1986 930 - Advice Needed - Stalling Issue

[jseiffer]

I have a 1986 930 that I have had for the past 5 years and it has been very much trouble free until a few weeks ago.

I had taken the car over to the cars and coffee at the Porsche Experience Center in Los Angeles (about a 12 mile drive) and everything was running fine. When I got there, the line to get in was very long (hundreds of cars) and as I was waiting and idling for about 20-25 mins, the temp gauge rose to the white line below the red area (high but not into the red) and the car suddenly stalled out and died.

The symptoms of the stall seemed very similar to running out of gas and afterwards the car refused to restart. I waited for the tow truck for about 40 minutes and when the tow driver arrived we tried to start the car again but it still would not start.

Many hours later, at my garage, the car started up fine and I let it idle for about 5 minutes when it suddenly stalled out again with the same symptoms.

Given this seemed like a fuel delivery issue, I disconnected the plug by the air metering valve and ran the fuel pumps and checked the fuel pressures. The results at exactly 20 Degrees Celsius Temp were:

Fuel pumps running fine

System Pressure = 6.8 Bar - This Seems In Spec

Resistance at WUR = 26.3 Ohms - This Seems In Line with Where It Should Be

Cold Pressure at WUR = 1.35 Bar - This Is Low to 1.5-1.9 Bar Spec

Warm Pressure at WUR = 3.2 Bar After 10 Mins - This is Low to 3.5-3.9 Bar Spec

The System Residual Pressure dropped to 2.7 Bar with Pumps Turned Off and Reached 1.6 Bar after 10 Mins

If folks could confirm that the specs above are correct (I found them online for the Bosch 0438140153 Model) and offer advice as to whether the low readings on the WUR settings could be causing the issues I am having, it would be very much appreciated.

Also open to any other ideas / tests I should be running if folks think my issue might be something else.

[Alan L]

Those low WUR pressures mean the car is running quite rich. It is possible with long rich idling it fouled plugs, but normally they would not be dying all at once. More likely an electrical issue shutting the pumps off. Next time (and there will be one) pull the airplate switch with key on and see if you have pumps. If not, then the hunt begins. One simple place to start is the over boost switch- on the back of the intercooler. White wire. Try wiggling it, or better still if you have a means, ground that wire some place else - pull it and ground it somewhere. If that doesn't get the pumps working (assuming no fuel), need to start looking at relays.
Alan

[mark houghton]

Adding to Alan's comments, are you absolutely certain that both pumps were running during your test? These cars can run on just one pump, but I'm not sure that enough pressure will build, allowing the fuel metering arm to deflect too far and create a rich condition. Maybe could explain your low WUR pressures.
As for relays and such: there are three immediate things that can stop you dead: fuel pump relays (obviously), the infamous yellow relay, and don't forget the overspeed relay under the drivers seat. And of course the over boost switch that Alan mentioned. All of those have plagued me at some point over the years.

[Alan L]

Your oil temps were also very high high. Next time it would pay to check the cooler fan is working (front rt wheel). You should hear it.
Not that I expect that will be the cause of the issue, but the thermo switch may be faulty or a wire disconnected. I am presuming all the 930s have the fan/cooler up front.
Alan

[jseiffer]

Thanks Alan - good idea on disconnecting the switch and checking the pumps right after it fails - am now wishing I had thought of that before I turned off the ignition and took the intercooler, airbox and AC unit out of the car. I forgot to mention in my prior post that after the second failure and before checking the fuel pressures, I swapped out the coil since the one that was in there was old and I have seen other instances where a coil overheated, started to fail and the issue was very hard to diagnose. I went ahead and ordered a rebuilt WUR since the one I have is not in proper calibration. While I was at it, I went ahead and replaced both fuel pump relays inthe frunk, the fuel pump fuse, the yellow box relay and the over boost switch (in the process, I discovered that a prior owner had grounded out the wire that goes to the over boost switch so I hooked that back up). Am planning to put in the new WUR and see if the problem happens again.

I actually had wondered myself about a problem with the oil cooling system (thermostats and oil cooler / lines) being a source of the overheating itself (although when the issue happened at my garage a second time the car had only been running about 5 minutes). I can say with confidence that it is not the oil cooler fan (there isn't one on 1986 911s).

Mark - appreciate the help - I can hear both pumps running and the system pressure at 6.8 Bar seems to confirm that the pumps are providing strong output that is in spec with both pumps running - I think if one was failing I would be seeing lower system pressure (can anyone else confirm this?)

Will report back after I install the WUR and get everything hooked back up. If anyone else has ideas, all input is appreciated.

[Alan L]

Yes with 1 pump your system pressure would be low.
You can adjust the WUR - all pressures were down so a single adjustment probably would have sorted that. The fact the white wire had been grounded suggested previous issues with the o/boost sw. The only role of that sw is to provide a ground for the rear (yellow) relay to energise the pumps. When you o/boost it breaks the circuit and kills the pumps.
Yes, I have seen that post about the coil heatsoaking. So it pays to verify whether you have fuel and/or spark when it stops. Instead of throwing a bunch of parts at things. There are enough wise old heads here to help you diagnose the issue. These things are common (and frustrating) to the 40+ yr old cars and their wiring.
The oil thing will be worth keeping an eye on - after you get this one sorted. It may be a thermostat issue, or maybe nothing. Dunno, but I get nervous with temps going that high. Mine has a fan in front of the cooler. I expected that would be common. Dunno, it came with it fitted. It has a thermo switch on top of the cooler. But mine has also been fitted with what I think is an after market sw in the cabin. I can manually engage it.
But crawling in a queue for a long period is not getting any airflow over that cooler. I would have thought there should have been a fan that kicked in.
Keep us posted.
Alan

[flightlead404]

Originally Posted by Alan L

Yes with 1 pump your system pressure would be low.
You can adjust the WUR - all pressures were down so a single adjustment probably would have sorted that. The fact the white wire had been grounded suggested previous issues with the o/boost sw. The only role of that sw is to provide a ground for the rear (yellow) relay to energise the pumps. When you o/boost it breaks the circuit and kills the pumps.
Yes, I have seen that post about the coil heatsoaking. So it pays to verify whether you have fuel and/or spark when it stops. Instead of throwing a bunch of parts at things. There are enough wise old heads here to help you diagnose the issue. These things are common (and frustrating) to the 40+ yr old cars and their wiring.
The oil thing will be worth keeping an eye on - after you get this one sorted. It may be a thermostat issue, or maybe nothing. Dunno, but I get nervous with temps going that high. Mine has a fan in front of the cooler. I expected that would be common. Dunno, it came with it fitted. It has a thermo switch on top of the cooler. But mine has also been fitted with what I think is an after market sw in the cabin. I can manually engage it.
But crawling in a queue for a long period is not getting any airflow over that cooler. I would have thought there should have been a fan that kicked in.
Keep us posted.
Alan

oil cooler fan started with '87 I believe. My '86 did not have it. I added one, made a massive improvement here in the southern US

[Alan L]

right - mine must be a retro fit. Very useful bit of gear.
Alan

[jseiffer]

OK - to give an update, I installed the new WUR and I am still having issues which I now believe are likely ignition related since the fuel system is in spec and will run with the plug by the air metering valve disconnected.

Here are my latest findings:

CDI box emits the high pitched whine when power comes on

I used an adjustable spark tester to check for spark off the coil HT lead and got reasonably consistent spark at 20KV but the spark was not present when the tester was set to 30KV - assume this would indicate weak spark? Can anyone confirm / advise that this is the proper conclusion?

I tested the new coil I got and it measured 0.4 ohms on the primary and 159 ohms on the secondary - I have not been able to find a spec on the secondary for a 1986 930 - does anyone know the spec?

I disconnected the 6 pin connector from the CDI box and tested:

31/1 pin receptacle - good ground confirmed
15 pin receptable - 12+ power present

However, when I tested for resistance / continuity from the 31D pin receptacle to the 7 pin receptable I got an open circuit - getting the 6 pin connector in / out from the CDI box is a pretty tight squeeze even with the intercooler removed and I had to twist it to get the proper orientation, so I am a bit worried I might have disturbed the wire to female spade connector connection - on the other hand, I guess it is possible that this could also indicate a break in the connectivity in the coaxial green wire somewhere or possibly in the distributor pickup coil itself.

When I reassembled everything, the spark tester showed spark only intermittently present at 20KV as the engine cranked (much less consistent than my initial test before I disconnected the 6 pin connector). This makes me think I might have disturbed something in removing / installing the connector.

One last question - is it possible for there to be spark coming off the HT lead on the coil (as in my initial test using the spark tester) if the distributor pick-up coil coaxial (green wire) is an open circuit or there is a break in the distributor pick-up coil itself?

Any thoughts / input greatly appreciated.

My next step is to remove the 31 and 7 female spade connectors from the 6 pin connector itself to make sure I did not jar something loose there.

[Alan L]

If that green wire circuit is broken, no spark. Or partly broken, intermittent spark.
Yes, that plug is a bit tricky. But you need to pull it again and verify. You may have found the problem. You should get 600-700 ohms across the green wire and its co ax earth wire (at the pins). You can check the pins by peeling back the rubber boot a bit - to make sure you are on the right terminals. Did same check on a friends 911 last week - on the side of the road.
Alan

[jseiffer]

Thanks Alan - the 930 connector is a little different from the SC connector from what I understand - there is no rubber cover / connector - just a hard plastic Bosch 6 pin but I can see the wires coming in from the rear and have confirmed that I am checking the right ones. Will post what I discover when I pull the connector and remove the wires / spade connectors.

[Alan L]

I think they are the same plug. Somehow yours may not have the rubber protector boot. My 930 and SC are same. Unless it changed for later model yrs. But you should see the wire split to two pins.
I just can't remeber which - but top/bottom at one end of the plug I think.
Alan

[jkkarrow]

You're right.

[jseiffer]

OK - more diagnostics today. Removed the distributor in order to confirm that the source of my issue was in the green wire rather than the distributor pickup coil. However the green wire checked out fine once the distributor was removed - good continuity across both pins from CDI connector to distributor connector. Checked pins on the distributor itself and could not get any continuity. Took the distributor apart to get a better look at the distributor impulse generator windings and again no continuity at the pins - also found what looked like a couple of small lengths of winding wire loose in the distributor. It looks like I have found my problem although the new issue is that replacement distributor impulse generator windings are no longer available. I am going to call around to the distributor rebuild vendors folks have mentioned here - that may be my best and most bulletproof solution.