Bucking at high rpm's under load

[hello]

This is a weird one. So i recently bought an 2002 wrx 50,000 miles. The guy i bought it from didn't know anything about the car or what has been done to it. The car had a bigger turbo in it, but was replaced because it was starting to go. It was replaced with a stock turbo, or one of the same size. Now for the problem. When i go wide open, right around 4k rpms the car starts bucking/jerking pretty bad and i loose all my power. Its been so bad at times it moves your body hard in the car. If i push in the clutch and rev it out, it's fine, so it only happens when under stress. I had a feeling my ECU must not be working properly, so i knocked on my MAS and moved some wires and it work fine. In about a day it started doing it again. Could a MAS allow this to happen? I've gotten tips that maybe the turbo could pushing so much pressure at the high rpms that its closing off a vacuum line? I'm open to all suggestions before i go drop the money on a new sensor.

[Sarra]

This is a weird one. So i recently bought an 2002 wrx 50,000 miles. The guy i bought it from didn't know anything about the car or what has been done to it. The car had a bigger turbo in it, but was replaced because it was starting to go. It was replaced with a stock turbo, or one of the same size. Now for the problem. When i go wide open, right around 4k rpms the car starts bucking/jerking pretty bad and i loose all my power. Its been so bad at times it moves your body hard in the car. If i push in the clutch and rev it out, it's fine, so it only happens when under stress. I had a feeling my ECU must not be working properly, so i knocked on my MAS and moved some wires and it work fine. In about a day it started doing it again. Could a MAS allow this to happen? I've gotten tips that maybe the turbo could pushing so much pressure at the high rpms that its closing off a vacuum line? I'm open to all suggestions before i go drop the money on a new sensor.

Uhh, the car had a big turbo on it, and now it has the stock turbo back on it? Bad. You will need to get a tune for the turbo.

Also, it's possible that if there is an aftermarket turbo inlet on it, that is being sucked shut by vacuum, but unless it's a cheap ebay pile of junk, that's probably not it...

You could toast your motor by driving it like that. Get it tuned quick.

[EvoEatr]

So is the entire car back to stock now? WAS/IS the car tuned for the other turbo? Do you have any idea what other mods where/are on the vehicle?....It sounds to me either the tune is off or you have a massive boost leak for the problem your describing seems to be noticeable while approaching the power band.....does the car get into boost at all?

[Anub1s]

You likely have a few more issues than one here. First off, you need to track down any and all information on the car. If you can't find out if the car was retuned for the bigger turbo, you HAVE to get a stock tune on there pronto, no ifs ands or buts about it. If that doesn't address the issue, come back to us, and we can offer more information.

I had the same issue on my '02 but it was a result of a cracked spark plug.

[hello]

I just replaced the plugs because i forgot to mention this...if you keep WOT during the bucking, the car throws a CEL that blinks and the diagnostic comes up with 1, 3, 4, miss-firing. (the cylinders do vary). And no the car is not all stock it does have the bigger injectors and such. I feel like the car is dumping fuel into the cylinders causing a missfire. Would a wideband help me?

[mycologist]

You need to take the car to a qualified tuner who can diagnose the mods and the map for the ECU as soon as possible and don't keep pushing it or even driving until you do. There is no generic map for this and you don't have time to learn how to sort it out yourself. It will probably run $300-500.

[EvoEatr]

I just replaced the plugs because i forgot to mention this...if you keep WOT during the bucking, the car throws a CEL that blinks and the diagnostic comes up with 1, 3, 4, miss-firing. (the cylinders do vary). And no the car is not all stock it does have the bigger injectors and such. I feel like the car is dumping fuel into the cylinders causing a missfire. Would a wideband help me?

From this info. here I agree with Mycologist...Get the tune sorted out first.. than diag. of your other problems (if theres still some) will be much easier..A blinking CEL means the misfire is so severe that there is enough raw/unburned fuel getting to your cat. conv. for it to explode...I HAVE seen this happen before..I would def not be getting into boost or beating the car at all until you get this striaghtend out..