cleaner to check for leaks. We also tried adding fuel though... in this case the extra air would have been accounted for right? And it would have been running lean.... this didnt seem to be the case.

I am at a complete loss.

 

I was slightly worried about a vacuum leak upon close inspection of where the intake mounts to the head. Unfortunately the truck wont idle to check it with carb cleaner, so I pulled the plugs and read them.... don't think I have an intake leak. It must be torqued down enough to prevent a leak.

The full view;


The left side of the intake where it meets the head (notice the slight gap)


The right side of the intake where it meets the head (notice the flush fit)


The first two plugs from the left


The first two plugs from the right


They both look equally fat, which leads me to believe there is no leak at the intake.

 

What does the map sensor read when its trying to idle? Have a video of it trying to idle?

 

None of the logs were saved. the map was reading 75-90 KPA, none of the numbers were making sense. When we first started bank 1 was adding 15% bank 2 was removing 17% and the wide band was reading 12.1... several seconds later ~16.5 +

Not sure if all of my o2 sensors are fucked up from the oil going through them when the last motor blew up or what. We also tried tuning with the 02's off but still couldn't get it to idle. The maf is not used at all on this truck.

 

A swing that big might be an exhaust leak...I would replace the o2s anyway...

 

Please feel free to offer more suggestions. But know that exhaust was put on this truck a few days ago. True dual 3", and there are 0 leaks. Had a man under the truck to confirm this while it was on the rack. I shouldnt have 30 lbs of air on my IAC table in the first place much less have that setting and the truck not idle.