sudden death

[sunquest]

Car is a '76 911S w/3.0l

Driving down the road, all of a sudden the engine dies - no missing.... just "off".... quickly depress clutch - turn key off (careful not to lock steering) and then back on... all lights ok on dash...ease out clutch - car runs fine until next episode.....(usually not too far off)

This has been plagueing me (and my wrench) for close to nine months ... and assorted failed remedies....

Any ideas?

Thanks,

Stu

[k9handler]

fuel issue? Filter, pump, relay...I would check these and see that everything is normal as rust in the fuel tank could be the root of the problem as well. Many other things could be under consideration and I am sure you will get some good advice here.

[Schrup]

What have you & your wrench tried so far?

[Tyson Schmidt]

I'd concentrate your focus on the ignition system. If it shuts off that quickly, it's usually spark. ignition switch, CD box, hall effect in distributor, green wire from distributor, etc. Basically everything in the primary circuit of the ignition system would be the first place to look.

[sunquest]

Hey,

Thanks for the replies...

new fuel relay, fuses (where appropriate), checked fuel pressure, new cap & rotor, and a lot of time consuming test-light testing... but to no avail.... of course

I suspect it is in the ignition because it is so abrupt, but short of just throwing more parts at it (namely a new CDS - mine is old preMotronic system).., Plus, I'd feel better if I knew for sure where the issue was...

It does seem "heat" related - ie after the car is driven a bit, but has never failed to restart - unlike an old coil that would have to cool down first....

Thanks again..

Stu

[trj911]

I agree with Tyson. I had a similar sounding problem where the system would overcharge and shut down. I replaced the CD box and ignition coil and I haven't had the problem since.

[GeorgeK]

Bad ground. At least it was that in my '76 Carrera a long while ago. Would cut out without a warning.
GeorgeK

[sunquest]

What about CDS alternatives? PermaTune, etc...

Thanks,

Stu

[Tyson Schmidt]

I'd go with MSD before Permatune. Just my personal opinion.

[RoninLB]

Originally posted by sunquest

It does seem "heat" related - ie after the car is driven a bit, but has never failed to restart - unlike an old coil that would have to cool down first....

is this predictable?
once every 10miles or 10X every hundred miles?

[sunquest]

Hey:

About the time the engine has reached operating temp... and then about 15 minutes after that....

somewhat disconcerting trying to get on the expressway and having your engine quit...

I just upgraded my oil cooler (to the carrera w/fan - no thermostat - but microswitch under dash for fan)... so now I'm anxious to drive car in summer heat w/o white knuckles over the oil temp....

but trying to figure out the gremlin w/o just replacing parts randomly .... I'm out of other ideas

Thanks,

Stuart

[sunquest]

I should have said "every" fifteen miutes....

-stu

[RoninLB]

Originally posted by sunquest

About the time the engine has reached operating temp... and then about 15 minutes after that....

well Stu, I'm not a pro.
but if I was looking for a needle in a haystack I'd run a good ground, like a 10ga from the tranny ground strap at the tub lug first to the CD.. then another 10ga hot, with a real switch, from the starter hot main lug to the CD. and have the switch off until you start the car, then turn the switch on.. that way if it didn't cut out again I'd have some idea on what direction to look.
naturally the battery clamps and chassis ground are clean.

does the radio cut out also?

[BGCarrera32]

Yeah, if the engine just caputs like that without stammering, its not fuel. There is an electrical harness problem there somewhere (or ground) look at areas where harness/wiring gets in close proximity with hot stuff- exhaust/block/etc.

-BG

[mb911]

I don't think any one mentioned this but Cd boxes either work or they don't. Coils on the other hand will work great until the warm up and expand and short out the internal windings. I have seen this countless times in the Modern aircraft industry. I have seen it many times as well with porsches. I would replace that first . If someone has one as a spare to try that would be the ticket. If changing cd boxes I would say the MSD is the way to go but I may be partial as Thats what I use. I think I may have an extra 6 pin permatune along with extra coil if your intrested. other wise good luck and try the coil.

Ben
77 911 3.0
75 914-6 2.7

[RoninLB]

Originally posted by sunquest

I'd feel better if I knew for sure where the issue was...

plagueing me (and my wrench) for close to nine months

sounds like you got some bucks invested in trackdown.

flipping parts would be easy.. but you want to know the issue. sometimes it's cheaper to divide and conquer.......... Ron

[IROC]

Originally posted by BGCarrera32
Yeah, if the engine just caputs like that without stammering, its not fuel. There is an electrical harness problem there somewhere (or ground) look at areas where harness/wiring gets in close proximity with hot stuff- exhaust/block/etc.

-BG

Actually, it can be fuel. On a CIS car, it takes something like 3.3 bar of fuel pressure just to open the injectors. When the fuel pressure drops below this point, the injectors close and the engine dies. Immediately. No stammering or hesitation.

I had a weird intermittent problem years ago where my engine would cut out (from running perfectly to nothing in an instant) whenever I made a left turn. Weird, I know. Thinking it had to be electrical, I checked everything, but found nothing wrong. Come to find out, the PO of my car had cobbled up the wiring to the fuel pump when he replaced it and the + lead was shorting to the fuel pump housing under left turn g-loads. The fuel pump would stop and engine would stop. Immediately.

So....don't forget to check for some sort of intermittent fuel pressure problem...

Mike