Flex Fuel vehicle owners beware

General technical discussion and troubleshooting
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MountainManJoe
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Flex Fuel vehicle owners beware

Post by MountainManJoe »

I have a problem with my Savana that I thought I would share, in case others are seeing strange issues. Upon researching into it more, it seems it's a fairly common issue. There's some kind of bug in the computers of GM Flex Fuel trucks, vans, and SUVs with a V8.

The computer will think you have E85 ethanol fuel in your tank, and the injectors will start to dump far too much fuel into the cylinders, causing a very rich condition. (E85 required an enriched mixture). Symptoms will be extended crank times (especially in winter), rough idle, a very black,sooty tailpipe, and possibly a tripped check engine light with P0172 & P0175 trouble codes. Long term fuel trims will indicate a very rich condition (in the minus 20's percent). If you know your way around scan tools, you will find the "Ethanol content" parameter stuck on some very high value, such as 60%, even though you have none.

The only way to fix it is to perform an ethanol content relearn. A dealer-tier tool is needed for this. It doesn't sound like a permanent fix though, so no guarantee the problem won't come back. I checked and there are no updated calibrations for my ECM. The problem is exacerbated by partial refuelling events (not filling the tank when refuelling).

Attachment: GM Service Bulletin PIP4792D (they say it affects vehicles up to 2011 but it's a lie. It extends beyond that. I have a 2013)
https://static.nhtsa.gov/odi/tsbs/2014/ ... 4-0335.pdf
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SB-10069954-0335 (PIP4792D).png
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Re: Flex Fuel vehicle owners beware

Post by MountainManJoe »

Some videos on the subject. (these are both excellent Youtube channels by the way)





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