930 randomly dies (only when hot)

StAmand · StAmand's Garage

My stock 87 930 randomly dies. You will be driving down the road and it's like someone shut the key off. Once you pull over and let it sit for a while it will start, but if it's real hot it will keep shutting down. It has never has done this when it's cooler outside. It happened a couple of years ago and it never happened again until today. Anyone have any suggestions on where to look ?

Robert

s5uewf · s5uewf's Garage

My bet is it is the yellow relay in the left rear area of the engine bay.
Mine use to do that often.

Now I have EFI and have spare yellow relays to sell at the swap meet.

Check the sticky post about why my car will not start. I think there is a lot of info there that may help you.

(It could also be a fuel pump, or other cause, but this is my bet)

1SwtRide · 07-24-2013, 04:09 PM

Quote:

Originally Posted by StAmand

My stock 87 930 randomly dies. You will be driving down the road and it's like someone shut the key off. Once you pull over and let it sit for a while it will start, but if it's real hot it will keep shutting down. It has never has done this when it's cooler outside. It happened a couple of years ago and it never happened again until today. Anyone have any suggestions on where to look ?

Robert

I had this problem with my '86. The CD box was shorting out and got to the point that is was perma-shorted. You should have a shop check it out.

pkracer21j · 07-24-2013, 06:36 PM

Check your Green wire on the distributor.

BlkBird · 08-20-2013, 10:15 AM

Mine was the relay powering one of the two fuel pumps. When it got hot the fuel pump would start to cut out and car would run leaner and leaner until she'd stall out at a stop light.

Not fun.

Shadetree930 · 08-20-2013, 10:32 AM

My money is on overheated fuel pump relays. Next time it happens, feel for heat on the relays and associated wiring.

IMR-Merlin · 08-20-2013, 06:23 PM

Bad pumps will do this too. When they wear, the bushing becomes oval and the pump will slow or stop. Usually the car will start right up by turning the key on then off. Tell tale sign is to listen for the pumps and see if they are noisy.

StAmand · StAmand's Garage

Well.... So far so good. The green wire looks good, I replaced both red relays and the CD Box a couple of years ago ( it did it again shortly after replacing them ). The yellow relay was replaced last week. I did notice when it shut down the last time that the red fuel pump relays were very hot. How can you keep them cool ?

I always wondered if the fuel pumps might be the problem. Can they be tested ? The pumps are not real noisy. I can hear them, but they aren't making any noises that seem to be out of the ordinary. This issue only happens ( so far ) when it is very HOT outside. When it shuts down it's like you just turned the key off. No sputtering, no misses.... Let it sit for a couple of minutes and it will start, but will quit again after 30-60 seconds or so. Let it cool for a hour and it's good to go again.....

mark houghton · 08-21-2013, 09:58 AM

Quote:

Originally Posted by StAmand

Well.... So far so good. The green wire looks good, I replaced both red relays and the CD Box a couple of years ago ( it did it again shortly after replacing them ). The yellow relay was replaced last week. I did notice when it shut down the last time that the red fuel pump relays were very hot. How can you keep them cool ?

I always wondered if the fuel pumps might be the problem. Can they be tested ? The pumps are not real noisy. I can hear them, but they aren't making any noises that seem to be out of the ordinary. This issue only happens ( so far ) when it is very HOT outside. When it shuts down it's like you just turned the key off. No sputtering, no misses.... Let it sit for a couple of minutes and it will start, but will quit again after 30-60 seconds or so. Let it cool for a hour and it's good to go again.....

Process of ellimination. Take a baggie of ice with you the next hot day run, wait for her to die, put the baggie on the CDI and draw the heat away from it. See is she'll start and run for more than 30 seconds after the ice-down. Try the same technique with the pump relays. Just some thoughts....can't hurt....might point to the problem.

StAmand · StAmand's Garage

Great idea... Now if it happened all the time. It only happens a few times a year. Just enough for me to feel uncomfortable driving it around ;-(

Shadetree930 · 12:19 PM

Quote:

Originally Posted by StAmand

Well.... I did notice when it shut down the last time that the red fuel pump relays were very hot. How can you keep them cool ?

Easy ....

930 Fuel Pump Fuse Overload - The Solution

This solves two problems, both related to the well known overloaded fuel pump circuit design in the turbos. #1 Blown fuel pump fuse and #2 overheating fuel pump relays.

mark houghton · 08-21-2013, 06:07 PM

Quote:

Originally Posted by StAmand

Great idea... Now if it happened all the time. It only happens a few times a year. Just enough for me to feel uncomfortable driving it around ;-(

Carry an instant ice pack....the kind you crush to activate. Could be fuel pumps, relays or connections to them or the main pump fuse, could be CDI, could be the over-speed relay under the drivers seat, could be a bad green distributor wire, could be a bad overboost sensor switch.....all as already suggested. Just trying to offer a means to narrow the field before doing a bunch of mods that may fix the symptom but never really point to the problem. Damn, aint it fun these cars?

pdx930 · 10:40 PM

I went through this with my 87 too, right after I bought it. It helps to narrow it down to fuel or ignition. Next time it dies, turn the key on and reach around the back of the fuel distributor and disconnect the safety switch on the air metering assembly. That should make the fuel pumps run and you can listen to make sure both are running. That should at least narrow things down a little bit.

In my case it was the alternator going and overcharging the CDI box. Sounds like you have already covered that though.

T77911S · 08-22-2013, 05:55 AM

you need to figure out if you have spark when it dies. CD unit or coil. there is also a plug up at the front of the car that can do it too.

if you have spark, then it is fuel. check the sticky. go to the end and look for my post.

StAmand · StAmand's Garage

Thanks Folks... All great suggestions.

Narrowing things down to either fuel or ignition is where the hard part comes in. First of all, it always happens at the worst time ( when you are at a traffic light or stuck in traffic in the left lane ). The only concern at that time is to get the car off the road. Once I get it pushed off the road and try to restart, it starts right away. Go down the road a couple of hundred feet it dies again.

When I finally get the car home everything and do some testing, everything appears okay and I can't replicate the problem. I think the car just misses the garage and doesn't like to be outdoors.

So far over the past couple of years I've replace both of the fuel relays, CD Box and the yellow Air Flow Sensor Boost Pressure relay. Is this relay the same as the overboost sensor switch ?

mark houghton · 08-22-2013, 09:28 AM

Go here to thread 11 for a small picture and description of the overboost sensor switch. It's tied in to the yellow relay circuit via a single white wire. It will shut down the fuel pumps in the event of an over boost situation. If the wire is not connected, the pumps will not run.

overboost switch question/wastegate malfxn

Miguel Antonett · 08-22-2013, 10:11 AM

I'd check the air flow sensor plunger for free movement; sometimes it gumes up and doesn't move freely promoting a symptom like yours.

valveman99 · valveman99's Garage

My '88 turned out to have a cooked harness (actually two) the first one we replaced fall '11, all was well for a spell, then the engine harness went (the on/off nature of the fault evidently related to near-open leads moving/connecting disconnecting with temp changes). Porsche took an order fora new harness now won't deliver b/c one Bosch connector is unavailable, so we're stripping out many motronic FI control features - leaving me right now needing a few feet of the fabled 'green wire' which Porsche also has but won't send or even identify...frustrating. Car has been out of action for 16 mos....anyone know where I can score the green wire??

Miguel Antonett · 09-09-2013, 05:12 AM

^^^ there are folks out there that can build the harness (not cheap, but worth the money). I'm pretty sure someone will chime in with the lead... if not, I'll get some info for you by the weekend. The harness on my 78 got cooked also, I found an used one for $1K... so far so good - after a couple of years.

valveman99 · valveman99's Garage

Miguel - thanks..I am interested in the custom harness lead. So you know, we did try some known guys who backed off the project. We also made the conscious decision to reconfigure the controls figuring that other sensors and things might crap out, so even if we got the harness remade, we'd be forever in the mode of parts failing and not being able to get them. This resulted in me now being partially into the conversion of the fuel injection system and other things associated with stripping out Motronic control functions, to essentially eliminate the need for most of what's in the engine harness. Just the same, if that doesn't go well, I could back-pedal theoretically, so the custom harness maker lead would be helpful. Meantime I'm definitely in need of 3-4 ft of the fabled green wire, which remains some kind of problem - can anyone help with the GREEN WIRE?!? Thanks.....