[Mark_WCE]

Folks,

Without warning the other day the truck died on me while driving. 1988 RC, 318 with TBI (fuel injection) Symptoms:

-Heater blower motor, lamps, and all in cab electrical (including most of dash) worked without issue.
-Able to turn engine over without issue.
-Temps and pressures where they were supposed to be.
-Noticed fuel level moved to Empty.
-Trying to start the engine, fuel pump would not 'prime.'

After popping the hood to look for point of failure, wasn't able to find one. Tried turning engine on again, fuel pump primed, fuel gauge went back to where it was supposed to be (3/4), and the engine started up without issue. In trying to inspect the electrical system, no mechanisms of failure were found.

Here are the diagrams I used from the FSM:

And the splice locations:

And a bit of text:

So, with all that, I was looking at a fault that would cause the fuel gauge to go to E along with the fuel pump not working. Initially I checked the the connectors and splice locations. The 8 point connector (D60 - left side, third of the way up from the bottom), Voltage was measured between Z1 and X2. During priming and engine running for a period of time, 13.5-13.9V, stabilized at 13.8V.

The splice at J9-1 (D47 top right corner, and Fig.5, beside the windshield wiper motor), no corrosion or physical fault found.

The problem has not returned after nearly 100 miles of driving through various conditions. However, when filling up the tank (needle was at half), I expected 30-33L of fuel... filled it up with 63L. Given the way the fuel level is measured with resistance, and that half a tank on the gauge was actually almost empty (text page 8E-1), this leads me to believe a ground issue.

In order for it to be a ground failure, the point of failure (for both gauge and pump to fail the way they did), needs to be somewhere between splice J9-1 and splice X2-1 (where X2 and X20 come together) - D60, lower left side.

As I haven't been able to duplicate the issue, and I don't want it happening when I'm driving to/from the hospital appointments, my thought is to cut X2 and X20 before the splice, and connect a short 18G wire and ground it directly to the frame to remove any failure in the wiring between J9-1 and X2-1.

Before I start cutting and connecting, what are your thoughts on this one? Anything else I should be looking at?

Mark.

 

[Mad Max]

Mark, going from memory...and I've changed a lot of poopy diapers and drank a lot of beer since then...but IIRC the fuel pump gets power/signal via the in-tank fuel level sensor...or something like that. 

When I did the diesel swap on my 93 RC (naturally, originally a gasser) I think I replaced the gasser in-tank fuel level switch with a diesel version, 'repurposed' the now-unnecessary fuel pump wire to signal the 'low fuel level' light on a 'diesel' dash...or something like that...

Bottom line is I think there is a correlation between the gasser in-tank fuel level switch and the fuel pump.  Maybe there's a faulty circuit in the tank fuel level switch/gauge that's causing the fuel pump to cut off?

 

[Mark_WCE]

It's a bit of a convoluted diagram and system. I miss the system on the '79, lol.

If that's the case, and without the ability to find an actual diagram of the fuel pump system aside from what is on D60, it's a crap shoot.

Best bet may be to simply drop the tank, replace the fuel pump, check over the 'bobber' and associated system, ground the X2 and X20 to the frame, and carry on driving. 

 

[Mad Max]

if you have access to one, check out a 93 diesel wiring harness and compare to the gasser you have now - it might help?

 

[dodge82273]

the gas anyway uses 2 ground wires at the fuel tank/pump . if gauge fails and pump fails , then works next try
( sometimes ) the gauge's failing is telling ME that its NOT an asd or pump / pump relay , I'd look at the ground wires bolted to the frame there near the tank/pump .

the older ones used a Z circut and splices X2-2 X2-3 to get their ground , but I agree because the 2 systems only connection is IN the tank OR the ground it self or its splices

please note , IF a pcm does NOT get a "crank signal " from the dizzy ( your year) it will only power the fuel pump two times before it then waits for a crank signal before powering it again . ( supplying ground to relay) YOURS sounds like it IS getting that crank signal , and this would NOT effect the gauge .

 

[Mark_WCE]

Thanks Gents! I don't have access to a '93 harness, but I did take a look at the diagram. I see what you mean!

Dodge82273, the ground wires don't bolt to the frame until after the J9-1 splice. But I think rather than having the ground wires going that route, I will have them connect right to the frame as a ground point near the tank.

So far it's working without a hiccup. No issues at all. Weird.

 

[Mad Max]

...IMO...many times when anything electrical get's really 'weird'...it's "grounds"...

 

[Elwenil]

Yeah, I'd be checking grounds and then checking continuity with wires while wiggling the harnesses and plugs.

 

[dodge82273]

yeah because that's the only thing that "relates" BOTH the dash gauge and the pump's not running , they get power separately from different places ,  BUT use a common ground ...  wiggle away  and hope to find it , those spot welded splices can come/go bad ...