fpena944

Luis,

After replacing numerous parts I am still running into my same problem as well.

With mine however it occurs only upon startup. I will start the car and the "Check Engine" light will come on. From there the car will idle from 0 - 1200 revving itself up and down. The exhaust smells very rich at this point. So what I have to do is rev the engine up a couple of times and the problem goes away.

But it seems as the temperature gets warmer the problem runs for longer periods of time. So far here is what I've replaced:

- Fuel pressure regulator
- Coolant temperature sensor
- Disconnected the DME and "reset" it
- Replaced DME relay
- Had my injectors rebuilt

Other than this issue the car runs just fine. Fuel economy is good and spark plugs don't look fouled at all. So for now I still live with it but it does irritate the crap out of me.

Roy LaZelle

Louis: Have you taken a look at the plugs for their story ?? A check of the fuel pressure would also be a good next step. I just got through de-bugging a problem on one of my Volvos which turned out to be a bad pressure regulator (too high=> too rich=>badly fouled plugs). Similar driving symptoms to yours. I swapped in a used pressure regulator (from a dead engine) which fixed the problem, I now have a pressure gage ready for next time.. --Roy--

gtroth

Luis,
Mine has done the exact same thing a few times. For me, outside temperature was always ~6°F (-14°C). Car was always cold except for one time when it happened after I was idling for ~2 hours in a blizzard. Has happended with new plugs, cap, rotor, wires. I ran through the DME Diagnosis / Troubleshooting section in FSM and all my sensors measured more or less nominal. FPR was bad (fuel pressure >100PSI, poor leak down), but the problem has happened since I corrected that. I even bought a replacement ICM based on your past experiences. I am waiting for this to happen again before I swap it out.

The thing about this one is I can't even tell if it's fuel or ignition related. It just intermittently refuses to stay above, say, 2500RPM. Anyone have any good ideas how to isolate fuel / spark problems while driving?

We are going to solve this some day.

'88 944S

Mark944na86

Yes, clearly it's the intermittent nature of the problem that is really making this problem so hard to track down. Thinking out loud: would one of those LED display AFM meters that replace the digital clocks be of any use here? I've always thought they were kind of cheesy, a cheap "dead clock" hole filler, but would something like this be of any use in deciding whether it's fuel or ignition related? I've also heard they're not particularly accurate...

Just a random thought.

-Mark

Tom R.

Luis,
on the 280Z there were two heavy wires about six inches long. they were designed to burn like a fuse, the only problem was that afer about 100k miles the inside of the wire started to fry itself causing a short when it got hot.

im not even sure if the 944 has something similar, but the symptoms were the same.

jonnybgood

Porsche did not put any fuses on any of the wires into the DME or any wires like you describe on the 280Z.
Luis, you reported earlier that the TPS had fixed the problem. Replacing the TPS required moving some of the wiring harness. Perhaps moving the wiring around improved the connection and now it has reverted back to the same condition. Could you start the engine and wiggle the wiring harness in different locations to see if you have a deteriorated connection in there somewhere.

Also I wonder about your battery to engine block ground wire. When I replaced mine the insulation was cracked and the conductors were oxidized and had turned green. Living in Barcelona would be a hot and salty air from the sea. Check your grounds and the conductors attached to your grounds.

One of the large brown wires that is grounded to the engine block goes into the wiring harness and is then soldered to four fuel injector leads inside the wiring harness. These solder connections for the fuel injectors are located inside the harness near the back of the cylinder head. If you loose this solder connection you don't have fuel from that injector(s).

Tom R.

johnny,
a fusible link is not a fuse. it is a wire designed to disintegrate over time and in extreme circumstances. from what i understand it is a failsafe that many cars have.

jonnybgood

I kind of replied with certainty because on the S there is a power steering switch 12v wire without a fuse in the DME wiring harness. The wire shorts to ground and becomes a heater. Then melts insulation, then melts the entire wiring harness. I wish my car had what you are talking about six month ago!

Also, I have the old harness torn apart in my garage and I don't see anything like you describe. Maybe Porsche cut a corner here??

Luis de Prat

I'm almost certain that the problem you described is caused by the Idle Stabiliser Valve. Very expensive to replace, but you could try cleaning it, like David Rios did.

As for me, I replaced the FPR and damper last night and so far, so good. We'll see how the car holds up!

This would be good to check. Are you referring to the ground straps at the back of the engine block? What do they look like on the late cars?

jonnybgood

The main battery connection to the engine block is under a 13mm bolt near the back of the block. The 13mm bolt will have two lugs under it one from the battery and one brown wire that goes into the wiring harness.

Adjacent to the 13mm bolt is a 10mm bolt, this is the ground for the DME. Under the 10mm bolt is another brown wire and it also goes into the wiring harness. I am not sure which of these two brown wires is used for the fuel injectors but both connection points should be clean and dry.

Mine is an 87 and I am pretty sure yours will be the same. I think this grounding scheme has been used throughout 944 and 968 engines.