RockStar951

Hey guys! First time, long time. I have been building up my 951 in the shadows for quite some time. It is a 86 944 turbo with stock K26, Autothority Stage 2 chip. After a year of work I have it on the road but with some hiccups. Here is the problem.

The car will not rev past 4k without severe sputtering, breaking up, coughing. When the motor is cold the problem is not as bad,revving to 4,500-5000k and feels great. Once at operating temp the problem is evident. Cars runs below 4k beautifully.

After using any P-Car owner's favorite tool, the search tool. I have been on every forum and researched the problem for 2 months. Here is the list of what was done since.

- New distributor cap, rotor, wires, plugs, & MSD Blaster
- New AFM
- New TPS (twice)
- New DME Relay
- Check the engine temp sensor to be within spec
- Removed the lindsey boost enhancer
- Did a fuel pressure check on the car. Passed with flying colors.
- Adjusted the FQS settings on Computer.
- Been through a whole tank of gas
- Checked all vacuum lines, all replaced with silicone lines.
- Cleaned the ground off the battery.
- Removed the boost line from the computer to determine an overboost problem.
- Replaced Fuel Filter
- Replaced oxygen sensor
- Inspected valve springs and replaced bad lifters
- Swapped out injectors

I am at a loss at this point. Hope you guys can give me some advice. Thanks!

SOLVED - finding out after everything above it was a battery cable problem. Priceless

ritzblitz

Could this possibly be a timing issue? Has the car ever ran properly since you have owned it?

RockStar951

First time a motor has been in it since I've owned it. Picked it up as a roller. Purchased a complete motor out of another car.

StoogeMoe

I thought this either means a clogged cat or a weak valve spring.

alxdgr8

Have you changed the fuel filter? I had a similar problem on my 924S and the filter fixed the problem.

Bri Bro

Sounds like you are going lean. When the engine is cold, it runs a richer mix. I would get a Wide Band sensor and check that your AFM isn't going much above 12.3 at 4K. If it is, don't go there until this is fixed. Doing the fuel filter and clean/flow test the injectors sounds like a place to start. You can also flow test the fuel pump. What chips are you running?

Multipass

Hmm, where have I heard about these symptoms.... Oh yeah my car:

and try the link in the first message.

The status is still sad, I put the camshaft housing back on, but found a small leak in the fuel rail, so car is not running and still no solution to the miss-fire problem.

V2Rocket

get rid of that leaky rail ASAP
i have seen even the most minuscule hairline fracture in a rail cause a 944 to burn...

Multipass

V2 Rocket, no worries, I am not running the car with the fuel leak, I have heard enough horror stories

RockStar, I really hope you find the problem, please let us know once you do. I am considering tacking my car to an experienced mechanic, there is a chance they had to resolve the same thing on another car.

RockStar951

I think it is a fuel or ignition type problem. Im hoping not a weak valve spring, but not throwing out that idea just yet. As far as clogged cat, its all emissions courtesy of opening piping with an atmospheric wastegate, no cat to clog.

I have 2 AFM that are tested and functioning properly. Problem is not there.

I have a new fuel filter to replace but need to start soaking the original fittings with WD-40. I have already attempted to remove it but it is on there pretty well. I did do a fuel pressure check on the system. With the return line clamped the pressure jumps to over 60 psi with no problems. Car idles and runs in the normal range with a 3 bar FPR. I have a pressure gauge on my rail. I have even attempted to run with the vacuum lines pulled and capped to the FPRs to increase pressure with no changes to the problem.

I also performed a check where I removed the boost line to the computer to ensure I was not going into an overboost problem.

I am going to swap out the fuel filter, rail, FPR and injectors with my spares over the weekend to see if there are any differences in performance. Also going to run the car with a spare engine temp sensor plugged in and not installed in the engine to fool the computer that the engine is cool.

Thanks for the ideas so far. I will keep you guys posted on the progress.

RockStar951

Saturday Update

Replaced the Fuel Filter. Nothing resolved.

Started doing some thinking. If the car warms up it should be reading the oxygen sensor and not going off set maps. So replace oxygen sensor. Nothing resolved. Replacing injectors tomorrow.

Bri Bro

Purchase a WB O2 sensor. Then post the results

RockStar951

Sunday Update

Removed the Cam Tower and all valves are fine. Nothing broken, inner or outer. I did find 1 soft lifter and 2 others that budged a little. Replacing all 3 from my extra parts bin.

Could a soft lifter be causing my misfire at high RPMs?? Anything is possible at this point.

After I get me a new gasket and replace everything lets see the situation. If unsuccessful think I will go for a wide band o2 and get some data as Brian suggested. Might also pickup another DME is I see any around.

RockStar951

TDC was exactly where it should be. Was not off a tooth.

RockStar951

Update

Reassembled the cam tower. Now have good lifters, 3 were replaced. Valve springs were all OK. Also swapped out the fuel injectors for another set.

Still cutting out. Going to swap out the FPR. I read an old post saying related issues to that. Fingers crossed.