Yello

I would really appreciate any help with this, and Thanks in advance!!

Okay, here's the deal: I have TAP Stage II on my '97 1.8TQ A4, which I bought from a private party in California (I live in Colorado) about six weeks ago. When I bought it, it already had the TAP upgrades. Shortly after the purchase, while still in California, as my friend and I were driving it around it started acting strangely on occasion, which I can best describe as convulsing, kinda like when the RPMs get too low on a car and it stalls. The car wouldn't stall or anything, just "convulse" momentarily until the rpms got up a little higher. Well as you can guess, it scared the **** out of me at first, but I figured it was just the chip not working properly (nothing seriously wrong otherwise), or possibly that the previous owner hadn't put high octane gas in it prior to the transfer and that that was just causing problems. It only occured with that original tank of gas, and hadn't happened in the six weeks since... until today!

Well, when it started happening today it really caught my attention and I made sure to figure out exactly what was happening. It does its little convulsing thing with WOT, boost around 12 psi (I happened to recently install a gauge), and between 2900 and 3300 RPMs. It doesn't do it outside that region of RPMs and will happen in 3rd, 4th or 5th (and assumedly 1st and 2nd, but I didn't try it). Obviously normal driving techniques (or at least proper driving techniques) would not lead someone to flooring a turbo induced manual car with the RPMs down at 2500, but that is beside the point (and why it hadn't happened in the past six weeks).

Anyway, imagine the RPMs starting at 2500 with WOT and the boost at 12.5 (the max for TAP stage II). Now, the RPMs rise smoothly until 2900 when the jolting starts. With each jolt the boost drops to approximately 10psi, then it rises up to about 12.5 again when the next jolt occurs. This continues for a few seconds until the RPMs reach 3300 and it then everything is fine. It always happens with the same 29-3300 RPM range, and only at the max boost. And the car performs normally immediately before and after the jolting.

Any ideas? My first impression was that it was because the RPMs were just too low, and thus there wasn't enough exaust and the turbo couldn't function properly. But, since it seems to work fine at 2500 or whatnot (and will reach 12.5 psi) that theory wouldn't make sense. I've also looked through the archives concerning other problems that have occured with turbos like pinging, detonation, boost failure, preignition, etc, but none of those sound anything like what is occuring for me... Please help!

Thank you very much for any input!

Zsan

I've experienced stuttering in that RPM range. If that is what you are experiencing it is normal. Many people have complained about this. It really occurs when it is hot outside. You might be experiencing something else, I would suggest you take it to the dealer.

Yello

Zsan,

Thanks, for the response. Stuttering is actually a better description than convulsing or jolting, and it makes me feel a little better that others seem to have had this problem before and it is apparently "normal". I already have an appointment with the dealer for later this week, so I'll plan on checking further into it with them...

Has anyone found out exactly what is happening mechanically when this is occuring? Although it may be normal, it's definitely not a settling feeling!

Thanks again!

pita

Like I said about the cChipped A4's reliabiliy...

Chris C

This happens in non-chipped 1.8t's as well.

DaveN

and I've wondered if its caused by running out of vaccum to run the wastegate with. The wastegate is a fail safe, meaning you need to have vaccum applied to it to close it and get boost. I don't know how they generate this vaccum, but I suspect it is much like the brake booster where they use manifold vaccum, which is shut off using a one way valve in boost conditions. I find that when I get this stuttering if I stop using boost for a while (I havn't made a study of it, maybe 30 seconds) then I can get back into it without the stutter. Anyone else notice this?

??

pain in the backside?

Yello

I have done even more extensive searching on this topic in the archives (starting off with keyword "stutter") and have come to the somewhat uncertain conclusion that what is happening to my car (and yours, probably) is pinging/knocking.

Although I haven't had a chance to really listen to the engine when it stutters, and have thus not heard any high-pitched metallic pinging sounds as described in some of posts I've found, everything else seems to point to pinging/knocking.

Take a look at the following posts for more info:

http://www.a4.org/forum/m/a4/171393.phtml (specifically that post, and the subsequent post also by "brian")

http://www.a4.org/bbs/a4/9926/messages/261.shtml
(detailed descriptions of what causes pinging)

http://www.a4.org/forum/m/a4/171540.phtml
(good final thoughts regarding pinging)

Anyone disagree with this pinging/knocking conclusion?

Thanks!

Jeff R.

Is pinging the proper term? From my limited technical knowledge and memory, here is my explantation. I had similar problems with my APR 1.0 Bar chip. APR told me it was the anti-pinging software in the ECU that was causing the stuttering. The ECU was detecting early detonation and adjusting the timing for it. The cause of the problem was crappy California gas and they gave me a modified CA. version chip. Now it runs smooth under WOT.

My first recommendation is to talk to Ivor at TAP. He should offer you a solution, whether its to change gas or octane booster or preferably a new version of their chip. It is not NORMAL and you should do something about it.

Jeff R.

P.S. According to APR the problem you are experiencing is not bad for your car because the ECU is doing its job. It just makes the car acceleration feel crappy.

Yello

Jeff,

I'm not sure that I have the same problem that you did. From my impression of your message, it sounds like your acceleration during the stuttering just isn't very smooth. Is that a correct interpretation? When my car stutters it's much more that just unsmooth acceleration, it's more like the engine is about to stall (like I mentioned in my original message). In other words, definite "jolting" going on...

Any further comments much appreciated.