Rexy8890

Hi. i'm having lack of power in my audi. Few minutes after start i would say everything is okay but when engine get warm throttle response is very poor and definitely i can feel that engine doesn't have full power. I did some log today so if anyone could have a look on it would be great. personally i think there is something with throttle or gas pedal but data from MAF doesn't look good for me too. thanks


Log #766638

MP4.2+6.0

Link says file doesn't exist.

Instead, please excerpt from log the relevant areas--typically engine. That also means BOTH ECU's, not just the default ECU1. Scan tranny too just in case it is in SAFE mode (though display in instrument panel then reverses, and is usually pretty obvious. Hopefully underlying log is VCDS, or similar sophisticated scan tool. Net, make it easy for folks to spend time to help you.

Also, include your miles/km, when last tune up (plugs, filters, etc. was), any prior possibly connected areas--fuel or ignition parts changes or failures, battery up to snuff or not, etc. All I know going in is the few sentences in this thread.

Rexy8890

No faults codes in transmission or ecu's , what is weird. . fitted new spark plugs about 500 miles ago and k&n air filters. fuel and oil filter new every 5k miles.what i can say more engine vibrating in idle, in vcds revs going up and down from 640 to 580 revs.

MP4.2+6.0

Well start with the K&N's. Proceed immediately to the trash can and toss them in. You likely oiled your MAF's, which likely ruined them. The K&N story line of them not harming MAF's is complete bull as far as I am concerned. I used them back to carburetor and pre-MAF days, when air cleaner filters were primitive and didn't have a lot of pleated surface area. No more. Found oil on a K&N factory oiled filter up to two feet (!!!) up an intake tract on a 4.2 with an MAF--the red factory oil color as a dead give away. Totally screwed it up, causing much lower measured air flow than reality, meaning car ran quite lean. Piece o' crap, that strong. On a W12, those MAFs sit right in the inside center of the filters, so they are basically swimming in the K&N oil vapor.

As one simple test, unplug the MAF's and try running that way temporarily and see if smoother. It will generate codes for them being unplugged, but those can be cleared. Unplugging simply forces the ECU's to do air fuel calculations with a default mode instead of measuring actual air flowing past the sensors.

You can try to clean the MAF's with a spray cleaner marketed as such. But, expect mixed results.

As one other simple check, look at the air fitting where the power brake vacuum booster takes off. If you removed the tops of the air boxes for the filters, you had to have undone this fitting. Sometimes I forget to plug it back in--it is just a push by hand fit. It is at the base of one of the air hoses/ducts that goes from the air box to the intake manifold on each side of motor. Look below the hose/duct closer to the intake manifold clamp up area. On a USA/Continental European model, it is on drivers side ("left" of car by nomenclature). If you are in UK, may still be on driver's side for you, but now right. The T itself may also come apart; mine did and I replaced. You typically hear a vacuum leak in area if it is messed up. Motor will run somewhat rough, and will eventually throw a generalized code about mixture. MAF will also misread on that side, since vacuum leak will then be between MAF read point and the intake and cylinders. If it is that, still dump the K&N's. With twin boxes and the ram cold air factory set up, air flow is not an issue. Each one is essentially handling 3 liters. On the same era 4.2, one of very similar size was handling the whole motor, and 4.2 was 5 valve pre-FSI.

Striker2237

I completely second that. The K&N filters very likely killed the MAFs, that's why it starts fine then has issues. Try to clean them with a MAF specific cleaner but you may be screwed...

What does the data stream show for the MAF sensors measured flow rate?

Rexy8890

On idle is between 3-4g/s, floored going up to 150g/s max which is weird because even vcds saying that should be 0-170g/s.

MP4.2+6.0

Rule of thumb is g/s at max should be .8 of rated HP. So you are looking for 450 x .8/ 2 MAF's = 180 g/s each. To read data, with have a co pilot or set VCDS to data recording mode. When I found my 4.2 MAF was bad, peak readings were right at shift point. They were low maybe 20%. The new one I put in to fix it read a little above the .8 rule of thumb. Given how fast it shifts 1-2, easier to read at 2-3 shift.

Check the air fitting I mentioned--it would also cause a low MAF reading on drivers side where fitting is, since air would be entering at the fitting hole and motor would be running lean at same time. Meantime absent a vacuum leak, that data says your MAF's are not up to snuff. Those readings would have it probably running lean too, and hence wandering idle and down on power. Likewise as mentioned earlier, if you unplug MAF's it should approximate correct readings (it will meter fuel based on engine RPM primarily) and then run better until MAF's plugged back in. Regardless, you want well functioning MAF's for all of performance, fuel economy and smoothness. Thanks K&N.

Rexy8890

Thank you guys. I think i will start with new oem air filters and run some more tests on both ecu’s.

dvs_dave

You need to clean both MAF sensors as well. Just changing the filters won’t get rid of the K&N filter oil that we suspect has already contaminated the MAF’s.

Rexy8890

Well i disconnected both maf sensors and it is much better. Obviously not great but throttle response is a lot better. What concern me when engine is cold i can feel how is pulling and can feel that power but the moment when is get hot everything changes. Even when is half hot it is such a difference between when was cold.