Whats the wrong? Misfire?

arlen · 10-12-2007, 08:55 PM

Hey guys, I have a 99' Mk4 GTI, with performance chip and shortened gear ratios and when I floor the throttle, between roughly 3200 - 4700 (so after full effects of turbo are realised) I cant get smooth acceleration? It still accelerates, sometimes faster than others, and I get a inconsistent, hoping, like kinda jerky acceleration? My mate thinks mis-fire, but recently had spark plugs replaced and it still happens? Funnily enough, once it hits 4700RPM it "buckles down" and I get REALLY good smooth strong acceleration to redline (approx 6200).
One idea is that the guy who I bought it off, Ian Johnson (ex carrera cup driver?) has tuned it to run optimal at high RPM (I say this b/c if u redline secong gear and change to 3rd, it drops back exactly to 4700, the start of the really smooth, fast acceleration?) Is this likely a possibility? Surely this is not normal, is it likely a problem with my chip? Any help would be much appreciated?

**99gti** · 10-12-2007, 09:05 PM

It sounds like either a leak after your MAF where it's sucking air or posibly a faulty MAF (quite common in the older Mk4's. Try disconecting it and see how she runs, Look for posible a clip missing after your airbox where there could be air leaking ing too.

**SoVeReIgN** · 10-12-2007, 10:22 PM

Im curious about the car - Shortening the gear ratios is not an easy task - Are you sure thats what has been done?

Tuning the car for high RPM is interesting too - The turbo in these things is so small it is basically useless over 5000rpm and no amount of tuning will make a difference.

Maybe he has fitted an aftermarket cam, if it were aggressive enough it could cause the car to run rough at low RPM and open up as it gets higher. But the car would either be idling like a pig or idling way over 1000rpm.

To do all that he'd need an aftermarket ECU too - Coupled with a cam and a shorten'd ratio box... sounds very unlikely.

Something is probably wrong.

**NGOLF.U** · 11-12-2007, 08:49 AM

could be a boostleak in the standard intercooler piping. or like 99gti said the MAF. they are so tempermental. mine did that some time ago....exact same symtoms.

**No457 Snowy** · 11-12-2007, 09:08 AM

Does the car have the stock airbox/filter fitted or is it an oiled K&N type filter?

Snowy.

**nashan** · 13-12-2007, 08:45 AM

He has the stock airbox so no K&N. Im thinking coilpack too. I originally said sparkies but they werent the problem. It feels like a spark problem but yeah could also be a number of other things.