My new VR has arrived and I will install it when I can. I'm not especially looking forward to pulling the alternator out again especially since the voltage readout has been very good (14.2v max) since I had everything out the first time and as I mentioned, it all checked out OK. But I have the new VR so I might as well install it and put that behind me.
I was out for a spin around town today and the vehicle quit again. I noted that the instruments still had power and no lights came on until I pushed the clutch in, at which point the alt light came on and oil pressure dropped to 0. I guess that's to be expected with an engine that isn't running. I'm quite sure the gas gauge kept indicating, so it didn't loose power.
Again, I just turned the key off and on again and the engine started right up. I didn't bother stopping or pulling aside, I just turned the key of and on and just carried on as if nothing happened.
I somehow don't think that heat is the cause as the vehicle starts right up ( less than 30 sec) so nothing has had time to cool off.

It is frustrating but I'm sure it'll get sorted out, and it'll be interesting to know the cause of it.
As far as getting towed, that happened back in June when the CDI box failed. Two hundred miles of towing isn't cheap. The good part is I feel confident the CDI unit is not at fault since it was rebuilt by B. Ashlock, but.......
I will somehow try to check that green wire (distributor) that has been often mentioned. I don't like the way that it is wrapped with tape in the wiring harness which looks to make it less than easy to replace.
I'll keep you updated as I can.
hughc

yea that was my point. if heat was the issue it would not start.

I think someone else had a problem like this and it may have had something to do with one of the electronic devices, maybe RPM limiter switch?

I am not calling into question your rebuilder of your CDI. What I am saying is keep the possibility in the back of your mind that the CDI could have been damaged by over-voltage after it was rebuilt. There are some people who suggest that the older CDIs lack internal protection against over-voltage and that could be the reason for your intermittent cut outs.. I’m not saying that is the problem — just consider it a possibility among others.

If it cuts out after getting hot and then works again after cooling off that will point to the coil or CDI. Keep a can of compressed air handy. The next time it happens turns it upside down and spray the CDI. If it will restart again immediately then you have most likely found the problem. Maybe try replacing the coil. Worst case, you have a spare now.

Check out the transmission ground strap, fuses and all connections for loose connections and corrosion. Deoxit D-5 and emory paper is great for cleaning contacts.

Have you validated your voltmeter?

Yes, I will definitely keep the CDI in mind. In fact the rebuilder has offered to have a look at it if I should so wish.
As I've mentioned previously the engine starts up IMMEDIATELY after it quits. I only have to turn the key OFF and ON and I can carry on. To me that pretty well rules out the possibility of any components being overheated.
I'm in the process of replacing the VR and will of course re-do the alternator ground wire. I'll have to at some point get under the vehicle to double check the transmission ground strap.
The digital voltmeter has been verified in that it has been used in other vehicles and has behaved as it should. It also has been used in the SC and has not shown voltages above 14.2v, so at this point I'm thinking the original VR was working intermintantly causing the voltage to spike to 18.6v. I hope with the new VR that problem has been laid to rest.
My friend is studying the electrical dwgs. to see what else might cause the ignition to fail.
Thx
hughc

18.6, you fried the CDI, search "overvoltage". Every symptom matches the multitude of posts on the subject. Total failure will follow.

ClickClick, thank you for your observation, but obviously I hope ur wrong, but I'm sure the possibility is there that the CDI has fried.
BUT, the thing to take into consideration is that the vehicle is running quite nicely (until it quits) and that would leave me to believe the CDI unit is working as it should.
The idle isn't as smooth as I'd like but I don't know if a lumpy idle can be attributed to a faulty CDI.

I'll soon get the alternator back in and we'll see then if there are any changes.
thx,
hughc

hugh,

I am wondering if the failure mode for a traditional CDI failure and an over-voltage failure are the same. Maybe they are, but I wouldn’t necessarily assume that is the case. If there are different faikure modes, that would be a possible explanation for your symptoms.

+100

Too late GaryR, I've had the restrictors in for at least a month and I don't think I'm worst off for it. Idle pressure is a little better than it was ( app 0.8 bars) and good pressure at hwy speeds (app 3.0 to 3.5 bars).

Before installing the restrictors I did open them up to 2.7 mm (up from 2.0) and that might explain why my idle pressure isn't quite as high as I expected.

If I was to do it again I would remove the original restrictors, weld the holes shut and re-drill somewhat smaller than the originals but larger than what is being sold as replacements.
In my case I opted for 2.7mm.
thx
hughc

There's something about the shape of the hole that sprays the oil where the manufacturers say not to drill them out. I think I read that somewhere. Feel free to disregard, I just don't want you to get any engine trouble.

Thank you Jason. When I was considering ordering smaller holed restrictors I read up on previous posts and there was never any mention of special shaped holes. I corresponded with a person that is involved in 911 engine building and he has used smaller sized restrictors and told me that my 2.7mm would be adequate.
I also just had a look at the restrictors that I removed from my engine and there is nothing to indicate that the holes are anything but just holes, ie, no special shape.
Thank you for voicing your concern.
hughc

I put the new VR in yesterday (pulling that alternator is getting easier all the time) and went for a drive. The car was running quite nicely and I was pleased up until the point where it quit again, and again, and again.
So, problem not solved. It's more than frustrating, as it starts right up again as if there was nothing wrong.
As mentioned before, there is still power to the dash but for some reason the ignition cuts out.


"I am wondering if the failure mode for a traditional CDI failure and an over-voltage failure are the same. Maybe they are, but I wouldn’t necessarily assume that is the case. If there are different faikure modes, that would be a possible explanation for your symptoms" Tim

Tim, You may have something there and I will correspond with the rebuilder of my CDI unit to see if what you are suggesting is a possibility. I may have to return the unit to him for testing, and I hate to have more down time but what can you do?
hughc

Heat, internal and external has a way of precipitating failure modes.

I had a similar problem last summer in the extreme heat. Turn the key off and on reset the CDI box and I was good for another sixty seconds or so. Weather hasn't been as hot since, so I haven't investigated further.

See the discussion here: http://forums.pelicanparts.com/porsche-911-technical-forum/958213-memorial-day-diagnosis.html

Thank you RDM, my problem also seems to be heat related, where the vehicle seems to need to be driven until it is well warmed up and then it starts to shut off.
I'll try to confirm that this week end by taking it for a couple of long drives.
hughc

Have you been following this thread at all? Similar symptoms of engine cutting off once warmed up.

http://forums.pelicanparts.com/porsche-911-technical-forum/928919-3-2-carrera-poltergeist.html

Great suggestion in that thread about running a hot wire to + coil to eliminate the key switch.

Thank you Rob and eastbay. I will read up on that thread. There may be something there for me.
I did go for a run today and the car ran well and didn't shut down. The weather today was much cooler and the engine temperature didn't get as hot as it would on a hotter day, which leads me to suspect my problem is heat related.
At this point I seem to be grasping at straws but I think I will ultimately send the CDI box away for verification because of the possibility tyat it may have been compromised when the charging voltage went as high as 18.6v.

hughc

You might want to jump to the end of that thread I provided above. His issue ended up being 1 or both crank sensors going bad once heat soaked. I believe there was a procedure where you could check the resistance cold and then hot to see it the sensors are failing once hot. Seems easy enough to try before sending your CDI anywhere.

Thank you Rob. I'll have to try to locate those crank sensors. I had a quick look at the Bentley manual with no luck. I'll have another look tomorrow.