Hey All,
1986 f250, dual tanks, electric pumps. Intermittently when trying to start the truck the starter relay (on pass side fender) goes "chunk" and the engine does not turn over. For a while I have been using a jumper wire from starter solenoid to pos battery term to start the truck. Condition seemed to be getting worse so I replaced the starter relay. Truck fired right up and seemed to be ok,,,for maybe a minute. It then died. Restarted several times and died. Then smoke rolled off the pink resistor wire located drivers side fneder area. Burned off the outer sleeving but not the wires insulation. Using the sites search engine found several good threads that helped me trouble shoot. Fuses good. Have power on the yellow wire from hot post starter solenoid to the fuel pump cutoff relay. Have power to the oil pressure switch. Jumpered the OPS connector to get power to the relay and still have the run for a few seconds then die condition (with very hot resistor wire).
I metered the relay and seemed in order but I could not hear it click when key to run position (or start). Replaced relay hoping but no Bueno. Still cannot hear a click from the relay. I am guessing that truck is running off the bypass circuit for a short while but then runs out of gas on the run circuit. I cannot hear the pumps running. Where to from here? Do I have a short somewhere? Why fuses do not blow? Maybe the new starter solenoid is stuck? Thanks for any tips you all might have.

 

You didn't say what engine, but I'll assume the 460. Anyway, could it be a red/light green wire? Here's the EVTM for your truck and you'll see that the resistor wire to the coil is red/light green: Start & Ignition - Gary's Garagemahal. Or, is it pink/black wire to the fuel pump control circuits, as shown here: Electric Fuel Pump Control - Gary's Garagemahal

I'm guessing it is the latter as you are working on the relays. If so, burning that wire would suggest you have a bad pump.

 

Thanks for the reply Gary. Yes 460. It is the pink/blk resistance wire at the fuel pump cutoff relay. I really hope I don't have to replace another pump.

 

It might not be the pump but maybe the wiring is shorting out. I'd check it stem to stern before replacing another pump.

 

D7AZ-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-213) / Obsolete ~ Available NOS & from auto parts stores.

49" long / Color coded red with green stripes / 1.30-1.40 ohms resistance / #16 gauge wire.

ALL: 1977/89 F100/350, Bronco & Econoline.

 

Thx. I guess I will look for a short. I don't know why a fuse hasn't popped. I replaced the fuel pump cut off relay but condition still exists. I cannot hear the relay "click",,,Does that indicate it is not doing anything?

 

No fuse is going to pop because no fuse is supplying power. Just a "fuse link", aka fusible link. Look at the top of the first page here (Electric Fuel Pump Control - Gary's Garagemahal) and you'll see the power to the inertia switch, fuel pump cutoff relay, resistance wire, and then the pump itself comes from Fuse Link S.

Look at the top left of Page 15 here (Charge & Power Distribution - Gasoline Engines - Gary's Garagemahal) and you'll see Fuse Link S is a blue wire coming from the starter relay, aka solenoid.

As for the relay, you should be able to feel it close if you have your hand on it. But if the resistance wire is getting hot then the relay is closing. And either the pump is bad or you have a short between the relay and the pump.

 

Gary,
Thank you so much for taking the time to respond. I am learning a lot and may actually get the truck running soon haha. I will hunt for a short. Another quick question if you don't mind. If a fuse link trips is it visible that it has done it's job? Seems like mine must be good as power is flowing. Just wondering.

 

A fuse link is a short piece of smaller wire with a special non-flammable insulation, as described here: Fuse Panel & Circuit Protection - Gary's Garagemahal. By being of a smaller wire size that means if there is too much current the failure will be in that wire - and the copper wire typically burns completely through. But the insulation usually remains intact so the wire looks good. But if you pull on it you'll find it stretchy since you are just pulling on the insulation.

If it isn't stretchy it is probably good. But you can test with a volt meter at the relay. If it has voltage the wire is good. Or if the relay clicks or the pump runs or the resistance wire gets hot. Anything that shows power is coming through means the fuse link is good.

 

Fusible links come in different sizes. For example, the fuel system fusible links coming off the starter solenoid are supposed to be 20 gauge which is really fine and will burn out quickly. So if the resistor wire associated with the fuel system is smoking hot I seriously wonder if someone replaced the 20 gauge fusible links with something heavier. I can't imagine a 20 gauge fusible link supplying enough power to cause your fuel system resistor wire to even get warm, much less "smoking hot" before burning out.

I also believe there is a resistor wire associated with your ignition system and I wonder if your smoking hot resistor wire really belongs to the ignition, and since this resistor wire is (presumably) getting hot with just the key on that supports this theory. If you disconnect all power from the fuel system and that wire still gets hot that really points to the ignition side of things.

Anyway. There should be a 20 gauge fusible link attached to the small I terminal of your starter solenoid. This is the fuel pump bypass wire and if you supply 12 volts to this wire the fuel pump should run if the pumps are good.

It sounds like this all started when you replaced the starter solenoid so you should revisit the installation.

I had a starter solenoid fail is such a way that it supplied power to the fuel pump bypass wire all the time resulting in a parasitic electrical draw that killed the battery and eventually melted some wires because a prior owner replaced the 20 gauge fusible link with a heavier gauge fusible link.

 

Thx Brnfree,
I will check the fuse link. Should be dark blue? I do know the resistor wire is coming off the fuel pump cutoff relay. I will double check the conditions in which the resistor wire gets hot,,,I was thinking it was getting hot while cranking and during the short period of time the engine will run. I need to see if it actually will get hot with key in run position, engine off. Your input is much appreciated!

 

If you've jumped the oil pressure switch then the fuel pumps should have power / run with the key in run.

If the resistor wire is getting hot but the pumps don't run that certainly points to some kind of a short, but I'd expect the fusible links to burn out before burning any wiring.

 

Thanks again Brnfree,
I have jumped the OPS and do get power to the fuel pump relay. Yesterday I put the key to run without trying to start the truck. The resistance wire did not get hot. I have had the truck since 1990 and the wiring does not appear to be altered. Is it possible my newly installed starter solenoid is already malfunctioning? I have heard the Chinese made parts are junk and fail often. How to check? I guess I will follow the resistance wire to the pumps and hope I stumble upon a short.

 

Okay, the shin bone's connected to... Wait! Wrong song...

You should always have power at the fuel pump relay. Power comes from the starter solenoid, through the inertia switch to the fuel pump relay.

Then, on the oil pressure switch side, power comes from a 15 amp fuse (#18 I think) that is hot with the key on, through the oil pressure switch (which closes when motor is running and has oil pressure) and then to the fuel pump relay where the power closes the relay and sends power through the resistor wire to the fuel tank switch and then from there on to the pumps.

 

Sorry that diagram doesn't include the tank switch wiring, which is another layer of complexity. I've seen a diagram that includes the tank switch wiring somewhere on this site, I just don't have it in my archive.

I went through a series of NAPA gold quality starter solenoids until I replaced the battery cable from the battery to the starter solenoid with a brand new heavy gauge cable. I read somewhere internal resistance can build in old cables as they corrode internally and the extra resistance causes too much draw through the solenoid and burns them up.

Don't know if there's any truth to that but (knock on wood) I've been good (on that anyway) since replacing the battery cable.

So yes, new solenoids fail. but I wonder about your alternator / power regulator? Maybe unregulated high voltage coming out of your charging system is overloading the resistor wire?

Anyway, you might try jumping 12 volts to the fuel pump bypass wire (bypasses to fuel pump relay and resistor wire all together) to see if the fuel pump will run on that circuit.