Porsche 930 (1987)

[Horneck]

I appreciate input from this forum as I am not getting further along solving my problem.
My Porsche 930 is refusing to rev over 3000RPM / 0.4 bar boost after sitting for 4 weeks in my garage. The car misfires when I exceed 3000 rpm. I can get it to rev past 4000 without load but have to be very careful with the throttle and only press it maybe 25%. If I press full throttle the misfire starts immediately. Between idle and 3000 RPM the car runs fine.
I assume it has something to do with the enrichment when the turbo starts to kick in. I have checked the fuel pumps and both work as well as the little connector at the mass airflow sensor. The turbo boost valve seem to be working as well.
What do you recommend to get the issue identified and corrected?

[70tangerine]

Not sure if this will help but I had an issue after my motor was pulled to put a new LTW fly wheel on many years ago also and 87 930.
The issue I had was the car would cut off or just act Erratic sometime stalling and or gauges with do weird thing.
I wrote to the PCA 930 tech guy at the time. He wrote back to me pretty fast and said check the ground for the intercooler. If the mechanic did not run or put the ground for intercooler back correct it will cause all sorts of problems. Ran a dedicated ground wire to some place and made sure all connected and car was perfect again.

One other issue I had a few Summers ago I stopped for Fuel 93 octain super at a BP gas station in Vernon NJ and drove away and car started Stumbling and almost died a few times then woud Rev up if i recall ended up as bad fuel.
Prob water in their tanks or something.
I used some high end fuel inj cleaners and ended up taking it in for new fuel filter and Fuel accumulator if I recall. Loaded 930 up with some Sunoco 94 and got on the boost and all sorts of black smoke came out and car woke up and ran as it should.

Not sure if any help but worth a try. Good luck.

[Alan L]

It could be a lot of things. Sticking fuel metering plunger?
Air leak?
It was running fine 4 weeks ago?
Alan

[Horneck]

My car was running 4 wks ago. The only think I did while the car was in storage was adding seafoam to the fuel to clean out my injectors. I have filled the car up with new fuel but no improvement.
Any other ideas what it can be? How about the turbo specific relays in the car ?

[Alan L]

There are no turbo specific relays that I can think of. Basically a mechanical system.
It does sound like a fuel problem, lots of places to look. But first I would check the metering piston is moving freely. Simple test. Air filter off and press down on the airplate. It should move freely and return. It probably is OK - if it was sticking it would probably be hanging up. But a simple test with no gauges etc required.
Alan

[908/930]

Are you just testing this while parked and not driving? Is your intake hose from sensor plate housing to pressure valve housing in good shape and not soft? Part 930 110 137 02 I think.

[Toddrivers]

Sounds lean, do you monitor AFR? Are you CIS, Do you have an adjustable WUR? If my AFR was running 15:1 or higher, I would adjust the bottom screw on my Wur 1/2 turn to richen it up an try it.
If you posted info on your system somewhere I guess I missed it.
Good luck!

[Horneck]

I have checked that all hoses are connected to the air intake system and that there is no leak in the boost side but not improvement to my situation. Car runs great with no load up to 3000 rpm but then misfires refusing to rev any higher. If I lift the throttle I can get the car to rev to 4000 rpm.
I felt the car was running rich and I had asked a mechanic to adjust the mixture a few weeks ago and he stated that he had to make the car richer even though my car blew black smoke during acceleration. This was a few weeks ago though.
Trying the remember what else I did and I pushed down the front relay block cover moving some of the relays but I have pushed all back in place.
To remove oil from the valve covers I had cleaner the engine covers and the turbo charger with brake cleaner and put a little penetrating oil on the crews of the exhaust and over boost valve.
Can any of that cause my problems?

[908/930]

You were looking for an ignition distributor before, was that removed from the car? Ignition timing checked? I would check your air filter and make sure nothing built a nest in there, the large rubber intake hose I mentioned are able to collapse when they get older, and limit airflow. Do you have access to CIS pressure gauges to check system pressure?

If it was running well prior to being stored I don't think the cleaning is the problem.

[Horneck]

I have rebuild my distributor and have found out that my coil was bad and I have replaced it. After that the car ran fine but I did not use it a lot.
Have checked the air hoses und I cannot find any of those soft or closed up. Now I don't know what they do under load.
Still think it must be something related to the boost (relays?).
What else would you check. Car fires right up and revs without load perfectly and idles fine. Under load it misfires.

[908/930]

Did you check or change your spark plugs? The WUR controls pressure to fuel head and riches up fuel ratio when under boost, you will need CIS fuel pressure gauge to check it.

As Alan mentioned, no relays that I can think of controlling boost pressure unless somehow modified, verify both fuel pumps working. Vac lines to your distributer correct?

[flightlead404]

I'm a little confused because in the first post you say you can get it to rev without load but you have to be careful and it misfires with full throttle. But in post #10 you say it revs perfectly without load. Can you clarify?

If the issue is only happening when the car is starting to come on boost while driving but revs perfectly when not under load, then I'd eliminate ignition related things for the time being.

Honestly it sounds to me exactly the behavior I had with my stock turbo when I had a bad or misaligned O ring/seal between the turbo and the intercooler. From memory there's an O ring there, and there's also a bigger seal. What I found was under a little boost the seal would get pushed out, leaking metered air.

It would help to know if you're going way rich or way lean when the issue occurs. However, a wideband AFR can register really lean when its actually really rich so take it with a grain of salt.

[Alan L]

It is starting to sound like a boost leak.
Alan

[Horneck]

I have not made any progress finding out what my cars problem is. Have removed the intercooler and have checked for loose hoses or faulty o-rings. Unfortunately nothing found.
I have a 40 year old CO tester that I am not sure works correctly and have used it to measure the CO at idle. It showed 6%. Not sure that I trust the device though. I bought a AF ratio gauge with an oxygen sensor but unfortunately it shows only 0. Somebody told me I have to calibrate it first which I will try in the next few days.
As my car is running fairly rich the sparks were very black last time I checked and cleaned them. Is it possible the fail under load? Should I change them? What do you think about changing the fuel filter as I have used seafoam engine restoration in the car.

The symptoms of the car are currently as follows:

Car starts immediately and idles great.

If I drive the cold car immediately I can rev it up easily to 5-6k but I don’t want to push a cold engine. After approx 5 min driving my rev problem kicks in again. The car starts now to misfire around 2500-3000rpm refusing to rev any higher. If I accelerate the car with only 25% throttle I can rev it to 4000 but the second I hit the throttle harder I get immediate misfire.
If I rev the warm car at idle I can easily rev the car to 6000 but this is without load. Am I right to assume ignition is not the issue and I don't have to check coil, CDI or distributor?
Appreciate your thoughts.

[908/930]

See what others think but I think your problem is the WUR, make sure you have power going to it. Checking CIS system pressures with gauges will help. Yes don't be revving to 6k when cold or you will have bigger problems. Also check your fuel pump relays.

[Alan L]

are both pumps running. it is a bit weird as only happened after sitting for a month.
Maybe a pump has quit. Key on and remove the airplate switch. Should hear one below the gas tank and one in left rear behind wheel.
Alan

[908/930]

Fuel pump relay 2 also supplies power to the WUR, try changing that relay.

[flightlead404]

Originally Posted by Horneck

I have not made any progress finding out what my cars problem is. Have removed the intercooler and have checked for loose hoses or faulty o-rings. Unfortunately nothing found.
I have a 40 year old CO tester that I am not sure works correctly and have used it to measure the CO at idle. It showed 6%. Not sure that I trust the device though. I bought a AF ratio gauge with an oxygen sensor but unfortunately it shows only 0. Somebody told me I have to calibrate it first which I will try in the next few days.
As my car is running fairly rich the sparks were very black last time I checked and cleaned them. Is it possible the fail under load? Should I change them? What do you think about changing the fuel filter as I have used seafoam engine restoration in the car.

The symptoms of the car are currently as follows:

Car starts immediately and idles great.

If I drive the cold car immediately I can rev it up easily to 5-6k but I don’t want to push a cold engine. After approx 5 min driving my rev problem kicks in again. The car starts now to misfire around 2500-3000rpm refusing to rev any higher. If I accelerate the car with only 25% throttle I can rev it to 4000 but the second I hit the throttle harder I get immediate misfire.
If I rev the warm car at idle I can easily rev the car to 6000 but this is without load. Am I right to assume ignition is not the issue and I don't have to check coil, CDI or distributor?
Appreciate your thoughts.

lol @ "engine restoration"

spark plugs are a cheap and easy test. I and many others like the the NKG. I think the part is BK8RS, but double check that. There may be two options for a solid and screw on tip, get the solid ones.

its a good time to check the status of your ignition leads and connections as well.

[mark houghton]

Boost leak o'ring seal most likely. Once you start building boost you'll lose some of the air charge and she'll go pig rich on you and just flounder away. You'll really only notice it under load.

[Toddrivers]

Have removed the intercooler and have checked for loose hoses or faulty O-rings. Unfortunately, nothing found.

Did you check the O-rings in the up pipe from just above the turbo. The O-ring in this connection is prone to being blown out or cut on assembly causing boost leakage and a lean condition.