Details:

87 manual.

About 8 miles away from home shifting from 1st to 2nd car dies. No warning. Feels like a thump as car coasts to side of road. Flat bed it home.

Turns over. All lights ok.
Tach needle bounces on startup
Looked in timing belt cover inspection hole belt intact.
No hum from fuel pump.
No voltage at #42 fuse with key on.
No click at the fuel relay.
Swapped Fuel relay with a spare no change
The LH relay clicks on key turn to on.

Where do I go next?

 

Fuel, air, compression and spark, all in the proper amount and at the proper time is what's required for your engine to run.

You need to find out which is improper.

On your 928, spark is required for fuel delivery to take place. I'd be inclined to check for spark next.

Be careful as the high ignition voltage can be dangerous. If you have a clamp-on timing light the job is quite simple.

 

Jump out the FP relay and see if the fuel pump runs even with the key off. If yes it's time to start troubleshooting the signal from the LH that energizes the FP relay. If the fuel pump doesn't run then you have a bad pump. R&R and you should be good to go.

Mike

 

Alan: "The fuel pump fuse is supplied by the fuel pump relay Relay XX. If the relay isn't turned on the fuse won't have power. The relay is turned on by the LH when it detects engine rotation."

The CPS is new. Next?

 

Hmm- how new? what else was done when it was replaced? Sometimes things like this trace back to the last thing you did.

 

Just because you don't hear the FP relay click doesn't mean it's not energizing. Test to be sure. Does the EZK relay energize? IIRC the CPS sends it's signal to the EZK which then tells the LH to turn on the fuel pumps. I would jump each of the FP, LH, and EZK relays one at a time until the car will start. Then replace each jumper with it's respective relay and after each one see if the car will start. When it won't you can start narrowing down the problem to one of these three critical systems.

Mike

 

I'm with Mike regarding jumpers, and to quote Jim Bailey, "Relay, relay, relay." (until proven otherwise). Hope it's not the LH. Tach bounce would be a sign that the CPS is OK. You could check for ignition spark while cranking to verify.

 

From http://www.jdsporsche.com/fault%20find.html

a) Cambelt snapped. Remove both intake airtubes and check if both camshafts are still turning.

b) Check fuel pressure at the test point on the fuel rail. A fuel pump can fail if fuel tank level is low and/or very hard sustained cornering momentarily starves the pump with fuel. Note that there are often two pumps, the external one, and often an in tank pump. Both may be damaged through fuel starvation. The intank pump hose inside the tank has been known to fail, and debris from it can block the external pump.

 

Be very careful jumping the FP relay. If you get the wrong pins you'll blow up the FP driver stage in the LH.

It sounds as though there's a spark, but best to check that first. Then check the rpm signal at pin 1 LH ECU while cranking, there should be a 12v pk-pk square wave signal there. You can measure that with a meter on AC volts. Check that pin 1 on the LH isn't corroded.

My best guess would be that the FP has been jammed with debris - try the fuel flow test at the return to the top of the tank. (disconnect LH before jumping the relay)

 

John, thanks for dropping in. Fuel pump is brand new. Fresh top end and fuel line refresh. New CPS, knock sensors. I did have to replace the female harness clip for the CPS.

I will check pin 1 of the LH ECU this afternoon. On a left hand drive is that the computer on the left or right?

 

I believe I would have a look at that.

 

Agreed.

 

It's the larger of the two boxes, usually the one nearest the outside of the car.

Although I've never worked on a LHD 928 :-)

 

Your CPS is ok, otherwise the tach needle wouldn't be moving when the engine turns over.

Test the fuel pump fuse in the tester.

Then jump the fuel pump using the handy factory-supplied bridge next to it, go check the pump is turning.

i.e. Remove the fuel pump relay, and move the brass bridge in the relay position to the right of it into the fuel pump slot. Then go listen for the pump (the bridge is the kickdown relay position, which obviously you don't have as you're not driving an auto.. auto owners need to make/carry their own bridge).

Have you checked for spark?

Likely relay candidates are:

Fuel Pump Relay (position XX)
Ignition relay X (position IV)
EZK relay (the one with the fuse tester in it - position XVI)

All three can be replaced with a standard 253 relay (i.e. the horn one, after you've tested the horn . I'd swap each in turn with the horn relay.. if no change, put the original back and use the horn relay in the next one.

I recently went through this in my '87 and it was a relay.. annoyingly one of my spare relays from the glovebox was also non-functional, so don't assume anything!

 

Fuse - good.
Heard fuel pump with bridge as soon as I plugged it in.
Swapped the horn relay(XII) with fuel relay(XX) - silence.