Looking for some technical advice. Recently took my 1997 A4 1.9 Tdi Quattro common rail 110 bhp to a 4WD rolling road test. I thought the results were good by all accounts. Advertised is 110 bhp at 4100 rpm and 173 lb ft / 235 Nm at 2100 rpm. We did two runs, I did the first one and the technician did the second. My run came out at 126 bhp at 3575 rpm and 298 Nm torque at 1575 rpm. Ray's run came out at 130 bhp at 3600 rpm and 303 Nm at 1620 rpm. Not so bad, strange that all the rpms are much lower than advertised though. He did say that it is common for the VW/ Audi group to be conservative in what power there cars put out when leaving the showroom. I have since heard though that these results may actually be a bad thing rather than a good thing.
I was told that it is unusual for the car to be putting out that much extra power and torque untuned, and at the lower rpms. I was told that there is a possibility of a problem with the MAF Maximum Airflow Sensor, and that the wastegate could be stuck or blocked, which would affect the turbo, with regards to over fuel loading, and injection timing. within the air induction tube. Told I should get this stuff checked out by a technician.
I thought the extra power and bhp was a good thing. Any of your technical gurus got any views on this, the fact that the rpms for the maximum power and torque were quite a bit lower than advertised, maybe the tdi quattro needs the power and torque lower as it has extra weight?
Regards

 

Sounds like a bunch of hogwash. The only thing that will happen is the MAF will cause the ecu to retard timing and you may go into full limp mode. This will produce less power. Get the MAF replaced only IF it is the culprit - it's pretty expensive to replace an a whim.

 

Cheers ImolaS4. I assumed that the engine was pretty healthy and just had a better compression ratio than normal and was well driven in early on, then some guy at a tuning Company tells me there could be a problem - sounds wrong to me too. If it is putting out more power, then it must be OK. have you any idea as to why the torque would be that high at such a low rpm though for a diesel, compared to the normal? Nice picture, if that is your car, I'm well jealous. Mine does a quarter mile in 2 minutes!
Regards

 

Well, a bad MAF can cause surging, which might give you more HP than is expected. I was in a TT with a bad MAF and it was going apeshit, up down up down, and eventually it did hit limp mode. However, it would "feel" wrong, and would not be a stable constant higher HP. Sometimes it would be a lack of boost.

Its possible your N75 valve is screwy, throwing more boost than it should, but then again your ECU is what controls boost production (in co-operation with the MAF, and other sensors).

I would question the tool he used to test your car. Was it calibrated correctly? What was it anyway? Gtech?

 

Hi brrrman
Cheers for responding. The car was tested on a 4WD Bosch rolling road/ dynamometer at the Automotive Department of a College. Bosch is good stuff, maybe the calibration was out, may car has a fault or is perfectly healthy and more powerful than I thought. I am gonna get it checked out by the Audi guys, what is an N75 valve, can they do a diagnostic plug in quick check of the ECU to see if it is OK, and what power/boost it is providing etc?

 

Anyone with a VAG com can do a diagnostic check on your car - its understanding the data that is the hard part.

A N75 valve controls the boost solenoid, which in turn actuates the turbo wastegate. Most times a bad N75 valve will cause premature opening of the wastegate, causing premature loss of boost and power. Sometimes, though, it will keep the wastegate closed longer than it should, and this will cause higher than expected boost.

There is even a replacement valve to safely replicate that overboosting function. Lot of the VW guys use it, though there's still a lot of debate as to its effectiveness (or safety).

 

I second brrman's comments.

The N75 (and the VAG comments) should be considered.

 

Yep, it's a pic I took two years ago before the mod madness began!

 

I always liked the Imola yellow... so much better than the Brilliant Yellow...

 

Thanks.
I agree. Brilliant Yellow looks a little like lemon sherbet!