car stranded - help

GostRidr · 09-28-2008, 10:35 AM

This is in reference to my 87 S. Ambient temp 85 or above. Starts fine. Runs strong. No recent work. After 2-7 miles, car just shuts down. Frequently, there will be a weird surge/pulse first. Then, shortly thereafter the car just stops. I wouldn't call it a stall. First 60 miles yesterday in the desert, higher temps, we stopped as described above, waited, then started again. Then, entering cooler mountain air (higher altitude?!), car went last 60 miles with no stopping all the way up to 6500 feet! Upon return in the evening, now warmer temps in mountains, shutdown occurred most of the trip home until we gave up. Took 4 hours to go about 70 miles and then we gave up.

Of note, tach sometimes freezes at 2500 with key off, does NOT bounce upon starting - for a couple minutes. No spark at coil. Wait 5-10 minutes and starts up no problem. Travel 2-7 more miles and repeat. All gauges in normal range, pressure, charging, even engine temp good at first hash mark.

Question: Can this be bypassed to drive home? where do I start to find the problem? some sort of temp sensor (likely)? Something to do with thinner air in the mountains (less likely)?

Thanks as always!

Rasta Monsta · Rasta Monsta's Garage

Fuel pump failing, fuel filter clogged, bad ignition switch, bad DME relay.

Ignition switch is cheap and easy to swap. DME relay even easier (you should carry a spare anyway). Ditto fuel filter.

GostRidr · 09-28-2008, 02:19 PM

Thanks for the reply Rasta! Will bad fuel pump give me a no spark condition? I was hoping to rule that out. I didn't think to replace the relay although I did try bypassing it with a jumper-still no spark. Until it 'cooled down'. I will try new relay later tonight.

As for the ignition switch, I am sure that would give me a no spark issue but would there be any other symptoms if that were the case. I don't know much about the ignition and will go read on it now.

Thanks!

kenk · 09-28-2008, 02:29 PM

Sounds like an ignition module to me. Anyone know if another manufacturer's module would work?

GostRidr · 09-28-2008, 02:41 PM

Thanks Kenk. Is the module the same as the switch? My choices here are ignition switch, ignition coil, ignition control unit...could any of these be the problem?

thekidd · 09-28-2008, 02:49 PM

If it is the ignition switch, you might here a humming sound under the car (starter) trying to engage. Just Replaced my starter, and someone said that the humming is either the ignition switch or starter.

kenk · 09-28-2008, 03:34 PM

The ignition module triggers the coil on the 87S. It's mounted on the drivers side inner fender inside of the engine compartment. (If memory serves me correctly.) Previous models didn't use a module.

I would take a deep breath and start with the basics. Check whether the coil is firing and if not, work backwards. If the car "cools down" and works for awhile, great. You can use that "awhile" time to check and compare signals from sensors (the reference sensor in particular) that would otherwise really need a scope to check out.

Could be bad ground wires (these cars are getting old and an occasional stuck tach make you go hmmm.)
Is the coil getting a trigger from the ignition module?
Is the ignition module getting a trigger from the DME?
Is the DME getting a trigger from the (single on your 87 944S) reference sensor?

DME relays went bad alot on older 944's partly because of the voltage needed for things like coil triggers. Your car wouldn't be affected by that so much (someone will correct me if I am wrong.) But it you insist, it wouldn't hurt to check the relay by checking if you are getting 12 volts to the fuel pump. The DME relay powers the DME (Duh!) and then the fuel pump in series. If the fuel pump is getting power; the DME is already energized.

You can't jumper an ignition module. If you need one, you need one (and I'm not saying you need one.) Luckily for you, the module is the same for the following cars and is easily swapped out if that's the problem (don't forget to use heat sink compound when mounting the module to the fender wall)

1989-1994 Porsche 911
1985-1995 Porsche 928
1987-1991 Porsche 944
1986-1994 Saab 900
1987-1990 Saab 9000
1990-1993 Volvo 240
1989-1989 Volvo 244
1989-1989 Volvo 245
1985-1992 Volvo 740
1984-1990 Volvo 760
1987-1991 Volvo 780
1991-1995 Volvo 940

You could definitely pick up a cheap used part from a junkyard or a you pull it. Just don't tell them its for a Porsche!

Ken

JivenJim · 01:53 AM

Try tapping on the DME Relay G5 (or all relays if you can't ident) while trying to restart. Hot DME Relay/main relay common failure. Also second the 2nd option of failing fuel pump. Filter not a funtion of heating up failure as far as I know. Same for bad grounds as I would think. Checking for 12V at coil is good idea for testing Relay. If you don't have a bunch of heavy keys on ignition ring (known source of switch failure, Check, if headlights go off would be an X-relay failure indication; Then if tapping on Relay doesn't start. I lean toward fuel pump failure. Relays fail more on warn restart while fuel pumps just tend to cut out based on there temp. And work fine after cooling 45 mins or so...

Good luck

GostRidr · 09-29-2008, 11:29 PM

Thanks for all the great info. I have to tackle these slowly as this is just beyond my experience. So, easy things first:

Can someone confirm that a failing fuel pump will give me a no spark at the coil?

My DME relay is VERY hot to the touch. I will try tapping next time and or switching it out. Is this a problem with the relay itself or the circuitry underneath?

If no spark to coil, what is the order of the other items to check going backwards; coil, module, control unit, switch...

Thanks as always!

JivenJim · 09-30-2008, 02:46 AM

Don't think fuel pump failure could cause no spark.

DME will normally get very warm but not burn your hand hot. Failure is common that solder joints on single sided circuit board will become loose. Then the circuit starts arcing. This makes it much hotter. The tapping can help to make a tempory contact to a loose connection for warm restart. But I don't think that would cause the car to stop while running.

I haven't worked with a newer 944 that had an ignition Module, but I like what kenk posted.

Please go here at do all these ignition tests:
http://www.clarks-garage.com/
search TS-01

Then IGN-04.

Fuel-05 for DME relay info.

Hopefully you will find something and it won't be a bad DME (CPU unit) as there is not much to check there except voltage output on certain lines.

PS if your stranded somewhere near La Quinta, I have a buddy who makes 944 spec cars here in San Diego and maybe able to help trouble shoot or tow. PM me if that' the case.