Hi Tim - I read your opening post carefully about 4 or 5 times. I experienced similar symptoms on my 83 SC (USA spec) a few weeks ago, particularly the bits that I've highlighted below. Like you, I also thought the FP (that I had just replaced w new unit) either went out or got clogged from fuel tank rust.
Eventually the car stalled out completely, and would no longer start. I towed to my local air-cooled tech/specially in here in LA. He diagnosed/tested and determined that the CDI had hailed. It was my original factory Bosch unit. He replaced it with a PermaTune unit, and also replaced the coil (Perma as well).
Just wanted to share a similar experience and data point with you. I saw you mentioned you had a fairly new CR CDI unit. If your other diagnosis does not reveal the culprit, then consider looking into the CDI.
Good luck, and look forward to your update.
Quote:
Originally Posted by Mothy
After trying to track down my problem for a few days and doing various searches here I need some help. ts been a while since I have posted.
I have a 1983 911SC which has been used for many years and has previously run well. It is quite modified, so it make the troubleshooting somewhat difficult. For instance it does NOT have any of the system under the passenger seat (OXS Control unit), so for all intents and purposes it is running as per an earlier SC.
About a month ago, the car started to play up. Started fine and would be ok driven for about 30 minutes and then start to misfire/hesitate when accelerating, almost like it had an ignition problem. Cruize would still be ok but any time I pressed down on the accelerator it would feel like it was cutting out - and occasionally backfire (sounded like it was in the intake - I have the pop valve fitted). Eventually it would get to the point where the car just would not run at all without pops and farts. It almost feels like the fuel pump is cutting in and out.
If I stopped the car and checked connections to coil and also the fuse board, it would start up again OK and run fine for about 5 mins then start the same issue, getting progressively worse with time until I needed to stop again - effectively to let things cool down I assume.
Interestingly, I was on my way to a Motorkhana meet and provided I didn't have the car idling while waiting in the queue for my turn, it would run fine. If I had the car idling for any length of time it would misbehave badly.
It has now added a further problem. I blows the fuel pump fuse 16 (25A) before I can even get it started. If I disconnect the electrical lead to the WUR then it starts fine and runs for a bit before complaining. If I plug the connection back onto the WUR, it blows the fuse.
Swapped Fuel Pump Relay - no change
Checked wires to the coil - no change
Recent changes to the car (well before the problems started)
- New Fuel tank
- New Fuel pump
- New fuel filter
- New coil
Checked the WUR part number and looks like mine is an earlier one - 0-433-140-033 from a 76-77 model??? Have no idea why that's the case. Its been fine for the past 18 years that I have owned the car.
Have checked a few things:
resistance across the terminals on the WUR is 24ohms which I understand to be OK
voltage to the WUR is 14v only when car is running.
WUR connection points are open to ground (not earthed which I understand is correct
I do not have the Supplementary Air Value
I do not have the OXS relay
I do not have RPM Limiter Switch
I do not have an alarm system
All these are normally associated with he Fuel Pump circuit.
I have the Classic Retrofit CDI fitted - has worked fine for the past 4 years.
The CIS is 40 years old so who knows what might be the issue. I am suspitious its going to the the WUR but thought it best to ask some of the wise minds on this board before I start down a track that might be a dead end.
Thanks
Tim
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