1990 740 hard/no start, no Fuel pump prime.

5ft24 · Post by **5ft24** » 05 Sep 2014, 09:27

Title says it all. Replaced both fuel pumps and the filter. Most of the time, I can crank and crank and never get a fire, turn the key off, then on again and it starts. There have been some days where I have had to use starting spray. New battery, alternator and fuel pressure regulator as well. Once it starts, it runs great. I do not have any fuel pump prime. I can feel the FP relay click when I turn the ignition on, but no sound from either pump, and no voltage at either as well. If I jumper the relay and turn on the pumps, it fires right up. Any suggestions???

93Regina · Post by **93Regina** » 05 Sep 2014, 22:26

5ft24 wrote:Any suggestions???

1. Examine wiring circuit and check relevant fuse(s)

2. Fuel Pump Relay (3523608)

Contactors do fail

5ft24 · Post by **5ft24** » 06 Sep 2014, 21:03

Not getting the ground from pin 20 of the computer to prime the pumps for 1-2 seconds... It does ground right before the car starts. Going to check the ignition computer tomorrow to make sure it doesn't have any corroded connections., and pull the fuel computer to make sure the circuitry off pin 20 doesn't have anything wonky going on

5ft24 · Post by **5ft24** » 07 Sep 2014, 21:02

Computer and wiring were OK. While skimming thru my AllData, noticed the fuel computer gets a signal from the ignition computer for engine rotation. Disconnected the hall sensor on the bell housing, and noticed it was pretty crusty. Cleaner the terminals and plugged it back in and it's all working

93Regina · Post by **93Regina** » 08 Sep 2014, 08:04

5ft24 wrote:Disconnected the hall sensor...plugged it back in and it's all working

RE: some days where I have had to use starting spray.

This statement indicated a fuel issue

RE: FP relay click...no sound from either pump,

Contactors do fail, and this relay gets warm to touch, but it suggests a lack of fuel pressure.

There is also a Radio Suppressor Relay, that controls power to injectors; this too can act up intermittently.

Good to hear its running.

5ft24 · Post by **5ft24** » 08 Sep 2014, 09:25

replaced the radio suppressor relay. wasn't getting a ground from Pin 20 of the fuel computer. According to alldata, the crank sensor in the bellhousing sends a signal to the Ignition computer, and it sends a signal to the fuel computer to trigger the pumps on... However my Aha moment yesterday crumbled when it did the same thing this morning... Grrrrr...
While I was troubleshooting yesterday, When the fuel relay finally made the 2nd click, the car started right up. with Ignition on, I got the first click and made sure I had voltage everywhere I should have, based on the diagram and Alldata troubleshooting chart. Checked continuity between the FP relay socket and everywhere it connects to as well. All grounds check good, no cold solder joints in the computer, etc. Going to trace back along the harness from the suppression relay and see if something isn't messed up there, because it is also giving a code for no voltage from the O2 sensor... I know that relay provides +12 to the injectors and all sensors under the hood that require 12 volts, including the heater on the O2... I have a new O2 to install as well.

5ft24 · Post by **5ft24** » 08 Sep 2014, 09:33

ok... Misspoke. Suppression relay only provides power to the injectors... Still could be the FP relay's first contactor not making a good connection. I'll order one before I do anything else

5ft24 · Post by **5ft24** » 08 Sep 2014, 09:40

Ok... I'm an idiot... Was checking voltages with things unplugged... The +12 to the suppression relay wasn't there until I cycled the key on.off about 3 times. FP relay clicked each time. once I had 12v there, the car fires right up. FP relay ordered