James86-951

I have recently found and repaired a large vacuum leak in my 951.(The oil/air separator vacuum line.) The eng had previously run very lean. (I also installed Autothority Chips before the vacuum leak was discovered.) The eng will now not stay cranked without patting the gas pedal. I have been through the manual and tested all of the fuel related components.(AFM, temp sensors, o2 sensor, and fuel pressure) I came accross a statement in the manual about hard codes in the computer that can only be cleared by disconnecting the battery. I have done that and cleaned the injectors last night. (I will put it back together tonight.)

My next step is to return the original chips back in the computers and see if there was a bug of some type.

Does anyone have any other suggestions?

Tom Carson

you didn't mention the TPS but I assume it was tested ok?

(wonder who will be the 1st to recommend putting the vacuum leak back?)

James86-951

Yes, the TPS was tested and the eng is in time. It backfired through the AFM, so I thought the t-belt had jumped. I have had to clean the spark plugs twice now.

The vacuum leak wouldn't be so bad if it didn't also create a boost leak. (aka my wife's minivan is faster than the 951!)

billybones

Perhaps a reference sensor. one is for start and the other is for running. I can not remember for sure, but if the running one goes out it refers back to the start one. Thus to much gas? Just a guess with a foggy recollection to the problem..

James86-951

It will run if the gas pedal is pressed. I didn't think of the reference sensor. It's on the list to check, but I thought it wouldn't allow it to crank. I will check that tonight.

James86-951

Is there a way to check it without a scope? Porsche has pretty pictures of waveforms, but I don't have an oscilloscope.

billybones

My foggy recollection has to do with previous posts on this site. It must be in the archives somewhere. All I remember is that one sensor starts the car and the other is for running. most times the start one gets creamed cause it has the shim on it. Thus the many posts on no starts. But the other one is the run sensor... Maybe it just got unplugged durring the replacement of the leak? they are both located at the back of the cam housing... HTH.

Perry 951

Have you removed and cleaned the idle control valve? If it is stuck closed, it can cause idle issues. This is how the stock setup regulates idle speed.

Remove the vac line from the manifold (the one connected to the ICV) and shoot some WD-40 into it. This may free it and resume operation.

James86-951

The idle control valve was replaced about 6 months ago when the engine was freshened with new headgasket, belts, rod bearings, etc.

Oddly enough, the new valve didn't make any difference, that's why I went back over the vacuum system to look for problems. I touched the oil/air separator vacuum line and it moved easily.

Now that I have been thinking about those sensors. I did notice the plugs were damaged and not differentiated. Would the crossing of those two plugs cause a running problem?

Perry 951

Crossing them will not allow the engine to run at all.

Have you adjusted your idle correctly by disabling the ICV?

James86-951

Yes, I put a jumper wire in the test port between C and B. (center hole with hole on right of center.) I followed an old procedure from Danno.

I have opened the throttle body bypass screw to the point of it coming out. The AFM bypass screw has been opened substantially as well. (I had to close it to get the engine to idle well previously.)

There is also a good chance I have really fouled things up and need to reset the adjustments. Is there any way to make the LED diagnostic tool specified in the manual? I really need to get the car to talk to me.

Tom Carson

the reference & speed sensors can do weird things

the reference sensor tell the DME unit when to 'start' the current going in the coil (crank angle) while the speed sensor calulates the rpm and with other sensors lets the DME 'stop' the current going to the coil...in other words, the spark 'dwell' (length)

they do get 'flaky'...sometimes just pulling them out and getting little bit of metal off them may help...were they adjusted recently?

Perry 951

Strange indeed. Does it have a miss at all? How does it run under load above 1500?

The LED is simple, Danno has distructions on his site. 3.6V LED inserted into the test port should take care of you... IIRC. Can't remember if you needed a resistor with it or not.

Vaino

The boost problem with this richness, may be an exhaust leak. A cracked header or crossover will bleed pressure, and cause the oxygen sensor to enrich the mixture.

James86-951

The sensors have never been adjusted as far as I know. Is there a procedure in the manual or on this site?

Before the problem, the engine was running weak and had an erratic idle. (high and low) I noticed the boost levels high in 1st and low in second under hard acceleration. If you accelerated hard, you would have to wait a second before you would get good boost again. This symptom fits the loose hose that I found.

The car never missed under a load and the exhaust system is in good shape except for the above mentioned problem which may be a result of an iffy wastegate.