82 928S cuts out intermittently at 3,000rpm?
10-29-2007, 12:36 PM
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82 928S cuts out intermittently at 3,000rpm?
Hi all, I have an annoying intermittent problem on my shark. When under load, about 30% of the time it acts as if there is a 3,000rpm limiter in place. All other times it runs up to the red line fine. When it does cut out the rev counter drops to zero. Allowing the revs to drop below 3,000ish either by changing gear or slowing down allows it to run sweetly again and the rev counter wakes up again.
Car is an 82 Euro 4.7 S - I've changed the rotor arm, cap was new last year and still looks perfect. It's unlikely to be a problem with fuelling as when the car cuts out the unburnt fuel pops and bangs in the exhaust... My suspicion is something electrical - any ideas?
cheers in advance
Matt
Car is an 82 Euro 4.7 S - I've changed the rotor arm, cap was new last year and still looks perfect. It's unlikely to be a problem with fuelling as when the car cuts out the unburnt fuel pops and bangs in the exhaust... My suspicion is something electrical - any ideas?
cheers in advance
Matt
10-29-2007, 02:41 PM
#2
Something in the distributor. There is an infamous "Green Wire" you will want to search this board for.
10-29-2007, 04:42 PM
#3
Electron Wrangler
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The transistor ignition unit has an inductive pickup in the distributor - this is the rpm sensor for the tachometer and also keeps the fuel pump alive except for a burst after the ignition is initially turned on. If this gets flaky at 3K it will cut the fuel when the tach goes dead - some fuel will still end up in the exhaust due to residual pressure but you will go lean and may get preignition before that...
Alan
Alan
Last edited by Alan; 10-29-2007 at 06:52 PM.
10-29-2007, 06:47 PM
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I had the exact same problem except cutout was at 3500 RPM.
I spent a LOT of money at a well known 928 shop who gave up.
Another shop found five (5) electrical problems with the car:
1. bad green wire - replaced with new
2. bad CD unit - replaced with good used
3. loose injector connectors - all replaced with new
4. one bad plug wire - replaced
5. replaced cap & rotor
The CD unit was the direct and specific cause of the cutout.
I would start by wiggling the green wire - it is the most likely suspect.
If the green wire is not the problem, try to borrow a known good CD unit or buy a used one with right of return.
Otto's rebuilds CD units to a high standard. I have one of his in my 911.
Phil
90 928GT
82 928S-look
71 911T
I spent a LOT of money at a well known 928 shop who gave up.
Another shop found five (5) electrical problems with the car:
1. bad green wire - replaced with new
2. bad CD unit - replaced with good used
3. loose injector connectors - all replaced with new
4. one bad plug wire - replaced
5. replaced cap & rotor
The CD unit was the direct and specific cause of the cutout.
I would start by wiggling the green wire - it is the most likely suspect.
If the green wire is not the problem, try to borrow a known good CD unit or buy a used one with right of return.
Otto's rebuilds CD units to a high standard. I have one of his in my 911.
Phil
90 928GT
82 928S-look
71 911T
10-30-2007, 09:13 AM
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Cheers for the tips guys. I guess I can narrow it down to green wire or ignition control module. Other than swapping in known good ones, is there any way to test these parts given the intermittent nature of the problem? I tested the resistance over the green wire from the ignition control plug and that showed 574 ohms when cold which is within range. Wobbling the wire didn't change the reading. Does this prove the integrity of the core but not the shielding of the green wire?
cheers
Matt
cheers
Matt
