EHLO

I can confirm that the runs *must* be done with the accelerator pedal all the way down against the stop, otherwise I was getting MAF values no higher than ~85, instead of the correct ~180 (450HP times .8 divided by 2 MAFs).

First I made sure the TBs were aligned;

Throttle Body Alignment (TBA) - Ross-Tech Wiki

A few tests confirmed that my MAFs are pretty good, but not sure why at least one of the TP readings isn’t 100%;

Engine RPM ( /min),Mass Air Flow ( g/s),Relative Throttle Position ( %),Absolute Throttle Position B ( %)

5314,138.75,75,87
5982,155.22,75,87
6636,161.88,75,87

5618,149.77,75,87
6310,162.75,75,87
6907,165.83,75,86

jeffkruse

Even though the readings were still not good with the new MAF sensor, the main reason I wanted to replace the MAF is to get rid of those CEL codes

17538 - Fuel Trim; Bank 2 (Mult)
P1130 - 001 - System too Lean
17536 - Fuel Trim; Bank 1 (Mult)
P1128 - 001 - System too Lean

which I thought was the cause of the codes. But no. I checked all the vacuum hoses for any cracks, leaks etc...... I am thinking oxygen sensor might be next

nathanwind

Did you ever run a bottle of fuel injector cleaner through it (BG 44K or similar)?

MP4.2+6.0

besides the injector cleaner, I see these codes seem to be on both sides. Normally that would seem to lessen likelihood it is something that is side (bank) specific like one but not the other of the forward 4.2 O2 sensors. Exception cases might be things like a history of general oil burning/tired motor that degrade both similarly.

Needs more diagnostics and ones I haven't done, but fuel delivery and pressure also come to mind, plus the buried vacuum issues, combi valve/SAI, intake manifold leaks/cracks/gaskets, leaky injector seals (but would seem less likely if both sides show lean unless you have multiple seal failures). Longer shot ones too like bad throttle; on that BTW consider mechanically cleaning inside of it if you remove the boot to it--injector cleaner doesn't get up in that area at all. I've been blessed not to have these kinds of issues beyond basic vacuum leaks and some SAI on prior Audis. But in general I think you probably should keep looking at BOTH fuel and air sides, and keep in mind diagnostically your pointers are to something that affects the whole motor and not one side specific. MAF thus qualified, but sounds like not it thus far.

Later edit: if you know or have service records, also look for any prior work that could be a clue. Thus, anything that required an intake pull would implicate a variety of things, parts involving vacuum or fuel their respective systems, etc. Not just that there was a prior issue that might recur or wasn't the real issue; I've certainly seen follow on problems from work both the dealer and I have done where something near the work area got overlooked, broke or was accidentally disconnected during the job, etc.

Alexxelax

Hi, i made a reading and i hope anyone can tell me why the two diffrent readings show diffrent values, what is causing the diffrent readings, and if either one is even right readings and possible solutions.



My RPM bounces up and down little, could this be something related?

MP4.2+6.0

1. Which motor?

2. Regardless of the two readings--for which I would look at VCDS documentation if it isn't an S8 or W12 that have two MAF's--I don't think this tells you anything useful. You should run it in the recording/instrumented mode, tracking at least MAF flow and RPM. Then go for a test drive and start the VCDS recording right before several runs where you fully floor the gas pedal, at least through first, but hopefully second gear as better since it doesn't shift out of second as fast so you will have more data points at various RPM's given the sampling rate. You are looking for the PEAK flow in g/s, which will be at an RPM close to redline and shift point. The peak flow is what you compare against 80% of rated HP for your motor. Thus, you need to see hundreds, not 2-5 g/s.

3. RPM bouncing a bit is often a vacuum leak. If not, then yes it could be a misreading MAF.

Alexxelax

1. S8 2006 BSM engine

2. Okey i will do that today so i need to come up to about 360g/s? (450hp)

3. Vacuum leak, is there the tube for the intake to throttle body? If not where should i start looking?

Thanks

MP4.2+6.0

Thus:

1. If S8, then two MAF's--MAF's are screwed into top of air box on each side. One reads much lower than the other from the info you posted, so probably look more at that side.

2. Yes, 360 g/s. Since you have twin MAFs, you should see about half of that (180 g/s) per MAF/side.

3. I don't know S8 with that degree of specificity, but in general you want to look at al the intake connections--air lines, oil vapor stuff, etc. Basically anything that attaches to the intake. If you can get better data on which side the lower reading is from from your earlier readout, that will help direct the search. Also look at the large rubber piece and clamps that go from the top of the air box to the intake manifold on the relevant side. On W12's the "suck pump" (also called suction valve and some other things) pushes into the side of that large rubber tube (on the U.S./left hand drive) on driver's side of the motor--anything loose or wrong with that could be a big air leak. From having forgotten to push it back in once, it causes some motor shake/vibration if off. Leaks can cause CEL to come on though, so it could be a faulty MAF directly.

Alexxelax

I cleaned the throttle body with carburator cleaner and the air mass sensor with air mass cleaner. Then i did a throttle alignment and sealed the tubes with rubber tape and i did a test, now i got:

1. 3.20
2. 2.95

A much better result i think, not much diffrent as before. I didnt have time to take it on i ride yet, but the engine sounded working much more smooth on idle.

For anyone that want to know i used

For throttle body: crc carburettor cleaner + torx 40 + Throttle Body Alignment (TBA) - Ross-Tech Wiki with video
For AMF sensor: crc air mass cleaner
For the tubes i used rubber tape that seals by itself used for water hoses.

SilverA8oh

I've seen this movie before. Also check the Pressure Control Valve and Fuel Pressure Regulator (4.0 BAR) if your 4.2L is pre-FSI like mine. Easy to change out for less than $75 in parts. The PCV on my car had a rattle in it when it was pulled and the fuel pressure regulator had a broken piece on it (the brown plastic internal gasket). I also replaced the MAF for good measure with my mileage with Bosch for under $100 online. Runs like a completely different beast now. Save your Catalytic converter before it's toast too...