1986 Ranger fuel problem?

marky_mark · Nov 7, 2015

The other day i went out to start my truck and noticed that the fuel pumps came on and stayed on rather than shutting off after a few seconds. It turned over but would not fire. After a few times of turning the key on and off while my dad was out there with me trying to diagnose the problem, it finally did fire up but ran horribly as if there were a vacuum leak (i have a vacuum/boost gauge and it normally runs at 20 for vacuum but was running at about 10-12). I got under to hear if the fuel pumps sounded odd, and the high pressure pump has a little bit of a chatter to it. After doing a fuel pressure test just with key on, it was at about 38 psi. My thinking is that the high pressure pump is either on its last leg or is failed and the in tank pump is doing all the work. Anyone have an idea of what it could be? Any help is appreciated.

Its an 86 ranger 4x4 with the 2.9.

Spott · Nov 7, 2015

The engine computer turns on the fuel pump relay for 2 seconds when the key is turned to "Run", then turns them off until the key is turned to "Start" or the engine RPM rises above 500. If the pumps are staying on, I can think of 3 reasons: maybe the relay contacts have fused together, or maybe the control wire to the relay has gotten damaged and shorted to ground, or (much less likely) the computer is failing.

If the relay contacts are fused then you might be getting low voltage to the pumps, which would make them run (and sound) poorly. Or maybe the pump is wearing out, but you need to track down the "pumps remain on" problem first.

I'd start by inspecting the wiring, and then by testing or replacing the fuel pump relay.

P.S. 38 PSI is within spec, and the in-tank pump can't produce that much pressure, so the high-pressure pump must be doing something.

kimcrwbr1 · Nov 7, 2015

Pull the vacuum line off the fuel pressure regulator and see if fuel is in the hose.

marky_mark · Nov 7, 2015

So I went and bought a new fuel pump relay. I didn't know and am still not positive which relay is for the fuel pumps because there are 3 different ones on the passenger side fender. I put it into the obvious one that stood out in front which has a green connector and nothing changed. So I swapped it around to the different plugs and finally got it to where the fuel pumps shut off after a few seconds with the key on. I tried starting it and it fired right but died after about 10 seconds. I turned the key on and nothing, no sounds and it wouldn't fire up. After messing with the relays again I got it back to the original problem.

So now my new question is what are those other relays for? There is a green, brown, and black connector with relays. I looked in my chiltons book but it doesn't say what the fuel pump relay looks like or which plug it is, only that its on the passenger side fender.

I checked the fuel pressure regulator vacuum hose and there wasn't any gas in it running or not. I actually had to replace that about a year and a half ago.

Spott · Nov 7, 2015

One relay is for power to the EEC, another is for the fuel pumps, and the third is for the A/C cut-out for WOT.

The fuel pump relay has red, yellow, tan/lt grn, and org/lt blu wires to it.

You fixed a portion of the problem by replacing the fuel pump relay, but then something else went wrong. It sounds like an electrical problem, like shorted wires or bad insulation or loose or dirty connectors, possibly causing blown fuses or fusible links. When you fiddle with the relays it moves the wires around and changes the intermittent contact points between them.

Put the new relay back in, and then proceed to troubleshoot the remainder of the problem.

At this point I would inspect fuses, fusible links, and the wiring. Bad wires or connections could be the entire cause of the problem.

Big Jim M · Nov 7, 2015

As cheap as they are I think I would be after replacing all three relays and see if that fixes the problem.
Big Jim

Spott · Nov 8, 2015

Big Jim M said:
As cheap as they are I think I would be after replacing all three relays and see if that fixes the problem.
Big Jim

That's not a bad place to start, although I'm sure the A/C relay isn't related to the problem.

1986 Ranger fuel problem?

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