Fuel Trims and 008568 - Bank 1; System Too Rich off Idle

B6/7 S4/RS4
#1

I’ve just recently started having the MIL come on with the following code:

008568 - Bank 1; System Too Rich off Idle
P2178 - 002 - - Intermittent - MIL ON
Freeze Frame:
Fault Status: 10100010
Fault Priority: 0
Fault Frequency: 30
Reset counter: 255
Mileage: 165406 km
Time Indication: 0

It first came on just under a month ago, and I cleared the DTCs. The car felt much quicker straight after the reset and for the next few days. Now the MIL has come back on again with the same code. This time I checked block 032 to check the long term fuel trims and got the following:

Idle 1.9%
Partial -12.9%

So, from what I understand, the cruise fuel trim condition points to a fairly over rich reading, and the MIL is indicating rich on partial throttle from idle.

Would this be more likely to be MAF, O2 or vacuum leak? Any other blocks I should measure to help narrow down what might be the cause?

#2

Vacuum leak should give lean conditions as unmetered air would be getting in. MAF is possible but there is only one MAF for both banks and you’re getting a code for bank 1 only which suggests something might be amiss specifically on that side. Could be the front o2 sensor but I’d first be looking at the fuel system on that side. Could be leaking injector(s) or even the high pressure fuel pump itself.

#3

Cheers for the quick reply. Which side is Bank1 on a RHD car?

Also, is it possible to measure long term fuel trims for bank 2 to see if there is a variance? I can only find reference to logging 032 which for me only shows bank 1.

#4

Bank 1 is on your driver’s side - standing in front of the car looking at the engine it’s on the left.

Not sure if you can check long term trims separately per bank - at least not at the same time. If you switch ECU number 2 (engine II) you can probably log long term trim there but not simultaneously. What you can do is look at realtime fuel trims for both banks, any large deviations should be obvious there.

Injector(s) or fuel pump “leaking” fuel would be more obvious at idle and low loads as the leaked volume is fairly constant and becomes a smaller percentage of fuel injected as loads increase.

Still, I wouldn’t rule out the sensors either. These kind of things are a bit of a PITA to troubleshoot really. A good thing to do would be to pull all the spark plugs (keeping track of which came from which cylinder) and compare the colours of the deposits on them.

This should tell you whether the issue is isolated to one or more cylinders, the entire bank, or if no obvious rich running is going on at all on either bank.

#5

It actually can be a vac leak so don’t rule that out. As noted the bank 1 will be the side of the car you drive on of if at the front of the car facing the back it’s on the left.

Sorry if I don’t remember are you a FSI car or SI car.

A good block to look at is block 001 that’s real time fuel.

#6

It’s a 2007 B7 RS4 with the 4.2fsi. Is it possible to have a vacuum leak that would only affect light load/mid rpm fuel trims and not the idle fuel trims? I would have expected the other way round. I’ve seen boost related high load vacuum/boost leaks that don’t show up at idle, but don’t have much experience with NA cars so just wrapping my head around it.

I’ll definitely pull the plugs on that bank on the weekend and give them an eyeball to see if there are any obvious signs of fouling or rich running. I had loosened off the intake pipe just downwind of the MAF about 6 weeks ago in order to spray in some upper engine cleaner just to see if it would make a difference, but double-checked all the clamps and they all seem perfect.

Would there be any other symptoms of a faulty o2 sensor on that banks exhaust? That’s the only other possibility in my head for the ECU compensating for a perceived richer mixture when there may be none.

Will do some more logging and investigating on the weekend. Any info is good info to put up on the forums for anyone having a similar issue in the future.

#7

Also, I just realised you can access the second ECU using 031 instead of 01 measuring blocks by the looks of things reading the VCDS documentation again. I’ll give this a try later on tonight and see what the fuel trims say for bank 2.

#8

Also, just to reiterate what you guys have said, would this be correct:

Measuring block 001 will give me the realtime AFR correction based off the wideband O2. So it’ll tell me in real time while driving whether it’s correcting for lean or rich condition?
Measuring block 032 is long term fuel trims, so only useful to see if there is an ongoing correction to rich or lean condition at idle and at partial load mid rpms (lean cruise).
Measuring block 031 is real time requested lambda as well as actual lambda to see realtime what the actual AFRs are during while the car is running.

#9

It’s actually very normal to get rich lean codes at part throttle due to how much vac the car is pulling. Those blocks and there actions are correct.

Start with a thuro vac test check the pcv system inspect the arms on the intake manifold for full movement or any other problem areas. The plugs should be fine. A rich code if it’s intermittent isn’t going to usually cause any issues because the car is already pulling away the unexpected fuel it’s just reached the limits before fault code

#10

The problem is, that it’s throwing enough of those codes, through a short enough period of time, that the ECU is throwing the MIL light which I need to continually clear. It must be operating outside what it’s expecting.

I’ll do the airbox flapper test again this weekend, as well as logging the intake runner flap actuation to see if it’s responding to the request for opening at higher RPMs. I’ve also ordered a hand vacuum pump just to do some more thorough vacuum testing due to the many different parts of the RS4 that rely on the vacuum system. Would be money well spent I think.

Any tricks to checking the PCV system? Just all hoses and connections? Can you spray some sort of accelerant around the hoses to see if the rpms change while the engine is running?

Very much appreciate the help you guys are giving!

#11

Yes I use starter fluid and I spray it around the usual suspects. The pcv isn’t east to remove but once you do give it a healthy dose of break cleaner through the passages to help clear up any contents. From time to time the check valves can get disturbed that will cause issues.

#12

Checked the second ECU last night and the long term fuel trims. Interestingly, they are almost identical to Bank 1.

Bank 1: 1.9% Idle -12.9% Partial
Bank 2: 1.2% Idle -12.5% Partial

I cleared the DTCs and will check how long it takes for it to return.

So whatever is causing a detected richening of the mixture must be affecting both banks, however it’s not throwing a code on bank 2. Would suggest to me, at least, that the O2 sensors are fine, or they’re both stuffed to the same level (unlikely).

I’ll clean the MAF on the weekend as well, as this could be to blame for a rich condition on both banks. I’m also only seeing 141g/s at 8000rpm 3rd gear pull, though that’s likely due to carbon as the car has 160 000 kms and I’m not sure if it’s ever been CC’d.

#13

Great work callin most people just look at the one code and never actually check to see what the other bank is doing. Both sides are clearly effected so this reduces a few possible issues. Check all the connections and let us know what cleaning the maf does.

#14

I didn’t get around to cleaning the MAF unfortunately, but hopefully my vacuum pump will arrive this week and I can do a good thorough vacuum test and MAF clean this weekend.

So far over the weekend, have done a fair bit of driving and no reoccurring MIL yet. Though it took a few weeks last time.

#15

Just another update to say that the MIL still hasn’t returned. I need to run VCDS again though and check the LTFTs again and see where they are sitting after cleaning the MAF.

Having another thought bubble, is it possible that a consistent rich negative multiplicative long term fuel trim across both banks point to some type of intake restriction? If the MAF is calibrated to expect a certain airflow from the factory intake system, and the 02 sensors report that the mixture is too rich, could that be an indicator of a carbon buildup restriction in the intake path? I’ve found references to dirty air filters being responsible for rich LTFTs but thought it might be interesting to see if anybody that knows they have bad carbon build up to see if they see negative LTFT values like I’m seeing.

#16

Another update, this issue has come back with a passion now. Got another MIL a week ago with the same code. I checked the LTFTs then reset the code. LTFT this time were:

Bank 1 -11.3%
Bank 2 -6.6%

After clearing, got another MIL a week later. Forgot to get the LTFT codes before clearing Bank 1, but Bank 2 was at around -6% again.

How hard would it be to check for a leaking high pressure fuel pump on that bank? Also, I’m guessing that 02 sensors would start reading anomalously richer as they age and get contaminated? Might be due to replace all the 02’s as well as the HPFPs to be sure now that I’m up over 180k kms.

#17

The -6 range or positive 6 is standard. The 11 would be something to look into. Check for vac leaks. They can be a big part of fuel trim issues.