Intermittent Starting Issue

[LucaScali]

Late 80s 930.

Periodically when I turn the key, the pumps don't blip (buzz) and the car wont start. To get it started, I have to turn the ignition off/on several times until I hear the blip, and then the car will start and run normally. The problem will go away for days or even weeks, and then suddenly occur daily for a period of time. It seem to be related to ambient temperature.
,
So far Ive replaced the front fuel pump, yellow relay, both fuel pump relays, and the #6 fuse; and sprayed contact cleaner in suspect areas. Car has a Bosch CDI rebuilt a couple years ago by Specialized ECU Repair.

Where should I look next? Any suggestions would be much appreciated. It's driving me a little nuts. I understand there's a speed relay under the driver's seat that's part of the system. Could it be the problem?

Thanks very much.

[356911930]

Hi Luca,

First I would move this thread to the 911/930 turbo forum. There are many experiienced 930 owners there. I do not have later 930 but similar symptoms on my early 930 would lead me to check for a broken or damaged "green wire" that is pluged into the distributor. When you have a no start or dead condition go back to the engine compartment and wiggle the wire or have a helper wiggle it while you try ot start the car.

Best of luck,

Rahl

[proporsche]

Hi Luca
do you have by any chance some kind of alarm on your 930
Ivan

[LucaScali]

Hi Ivan,

Yes, I have a Viper alarm, but it's always worked fine and doesn't seem related. I don't think the ignition immobilizer is even installed.

Today the ambient temp was about 60 degrees and there were no issues.

Thank you, Rahl. Appreciate the suggestion. I'll try that.

[proporsche]

if it is aftermarket alarm ,the wires go most likely through some relay,that one could be your culprit...trace the wires if they go to the fuse for fuel pump or take a picture of the fuse box with the 6th fuse wires showing...
Ivan

[kev01]

Originally Posted by 356911930

Hi Luca,

First I would move this thread to the 911/930 turbo forum. There are many experiienced 930 owners there. I do not have later 930 but similar symptoms on my early 930 would lead me to check for a broken or damaged "green wire" that is pluged into the distributor. When you have a no start or dead condition go back to the engine compartment and wiggle the wire or have a helper wiggle it while you try ot start the car.

Best of luck,

Rahl

Unlikely to be the green wire ... this would affect spark but fuel pumps should still run when ignition is turned on.

[mysocal911]

Originally Posted by LucaScali

Late 80s 930.

Periodically when I turn the key,

What does this mean? Are you just turning the key to the run position or to the start position? Remember, the fuel pumps only run while the engine turning over (cranking).

Originally Posted by LucaScali

the pumps don't blip (buzz) and the car wont start. To get it started, I have to turn the ignition off/on several times until I hear the blip, and then the car will start and run normally. The problem will go away for days or even weeks, and then suddenly occur daily for a period of time. It seem to be related to ambient temperature.

If you are really having the engine turn over (cranking) and the pumps are running, then you may be losing pressure when the car is not run for awhile.
You need to monitor the system pressure with a gauge when starting the engine. Also, you can spray carb cleaner into the air filter to see if it starts easier.
If so, it's a fuel problem. With key in the run position, you can push on the sensor plate and listen for the pumps to run.

It's simple to troubleshoot, when you isolate the problem to fuel or ignition!

[LucaScali]

@mysocial Thanks for your note. it means it happens periodically, as in every so often; not every time. When it's working properly, the fuel pumps are primed for a split second before the engine is cranked. In any case, even with the airflow switch disconnected, it's the same story. It isn't related to the interval between starts and cold/hot starts make no difference. When it fails I've got to turn the ignition off/ON (position) a random number of times until the pumps come back online. Could take an extra attempt, or I could be sitting for 20 min.

For the last couple days it's been perfectly fine. Today was relatively warm and the problem was back. After a few turns of the key, I gave up. The outside temp has since dropped by 10-15 degrees. Tried again and lo and behold, no problems. Turn the key, "buzzes" (and starts) every time like clockwork. Nothing was touched in the meantime as the car sat.

I had this issue from time to time all last summer and into the early fall. Weeks/months went by over the winter with no issues. Whatever is happening may be sensitive to ambient temperature. What might be affected by changes in outside temps?

Incidentally, another (related?) problem is when it gets warm out Ive got to give it a little gas to get it started cleanly. Think the mixture is off.

I discussed this with one of the best mechanics in this area while he had the car, and he pointed to the yellow relay. I've since replaced that relay and the fuel pump relays with no joy. Some Porsche guys around here have also been puzzled, even when we were able to recreate the problem briefly.

[LucaScali]

@Ivan

Thanks, I'll check that out today.

[mysocal911]

Originally Posted by LucaScali

In any case, even with the airflow switch disconnected, it's the same story.

With the sensor plate switch disconnected, the fuel pumps should turn-on immediately when the ignition switch is in the run position!
If not, then it's a relay problem, a bad fuse connection, or a wiring problem (bad wire connection at fuse connection). It's that simple!

I've seen this problem on turbos before, because of the old type fuses and wire connections at the fuse box.

[991gts6s]

those two pesky round red fuses that run the pumps in the trunk.... if failing they act intermitte
and will leave you on the side of the road if you don't know about them and have spares..
and the green wire has the same type gremlins..

Seems all 930 i have messed with always the same stuff

P.s CIS need the good fuel accumulator to start nice is all temps..

[LucaScali]

Thanks guys, I've already replaced the fuse, both red relays, the yellow relay, the accumulator, and the front fuel pump.

If it's a bad wire, wouldn't it affect the pumps when the car was running? Once the car starts, there are no problems at all.

On cold starts with cool ambient temps, it rarely if ever occurs, that I can tell you. Otherwise it's almost totally random, although it seems not to like quick restarts. Other day it started fine, got gas, but couldnt get it restarted. I let the car sit for 15-20 min and lo and behold it started perfectly on the first try. Since then it's been hit or miss.

Someone suggested the ignition switch. Could that be it?

Thanks again for all your responses.

[LucaScali]

Still struggling with this. It seems totally random. I don't know what else to look at.

Aside from the fuse, the red relays, and the yellow relay, what is involved in priming the pumps in the ON ignition position?

Could this be the ignition switch? Bad ground somewhere? Any theories would be helpful at this point.

Thanks

[911obgyn]

It would not hurt to exercise the bulkhead connectors under the dash and the 14 pin connector in the engine compartment, take a razor blade to the pin side and spray some DeOxit or other contact cleaner to them.

[david.avrahami@]

I had, a few years back, the same problem...
It was a short in the yellow ignition wire. The problem was that We could not find where exactly was the short...
My mechanic disconnected it at the ignition and every where else along the way to the starter AND replaced it with a brand new yellow wire , soldering it at each connection along the way. It worked like a charm...(no replacement of the whole strand of wires that costs quite a bit...

[LucaScali]

So I'm still at this. This is what's been tried so far:

* cleaned and exercised the bulkhead connectors and 15 pin connector as suggested by 911obgyn
* two new German fuel pump relays
* new fuses
* new battery ground strap
* tested new ignition switch (now I have a spare)
* new German yellow relay
* grounded overboost switch wire
* cleaned speed relay pins/connector
* unscrewed and checked connection at the fuse
* all the wiring I can see looks good


--at one point thought I had solved it by spreading the yellow relay pins for a more secure fit, but it had coincided with a period of relatively cool temps, and the problem resurfaced as soon as it got hotter. the connector itself is a little rough, so that could be something to look at.

--when it's not working, the fuel pump relays do not click.

--once the car is running, it runs perfectly.

So what else is involved in priming the pumps in the ON position? Would it make sense to replace the delayed ignition cutoff relay next? Could it be a problem with the ignition box? Throwing parts at the problem is not ideal, but it would probably cost less than a couple hours of "diagnostics" to replace everything left anyway.

Incidentally, the boost gauge pegs at 1 with the ignition ON. Not sure if that's at all related.

Thanks for all the advice/support.