suddenly started running very rich?

[cpnnz]

Have just taken my '86 951 for a 'spirited' run.
Was performing very well, but after slowing down at one stage and going to take off again I noticed I was down on power and a missfire had developed under load and the engine did not want to rev easily.
It is still idling, but is running quite rich, and if I give it a rev I can get lots of black smoke ( unburnt fuel? )
I wonder if a vacuum line(?) has come off under boost, of maybe an injector is stuck open (?).
It's not making any strange noises at all.
After sitting for a few minutes, I can restart and it seems to be a little better, but the miss and rich smoke come back after a light rev.
Can anyone point me in the right direction please?
I wonder if it's worth changing the plugs, as I have never done these?
Thanks.
Chris

[rberry951]

yep, change your plugs.

[cpnnz]

Thanks Russell,
Changed plugs this morning. They were all very fouled.
Started well and ran well initially, but soon started to miss and run very richly again.
Now is chugging like it was before plug change.
I notice fuel pump seems noisier sometimes than it was before. I guess it must be a problem of too much fuel rather than too little if the pump was failing? Could the fuel pressure regulator have failed? now supplying way too much fuel pressure, hence a lot more fuel each time injectors open?
What else could cause this type of problem? especially after a bit of a hard run?
fuel level had got down to about 1/4 tank, it could have sucked up some debris from inside the tank, but that would restrict the fuel i would have thought.
Any more ideas?
Thanks.
Chris

[rberry951]

Could be a few things. Start up the car, then turn it right off. Pull the vacuum lines from the fuel pressure regulator and damper. If fuel comes out either one than it has a bad diaphragm. I think this may be your issue. Your filter could be causing another issue, but I believe that would make you run lean, not rich.

It is also possible that you're turbo has blown a seal and is dumping lots of oil into the system, pull an intercooler pipe and see if it is soaked with oil.

I'll give it some more thought whilst you check these things

[cpnnz]

Hi Russell,
Thanks for your quick reply. I'm not too familiar with the Porsche's layout under the bonnet yet.
Where is the fuel pressure regulator located? it's a fair plumbing nightmare under the bonnet!
Thanks.
Chris

[rberry951]

As you look at the front of the engine, to your left you'll see two fuel lines coming up out of the wheel well. They connect to the fuel rail. The small round thing on the back of the rail farthest from you is the fuel pressure regulator, the one nearest you is the pressure damper. They both have vacuum lines on a nipple on them. Pull those off, but not while the car is running in case they spew fuel on you, the damper is right over the distributor and if fuel goes in there while the car is running...BOOM!

Regards,
Russell

[cpnnz]

Yes found them. no fuel leak at either vacuum line when removed.
car seems to start & run quite smoothly, then will hold 2,000 to 3,000rpm smoothly, and does until I give it a good rev and then it starts to run rich and will not hold a smooth idle ( or faster ) without 'chugging' out black smoke(fuel?) does not seem to be oil smoke as it's black.
after turning off and restarting seems a bit better until the next rev up.
Chris

[rberry951]

Well I suppose the fuel pressure regulator could be going bad. There's no way to check that except to unscrew the bolt at the front side of the fuel rail and install a fuel pressure gauge..

On your throttle body, where you see the throttle cable connected at the front of the intake, there is a little black box on the left side. This is your TPS, or throttle position switch. With the car off, move the throttle open a bit, and let it slowly go back to its stop. You should hear/feel a click from this TPS just as the throttle closes all of the way. This is your idle switch engaging. This is a common problem with idle. Another thing to check while you're right there is on the top of the throttle body you'll see a screw or hole. This idle adjustment screw sometimes backs out. This will cause erratic idle. Do not try to adjust this thing, there is a procedure for it. If you just try to turn it to get a good idle you are just battling against the idle stabilizer valve.

Once you have located the TPC, disconnect it and see how the car idles. If it magically starts idling fine, that's your problem.

Regards,
Russell

[cpnnz]

Russell,
Tried with TPS unplugged/plugged, made no difference.
Could hear the light click in the TPS as I moved the throttle by hand.

I had not really noticed the fuel pump being noisy before, but if I lie down under the rear of the car, it's quite loud. Almost a rough whining noise. not really constant.
Also, If I touch the metal fuel line from the tank to the fuel filter I can 'feel' the noise louder. and this line is quite warm to touch. Is this normal?

Does the car have a '5th' injector which would open under heavy throttle? it gets rich only after it has a rev up. then stays rich until you turn off.

I don't think the car had been driven hard for a while before I got it. Came from Japan to New Zealand where it might have been a one owner car. Has only travelled 105,000km. Has had good maintainance going by the records.

Thanks.
Chris

[sh944]

I'm suspecting a vac leak somewhere. If it was fine before you took your spirited run and not fine afterwards, I'd be looking for a line that is disconnected or a torn j boot. What condition are the vac lines and the j boot in? If they are hard and non-pliable, I'd start there.

Regards, ...Scott

[nize]

check cylinder compression.

[cpnnz]

Was faulty FPR which had caused pump to 'grind itself to death' ( pressure was reading off the top of 100psi guage )
New fuel pressure regulator & pump now fitted and running great again. Should I also change the fuel pressure damper? how do I test this?
Thanks.

[rberry951]

Congrats on tracking down the problem! It is possible and actually quite probably that the damper is damaged. Quick check is to lay a rag under it (so if any gas comes out it doesn't go in the distributor) and pull the vacuum line off the back, plug the line and have someone turn on the key. If the damper diaphragm is damaged gas will come out the vacuum line hole. That's about the only test I am aware of, but I suppose it could be 'damaged' and the membrane still be intact. So I would say watch for surges in pressure while driving the car, sudden richness/leanness, and if you get any go ahead and change the damper. I'm not even sure where to buy a new damper other than used, they typically don't go bad unless they have been exposed to 100psi

Regards,
Russell

[cpnnz]

I think Pelican do list a damper... I'll price it up here in NZ and see if it's worth sending for it!

[rberry951]

Well that would be a good place to look! (Pelican)

Brainfart above, turning on the key won't turn on the fuel pump, they'll have to actually turn over the engine, you can disconnect the coil wire to keep it from starting.

Regards,
Russell

[soxnail]

Well I figure this also answers the question what would happen if some one puts in a 3 bar regulator with out the chip change to go with it. The car runs rich !

[Keithr726]

O2 sensor?