928 GTS fuel relay problem

I have been going crazy for a week trying to figure this out.

The other day, I went to the store and when I came out, the car started, I put it into gear, moved about 3 feet, and the car stopped. I could not get it to start, so I had it towed home.

Once I got home, I cranked the car and applied starter fluid and the car ran, so I felt it was a fuel delivery issue. Upon checking, I found out that the fuel pump was not running, so I removed it and checked it with a 12 volt power supply...it ran fine. I re-installed it and swapped both the MFI and fuel pump relays with known good ones (tested in the horn position). The car still would not start.

Upon inspection, I noticed that the fuse socket for the #38 fuse was melted, so I removed the fuse panel and replaced the 5 position fuse block from an extra fuse panel I purchased on Ebay. I have thoroughly checked that the wires are in the correct position. Upon re-attaching the battery cable and trying to start the car, it still did not start and the flasher relay clicks rapidly. Also, I am getting an air bag failure alarm on the dash display.

I removed the cover from the fuel pump relay. When I start the car, and manually latch the relay, the car runs fine. This led me to believe that my LH brain had failed, so I removed the one from my 87 that runs fine. I connected the plug to it and it made no difference. I still would not latch the relay by itself, but if I manually close/latch the relay the car runs fine. I checked it twice. By the way, I always remove the ground battery cable when I am doing any work.

I have checked all the wires on the fuse panel for corrosion or shorts and have found nothing. I have checked for continuity between the fuse panel and the LH and EZK brains and both connections are at 0.6 ohms. I removed, sanded, and re-tightened the ground wires going to the fuse panel at ground position #5. I have rechecked, rechecked and I am at a loss.

Basically, I am not getting a 12 v positive signal to latch the fuel pump relay. Once the relay is closed, the car runs fine.

HELP PLEASE.

Thanks,
Scott

It sounds to me that you may have a bad wire or connection.

They can be really hard to find because it looks like 12 volts at the pump but it may be only 2 or 3 strands of wire (or corroded connection)

The way I check for good current flow.

On heavier wire I will connect a head light in place of the (this time a pump)

For your purpose connect a horn to the fuel pump wires.
then start your checks and test.
When you get a good strong honk then it is good current flow.

BTW a strong head light hooked up like that may overload your wires
but I have watched for smoke to find the bad connection

Thanks. I will check this and use the idea in the future.

Sounds to me like the Crank Position Sensor has crapped out.

Thanks, I found out that I am not getting 12V+ to any of the terminals (#86). Thus, the coil on the relay can't close because it has no power. There is a power wire that jumps from a number of relays, but I can't figure out where it gets its 12V+. In the wiring diagram it is labeled at #15.

The signal comes from the computers when it detects the engine has rotation. The rotation signal is picked up from the crank sensor. Once that happens the fuel pumps are told to turn on, injectors fire etc.

The CPS is located under the air box on top of the bell housing. The issue will be the connector at the rear of the engine, in the V, under everything.