Douglas Sorrells

I'm having a devil of a time figuring out what's wrong with my 1987 951! It had been acting like it had fouled plugs. I cleaned them and it ran fine for a few days before it started acting up again. I replaced them all with new plugs. It didn't seem to make any difference. It will typically start right up and immediately going to a high and increasing idle (about 1800 RPM and rising) if I give it any throttle at all it will immediately die and may or may not start right after. This is 7th 944 I've owned and the 5th turbo so I have my fair share of good backup parts stashed in my shed. So far I've swapped out 1) the DME and KLR units twice with what I believe are good replacements. 2) I've replaced the throttle position sensor mounted on the intake manifold. 3) I've replaced the airflow meter. 4) I've replaced virtually all the big fuses in the fuse box and nothing so far has seemed to have any effect. I've replace the blowoff valve with a billet replacement. The plugs are wet when pulled and I do see a yellow spark when cranking it over. The timing belts were recently adjusted and the timing is correct. The car is mostly stock except for a 4'' exhaust from bottom of the down-tube, an adjustable fuel pressure regulator with rail gauge showing 46 psi, a wideband O2 sensor that had been showing 14.7 at consistently at idle. I'd recently discovered a major leak in the stock air box so I replaced it with one of the adapters that hooks a cone filter directly onto the airflow meter about probably 200 miles ago. I've also gone through the inter cooler pipes and hoses and have not found any major leaks.

Please any ideas on that this could be would be greatly appreciated. Thanks so much!! Doug

Chapman951

Maybe a frayed wire?

Noahs944

Sounds like maybe a no spark issue, I'd check under the distributer cap as the rotors can come loose from the rotor drive at end of cam or get damaged on dist cap re-assembly. While in there check the condition of the conductors under the cap. If good, reassemble and check spark at wires (disconnect batt, remove plug, place in wire and lay in safe place while cranking. you can visually watch the spark. Easier with lights dim, repeat for each). If good-verify the plugs are in correct order on cap.

divil

I have a hard time seeing how this would cause an 1800rpm idle though.



The high idle and we plugs suggest it's running rich. Your fuel pressure should be 2 bar/30psi for a stock car at idle. Why do you have it adjusted to 46psi? The WB02 sensor showing 14.7 is a little strange. Are you sure it's working correctly? It might be hard coded to display 14.7 when it's not working. Does it fluctuate back and forth above/below that value?

Tom M'Guinn

If I understand correctly: when you start the motor, the idle immediately goes up to 1800 and continues to increase from there, and if you touch the gas pedal then the motor will die? The engine needs air to get to 1800+ rpms. Where is your motor getting all that air with the throttle plate closed? (It is closed right?) I'd start by checking for leaks (again) and perhaps blocking off the ISV ports to see where all that air is coming from... If the TPS idle switch is working, the fuel should cut off at some point and the motor will bounce up and down as DME switches back and forth from idle to over-run fuel cut off... Is that happening too?

fast951

As Tom already suggested, a vacuum leak is a good possibility.

The stock fuel pressure is 2.5bar why are you using 3bar FPR (assuming you measured FP with line vacuum off) ? If the chip you are using is not configured to run 3bar fuel pressure, your fuel delivery will be about 9% higher than what it should be (running rich).

The extra fuel (9%) and air from a vacuum leak will cause the RPM to go up. When you open the throttle, you get more air (metered) + air from vacuum leak could be causing a lean condition where the engine does not run. Do you hear a "pop" or backfire from the intake when uou try to Rev it up?

Douglas Sorrells

Thanks for the replies, I pressurized the intake manifold and found 3 vacuum leaks. Thanks fast951! The closest spark plug to the fire wall wasn't seated completely and was leaking a slight bit. The vacuum banjo bolt that goes into the intake manifold was leaking and the vacuum line that plugs in directly below the front of the intake manifold below the throttle position sensor was completely off. I addressed those and the car started right up. Still a little confused as to why it was occurring intermittently earlier, but I've put 2 miles on the car now with normal operation. We'll see how long that lasts. Thanks again all! d

divil

I'm glad it's improved, but you still need to address that fuel pressure issue.

Stephencs601

I had issues with my coil. Car ran then finally died. Was popping a bit before it stopped going. That is a cheap part to replace and I do it every 5 years or so. just in case.

Chris White

"Please help me!! 951 wont run right anymore"

join NASCAR?

Douglas Sorrells

Car died again today. It started a couple of times roughly. I reduced the fuel pressure to 30 PSI and swapped out the coil with another I had, that did seem to help. So far I've put 4 more miles on it without it dying again or running rough. Was able to put about 16 miles on the car without issue and then it started running really rough, like on 3 cylinders. I cut it off and it would not restart immediately. I let it set for about 5 minutes and then it started and ran fine the 100 yards back to the house. It seems to me an electrical air fuel mixture issue. Still very perplexed..