3.2 Carrera won't go past 1500rpm

[mschuep]

The Porsche:
'85 Carrera, 37k miles, wong chip, sport exhaust

The Problem:
Car acts like it hits a rev limiter at 1500rpm, in neutral or any gear. Not a miss, but the whole engine quits on me until the revs come back under 1500. This started about a month ago on my way to get gas. (Car has about 3-4 gallons in the tank) I was cruising at about 3500 and the revs just dropped. It felt like the throttle linkage had popped off.
If the car sits for a day or so, it will usually fire up and run great for about 30 seconds to a few minutes. Then poof, time to limp back home. The car doesn't like to startup after this issue has begun.

Troubleshooting I have done and/or replacements since this started:

-Verified correct fuel pressure, also, when the car hits 1500rpm and starts to surge at that mark, the fuel pressure momentarily increases, leading me to think that the pump is working fine.
-Swapped out sw chip with stock chip, no change (switched back to sw).
-Replaced dme relay, no change.
-Replaced and gapped speed sensor, no change.
-Checked idle position switch, ok.
-Replaced cap and rotor (looked fine really)

In the past 6 months I have:

-replaced fuel pressure regulator
-idle speed adjustment
-injector cleaning (witchhunter)
-verified correct AFM function
-replaced CHT sensor
-changed oil, oil filter, air filter
-last replaced fuel filter about 2 years/10k miles ago

I am leaning towards some type of electrical issue, since the revs are always cutting off right at 1500. Seems like if this was a fuel issue it would be more sporadic and missing/surging at other rpm. Where do I go from here? Does this sound like an electrical problem? Fuel problem?

[David]

I saw this when I was motorcycle mechanic. The customer put a bag of weed under his seat and it got sucked into the intake . Fortunately it did no damage to the engine or the bag of weed.

[cgarr]

If its a 2 year old fuel filter I would at least replace that to start and cut your old one open and look inside it, or blow thru it, see if its restricted. Do you have a gauge to check the fuel pressure?

[mschuep]

Yes, I checked the pressure. It is correct, and it will actually increase a little bit when the surging starts @1500...I'll replace/check out the fuel filter, that is easy enough, but I just don't think these symptoms match that cause...

[cstreit]

have you Ohm'd out the coil?

[mschuep]

Originally Posted by cstreit

have you Ohm'd out the coil?

I did check resistance on the coil...One of the resistances was on the high end of the resistance range...I don't have the bentley with me now but I want to say the range was like .3 to .8 Ohms, and mine was hovering between .8 and .9.

I just figured this was due to temperature or something. Can a bad coil cause this type of behavior? I thought that they were pretty bulletproof, and when they go they go?

[DonMo]

Motronics, heat related component on the board failing fast. Try this. Once it goes bad in your driveway or garage. Take out the box. Put it in th refridge for 30 minutes(no worst for it than being outside in the winter overnight). Put it back in the car and see if it starts and runs okay until it gets hot again. My bet it will .

[mschuep]

Originally Posted by DonMo

Motronics, heat related component on the board failing fast.

That is kinda what I was thinking, but didn't really want to admit it.

[DonMo]

Not the end of the world, $400 repair or a science project if you are handy with a soldering iron.