Jsulli

82 Weissach 5 spd. Just put motor back in after rebuild. Has been sitting since I pulled the engine in 2018. First started and ran fine while allowing coolant to purge and maintain constant level. Turned off to tighten some hose clamps and now only fires briefly and dies. Will not take any throttle. I noticed i can hear the fuel pump run but only right before it dies. Fuel pump does not run when key is turned on. Any help would be appreciated.

Rich9928p

The fuel pump will not run when the engine isn't turning. For your 1982 model L-Jetronic 928 the RPM signal from the spark box connects directly to the fuel pump relay and only turns on with RPM > 50.

To make the fuel pump run regardless of the cranking RPM, follow these instructions. Check for 12V at relay XVII socket position 30 (should be 12V at all times). If there is 12V at position 30, insert a jumper wire between relay socket positions 30 and 87. You should hear the fuel pump run. Crank the engine to start, if it does the fuel pump relay or wiring between the spark box RPM output and relay socket may need repair. If it doesn't start, unplug the jumper wire and look elsewhere.

The 1978 - 1984 928s use a special fuel pump relay P/N 928.615.113.01, a standard relay cannot be used. Note, the Euro 1984 model year 928s use a standard relay for the fuel pump.

Since there has been a large amount of work done on your engine installation, I'd be looking at connections that may have come loose or a hose that may have come loose causing a large vacuum leak.

Rich
928 Owners Club Membership Chairman
1993 928 GTS cover girl
1987 928 S4
1979 928 5-speed rescue cover girl
1979 928 Euro track beast

Jsulli

Thanks I’ll check the relay.

Jsulli

What is a spark box? Where is it?

Jsulli

Couldn’t wait until tomorrow. Jumped 30 and 87 and it started and ran.

Petza914

Awesome. Buy 2 correct fuel pump relays and keep 1 and the jumper in your car. The only 2 times my 79 928 would have stranded me were because the FPR died, but because of this site I had a spare and switched jumper with me I could swap to make it home.

Actually there was a 3rd time when the crank position sensor plug on my 84 euro came apart when driving down the road, but when I saw no tach bounce on the restart attempt I knew the problem and fixed it on the side of the road. That's wire tied together now

Glad you found your issue 👍

Mrmerlin

Good that you found the issue ,
while your ordering relays also get a new fuel injection relay,
this relay works with the fuel pump relay.

NOTE also make sure you have a good Bosch green wire installed,
if you have the URO version they made a batch of them that have failed.

Rich9928p

The 1978 - 1984 US (not 1984 Euro) have an old style "transistorized" spark system. There is a Hall effect sensor on the distributor shaft and a shielded cable (aka "green wire") that sends the spark signal to the Transistor Spark box that is located on the passenger side of the engine bay. This box drives the ignition coil.

Rich
928 Owners Club Membership Chairman
1993 928 GTS cover girl
1987 928 S4
1979 928 5-speed rescue cover girl
1979 928 Euro track beast