bdodd444

My 87 944 was not starting after sitting 6 months. I finally towed it in, and after about $800 in tune up, draining old fuel and replacing both Crank Position Reference Sensors. The mechanic says the car will turn over but once the key is released it loses fuel pressure and won't continue running. He says he is stumped and it will be 6 hours of labor at least to figure out what is going on. He says the fuel pressure is fine for starting but there is none for running. He says there are two different signals sent to the fuel pump. I believe I have all of this right. If anyone has any ideas, I would appreciate it. I'm in Northern Virginia if someone wants a parts car or take a crack at it. I'm pretty close to selling or donating the car, but would be willing to try one more thing.

MooreBoost

try a different dme

Jfrahm

DME relay would be the obvious check. Maybe the key switch. Clark's Garage has a diagram for making a jumper wire to bypass the DME relay for testing.

-Joel.

Bri Bro

The problem does sounds like it is the DME. Here is why.
The fuel pump is turned on and off by the second DME relay (there are two relays inside the DME realy can). As soon as starter voltage is applied to the starter, pin 4 of the DME senses the starter voltage and pin 20 of the DME is driven to ground which turns on the second DME relay. Inside the DME, a bit from the computer " OR " the starter voltage causes pin 20 to go to ground and turns on the second DME relay. So there are two paths to turn on the second DME relay, one from the starter voltage and one controlled by the DME.

So as soon as the starter wire sees voltage, the fuel pumps starts working. After it is started, the DME holds the fuel pump ON. If the RPM drops below some very low number (300 rpm?) and the ignition is on, the DME releases the second DME relay and the fuel pumps turns off. This insures the fuel pumps is stopped in an accident.

bdodd444

Thanks for the replies. When I was trouble shooting myself, I replaced the DME relay (figured at the worst I would end up with a spare). It didn't help, so do you think it could be the actual DME?

oazix

i have a DME from an 85.5 NA , im in dc

Bri Bro

Yes. I bet if you jumper pin 85b of the DME relay to ground (with the relay installed), it will run. The DME switches that pin between open and ground so grounding it will not fry anything. You could also ground pin 20 of the DME, that is the other end of the wire.
http://www.the944.com/dmerelay.htm

Grandpa#3

Hi, What Brian wrote about the DME Relay is correct, however, I believe it is the ignition switch module forward of the key switch that is bad. Once the key is released from the start position it dies. It is a $55.00 part that you can change yourself, but takes some work to get to it. Clark's garage.com tells how to change out the early one, but yours takes a little more work. I had to change mine out. I bought the car not running because the PO and his mechanic could not figure why it would try to start and just died. If you want to try this just let me know. It just might save you hundreds of dollars or cost you $55 and some time spent putting in a new part.

Cheers,
Larry

Grandpa#3

Hi bdod444, Here is a "No Start Checklist"

No Start Check List, I hope this will help.

This has been extracted from a past post, authors Billysdad and John_AZ on a Start Problem.

Posts: 364
Re: 1987 starting problem
« Reply #1 on: Jul 25th, 2009, 10:28pm » Quote Modify

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Hmmmm.... that could be alto! you really have to go step by step and check the ecu harness and voltages to each area as you go. Here is a list of some test you should do one by one and eliminate problems.
Air/fuel/spark/compression
start by making sure we have a battery that is in spec.
all fluids topped off
no obvious broken wires and all vacuum hoses intact on visual inspection.
OK we have 12v at the battery with adequate cranking voltage we get in and turn the key.
12v from battery to ignition switch
12v from pin 50 on switch to pin 4 on DME plug (start signal)
12v on pins 1 (ignition pulse to ign. coil) and 18 (to G5 dme relay power supply)
12v pin 30 at DME Relay (fuel pump power supply)
12v to pin 86 at DME Relay in the run position (primary coil voltage)
12v to coil + black wire to ground 12v to - (green wire) to ground
12v to one side of the injectors
All ground contacts are clean
Fuel pump will run if DME Relay is jumpered 30/87/87b
Fuel pressure at the rail is psi +/- 3 (jumpered 36 psig)
20 minute leak down not under 14.5 psig
Fuel flow rate is 28oz after 30 seconds
Ignition coil primary resistance across + and - is between .4 and .6 ohms
Secondary resistance is between 5000 and 7200 ohms
Ignition wires are good no cracks or splits including coil wire and seated
Plugs are properly gapped
Ignition rotor is seated correctly with the set screw
Timing belt is installed correctly
Firing order is correct - 1 - 3 -4 - 2
Reference sensors are gapped correctly with .8mm clearance off the flywheel
Reference and speed sensors resistance checks in spec pins 8 and 27 speed 600-1600 ohms and pins 8 and 23 >1m ohm
Reference and speed sensors voltage checks 2.5 and 2v on oscilloscope (good luck)
Reference and speed sensor wiring is not broken at connector to sensor or to dme
OK, I'm tired anyone else want to add or be more specific?

John_AZ
Do a compression test.
Reference Sensor Tach bounce when attempting to start the engine. The Tach bounce is very slight-1/16 of an inch. Clean connections as mentioned above.
Injector "noid" light. Very basic tool but will tell you if the DME is sending a signal to the injector. An oscilloscope is the best.
Clean connections at major parts like AFM, ISV, throttle body.

Cheers,
Larry

bdodd444

Thanks so much for everyone's help. I have a couple quick follow ups:

1) Brian, when you say "jumper pin 85b of the DME relay to ground ". Where is the ground I should run the wire to, just anywhere that will ground it?

2) If this test works, that will show it is the actual DME that is the problem or is there another test?

3) Grandpa, I appreciate the input on the ignition switch module. If the DME isn't the problem, this would be my next step.

4) Oazix, thanks for the offer of the DME. If I need to go that route, how much do you want for it?

Finally, I want to get the car back from the mechanic. I really don't have any faith in him. Do you think I would be ok bringing the car home on a car dolley from Uhaul or should I use the vehicle trailer?

Again, I really appreciate everyone's quick responses. A couple hours ago I was ready to get rid of the car, now I have some hope.

bdodd444

Another follow up. My fuse 11 has a short somewhere, fuse blows instantly. I figured in the cigarette lighter or something. Could this in any way have an effect on this problem? I'll ask for help with this if I ever get it running again

Bri Bro

1) Yes, any chassis ground will do. I would put a small wire into the terminal and then plug in the DME relay. You can also ground the pin at the DME.
2) If it works, the DME is the problem.
3) How the car runs after the ignition is taken out of the start position should resolve this. I was reading it didn't hold fuel pressure and died. This would take a second or two after start up. The ignition switch would be immediate since it would also kill the coil, spark, DME, DME relay etc.

I have towed with a dolley put it is a pain to get it on/off due to ground clearance. If you have AAA, they will tow it to or from a shop but you have to wait for some slack time when they don't have an emergency call. It isn't just an emergency service. Best $100 I have spent.

Bri Bro

Lighter and interior/luggage lights. Shouldn't effect the engine.

Jfrahm

If you jumper the DME relay you might be able to drive it home. You could also show up with a DME. If that does not work you could come back with a dolly but maybe you can save that trouble and expense.
Plus it'd be satisfying to fire it up and drive it out of there.

-Joel.

oazix

if i dont have to ship it $100 and its yours, its part of the left overs from the 968 swap