Miss Fire - under hard acceleration

[youfamissim]

Hi fellahs. Newbie here - not to Porsche. My trouble - 1987 930, 27K original miles. Engine was out, regasketed, new exhaust. New coil, plus, & wires. 2008

Car just came from dealer shop and runs perfect - EXCEPT under hard acceleration. The engine miss is most dramatic in 3rd and begins @4K on tach - turbo is engaged and @ full boost. It is NOT a consistent miss. Intermittent as the RPMs climb. This is not new trouble. I've had it for a while now and related to the dealer shop - not happy with them at this point = another story. Lived with the miss and I avoid hard acceleration; which denies my thrill of owning this car. HELP! Slowly pushing the accel pedal lessen the miss.

Had the "Silly" $ plug wires and plugs installed last trip in for maintenance. 3K miles on these items.

Coil New 2 years back.

I run premium fuel.

And while I'm begging... I'm planning Major HP modifications. I want to solicit Ideas from everyone here. Desired HP = 450- 500 with corresponding toque.

What is the best path to achieve this? Additionally - school me on other mods required to make this upgrade safe on the street. Just added 18" wheels to accommodate larger calipers; etc... and will keep the progress posted. Thanks for any assistance.

Youfamissim

[mca]

I'd try a different coil first. Then I'd try different wires.

[TheWerkstatt]

I have seen this exact problem on more than one 930. The wire that triggers the coil from the distributor degrades. The wire degrades at the push on connector coming right out of the distributor. The dealer will have in stock.

[RWebb]

search on green + wire

[Bob Kontak]

Also for fun, try the night time - no lights - looking at the wires for arcing while revving it up.

[frankc]

Were the spark plug connectors (boots) also replaced with the wires? I had a similar mis-fire under load condition on both the 911 and M3 and faulty boots were the cause in both cases.

[lite75]

I wouldn't rule out those new plugs either.

[youfamissim]

Looks like a new GREEN coil wire is in my future.

The Coil wire replacement solution begs a second question - and this goes directly to that Other Matter I mentioned in the original post -
I've had it (the miss) for a while now and related to the dealer shop - not happy with them at this point = another story.

"Could a degraded coil wire account for NOt starting and/or extreme rough idle (undriveable) on start up?"

IF yes... there'll be some Splainin' to do...

Yes the entire plug wire assembly was replaced - spent plenty to buy peace of mind.

[T77911S]

new cap? new rotor? plug wires, as MCA said, he had problems with new wires. try a different CD unit if you can borrow one. advance/retard working as it should. check for wires that could be rubbing and grounding out, perhaps they only ground out under hard acceleration. i have seen wires ground out in left or right hand turns.

after that, start looking at air leaks and fuel problems. fuel pump putting out as it should. an injector, perhaps does not show its ugly head until a large amount of fuel is needed. fuel pressures? how is the fuel delivery to each cylinder? you can put each injector in a jar, with the key on, hold the sensor plate wide open. the longer you can hold it open, the better. then compare each jar for equal amounts.

pull the plugs after a hard run where it missfired. shut it down as soon as you can, i know it is bad for the turbo, but youmay have to. compare the plugs to each other, even after 100 or 200 miles and look for one that is bad. keep checking the plugs if nothing shows.

even though it is a random thing, perhaps a compression test.