Greetings all, I have a 98 D1 with fuel problems. It was behaving perfectly until last week when it refused to start at the grocery store. There was no pressure in the fuel rail so I narrowed the problem to the fuel system. Got it towed home and began diagnostics. I read a ton of threads here and determined that it is one of four problems:
1. crank position sensor
2. multi function relay
3. fuel relay in the passenger kick panel
4. the fuel pump.

I found that I had 12.5 volts at the fuel pump plug for about 5 seconds when the key is turned to position 2. I thought that this pretty well isolated the fuel pump itself so I removed it and I planned to swap the pump itself instead of the whole assembly. One last test of the pump showed that when 12 volts were directly applied it worked like a champ. I put the whole unit back together and hooked the fuel lines back up. The truck started right up. Turned it off and I'm dead in the water again. My two questions are: 1. can a fuel pump have a sudden onset of intermittent failure? 2. Am I overlooking something else?

Thanks for taking the time to read this and thanks for any insight you may have.

-elliott

 

Elliott,

Welcome to the Club. The power to fuel pump is supplied for approx 5 seconds with key switched to position II, so all that is good.


What about filter? It is in the rear wheel well passeger side. If it is not fresh, replace it first.

Also, when you say it was dead in water, was starter turning the motor over and it not starting or was it completely dead as in no turn over?

 

The fuel pump is only supposed to have power for about 5sec when you turn the key to the run position but do not start it.
It is a safety thing, if the engine quits for whatever reason you do not want the fuel pump running constant and possibly feeding a engine fire.
SO no crank position sensor signal and the fuel pump shuts off after 5 seconds.
You do not have the fuel pump relay behind the kick panel, only the multifunction relay under the hood.
Yes it is possible for a fuel pump to work and then bind up and not work.
My money is on the multifunction relay.

 

Thanks so much for the quick replies. Danny: fuel filter has been around for about 30k miles. The motor cranks over just as normal but doesn't run. Spike: Thanks for the clarification on the kick panel relay. Do you know of any way to test the multifunction relay? I guess that I'm still confused that I can get 12v at the plug but not have the fuel pump come on.

 

Is your volt reading with the pump also connected, or just with a meter attached to the disconnected plug? A bad relay can make a high resistance connection, so it will pass enough "micro-amps" to make the volt meter work, but not enough full load amps to push the pump through its paces. However, if you back probe the connector while it is connected to the pump, and you get 12 volts+, and no noise from pump, then the pump is dead. Yes, it could be work/no work. But relay is easier to get to, and check out. You can also use a tail light bulb as a test light.

Attached is the schematic. You can meter from chassis to either side of the inertia switch and see 12 volts going toward pump. This happens for 2-5 seconds when you switch on, but ECU stops it if engine does not crank. You can also pull fuse F6 in the underhood box, and set your meter for amps (warning - most digital meters won't handle this much amps), and poke leads on the two places where the fuse came from (the meter replaces the fuse).

 

Fuel pump may not be the issue but 30,000 miles is running it to death, change it, at least it will give you cleaner fuel to the rail.

 

The mulitfuntion relay have 3 relays inside of it, one of them can go bad and the other 2 still work.
Some have reported a problem with the multifunction relay wiggling and causing intermittent problems.

 

Great info. I'm going to try the test light option and if the light won't shine then I think that Spike and Savannah will have pointed me to a new relay. The fuel filter will definitely go in the same order as the relay. Back to the garage!