2008 Tahoe LT with 65,000

I was driving uphill, when the engine started to shudder and was about to quit. I floored the accelerator, climbed a short distance to the top of the incline and the engine had shut down. I waited a couple of minutes, then tried to restart, it started rough and then quit again. After that I couldn't start it anymore.

Towed the Tahoe to my place, hooked up a fuel pressure tester, it reads 60-70 psi, pressure dropping slowly, fuel tank is almost full. Checked all the fuses and relays located in the engine compartment and they seem to be fine. Removed all spark plugs, one was darker than the rest. Replaced all of them with Autolite Iridium XP plugs.

Tahoe started, but the engine works rough, uneven and gives P0300 Random Misfire.Also these messages: Service Traction Control, Service Stabilitrak

Where is the ignition control module(if equipped)? What's the best way to test coils and spark plug wires? What else should I check?

Please help and thank you for your time. Also the vehicle is out of warranty as of July 2012.

 

Welcome to the forum...

Do you know if your vehicle has the Active Fuel Management or AFM ( does is switch from V8 to V4 in the DIC)
if so you may want to check compression...

 

Thank you. Yes it goes from V8 to V4 and back. Regards!

 

What controls the ignition, in particular the firing order of the cylinders in my Tahoe? I think it's messed up.

I also treated the vehicle with SeaFoam spray into the throttle body and SeaFoam Motor via fuel tank. No effect whatsoever.

 

Ignition is controlled by the ECM. However I suspect you may be the victim of the dreaded AFM engine failure... I hope I am wrong but a diagnosis by a trusted mechanic may be in order...

 

Do Not use seafoam. That will only make things worse. Seafoam is very bad for engines over long term. It seems that the AFM firmware has got corrupt and is making the motor run bad. I do not know all the problems that AFM motors have but my suburban has the dreaded squeaky AFM lifters... But this started at 96k mi and has been going on and now the suburban has 121k mi on it. (Just went to Fl and back, AFM works fine)

You will probably have to go to a dealer to get the firmware checked. My best advice I can give to you is GET RID of the Tahoe before 96-98 k mi. I have had so many things go wrong since 96 k mi it's not even funny.

 

I can't believe it! The more I read about the AFM problem the more I get convinced that my truck has it. The symptoms match to what other unfortunate GM owners suffer from. It is simply unacceptable! 64,000 miles and a major engine problem. It is out of warranty for 8 months and THIS **** happens?!?! I don't have proper words to describe my anger with chevrolet. I will have to bring it to the dealer to confirm the problem. Man I am so mad now

 

http://www-odi.nhtsa.dot.gov/acms/cs...47220-3332.pdf

 

Wow. I wonder what they changed and why they changed it. 2007 should have same motor..... Or at least I thought it was the same motor.

I thought they only took away the windshield washer fluid heater away. Our suburban still has the heater and every other month gm sends me a notice saying that they'll pay me $100 to get the heater removed.

 

Its possible it is something simpler, however as you stated a lot of the symptoms are the same...
That is why I suggested the compression check, if all 8 cyl come out even or within the same range then it may not be the AFM, however It would be my guess that if you see low or no compression on any of the AFM cylinders you may have your answer...
Working with your local dealer may get you a reduced or 50% cost of the engine rebuild IF that is the case...
But lets not get ahead of ourselves... get it checked out, it could be a throttle position sensor or a bad coil...

I don't know if the compression test would be a tell tale sign of the AFM but it seems logical...