# CEL on.. Bad Fuel Mixture.. What else to try ?



## znorad (Nov 20, 2009)

Hello, I've had my GTO for a couple of months now ('05 m6) and recently drove it from PA to CA and ran into a snowstorm near Reno. I had to put on chains and drive roughly for about 30 miles. After I removed my chains, I noticed a CEL and the car shakes when idling and when I put it in gear and try to drive, but when it gains speed, it's fine. 

Today, my mechanics and I tried just about everything we knew of. Our computer says the mixture is bad (Low fuel in the ratio). We changed the fuel pump, problem persists, then we changed the spark plugs (reused the wires), problem persists.. we even changed that sensor by the LS2 sign (sorry, forgot what it's called) and it was fine after that for a little while, but the CEL went on again and shakes started. Also, not all of fuel gets burned, due to low fuel ratio (only when CEL is on)..We also cleaned the maf sensor. But it's a low mileage car (22K) 

I should also mention when we erase the code, the car works fine, but when the CEL goes on after driving for a little while - the car shakes again at idle and take off. 
You can continue this cycle of erasing the code, and it will go back to working fine, and after a while it still screws up. Also, the previous owner had headers installed and a tune was probably done properly judging by me driving it for so long without a problem.

I'm leaning towards a computer problem, rather than a physical problem. But it's a point when I am personally clueless what else to try. 

Sorry for the long read, but this is one of those unique GTO problems that we don't know of and never seen in other cars, and need assistance from fellow owners. We have all the equipment and any advices can be tried right away. 

Thanks in advance.


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## Rukee (Feb 8, 2007)

It would be helpful if we knew what code was being set.
Could it be fuel contamination? Did you happen to notice/correlate this change with a fuel tank fill?


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## znorad (Nov 20, 2009)

It registers a couple of messages integrating this issue.. "Mixture lean.. a couple of missfires" stuff like that but no error messages regarding any parts.. We also ran a couple tests, and one O2 sensor was getting strange readings compared to other sensors when the car runs fine..Not sure what that could indicate... 

Perhaps I should also mention that when I unplugged the sparkplugs they were black.. We changed them, and ran the troubling car for only a couple of seconds... and the sparkplugs became yellow.. We then turned off CEL and unplugged that sensor, and I drove it hard for a couple of mins and it worked fine, and spark plugs looked the same color they were.

But over time the CEL went back on, and the car starting shaking again at idle and low gears.

We also inspected the fuel tank and it looked fine. It wouldn't make sense why it works fine with CEL off if it would be fuel contamination. That was our first thought too. 

Very frustrating issue here.

Thanks for replying.


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## Rukee (Feb 8, 2007)

What are the exact code #s that come up? We may be able to help if we know which codes are being thrown.


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## 05GTO (Oct 6, 2004)

Could be bad gas or moisture in the gas tank, the best treatment would be to use something like seafoam to remove the water or drain the tank and fill with fresh gas.


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## AlaGreyGoat (Jul 6, 2006)

:agree

Also, may be an O2 sensor dying.

Larry


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## znorad (Nov 20, 2009)

I forgot the exact codes, but I will get them all on Monday. And we will also try to empty the tank and fill with other gas. Probably should have done that when we changed the pump..

Thanks for the support guys.. I will post the exact codes on Monday


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## znorad (Nov 20, 2009)

It registers 2 codes: p0171 (bank 1 sensor) & p0174 (bank 2 sensor) -- both read lean mixture

After we switched the map sensor, bank 2 sensor showed good indications, but bank 1 still registered lean. After running a couple of tests, we changed the bank 1 sensor 1 (O2). and for now I drove it a seemed fine and didn't register error codes, but this happened before, so the problem could resurface again after more driving.

What are you guys' thoughts ? And what could have caused bad readings from the sensor (even after we cleaned them) ?


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## Bluegoat05 (Mar 22, 2010)

what happens a lot is there will be a problem and the computer will try to fix it and mask it and cause other problems.. i never notice a fuel filter change in there because that kinda sounds like that could be it or atleast part of it.. also did you do a live data check? like did you leave the car running while plugged in and checked to see what cylinders were misfiring? because if its just a couple that would be a start on where to look. but the first thing i would do is change the filter because its lean. i would not be driving it around too much if its lean you could ruin your engine..


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## Bluegoat05 (Mar 22, 2010)

oh it probably wouldnt be a bad idea to check the fuel pump relay too


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## znorad (Nov 20, 2009)

yes, we've done the live diagnostic, and we changed the pump... I don't think it could've been the relay, then it would definetly show on the diagnostic.

But we changed the O2 sensor on bank 1, and it seems to work fine so far.. hopefully this will fix it..


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## Red Devil (Dec 31, 2006)

HI
I think I´v got similar problems with my -06. The problem often appear when it is cold and rainy. Drove for two months this summer without problems after the change of O2 sensors and new MAF + new computer. This did not solve the problem and now the car leave a smoke trail and the idle is irregular. The only mod is American Racing headers and a short shift. Anybody recognize this or similar problems?
Tomas


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