Possibly Haunted 964
02-07-2024, 06:11 AM
#1
Possibly Haunted 964
Hi all,
I picked up a 1992 Carrrera 2 cabriolet about a year ago. It’s been in my family since new, has It has less than 50k miles, is entirely stock, and has usually been great. Except that . . . maybe it’s haunted. Or at least it has a strange gremlin, probably electrical.
It started late last summer when after a drive, while garaging it, I heard a loud buzzing noise. It sounded a bit like static from a speaker. Until the next time I drove it I wondered if a huge hornet had followed me into the garage. But the noise recurred. Usually it would happen almost exactly 20 minutes into each drive, and the buzzing would be accompanied by very rough running and occasional stalling when at a stop light.
Scanning the boards here suggested a few things, and we started by changing the DME relay, twice. No joy.
More research suggested it was the fuel pump, and it was. The sound was loudest in front, and underneath. We have a fairly established Porsche mechanic. His first take on it was that it was the distributor, which he rebuilt, to no effect. Then he replaced the fuel pump, and the screen. This was all a long and time consuming process. And an ineffective one.
Now, the constellation of symptoms includes the following: the buzzing and rough running, and also occasional significant hesitations in acceleration. The buzzing and roughness tends to start after 10 or 15 minutes of driving. When things are working, it drives great, btw. A cigarette-lighter voltage meter shows no change during any of these events, which perhaps proves only that the voltage to the lighter is not changing.
Another red herring, or clue: the odometer stopped working around the time this started. These are known to fail due to crumbling plastic gears, but they also draw electric power, so it could be linked.
From scanning various threads, the coils and plugs seem like potential culprits, and are probably my next targets to change. Some folks have cleared up mystery issues this way. Grounding straps are another candidate, but it seems odd they would cause the problem only after 10-15 minutes. Some loose wiring or short could also be involved, perhaps near the odometer, but again, the 10-15 minutes. Or maybe the ole computer is changing things up once the engine warms up. It does seem to happen when it first gets warm. But, even then, it comes and goes. It may buzz for a while, then stop and drive beautifully, then misbehave again.
Thanks for any light any one can shine on this! I think my current mechanic, who I like, may have gone as far as he can with this. I'm reluctant to re-start the process with another mechanic so am hoping to narrow things down a bit.
I picked up a 1992 Carrrera 2 cabriolet about a year ago. It’s been in my family since new, has It has less than 50k miles, is entirely stock, and has usually been great. Except that . . . maybe it’s haunted. Or at least it has a strange gremlin, probably electrical.
It started late last summer when after a drive, while garaging it, I heard a loud buzzing noise. It sounded a bit like static from a speaker. Until the next time I drove it I wondered if a huge hornet had followed me into the garage. But the noise recurred. Usually it would happen almost exactly 20 minutes into each drive, and the buzzing would be accompanied by very rough running and occasional stalling when at a stop light.
Scanning the boards here suggested a few things, and we started by changing the DME relay, twice. No joy.
More research suggested it was the fuel pump, and it was. The sound was loudest in front, and underneath. We have a fairly established Porsche mechanic. His first take on it was that it was the distributor, which he rebuilt, to no effect. Then he replaced the fuel pump, and the screen. This was all a long and time consuming process. And an ineffective one.
Now, the constellation of symptoms includes the following: the buzzing and rough running, and also occasional significant hesitations in acceleration. The buzzing and roughness tends to start after 10 or 15 minutes of driving. When things are working, it drives great, btw. A cigarette-lighter voltage meter shows no change during any of these events, which perhaps proves only that the voltage to the lighter is not changing.
Another red herring, or clue: the odometer stopped working around the time this started. These are known to fail due to crumbling plastic gears, but they also draw electric power, so it could be linked.
From scanning various threads, the coils and plugs seem like potential culprits, and are probably my next targets to change. Some folks have cleared up mystery issues this way. Grounding straps are another candidate, but it seems odd they would cause the problem only after 10-15 minutes. Some loose wiring or short could also be involved, perhaps near the odometer, but again, the 10-15 minutes. Or maybe the ole computer is changing things up once the engine warms up. It does seem to happen when it first gets warm. But, even then, it comes and goes. It may buzz for a while, then stop and drive beautifully, then misbehave again.
Thanks for any light any one can shine on this! I think my current mechanic, who I like, may have gone as far as he can with this. I'm reluctant to re-start the process with another mechanic so am hoping to narrow things down a bit.
02-07-2024, 12:07 PM
#4
Rennlist Member
Did you check your alternator? Any voltage drop at the battery when you hear the buzzing? Any ac voltage leak, ie ac voltage in the dc circuit?
Also check your belts.
You said you changed your fuel pump. Did you change the fuel filter in the tank? Fuel filter in the engine bay? Sounds like the fuel pump could be starved of fuel due to a fuel blockage.
Also check your belts.
You said you changed your fuel pump. Did you change the fuel filter in the tank? Fuel filter in the engine bay? Sounds like the fuel pump could be starved of fuel due to a fuel blockage.
02-07-2024, 10:22 PM
#5
The fuel filter in the tank was replaced, but not until after the fuel pump had been replaced and the problem persisted. The tank filter to me it looked like it was falling apart a bit (the mesh). So my thought was that perhaps some of that mesh got into the fuel pump and was causing the problem to recur. But the 10-15 minute delay doesn't seem to make sense for that.
Not sure if the alternator was checked. My mechanic, iirc, said it was tricky to check the voltage at the battery while the car is running, so I don't think that's been done.
Thanks for the input - everything helps! At this point it's a lovely but awkwardly-sized paperweight.
Not sure if the alternator was checked. My mechanic, iirc, said it was tricky to check the voltage at the battery while the car is running, so I don't think that's been done.
Thanks for the input - everything helps! At this point it's a lovely but awkwardly-sized paperweight.
02-07-2024, 11:36 PM
#6
I have a very low mile Targa and in going through the records I saw that it had been through about 3 fuel pumps rather quickly and several fuel filters. Finally, it looks like they realized the tank filter was disintegrating. They replaced it. Still had a problem so they replaced the fuel line and that finally cleared up the problems.
Regarding bizzarre electrical problems. Did the car sit for any extended period of time? Any mice issues? You may want to make sure fuse box wiring wasn't chewed.
Regarding bizzarre electrical problems. Did the car sit for any extended period of time? Any mice issues? You may want to make sure fuse box wiring wasn't chewed.
02-08-2024, 03:36 AM
#7
Rennlist Member
Chach/clean all grounds and clean them again. It sounds thermally (expansion) related.
Alternator bearing?
Alternator bearing?