Disco 2 no fuel pressure

[Steve Rupp]

So I picked up a disco 2 this fall with a possible slipped liner. It ran but would overheat. I pulled it over to the garage one day and when i went to start it up again it wouldn't start. It was extremely low on gas so i figured i ran out and put a few gallons in it. Still wouldn't start. That was last fall.

So now that the weather is starting to get nice i decide to get started working on it. The battery was completely dead so i put it on the charger for a while. It's holding a charge fine. I checked the fuel pressure at the rail and there was nothing. Then i checked all the fuel pump fuses and relays. There is power to the relay when cranking, and the relay definitely clicks when i put it back in. Next I went back to the pump. Pulled it out and tested the voltage at the connector. When the key is in position 2 i get around 7 volts. When cranking i get around 10 volts. Pump does not run. I pulled the pump and hooked it up to a battery at 12 volts. It runs and sounds fine.

I've been reading the rave and it says that the pump should run for 30 seconds when the key is in position 2. In my case I'm getting different voltages when in position 2 and position 3. Is this normal?

Ok forgetting about the different voltage readings i'm getting, would the truck being dead for the winter have anything to do with this? I doubt it since it obviously had no fuel pressure in the fall and now also has no fuel pressure. I was going to just buy a new fuel pump but after testing on the bench I'm starting to wonder if this is the problem. One other thing and i'm not sure if anybody knows what kind of resistance the pump should have when it's good but i'm getting about 2.4 ohms right now.

Any ideas from you mechanics out there?

 

[ptschram]

Jumper it from a good source of power and check the voltage with the pump running. A pump going bad can draw the voltage down to zero.

 

[flyfisher11]

For the hell of it have you checked the inertia switch?

 

[Steve Rupp]

just checked it on a good battery and the voltage doesn't change a bit. It's just weird how the pump will run fine at 10, 11, 12 volts, but with the pump plugged into the harness and out of the tank it doesn't do a thing. I did notice that the d2 has a tank pressure sending unit. Would the tank having no pressure have something to do with why i can't get the pump to run? Again I don't think it has anything to do with it because with the pump in the tank i was getting no pressure. When i hooked up to the schrader valve before pulling the pump out and messing with the lines, there was also nothing. A little dribble came out unlike the spray that is usually there.

 

[Steve Rupp]

For the hell of it have you checked the inertia switch?

LOL first thing. I thought that the switch might be bad but then i would be getting no voltage at the harness right?

 

[Steve Rupp]

Anybody know where the fuel pump harness sources it's ground? I'm not working on it till this weekend so i'm just thinking out loud now.

 

[ptschram]

Anybody know where the fuel pump harness sources it's ground? I'm not working on it till this weekend so i'm just thinking out loud now.

Force it to ground.

Before we do that, (again, thinking out loud, I'm on a computer that does not have the RAVE on it), is the relay easily accessible? Can we jumper the relay terminals? Perhaps the relay is going bad (high resistance across the contacts?).

 

[Steve Rupp]

That's a good idea Paul. The relay is under the hood so it's super accessible. I did test the battery terminal in the relay block and it's getting battery voltage, so I might just run out now and throw a jumper in there and see what i get on the other end.

 

[Steve Rupp]

ok so curiosity was killing me. i jumped the relay and did indeed get battery voltage back at the harness. i tested the resistance across the coil on the fuel pump relay and compared it to another relay next to it and both were 73 ohms. so the coil must be ok on the relay. next i'll jump the coil on the relay and see what kind of resistance i get across the contacts compared to another relay. i guess after that i'll check all the grounds.

here's the kicker though. with the relay jumped and batt voltage at the harness, i plugged in the pump. nothing. it's gotta be some damn ground. i just still don't understand why i'm not getting batt voltage to the coil of the relay. i'm wondering if it's a ground up front somewhere and not necessarily the ground to the harness. who knows, maybe they pull that ground all the way up front. i guess when it stops raining i'll get the creeper out and track that ground down.

man i love my d1

 

[SGaynor]

When the key is in position 2 i get around 7 volts. When cranking i get around 10 volts. Pump does not run. I pulled the pump and hooked it up to a battery at 12 volts. It runs and sounds fine.

When I read this, this jumped out at me. Seems like you aren't getting enough juice to the pump. I was thinking poor relay/wiring.

When you jumped the relay and got 12v at the harness, I thought that was it, but as you've said, still no go.

Before climbing under the truck to track down a bad ground, maybe try this?: wire up the pump in the engine bay. That is, connect the pump to the relay positive and then ground the pump at the ground terminal block near the battery. Turn the ignition and see if the pump runs. This way you can check the "circuit" (pump, relay, switch, wiring) without having to run wire from the front to the back of the truck.

If all works well, just rewire (reground only?). If not, then you know it's something else (relay, etc).

Good luck with that gremlin...

 

[Steve Rupp]

that's a good idea. I will have to pigtail the relay out of the block so I can connect to 87 but that'll work. If the pump I'll track the harness from back to front.

 

[peter sherman]

I had the same problem & replaced my fuel filter & good as new!:seeya:

 

[Steve Rupp]

Yeah if it were only that easy. I thought it was the dual carb muffler belt but i checked that and it's fine.

 

[benlittle]

Damn Steve, this sounds like what I went through with my Rangie. I ended up cleaning every contact associated with fuel and it worked somehow.

 

[Ron L]

Yeah if it were only that easy. I thought it was the dual carb muffler belt but i checked that and it's fine.

Thats the problem... the D2 has a quad carb muffler chain

I would check your grounds. Ford EEC systems exhibit identical problems and they are all due to poor grounds. Yes I know you are not working on a Ford, but inertia/ground and fuel pump wiring are very similar in this case. Make sure the inertia switch is grounded properly, no corrosion. An inertia switch that has a bad ground will exhibit perfect voltage because of the way it is wired. An internally corroded inertia switch will soak up voltage that could be used at the pump.

If you can get the pump to run, I would run a mild solvent through the pump and lines just to make sure nothing "cured" from sitting for so long.

 

[Steve Rupp]

ok here's what i've concluded so far. testing the fuel pump relay here's what i get. this is with the relay out.

between hot and ground of the coil (key in position 2) is the 7 volts
between hot and ground of the coil (key in position 3) is the 10 volts
between coil hot and battery ground (key in both positions) is battery voltage

now here's a kicker. with the relay out and the pigtails in (relay not plugged into the pigtails) i still get the 6 volts between the coil terminals. with the relay plugged in testing the coil i get no voltage but with the relay plugged in and key in position 3 now the coil engages and i get the 10 volts. this is what has me stumped a little bit. I'm still going by the ground theory because when i test the coil hot and battery ground i get battery voltage.

the question now is where is the coil ground supplied from. the rave should tell me but i'm going to have to pull out the fusebox to get a look.

 

[ptschram]

Steve:
When you refer to "coil", do you mean coil or switched contacts?

It is probably as illustrative to know what the voltages are going to and from the switched contacts.

Coil voltage only has to be enough to pull the switch closed. Contact voltage goes to the pump.

Have you jumpered the switched side of the relay to see what happens at the pump?

 

[ptschram]

the question now is where is the coil ground supplied from.

Per the Rave, the fuel pump relay is grounded through the ECU. Power to the coil is supplied through the "Main" relay in the fusebox, powered by a fusible link (link 8, 50 amp).

The ECU is grounded through pin 5 of connector 0638 and pin 5 of connector 0634. These two pins are grounded at a lug behind the fusebox, between the fuse box and the bulkhead.

 

[Steve Rupp]

Thanks Paul. i wonder if there's something up with the fusible link. i'll check it all out and see what i come up with.

 

[Steve Rupp]

when i say coil i mean the coil in the relay and not the switched contacts. it appears from my testing that the 7 volts i'm getting in position 2 isn't enough to pull the coil closed but the 10 volts in position 3 is. here's the thing though, the hot side of the switched contacts is battery voltage. i jumped the switched contacts with the relay out and did get battery voltage at the harness but the pump still did not run.