Fuel shut off solenoid

[olg1355]

1996 Dodge Ram 2500 with 297,000 miles. The fuel shutoff is not getting power on startup. If I turn the key on and manually pick the plunger up it locks in place. How does the shut off get powered? I changed the 20 amp fuse in the power distubution box but it only helps for several starts. Thank You

[ISX]

The shutdown solenoid is grounded to the front of the cylinder head.There is a relay above the cylinder head on the firewall that energizes the solenoid, but is only in use when the truck starts. It gives the solenoid a big kick and turns it on, which only occurs while starting. After you start it, the relay turns off but a separate wire keeps the solenoid energized and holds it in position until power is lost. If you just turn the key on, nothing will happen, it only energizes the relay in the start position. In the on position, the other wire has power but it is a small wire that can only hold the solenoid in place, not move it. One wire goes to the relay (contact 87) on the firewall. The relay feeds that wire power using another wire on the other side of the relay (contact 30) that is connected directly to the battery. The relay is energized with 2 more wires (ground on contact 85, positive wire on contact 86). The ground wire runs through a few connectors and is essentially grounded below the a/c compressor. The positive for the relay goes from the key, through the clutch pedal position switch (if you have a manual) and to the relay. The other wire that just holds the solenoid in place is spliced into a whole bunch of other connections that all have power when the key is on or starting. You said it locks it in place when you have the key on, so the last wire I talked about is fine, the relay is where your problem lies, or the wiring going to it or the solenoid. I do want to hear more about this 20A fuse you changed as the only 20A fuse in the power distribution box is for the fuel pump.

[olg1355]

Thats the part that confused me too(the 20 A fuse). I had the solinold off and just pluged into the connector. When I removed the fuse and just used a jumper wire the solinold worked, but if I put the fuse back in it would not. A testing of the fuse shows it to be good, replaced it and the engine started. Where is the relay on the firewall?

[ISX]

The relay is right above the back of the cylinder head on the firewall, just screwed in right under the cowl, basically above the shutoff solenoid. As for the fuse thing, thats very interesting. I tracked everything down and the 20A fuse marked the "Fuel Pump" doesn't have anything to do with any of this. It gives power to part of the PCM (Fused B+) but the PCM has nothing to do with the engine starting. The battery goes directly through fuses and to the key switch which then gives power to the solenoid relay, the PCM isn't involved. It is involved with the wire that holds the solenoid but we know that part works. I'll have to trace some more, theres some wires in the schematics that aren't right.

[MnTom]

There is a big (in size) 40A fuse in the PDC under the hood for the shut down solenoid. If you need one NAPA has a replacement. ISX is on the right track, look at the relay first. When you try to start the truck the starter powers the coil side of that relay and puts power from the PDC to the lift (start) side of the solenoid. The run side is nothing more that a hold for the solenoid.

[olg1355]

Update. I thought I had it but today it quit again. The only differance is that both days that the problem started it was wet or raining. When it dried out last week it worked fine. I hate electrical problems! Thanks for the info.

[ISX]

That adds a twist to the problem. If rain gets in the relay, it won't work right. The solenoid might work, but the relay is only used to turn the solenoid on, and if it has water in it then the thing won't work right. I would make sure it isn't cracked anywhere, same with the stuff in the fuse box, make sure they can't get wet.

[MnTom]

Since you said it happens when it gets wet, check the harness that goes from the firewall to the PDC. Right where the harness goes over the shock tower the harness can wear and cause a bunch of issues. I fought that one for a year on my daughter's truck before we found it. Hers is a '98 12v.

[olg1355]

I got it. The fuseable wire that attaches to the battery was bad. Had 12.6 volts at the relay until trying to start, then dropped to Zero. Thanks again for the help.

[MnTom]

I never would have thought that a fusible link would act like that! That is good news!!

[Rogan]

I never would have thought that a fusible link would act like that! That is good news!!

That was/is a common issue with the 12V. It's usually the blue wire that causes issues/symptoms as described.

[MnTom]

But generally if a fusible link melts there is no power any time.

[Rogan]

True, but I doubt the actual link was the issue. Most likely, the connector/terminal was the culprit.