MAF, O2, and Fuel Trim Help Needed

[threeputtpar]

2003 Audi A6 2.7t with a mild performance tune.

The tune is designed to increase the boost pressure and increase timing/fuel to match, increasing the power by ~60hp. It is doing just that, but for some reason it thinks it is always running rich (at idle and under load). I did post about this a while ago, but I have new info now and am hoping someone can solve the mystery.

I had sent the ECU back to the tuner so he could reporgram again and rule out human error, and it came back with the same problems. So I believe the tune is good.

I can drive the car about 10-15 miles before it hits the max of how much fuel it can pull, and then it sets the CEL and power is reduced but not into a limp mode failsafe. It actually drives about the same as it did without the tune, which is still pretty good.

I've done the simple things like check the coils, replace the plugs with stock, replace the plugs with one heat range colder, and run diagnostic tests on the MAF and EGT sensors. The MAF and EGT readings are just where they should be for the tune. I even unplugged the MAF and ran without it last night and it seems that it would get to the maximum much faster than before, after about 3-5 miles. I don't know if that means that it's on its way out or not.

The strange thing is that the two sets of plugs I pulled out were not black and/or fouled, so I'm not convinced that it is really running rich. I monitored the O2 operations, and the voltage bounces around between 0.89v and 0.11v and the short term fuel trim is always trying to pull fuel.

Anyone have any other ideas for what I can check besides what I've already done? The O2 sensors are somewhat easy to get at, so I could replace them if need be but they are pricy so I'd like to do that only if they are the problem.

Thanks in advance.

 

[Brybo86]

what is the CEL code?

 

[Daigle]

huh... typically if you unplug the MAF while its running and nothing happens, your MAF is bad. Also MAF cars usually start in limp mode if started with the MAF unplugged.

the fuel trim you are fighting is related to coolant temps, i dont think this is related to the function that stabelizes AFR's. its actually an enrichment table, it simply adds fuel for cold start up. once warm the car goes back to its normal hunting for stoich.

theres also a fuel trim table for adding fuel when ambient temps increase but thats a seperate deal.


sounds to me like your CTS is either reporting the wrong coolant temps or the cold start enrichment maps need work.

interesting stuff, i'll stay tuned.

edit: also narrow band widebands are pretty useless. their only function is at idle as thats all they can really read. turbo cars run in the 10-11s and a NB gauge cant even read that.

 

[threeputtpar]

P1127 Bank 1 Off Idle
P1129 Bank 2 Off Idle
P1137 Bank 1 Idle
P1139 Bank 2 Idle

All 4 are System Too Rich

 

[threeputtpar]

Originally Posted By: Daigle
the fuel trim you are fighting is related to coolant temps, i dont think this is related to the function that stabelizes AFR's.


I forgot to put that in the original post, I did replace the coolant temp sensor at the back of the heads that feeds the ECU data for A/F ratio. I guess it is possible that the one I got was bad, but the scanner shows that the operating temp is correct so I assumed that the sensor was functioning correctly.

 

[LeakySeals]

Can you de-tune to verify all is ok and no coincidental issues like vacuum leaks, lazy MAF, etc?

 

[threeputtpar]

I was hoping that it wouldn't come to that, since I would have to send it back to the tuner again or source another ECU and defeat the immobilizer to have it work. I had asked on the Audi forums if anyone would lend me one for testing purposes, but no volunteers.

I have verified all vacuum lines (took quite a few hours and a sore back), and found no leaks. With a vacuum leak, wouldn't that cause a lean issue instead?

 

[Daigle]

Originally Posted By: threeputtpar
With a vacuum leak, wouldn't that cause a lean issue instead?


unless in boost, then it would cause a rich issue


yeah id trust the sensor if the readings sound right.


ever heard of a boost leak tester? well worth making/buying one. i hook it up to my turbo and pressureize my entire system to 30psi. yeah som of course slips by the valves but the air tank can more than keep up with it. with 30psi, when there s a leak, you hear it!

 

[threeputtpar]

I guess I failed to mention that in my OP, too. I built the tester on AWE's website, but instead of using an air line fitting in the tester I used a tire valve stem and pressurized it with a bicycle pump. I think I did everything right, because at one point the system released pressure through the updated oil fill cap. Up until it did that, I heard no hissing noises.

I'll probably install an air line fitting and regulator and try to pressure test again.

 

[01rangerxl]

Have you tried cleaning the MAF sensor?

 

[threeputtpar]

Yes, I soaked it in alcohol and let it air dry with no change. That is why I unplugged it and ran the car for a night to verify it was still working.

Wow, I really failed in providing the pertinent information in my original post.

 

[mattd]

are you still running factory injectors? It still sounds like the fuel map is off. Other things that will cause rich fuel trims are tight valves, stuck/lazy 02 sensors (but you say yours are switching properly), MAF (usually will result in lean trim codes with they fail), high fuel pressure, leaking injectors.

I still say there is something wrong with the fuel map. If you load the stock tune does it set the codes? also, monitor what the ECU is seeing for coolant temp at operating temp.

 

[threeputtpar]

Yes, I'm still on factory injectors and just about everything else is factory level (no upgrades).

I'm to the point where I will do another intake pressure check tonight and see if there are any leakes, but if not I'm out of easy things to chase down.

The O2s are bouncing around, and they are actively trying to lean out the mix under throttle. They are also enriching the mix when I let off the throttle and coast from highway speed down to city speed or a stop, such as coasting down the highway off ramp to the intersection. At idle they seem to be doing nothing, and read a very low voltage.

I have not done a fuel pressure test yet, nor have I even pulled the vac hose off of the FPR to see if there is any fuel on the wrong side of the regulator. I suppose if the FPR is leaking, it may be pulling in additional fuel through the vacuum hose and that is enriching the mixture post MAF. Is there any chance that the FPR is failing in a manner that would force more fuel throught the injectors, thus causing the rich condition?

The ECU is seeing the appropriate coolant temp, ~195°F. I don't have the ability right now to put it back to stock, but I'm trying to find a way to do this.

 

[mattd]

Does this engine use a MAP sensor in addition to a MAF sensor? Make sure MAP readings are correct. If the FPR is pulling fuel through the vacuum line, it will result in a richer fuel mixture that the PCM cannot control. This however will usually be associated with poor running, and even possibly black smoke emitted from tail pipe. The amount of fuel that flows through the injectors is controlled by the PCM through the injector pulsewidth. Is the PCM reducing the IPW to compensate for a rich mixture? If the pressure is higher than normal at the injectors that can also play a role in fuel trims. As you can see, there are many variables.

 

[threeputtpar]

Yes, it has a MAP sensor in the boot right in front of the throttle body. I'll track down the measuring block and see what it says.

I think the ECU is trying to reduce the IPW to lean out the mixture, but it is hitting the -25% maximum it can adjust it and then setting the CEL for exceeding the maximum limit.

The car runs pretty well for thinking it is overly rich. I've been tracking fuel mileage this week and it is the same as it was before the tune, so I'm still not 100% certain it is running rich at all. It's cold enough here that I do have visible exhaust from the tailpipe all the time (not just during warmup), but it is not black like I would have expected. It has full chipped power right after I reset the CEL, but it slowly diminishes as the miles add up. The plugs I pulled out were not black and carboned up, they were the light tan that they should have been.

I think I'll focus on fuel pressure for now and hopefully the FPR just took a dump and the coincidental time of the tune, and that is the core issue.