Car Jerks Violently at high RPM

[EIPtuningR32]

1982 928S euro is having some problems when revving to higher RPM. when i rev it in neutral or with clutch in, its fine. but when im driving and i floor it and i get around 5000 rpm, the car starts to jerk violently. its almost like im hitting a rev limiter x 2. its a vicious jerk and it persists until i change gears or let off the throttle. could it be running lean?

[MPDano]

Hmm, mine didn't do that when i was running lean. I suspect it's something else. Did you turn the A/F clockwise to richen, then test drive again?

[DanielDudley]

I have seen bad wires going to the pickup in the distributor play intermittant havoc with the spark when the advance changed at WOT. Make sure that the wire to the pickup is good. The actual wire can deteriorate in the insulation, so check carefully.

LOL.

[EIPtuningR32]

Originally Posted by DanielDudley

I have seen bad wires going to the pickup in the distributor play intermittant havoc with the spark when the advance changed at WOT. Make sure that the wire to the pickup is good. The actual wire can deteriorate in the insulation, so check carefully.

LOL.

i have brand new wires so i couldnt be that. but to be sure ill put the OEM back on to see if it isnt that.

[Barbapapa]

It wouldn't be plug wires or fuel. A poor connection or the coil are some possible culprits.

[lizard928s]

The wire which Daniel is refering to is the green wire which connects the distributor to the brain. This could be suspect, as if the spark cuts out it will be like hitting a rev limiter.
The other option could be fuel, a seriously lean condition will cause these issues.
As well the other thing is as Mike points out a loose wire on the coil or a bad/intermittant connection.

I would start off with a CIS pressures test for the componants to make sure that they are all within spec. I would also look at the green wire, if it is origonal I would replace it.

[Normy]

My car for a while had a problem with a sudden cut-out of the ignition at full-throttle and high RPM. It would only do it for a 1/10 of a second or so...but it was enough to put me against the seat belts. It felt like it wanted to launch me through the windshield....

Cause: a bad connector between the engine harness and the timing and reference sensor on top of the bell housing. I discovered this in the driveway by moving all the wires at idle until I heard a slight stumble from the engine. I removed the connector, soldered the wires...and fixed the problem. The only thing is...I can't remember if your car has a timing and reference sensor or not. I suspect it does, but I don't have my manuals available.

N

[EIPtuningR32]

Originally Posted by Normy

My car for a while had a problem with a sudden cut-out of the ignition at full-throttle and high RPM. It would only do it for a 1/10 of a second or so...but it was enough to put me against the seat belts. It felt like it wanted to launch me through the windshield....

Cause: a bad connector between the engine harness and the timing and reference sensor on top of the bell housing. I discovered this in the driveway by moving all the wires at idle until I heard a slight stumble from the engine. I removed the connector, soldered the wires...and fixed the problem. The only thing is...I can't remember if your car has a timing and reference sensor or not. I suspect it does, but I don't have my manuals available.

N

wow thats something i need to look at.... but it doesnt only last 1/10 of a second for me. it lasts till i let off the throttle (which isnt very long due to the fear of breaking something)

[Danglerb]

Normy's 85 Euro is LH2.2, your 82 Euro is L, you don't have a reference sensor on the crank, just the green wire from the distributor.

[EIPtuningR32]

Originally Posted by Danglerb

Normy's 85 Euro is LH2.2, your 82 Euro is L, you don't have a reference sensor on the crank, just the green wire from the distributor.

I think, if possible, i will replace that green wire and see what happens. over time couldnt the wire get cracks and stuff in it that disperse the electrical current everywhere but the place you want it?

[Danglerb]

Green wire is some high temp coax, not sure on details, just that they sometimes go bad. Coax is one wire in the middle with an insulation layer and either a foil or woven shield around the insulator.

[MPDano]

If that wire looks bad or the insulator is cracking off in places, replace it. Plus it looks real neon greeny and cool.

Here's is my write up on it:

http://www.porsche928forums.com/viewtopic.php?f=9&t=4&st=0&sk=t&sd=a&start=330

[EIPtuningR32]

Originally Posted by MPDano

If that wire looks bad or the insulator is cracking off in places, replace it. Plus it looks real neon greeny and cool.

Here's is my write up on it:

http://www.porsche928forums.com/viewtopic.php?f=9&t=4&st=0&sk=t&sd=a&start=330

awesome!

[DPW928]

The US versions have the rpm cutoff programmed into the ignition box but not on the Euros. They use a rotor that has a centrifugal rpm cutoff. It's possible the spring in the rotor has lost tension and is cutting off spark. Hold old is your rotor and distributor cap? BTW the US version of the rotor will work.

[EIPtuningR32]

Originally Posted by DPW928

The US versions have the rpm cutoff programmed into the ignition box but not on the Euros. They use a rotor that has a centrifugal rpm cutoff. It's possible the spring in the rotor has lost tension and is cutting off spark. Hold old is your rotor and distributor cap? BTW the US version of the rotor will work.

actually funny you mention the cap and rotor cause i replaced them about 3 days ago.

[porshapower]

On my 86 I have yellow,black,blue coming from the sensor. Coming from the harness I have brown,white,black. I was digging around in that area looking for vaccum lines unconnected and they pulled apart...now the car doesnt start. I tried yellow to white and blue to black and brown to black with no luck. Please help Thanks in advance everyone! Nel

[Rupesy]

I suffered with that exact same problem until I changed the fuel filter. I refused to believe it was the reason for the longest time. Car idled and would rev up beautifully until it was under load at high rpm where it really needs a lot of fuel. Eventually I could not even reach 3000 rpm and found myself on the side of the road many times. Some people may remember my saga...LOL

[Mrmerlin]

put the old rotor back on the distributor and road test the car