Boost issues with ur quattro rr engine still!!

[robbie100hp]

Hi guys Iv posted before on this and I'm getting a bit frustrated with it!

I bought the car about 3years ago now and I knew it had a boosting/flat spot intermittent fault.

At first it would be OK for weeks but it has steadily got worse to the point were I am now that it will boost/Rev ok for one pull then almost go into limp mode and not really boost/pull. If I then stop and turn the car off and then on again the car will almost reset and do the same as above.

The car is a 1990 Audi ur quattro 20v rr, car has been chipped, exhaust without cats, cone air filter and forge splitter valve.

Iv had the vacume hoses changed, put a new spring in the waste gate and fitted a new n75 valve.

Iv also done a diy leak test and all looks ok, I know the hoses are 25years old and need replacing but before I spend the best part of £500 I just wanted to ask for any ideas?

Someone has suggested that the chip maybe causing the car to over boost then the ecu hold back, but this hasn't always happened?!

[martinws]

Get vagcom on it and check for fault codes. I had a similar intermittent issue I could not trace as I never had vagcom or a code reader when the fault occurred. It turned out to be heavily corroded N75 plug inside the rubber boot.

[twoqu]

It would be useful to know what chip it is i.e whether its reputable. If you are confident enough to open the ecu up you may get lucky as most reputable tuners would stick a label over the chips with ID.
How have you configured this splitter valve? Is it in recirculation configeration and is it orientated correctly?
When you say you have replaced the wastegate spring, have you replaced it with a standard or aftermarket (stiffer one)
Has the wastegate cap been modified to make it adjustable?
It is always useful to interogate the ecu to see what faults it is registering.

[twoqu]

Plus of course general wear and tear items plugs leads fuel filters etc, not to mention the basic ignition timing!
Really can't see the appeal of cone filters and bling diverter valves. They are not necessary on a vehicle that has been chipped up to the level of what the standard components allow anyway.

There is not a lot of info on the RR but another possibility might be a faulty MFTS sensor. This is the large sensor on the water rail on the inlet side of the head. It provides a signal for the coolant guage and overheat signals. If an overheat signal is triggered boost is lowered back to 0.4bar which is the stock spring pressure. It is not uncommon for these to fail. A quick check is to pull the large connector of and see if it cures it or not! Not very scientific.
Other than that, its a matter of elimination but you have been offered advice of a similar nature previously and we are not sure whther you followed it. For example it has been recommended to replace that divertor valve but you are still running it! Have you found the diagnostic terminals yet?
The usual mantra is leak test and pull codes first.

[robbie100hp]

Ok the fault code has been read by Tonks a month or two ago, Iv replaced the splitter with the standard diverter no difference

The car has new leads plugs, cap and arm including a reconditioned maf by Bosch in Germany and a new n75 valve.

Iv had the ecu out when it was resprayed but I couldnt see any signs of the company who chipped it, I do have a standard ecu but as I'm sure you guys are aware it's a nightmare to change (my next job)

I'll try the mets sensor now!

Springs Iv tried a used standard and uprated

Thanks for the help

[Error404]

I would suspect knock sensor(s). They do often throw codes, but not always.
Turning the ignition off and back on will clear the fault, until the ECU detects it again.
They are not expensive to replace anyway ~(£30 each), if they have never been changed they will be past their best.
MFTS overheat signal and knock detection / sensor fault are the only two conditions where the ECU will cut all boost control.

[twoqu]

Out of interest where are the diagnostic plugs?
Also we need answers to questions. The reason behind asking whether the wastegate cap is modified is that it might indicate certain underisable tuning companies handiwork! If you are not sure then post a pic so we can have a look.
In an ideal world it would be nice to interrogate the ecu immediately after the fault occurs.
Having found what appears to be an RR wiring diagram it does appear that the MFTS is connected to the Ecu like on 3B models so that safeguard should be on the RR. If it is faulty it would not leave a fault code.

[Error404]

Agree, MFTS will cut boost also

[robbie100hp]

Can someone point me to the mets, I disconnected what I think it is. Is it the one with the orange plug with four pronge? If so it made no difference. I'll try and get it plugged in next week and report. I think this was in the passenger footwell.

If I change the ecu I'll open it up and report with pics if needed

[twoqu]

Sounds like the right one! I expect some might argue its brown. Oh well, that would have been a quick win.
Swapping back to a stock ecu is not a bad idea as if the car does not drive as expected stock, its not going to perform with a modified ecu putting strain on the engine components. Again unless you are certain that the wastegate has not been tampered with and has a stock spring you might still get issues.
Is the anti tamper cap still on the distributor. If its not I would check the basic staic ignition timing which is pretty critical on the earlier 20V. My dizzy was so far out that it was causing a rich mixture and the car was very flat even though it made the right boost level. So even basic things can cause problems and you need to do is test and eliminate what you can.

[twoqu]

Error has pointed to the knock sensors and off course it might actually be knocking!
I think you had a boost guage so what level does it reach before and after the problem. Just trying to get whatever info we can.

[twoqu]

You say you have replaced the dizzy rotor arm. Was that the correct 10mm width one?

[UrS4boy]

Robbie: Just for you (and everyone else with boost issues):

http://www.s2forum.com/forum/showthread.php?t=79960

[newsh]

You must do a proper boost leak test and you should clean and preferably re-pin the MAF connector.

If the car goes into limp mode and feels sluggish but resets when you switch off the ignition and is ok till you floor it again .. I'm almost certain it's the MAF connector.

If it does a massive cut out and nearly throws you through the windscreen it will be a boost leak, maf problem or combination of the two..

I chased this problem for about 2 years when I first got my 3B (same setup as RR)

Read this http://www.s2forum.com/forum/showthread.php?t=24544

[george21]

Fuel tank clean? Pump tested, filter new?
My recent experience with 3b
Took me a good week to find it,
fuel pump was starving SOMETIMES on higher boost
due to a bit of sh*t in the tank