Phil s

OK, here is a problem I have been working on since Oct. I have a 97 1.8TQM, K+N, Scorpion, and currently a Wett 1 bar chip. I get a backfire under "mild" acceleration, when shifting between 1 and 2, and 2and 3. It is a very mild "pop" that happens after you let off the gas to shift, then as soon as you give it gas in the next gear you get one single "pop" that seems to be in the exaust, but I am not sure. I have a second ECU with the TAP stage I, and it does not do it with that chip. I had a TAP Stage II and it DID backfire with that one. Wett origanlly sent me a chip that did not do it but it also only gave me 10 psi boost. They sent me another chip that had better boost but it did backfire, but not as much as the TAP Stage II. It seems after several chips and ECU's that higher boosting chips bring this problem out. I ran the car for over a year with a stage III chip and no problems all this came after a problem with a bad Coolant Temp Sensor. In the process of swapping ECU's with TAP in order to bring the car to my dealer in "stock" condition per my dealers request, I have been unable to get a chip that performs as advertised. My best guess is that the chip tuners are not getting the fuel maps right for my ECU or the timing. It also has crossed my mind that it might be outside the ECU? Any input on other things that might cause a pop (can a small leak in the exaust do this)will be much appreciated. Also keep in mind this is not any kind of "normal" burble sounds you get with a performance exaust, it seems to be unburned fuel lighting up in the wrong place, and this car has had these options since 1000 miles to about 20000 miles with no problems untill the first Chipped ECU was taken out.

Steve S.

Since I'm not a turbo guru, I will refrain from any more comments...btw, I have heard of a TAP Stage I chip backfiring on a 1.8T Passat before...I kinda helped check it out when swapped into a 97 A4 1.8T....I was used for "ear power", and it didn't backfire in the A4.... :-)<p>Steve S.<br>97 2.8QM

MK

If you are using Premiumn (92 oct), try another gas station or brand...

KeremD

Can this be backfire. I have the Klasse and when I rev the engine and pull my feet from the gas in neutral, I hear a small pop coming from the exhaust. I did not have this before the exhaust. Is it something that I should worry about? I always see this kind of reaction from rally cars in the rallies.

Phil S

Re: 94 Sunoco, C'mon guy's, I said Guru's!!!nt

Phil S

My ECU with TAP stage I is great and does not backfire.

Phil S

This is NOT at all what I am talking about!

Rich Quinlan

I asked someone about it, and I was told it's the ignition system going rfom on-boost timing to off boost timing and back again.. yeah, OK.<p>From what I gather, from looking at my A/F and boost gauges, what causes this pop is this:<p>Rich condition created in exhaust during acceleration.<br>Lean condiditon when shifting, because the injectors shut off with no throttle above 1000rpm.. lean is hot, right..<br>when you get back on the throttle, you once again dump fuel into the engine, and maybe the manifold is now hot enough to ignite this? hence the pop.<p>Mine has been doing it from day 1 @ 1000 miles, and I now have 34000, with no probs.<p>Chip is Hoppen 14psi.<p>Hope this helps<br>Rich Quinlan<p>P.S. i think the heating of the exhaust manifold by running 14psi boost has something to do with it maybe?<ul><li><a href="http://home.att.net/~richquinlan">Quinland</a></li></ul>

ErikR

Rich is exactly right. If your symptoms are really backfires (you can take off the rear muffler to check), then there is an over rich condition which is igniting in the exhaust.<p>This could also be a leaking injector. There can be damage to the cat, which the dealer can check with the smog sensing equipment.<p>good luck

Phil S

Rich this seems like the right explanation. My concern is that for me it's new, but then my latest round of chips may be the reason it's new to me. Do you get a full 14.5 or so on your wett chip? Mine has not been able to get past peaks of 13 max and I think it should get more? I know they hit those highs for only a split second but mine never gets above 12.5 to 13.