Engine/Transmission (1994 - 1998) Hard Starting Fuel Shut-off Solenoid Won't Engage

[davidWilliams]

Hi all, any help you can offer here is much appreciated.



Truck began having difficulty starting about a month ago. Doesn't seem to matter if its hot/cold, overnight (doesn't get below 60 here this time of year). Replaced the lift pump, fuel lines. Started great for about four days then problem returned gradually and within a week it was hard starting every time. I've replaced the fuel pump and starter relays after researching at tdr.



If I turn the key to the run postion (but not start) and manually engage the fuel shut-off solenoid the solenoid will engage (stay up) and it starts great.



Does this mean that the solenoid is bad? I was hoping it was a voltage problem as that is easy and cheap. I also cleaned the terminals, perhaps replace the battery cables?





David

Tulsa, OK

97 2500 5sp 2wd 225K

 

[Joe G.]

The solenoid is hardly ever bad. It's most likely the relay. There are two of them on the fire wall near the master cylinder. The big one is for the solenoid. The other suspect is the blue fuseable link wire on the positive post of the driver's side battery.

 

[PKemp]

Well... ..... I don't believe there is anything left but the fuel shutoff solenoid itself and its associated wiring in that circuit. You may have no choice but to change it. You did say you replaced the relays already?

 

[TMitch]

I tend to agree with Joe G. You've eliminated the other common hard start conditions like fuel lines. It is probably the fuel solenoid relay if the solenoid holds in the up position when you manually push it up. I had the same problem.

Sometimes lubricating the solenoid mechanism helps for a while.

Check out: http://fostertruck.com/dodge/default.htm and scroll down to the Fuel Shutoff relay and there is a link to a wiring diagram and picture of the relay location.

 

[KYOUNG]

Dave, make sure the boot on the solenoid has not gummed up in your spring, mine did it and all it took was a removal and clean.

You can make a new boot out of an old bicycle tube... ... ...

 

[davidWilliams]

The starter relay and fuel relay I replaced are both part located in the PCM along with a few fuses. George, is there another relay external to the PCM located near the firewall?



I did remove the rubber boot on the shutoff solenoid as it had fallen apart and cleaned the parts as best I could with a shop rag and then a silicon based spray on cleaning fluid. Haven't replaced the boot though yet.



I'll look for the other relays on my wiring diagram and the fusible link and let you know what happens.



As always, thanks for the help.

 

[Joe G.]

Here is what my '95 service manual shows. The larger relay on the right of the two in the picture is the one that causes symptoms like you have. The blue fuseable link is one of the smaller wires on the postitive post of the driver's side battery. In some cases it just gets loose.

 

[davidWilliams]

Joe, thanks for the pic, I know exactly where that is. Obviously my Chilton manual isn't up to the task, I'll get the shop manual ordered soonest. I'll pull the relay in question and have it ordered (probably not in stock locally). I've seen the blue fusible link from the postive battery terminal nearest the fuel system. I had my son turn the key back and forth from off to run and could hear that something was trying to engage, probably the there's not enough current getting to the solenoid.



I'll let you know.

 

[Joe G.]

The only manual for these trucks is the one you buy from Dodge. The aftermarket manuals may be useful in an outhouse. The manual you have probably has the gasoline powered truck schematics for all the trucks. I don't think there is anything in the PDC box under the hood that has anything at all to do with the fuel system. The power for the pull up coil is on the blue fuseable link. The relay on the firewall connects that to the fuel solenoid pull up coil. That's all there is in that circuit. The hold coil is connected directly to the ignition on circuit from the ignition switch. Pretty simple thing. There is nothing else in the P7100 fuel system except the fuel heater that is electrical and you can throw that thing away. The fuel solenoid can get dirty or the boot gives up and jams things.

 

[davidWilliams]

Fuel shut-off solenoid relay was the problem! Replaced it and it starts like it should. FWIW the fuel heater relay and the shut-off solenoid are not available separately, about $50 at the local Dodge dealer. I wouldn't have know what part to place without Joe's pic, thanks for the help, hope (but doubt) that I can return the favor someday.

 

[davidWilliams]

One other note, I didn't replace the solenoid relay previously, that was the fuel pump relay which I incorrectly assumed also controlled the shut-off solenoid, hope this comment helps a future troubleshooter.

 

[Joe G.]

Your 12 valve has a mechanical fuel pump. There is no relay. There is a fuel pump relay on the gasser but not on the diesel. I hope you didn't throw away the old relay. It is still good. I think that the relay marked as a fuel pump relay is actually not used so it is a spare. If I were you I would throw that Chilton manual away before it costs you any more money. I was going to suggest a relay to use for the solenoid relay, but you had already bought one from Dodge. You can get a 70 amp automotive type relay from an electronics store for about $10. It will plug in where the old relay was with no problem. 70 amps is a little more than is required. A 30 amp from Radio Shack ($6) will work but it will get tired after a while.

 

[davidWilliams]

I think you're right about it being a spare, I've kept the original due to replacement not fixing the problem. I've already ordered the shop manual from Geno's. I don't know too much about relays but after having looked at three of them they appear to have similar features, I didn't realize that they are more or less interchangeable if they have the right amperage and form factor. In order to replace one with a model from an electronics store I assume that I can simply take the old one in and have them match it?

 

[Joe G.]

Automotive relays normally have the same pattern for the connectors. There are two common types: single pole single throw and single pole double throw. The fuel solenoid relay is the first type. They are easy to check. Get a couple of test leads. Put a ground on pin 85. Put an ohm meter on pins 30/51 and 87. Touch 12 volts to pin 86. The meter should show conductance when you do that. The pin numbers are usually on the plastic bottom. I always check a relay if it acts like it is bad. Many times the problem was not the relay so I had some more trouble shooting to do. In this case if the fuel solenoid relay was good then you would have had to check to see if 12 volts was getting to the load input (pin 87) from the battery (blue wire) and check to see if there is 12 volts from the start circuit (pin 86).



If you are not sure just take the old one into an electronics store for a match. Beware of the nerds in the store. They may not know what an automotive relay is.

 

[davidWilliams]

I'll take a couple of my "samples" in to a local store and see if they know what to do with them, good to know I can save about 80% on these components going forward.



I appreciate all the help offered and hope this helps someone going forward.