I went to start the car after rebuilding all the suspension and it won’t start. With a freshly charged battery it cranks over fine. Turning the ignition to on, sometimes I hear the fuel pump running and sometimes I don’t. I opened the fuel hose by the intake to the rail and it’s dry, so clearly no gas is getting there. Since the pump runs sometimes but the engine cranks every time, I’m suspecting the fuel pump relay. Is there anything else I should look into? The car last ran in May. ‘87 V12

 

The relay is a likely culprit, yes. As guesses go, not hateful in expense or effort. Worth a try

Sometimes, though, the pump itself will deteriorate to come-n-go operational status.

Lastly, the ECU circuit that triggers the relay can give problems. This can be diagnosed by grounding the orange wire at the relay. If pump operation then returns to normal then you'll know the ECU circuit is failing. This bypass allows the pump to run whenever the key is 'on' so it presents a safety issue. Some just leave the bypass in place; I wouldn't recommend it, personally

All that being said.....

If the pump remains non-operational for a few minutes at a time it shouldn't be hard to actually diagnose the problem with a 12v test light or DVOM. If you wanna go that route we can give instructions

Cheers
DD

 

Well, turns out its not intermittent after all. What I thought was the pump running is actually the antenna going up and down, which explains why it does it the first time and not the subsequent times. Tomorrow I shall dive in with a multimeter and see whats getting power. Both relays got replaced while I was in there with no change, so I probably now have two used spares.

 

I don't have that much experience on older cars but I had a long standing issue with my fuel pump on my 94.
After driving it around with a hot wired fuel pump for months I sought professional help.
He took a look at the wiring diagram and schematic.
The next day he told me to check the fuse for the oxygen sensor heater.
It was blown and replacing it fixed the problem.
Does your car have that?
On the 94 it is the #9 fuse in the trunk right hand side.

 

I've been working through Grant's no-start guide. I tried to jump the orange ground wire from the fuel relay and that made no difference. So I replaced the pump. Pretty easy and $24, so why not. But it didn't change anything either. So I tried to jump the orange wire again and this time I had a strange result. Its the ground wire for the fuel pump relay. Normally it grounds through the ECU but there's a timer circuit that stops the pump running if the engine isn't running. Bypassing this lets the pump run whenever the ignition is on.

However, when I was connecting the wire the pump ran as soon as I completed the circuit, with the key in my pocket. So something is clearly wrong with this circuit. I'm going to look at the diagrams and see if I can find it, but it anyone had experienced this before I'd like to hear it.

 

Sounds like Terminal 86 of your FP relay is getting 12v at all times. It should get 12v only when the key is "on" (as you realize).

Terminal 86 of the FP relay fed from the "main relay"...... which itself should be triggered only with the key "on", also on terminal 86.

Strange.

My immediate gut thought is that somebody ahead of you has been monkeying around with the circuits !

Cheers
DD

 

I will test the relay terminals and see what they're getting for power. I'm also noticing that there are two "fuel pump relays" on the wiring diagram, 202 and 203. 203 is the one I've been looking at, its connected to the ECU, fuel pump, and relay 202. 202 is connected to the inertia cutout and the fuel injectors. Is 202 what has been called the "main relay" or is that somewhere else?
I did test the inertia switch. Pulling it up and the car won't crank, push it back down and it will crank.

 

To make things weirder, when the main relay is pushed in halfway it works and the car starts. When it is pushed in all the way it doesn't work. Anyway, the car starts. Time for the first ever test drive.

 

In that case Gareth, it would be best to rewire and replace the socket as well as the relay.

 

for reassurance and just because,,, i replaced both relays and the sockets with something like . Im not sure if the THESE are the exact right and correct plugs for your needs for fuel and main relay/socket replacement but its just to give an idea. then, the while youre in there stuff started happening with other shotty looking wires hanging around after 30yrs of PO's tinkeering and messing. it just seemed like th right thing to do. all and it all it took only a couple hours - neatened things up as well. cleaned up the grounds on the RT side of the battery, too. plugging the new relays into the new sockets, the fit was tight as hell and quite satisfying. jus say'n