ViribusUnits

My 1983 Porsche 928s "misses" somewhere between 3000 and 4000 rpm, depending on the exact occurance.

When it does this, the tach. falls to less than 1000rpm nearly instantly. There is no way the engine falls that far that fast. The car is a 5 speed manual, and when the engine misses it stop accelerating, but doesn't deccelerate very quickly.

The exaust smells like it's running rich, but that could be due to the fact that it doesn't have a cat. I am getting very good milage, about 20 mpg depending on the highway.

The car is very quick on the low end, and doesn't seem to be lacking power under 3,000 rpm.

Thanks

Normy

For a short while, after I changed out my plug wires, my '85 S2 5 Speed developed a sudden instantaneous miss that would nearly launch me through the windshield. For a second, the ignition seemed to fail completely. I tracked it down to a bad wire leading to the timing and reference sensor on the top rear of the engine.

Might be wise to pull the airbox and wiggle some wires while the car is running in order to see if moving one of them causes the occurance.

Normy-

richard glickel

Sounds like a wire or a distributor problem (if 928s have distributors). Sometimes you can't see a crack in a distributor until you remove and visually inspect the part.

Richard
'87 Carrera-3.6L

ViribusUnits

My car deffently has a distributer. It's right behind the T-belt. (that's going to get replaced this winter)

It certanly looks OK from the outside. When I remove it, what should I look for?

Is there any test I can do the the wireing? Other than just condutivity tests.

Normy, my car's situation is very diffrent. The car will hold what ever rpm it's at, just won't go any faster. It's very rpm related, and does it under any just about speed or load.

Thanks

John Struthers

Viribus,
Can't help but curious. How's the idle?
Norm,
Speaking of distributor problems...
Do you still have that High speed/high RPM miss?
Rich Glickel reminded me of my older brothers' group of greasers and motorheads.
Before ECU's and black boxes et all they used to yank the distributors and check em out on a regular basis. Maybe because of the metallurgy, or looser tolerances back then. They mic'd everything, checked for wear, loose gear pins, bushings, condition of springs and advance arm pivots.
The old 'Sun' machines were also set up to find,
or, isolate problems in this area(dwell?).
In any case, maybe Wally or someone can figure a way to detect possible slop or a worn gear tooth without disassembly. Perhaps thru use of a simple timing light, dwell meter.
Viribus, hang in there this has got to be something simple. Electrical, maybe Vacuum...it seems to solid a rpm range for the engine to top
out because of injector/fuel issues.
BTW have you checked to see if that jumper is connected or not...the one for running on PEMEX or other gasolines with low octane ratings. My 82'
is sitting in plain site below the brain -pass. footwell- when you pull the carpet should not be plugged in but should be capped.
later <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

richard glickel.

Well, the distributor is easy enough to remove. If you decide to take it off, make sure that you number each of the wires so that you plug everything back exactly where it belongs.

You'll be looking for hairline cracks in the plastic either on the top or along the sides.

As for checking for electrical wiring problems, I have heard of some guys turning out the lights in the garage and having someone get on the trottle to try and detect any sparking under the hood. Some even go so far as to spray a little water with an aerosol sprayer (not with a hose), to see if they can detect sparking under the hood.

ViribusUnits

To be honest, this isn't my hghest priority problem, so I've just started trouble shooting it. Nothing looked "broken" so I'm not exactly sure where to look. I just bought the car about a week ago. I'm going to get the service mannuals "for Christmass" so to speek.

Idle is fine, it seems to be about the right speed, and it's stable. The only problem is when I hit about 4,000 rpm, it just won't go no faster, and the tach falls dramaticly.

What is the PEMEX, and what does it do?

Thanks

Kirkg

If by chance you have not found your problem yet I have to agree with a previous reply. I have spend all summer trying to track the same problem on my 86.5 ( a miss at about 4000 with a instant tach drop). The problem was tracked to a faulty impulse sensor. Once I replaced the unit, my car was back. Good luck.

AO

Hey ViribusUnits. Check your private messages.

Normy

Hey John,

Yeah, I've been all through that ignition system. New wires, new rotors [S2's have two 944 distributors] and new caps. I even hit it with a timing light, which turned up nothing. Last time I was home [ages ago, it seems!] I went to pull the coils to test them, but they are buried in there so deep that I gave up for lack of time. I suppose it is possible that the new caps and rotors are bad, though I doubt it as the symptoms were the same both before and after. When I had the caps/rotors off, I pulled the little assembly apart and checked the condition of the little belt that ties the distributors together, and all seemed pretty tight. Overall, I've poured gallons of injector cleaner into the car, replaced the seals around the MAF sensor, and have been through the ignition from one end to the other [though I still need to check those coils-]. The car even stopped doing it the time I took it to a reputable local garage in order to have the ignition/injection troubleshot. I've come to the conclusion that it is probably just a damn broken wire or some other simple thing...but it is rapidly making me bald...

[I'm pulling my hair out over it!]

Normy!
'85 S2 5 Speed

PS- As strangely as the full miss that would nearly launch me through the window came, it has gone away. Anyone know of a good Witch Doctor?

drnick

normy, my 86 s2 also has twin dizzys and is developing a more subtle miss in the higher rev range.
i wondered if you had advice on plug leads to upgrade from stock?

cheers,

Normy

drnick-

I went "all the way" and purchased the Nology wires from 928 Specialists. They look cool, and appear to be strong enough to hang from! I think there are less expensive wire sets around that would work fine as well.

Normy-
'85 S2 5 Speed