Enigine Misfires and pulls timing.

[mbailey]

Hi all! I heard on 6-speed that this was a great forum for engine trouble-shooting so I thought I would try to get some opinions here.

I have a 2003 996TT with EVOMS 660 kit. The car ran very well with the 610 kit but since I upgraded to the next level (upgrade included 60lb injectors, rails, and program) the car has not run as well. There are no lights or codes. The car runs well tooling around town. It even runs well in mid-ranges at WOT. But it pulls back significantly at wot above ~5000rpm. I inspected all hoses and they look good. The car boosts to 1.3 bar on race gas so I doubt a boost leak. I hooked up to a durametric and saw runs of misfires in all cylinders with the most being in #4. These runs were not during WOT but rather just cruising along. They last from one second up to 45 seconds. I cannot feel or hear any of these misses. The ECU apprears to be pulling timing under WOT. When I floor the gas the timing falls to 9 degrees at 3500 rpm and gradually increases to 16 degrees by redline. Iam not sure what timing advance should be at redline but I would think 23-27 degrees maybe more. Iam down on power probably at least 50 whp at redline. I initially thought plugs/coils but I changed these yesterday without any improvement. I have a Hitachi MAF which is felt to be next to indestructable so I dont think its that. I wonder about cam timing...

What can I do to further chase down this problem? Any other ideas greatly appreciated.

Thanks, Mike

[Brad Roberts]

Mike,

it sounds like you have some good pieces in place :) You are the first person to mention having the "hot" new ticket item in a public forum (the Hitachi MAF) I installed my first one at GIAC back last summer on an 01TT. They are bullet proof :)

Now, onto the issue: So many things can effect timing, it will hard to pin point unless you have easy access to a chassis dyno and can perform multiple pulls.

You said something about race gas, is the car pulling the timing back while on race gas? or pump gas? or both?

Something as simple as a knock sensor failing or coming loose can cause timing to be pulled out.

Fuel pump/s if the pump cannot keep up with VOLUME.. not pressure, it will cause a lean condition which in turn will cause the car to knock and pull timing..

Traction control: if the car is now spinning the tires and causing the traction control to kick in.. it will pull back timing..

Have you talked to ToddZ about this? They sold you the kit and the tuning?

B