InC

thanks guys.

It really feels like fuel starvation or ignition cut out. It was very violent. So why the Plugs? just curious, trying to understand the system. As it didn't feel like a normal misfiring but a violent surge felt really bad. Certainly hope the plugs will solve the problem will change them anyhow, it's about time, never too soon I guess. Any recommendations? Bosch super 4, NGK?

The thing is how come it only happens in 3rd or 4th gear not 1st and 2nd.

would a clogged fuel filter cause the problem?

DonE

So, you are saying you can go WOT in 1st and 2nd, but once you shift into 3rd, the car hits a wall at 4,000rpm?

Can you "sneak up" on higher (than 4000) rpm if you take it real easy?

The reason I said fueling problem is because my CIS motor lost voltage to the WUR. This kept it at cold pressures (rich) even though the motor was at operating temp. So, once I got past 1st or 2nd gear (where these cars can nearly take as much fuel as you can throw at them because the turbo spools fast - lots of air) and into 3rd, you really start to load the engine and they can not produce enough boost to compensate for the mega fuel being introduced. When you hit that point (rpm), you flood the engine and its like hitting a brick wall. Once the rpm falls to a level that the air and fuel are the right ratio, you fire the cylinders again and can limp home. You will foul the plugs on with this problem.

Another way of checking this is very easy. Disconnect the 12v source to the WUR, connect a DC volt meter, turn the car on (not start) and look for at least 12v. If so, you should then check the pressures cold, warm and enriched. In any event, most likely the plugs will have to go. I recommend Bosch FR5DTC at stock gap.

Good luck

Jim McDade

Thought I would let everyone know that I got my 930 back from my mcehanic. He changed the plugs and the fuel filter. Everything else had been changed already. I took it out about an hour ago, and believe me it is scary fast!! I blew off a Z06 Corvette (last years model) like he was backing up. He was surprised as like most Corvette drivers, he thought a Porsche is a 4 cylinder 100 hp VW. He knows differently now. In any event, the car pulled all the way to red line in 2nd 3rd and 4th gears. Sounded awesome, and never missed a beat. Wow, what a ride. Can't wait till tomorrow. I have to believe that all of you were correct, it must have been the plugs. However, they looked great when the old ones were removed.

DonE

Glad it worked out.

I think I'll sit in the corner over there......

InC

Thanks everybody.

'DonE', Thanks for your explanation. Sounds very logical to me. Will sort it out today! Probably do the plugs first because I think they are probably gone. Wacked the car really bad before this happened. Was having some fun with my friend's Skyline R34.

Are the speedos in our cars inaccurate? My friend clocked 150mph and it only showed 140mph on my car...

Thanks again everybody!

SGOGT4

Glad to see it all worked out. In most instances there will be atleast one person who has learned the hard way how to fix almost any problem that comes up with our cars. We all might as well learn from those people rather than trucking down that long, arduous and often expensive path ourselves.

Last930

I am having the same stuttering/missing problem on full boost above 5000 rpm in my 79 930. Any suggestions on the best source for new plug wires? Mine are very old wire-braided wires, probably at least 10 years old. Suprisingly, it runs very well at lower rpm.

Jim McDade

We replaced the plug wires with Porsche factory wires. As mentioned above we changed the coil, distributor cap, rotor, one fuel pump, etc. etc. Finally even though the plugs were only a few months old, my mechanic changed them along with the fuel filter and all the problems went away. The plugs looked brand new, so did the fuel filter, so who knows which item fixed the problem. All I know is that it is faster than ever now. I think it was probably the fuel filter, but what do I know?? The car pulls so hard and fast it is scary, must be careful in lower gears as it breaks the tires loose. FYI plug wires are available thru Performance Products at different levels of performance and price.

TazioNYC

I'm getting this same thing -- moderate to hard acceleration, 4K +. Did new plugs solve it?

Last930

I swapped out the plug wires on my '79 last year - they were actually the original wires. My car ran great at low rpm's and off boost, but when the cylinder pressures came up when on boost the plugs would missfire in 3rd and 4th gear just like the others described. New wires fixed it.

Mark Houghton

Glad you found the problem to be plugs. But also, Nathan was correct in his analysis as ONE of the possible problems. I had a similar problem, but only under boost. The overboost relay was malfunctioning....and even on one occasion prevented me from starting the car (fuel pumps wouldn't run). Simply unplugging the relay and cleaning the pins did the trick for me. As always, there are several possible explanations.

TOXNER

When I bought my 930 the PO told me that it would not pull over 4000 without missing. He was correct. He had replaced the CD box, plugs, wires, etc. The problem was the front fuel pump. It was self destructing and leaving metal filings in the fuel which trashed the second fuel pump. Replacing both fuel pumps and cleaning the fuel distributor solved the problem. Your problem may be caused by something completly different, just a data point for consideration. Good Luck.

Tom

oildog

Funny, but right after this thread came out, I took my "85 for a spirited ride and expirienced the same miss when going to 3rd under full boost. We went through plugs (slightly fowled), fuel filter a little gunk, tested the fuel pumps, didn't solve the miss. Finally pulled the injectors and they were a little gummed up. Sent them to Diesel Injection in Louisville to be cleaned up. Still didn't fix the problem. Futher testing found that #6 had a bad spray pattern. Ordered a new injector installed it and now the car runs better that I ever remmember.
The only thing I can think of that would of caused this is that I had let the car sit for over a month without starting it. Won't ever do that again.

dholling13

Best part of this post: "I blew off a Z06 Corvette (last years model) like he was backing up."

Glad to hear you fixed the problem!

srupp1969

Hi,

I had a similar problem yesterday during a DE.
Full accelaration in 1st - stuttering, 2nd - stuttering.
After finishing the lap and switsching the engine of it didn't start again.
After testing the usual things I changed the 2 fuel pump relays my neighbour in the box lend me and the everthing was fine and it was running again in its best behaviour.
What i have learned: always have some spare relays with you, when going on the track or for a drive :-).

Cheers
Stefan