94 Dodge Ram 2500 Pickup Fuel Circuit

dodge
electrical-wiring

#1

Dodge Ram 2500 Pickup, 5.9L, EFI, 110" wheelbase, regular cab.

A little while back (maybe a month or so) my truck began refusing to start. It would crank and act like it had spark (halfway firing once or twice} then stop trying. I checked the fuel pressure and it had none. I assumed it was the fuel pump since I had been through this a couple years before and replacing the pump assembly solved the problem, at that time. This time it solved it again, for about a day. I made it to a neighboring city where it decided to stop running just as I was turning into a parking lot. I had installed a tee in the fuel line with a valve on it some time back to facilitate a project I was then working on and decided to use it to see if the fuel pump was still pumping. It was not.

Eventually, I got the truck home and started troubleshooting. I found that I was unable to force the pump to run from under the hood, at the fuel pump and ASD relays even though the relays had passed their tests. This seemed to say to me that there was a problem with the connector at the fuel pump assembly. I played with the connector, tightened up the barrels, added a dab of dielectric grease and ensured the weather packing was as it should be. The truck started and ran like a champ … until I got to town again. I parked, went in and did my shopping and came back out. The truck started, but before I could get out of the parking lot, it died. I crawled under and played with the connector some more. But, this time it wouldn’t start. I figured the plug was somehow at fault so after I towed the truck home once again, I ventured to our local U-Pull-it and snagged me a different connector, came home, cut the old one off and soldered the ‘new’ one in place and sealed up all the joints nice and snug. Once again the truck started and ran. This time I decided not to drive it off my property until it earned my trust. I used it around the house here pulling a trailer around behind it to do some end of summer seasonal chores and low and behold, it quit starting again. This time when I crawled under and played with the connector. All I did was unplug it and plug it back in. It started. I moved the truck to my work space and parked it. I started the thing once in a while just in passing as I was doing things. It started twice more then quit again. I unplugged and replugged it, it wouldn’t start. I tightened up the barrels on the pins again and now it still won’t start.

My question is, is there a condition that can be encountered wherein the ECU might set up a persistent (as in, carrying across attempts to start) no-start condition … maybe … (as in sometimes, but not all the time) that would be reset by unplugging the fuel pump connecter, allowing the pump to behave as intended once the connector is plugged back in?


#2

I doubt that disconnecting the connection to the fuel pump is going to reset anything inside the ECU. Going by what you stated, I would guess there is something wrong with the fuel pump relay, in the power connections to it, or after it, but before the pump itself. This problem should be pretty easy to pin down using either a test light probe or meter to verify where power is getting to and where it isn’t. If you aren’t using one of those things already to test with you really should consider it.


#3

Each time the truck doesn’t start, bang on the gas tank with a rubber mallet.

If the truck starts each time tells me you installed a defective fuel pump.

Tester


#4

<blockquote=“tester”>Each time the truck doesn’t start, bang on the gas tank with a rubber mallet.

If the truck starts each time tells me you installed a defective fuel pump.

That got it started this time. Of course, that doesn't say how long it will continue to work. At least now I have something else I can try when it quits. I guess I'll still have to pull it out again.

Thanks for the input, now I can drive it up onto the ramps.


#5

Cougar, sorry, yes, I’ve always had expected voltage (about 12 volts) on the power side (green/blue?) wire at the plug on the pump module, outside the tank. I should have mentioned that. It’s part of what had me confused. I had reached a point of not wanting to admit that I’ll have to pull the thing out again and I guess I just had to hear it from someone else. Thanks, you guys are great!


#6

Follow-up:
You were right Cougar. Tank is out and I found in the plug on the underside of the connector (inside the tank) where the barrel on the ground wire wasn’t inserted correctly. It was slipping back into the plug instead of slipping around the pin, barely making contact on the end of the pin. Hence, the reason Testers suggestion worked for me. Kudos, y’all.


#7

You’re welcome for the help. If you find that the power side is okay then you should also make sure the return side is okay. I don’t know how your system is designed but some designs use a controlled return for the pump motor.


#8

There is no return line on this one, it has a regulator and it’s new, came with the assembly.


#9

Okay. When I said return, I was talking about the electrical return to ground.


#10

Oh, I’m not sure what that means. Doesn’t every circuit return to ground? Are you referring to the path the ground takes back to the ECU or ground? I think the wiring diagram for this circuit shows direct ground. I don’t think it goes back to the ECU. The control is on source voltage.

Also, I have been using a meter and a test light both. My problem has been in the fact that I was confused by my ‘really not wanting’ to open it up again. Seeing it start right after I banged on the tank was sufficient to convince me it really had to be done.


#11

It seems to be fixed now, time will tell.


#12

If it acts up again you might consider the possibility of an iffy Auto Shutdown Relay. That powers the engine management system along with a few other things including the fuel pump.

A lot of current passes through them and over time they can become hit and miss.


#13

Ok, thanks!


#14

Sorry for the confusion. All circuit paths have a ‘return to the battery’ which is another way of refering to the ground side of the circuit. Some fuel pump circuits control the ground path by placing some sort of device in series with the ground path in order to control the operation of the pump. It doesn’t matter which side of the electrical load the control portion is located. In your case it appears the return side ties directly to ground and dosen’t pass through anything before tying to ground. Hopefully things will work good now but I wouldn’t be surprised if the trouble returns since it seems that the real trouble hasn’t been located yet. If it does come back just try to find easy locations you can check the voltage going to the pump while the problem is occurring and the pump is supposed to be running when you check the spots.


#15

Ok, we’re on the same page now. I was aware of what you’ve explained here, just never heard it referred to as that. I believe the problem was solved when I correctly inserted the barrel on the ground wire into the plug inside the pump module assembly. If it’s not fixed, I’m pretty sure it won’t be in the tank. If that’s the case I’ll come back and extend this thread.