C2 Turbo

If i'm driving slow and if i decide to accelerate,right before the boost kicks in ( 3700 rpm ) the car jerks few times before it takes of.Now if i am driving hard i don't feel this jerking thing,seems only if it's kinda partial throttle ? Does that makes any sense to you guys ? I'll try again,punched half heartedly the car shakes few times before the boost kicks in but if i have the throttle nailed in the jerking thing is not noticeable at all ? Normal ?
Thanks.O forgot car has B&B headers,car bypass and an exhaust.
Later, Yasir

PorschePhD

There is a transition that of you start to crest the surge of boost and let off the car will hop like a rabbit. The surge can't stop faster than the momentum of the car. That is a ton of force. At 3700RPM this does sound like it is it.

fc-racer

Stephen, that surge or "jerk", as we described it a long time ago in another thread, seems to be caused by the turbo's unused pressure forcing the metering plate to move. The reason why I say this is that when I changed out my brand new plastic 993 Turbo compressor bypass valve with a Forge metal unit that is more efficient and stable, the "jerk" became much, much less. I went back and forth to see if it was my imagination but it wasn't.

My theory is that when you lift off, the plastic valve flutters in trying to release the pressure back into the pre-turbo side, thus causing the plate to move around. With the metal valve, it does not flutter so you only get one "jerk".

My other theory is that the plastic valve opens much easier than the metal Forge valve does so in partial throttle applications, it is not dumping that air into the pre-turbo pipes and so you don't move the metering plate.

I don't know which, if either, is right, but the Forge valve considerably lessened the partial throttle "jerk" that all C2 Turbos I've driven have.

JBH

I think what YS is describing is a hestitation (or quick series of) that happen when he stomps the acceleratior. This is not normal or typical of the C2 Turbo.

C2 Turbo

Farzaan,
I'm not referring to backing off the throttle instead once i push the throttle all the way down without downshifting the car jerks/hesitates few times and if i keep the throttle pushed all the way down it goes away as soon as the boost kicks in ( around 3700 rpm ).However if i downshift and really pulls the car through the gears then those jerks are not noticeable at all ? Well sometimes it feels like bad plugs or fuel starving as if the engine needs the fuel and for some reason it's not getting it ? If it is fuel or even the plugs then why does it drive fine under hard acceleration ? I hope i am able to explain myself here.Btw thanks for helping me out here.
Later, Yasir

maverick

I would check you plug wires. Mine acted this way and I found out it had a bad connector.

fc-racer

Yasir, please disregard my note above, it will not help your situation. The one time I had a hesitation problem on my C2 Turbo, it originated from a loose hose after the turbo and a vacuum line that had split. My hesitation was nowhere near as dramatic as yours however.

C2 Turbo

The dealership that did the PPI did not change the sparkplugs so i made them pay for it and bingo,the hesitation all gone The car is as smooth as it could be The thing that surprises me is i had the car looked at by 2 Porsche mechanics and they both said it drives fine.
So i guess Maverick was right on track with the Spark Plug wires.
JBH,
Yes i knew it wasn't normal so thats why i kept pushing it and finally after 4 weeks the car is running smooth as silk,yeehaaw
Thank you all.

JBH

Glad it worked out. If you got the dealer to pay for labor and parts on a plug change, you did alright. That is a time-consuming procedure.

Enjoy your car.