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Discussion Starter · #1 ·
Been searching for similar issues but have yet to see one to match.
2011 Terrain v6 recently threw a set of codes for bank 1 and bank 2 too rich. Long fuel trim numbers sitting around -20 for both banks. Recently changed the MAF after it threw a fail code a couple months ago.
how long does it take for long trim numbers to change? Could it be the MAF I replaced acting up? Was debating O2 sensors but can’t see how it would change both banks. (No common sensors for the banks)
Any input is appreciated.
 

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Discussion Starter · #3 ·
I’ve been monitoring my fuel trims the past few days and the long term trims stay pretty steady at -7, then randomly will shoot up to -25. No sensor faults or odd values on anything else. I’m just lost as to what to do next.
 

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Discussion Starter · #5 ·
Was the new MAF an OEM part? What are the codes it threw before and after new MAF sensor? More detail may get more responses.
The original code was for a MAF fail.Replaced with one from Autozone. Matched everything I could find online. Drove fine for about a month then threw the Bank 1 and 2 too rich codes at the same time. Reset them and a week later they came back. Bought a code reader to monitor fuel trims and your need load long term trims are almost 0 (bank 1-0, bank 2-1.5). At idle they vary from -7 all the way to -30.
 

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Dont know answer, but being a 2011, how many miles?
O2 sensors get lazy, response slows down, eventually fail.
I simply replace all at 100,000.
Did it recently on my v6 equinox. And my Traverse yrs ago when i hit 100k. Nearing 177,00
 

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Fuel trims both long and short should normally cycle between -3 and +3.
MAF and MAP sensors can affect it if no leaks along with the front O2 sensors.
Vacuum leaks and the MAF and MAP sensors having an issue are more prone to affect both banks at the same time as usually both O2 sensors do not go bad at the same time.
I chased a bad MAP in my Tahoe that did not set any codes but killed my MPG by 3 and would not allow emissions monitors to run its self-test for inspection.
 

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Discussion Starter · #8 ·
Fuel trims both long and short should normally cycle between -3 and +3.
MAF and MAP sensors can affect it if no leaks along with the front O2 sensors.
Vacuum leaks and the MAF and MAP sensors having an issue are more prone to affect both banks at the same time as usually both O2 sensors do not go bad at the same time.
I chased a bad MAP in my Tahoe that did not set any codes but killed my MPG by 3 and would not allow emissions monitors to run its self-test for inspection.
Been a bit and wanted to check in with an update.

Replaced MAP and have been monitoring the trims for a week. Under load all trims look really good. Long trims are between 0 and 3. Short trims bounce around but never above 10 (all depends on how quick I am with the throttle). Problem remains when I idle and only when the engine is at temperature. The long trims slowly rise until about -27. Im debating going out and replacing the MAF again. Its only a few weeks old but you never know what you're gonna get these days from the zone. I've checked for vacuum leaks at the intake using the brake cleaner method and never a rise in rpm. Any additional ideas you all have send them my way. I'm beginning to lose my temper with this thing but not interested in trading it in right now either.

Thanks
 

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2011 GMC TERRAIN AWD SLT-2 3.0L V6 (LF1) 6T70 Gen 1 Transmission
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I had high long trims as well especially at idle, mine where in the -40s.
I had the dreaded run on after turning engine off.
All is normal now, I had the HPFP replaced.
The stupid mechanic neglected to tighten down and torque the intake bolts after the repair
which caused high trims to return but after I properly torqued them to 18 ft lbs, trims behaved.
I had P0172 and P0175 and the HPFP was the problem child in my case.
 

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Discussion Starter · #11 ·
I had high long trims as well especially at idle, mine where in the -40s.
I had the dreaded run on after turning engine off.
All is normal now, I had the HPFP replaced.
The stupid mechanic neglected to tighten down and torque the intake bolts after the repair
which caused high trims to return but after I properly torqued them to 18 ft lbs, trims behaved.
I had P0172 and P0175 and the HPFP was the problem child in my case.
Quick question on the fuel line that is called out to be replaced when the pump is changed, did you see any reason that it couldn't be reused? I'm not trying to go cheap or anything but everyone is out of them and I'm trying to get this fixed before a upcoming work trip. Im debating trying to reuse it until they become available as long as it doesn't leak after the replacement.
 

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Use Genuine GM parts only for electronics and sensors. Duracrap parts are exactly that. Lifetime guarantee with a lifetime of replacing them. I've learned my lesson with that stuff.
Plus those ''new'' aftermarket parts being bad just complicate repairs / diagnosis's.
 

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Discussion Starter · #14 ·
Last thing you need is fuel being sprayed in engine bay. I would not reuse that 1 time use part.
My question was why is it a one use part.
The answer is they use compression fittings that distort under torque to give a proper seal. While using them again on the fuel rail side shouldn't be an issue as they are molded to it, the fuel pump side wont match.

Thankfully I was able to locate one. Now just waiting for parts to arrive.

Update once they are in.
 

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Any luck fixing it with your vehicle?
Negative. I also now have a P0117 which is something with the timing chain. My replaced transfer case is making noise again so it's going in Wed for that. I think after that I might leave it at a garage here in Sarasota that a YouTube Mechanic works at and have him do the timing chain, O2 sensors, etc and just sort it out. It will be the last major expenditure I do in the car. It's a 2010 with 153K miles on it. After that is done the car will have 3 of the major fail points addressed and I should be good to go. Thankfully I've been good about oil changes and have always used a quality synthetic oil.
 

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Discussion Starter · #16 ·
High pressure fuel pump for the win.

Replacement went smooth and car runs so much smoother. Appreciate the help and insight. Hopefully this thread helps someone else out in the future.

Cheers
 

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I have the same issue... 02 sensors are working... Extremly high ltft and various stft. I do need to check the hpfp... But the i e i ordered dont fit so that got sent back.... Trying to find the same oem..... Now just need to get the extra $ to get the new replacement. Anyone have the part numbers to those fuel.lines that connect to that hpfp on a 2011 3.0 v6?
 
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