james1

My fuel gauge has begun bouncing all over the map. But the Low Fuel light still appears to function properly -- coming on when about 6 gallons remains in the tank.

Does not the fuel sending unit in the tank control both the fuel gauge and the Low Fuel light? If so, what else would cause my malfunction? I've lately been burning B100 biodiesel if that matters...

I understand that to replace the fuel sending unit I'll also need to line up two new gaskets -- the large one for the top of the fuel tank and the grommet that connects the fuel filler tube to the tank.

Once I've run the fuel level as low as possible, are there any tricks to lowering the tank? Should I count on replacing the fuel tank straps as well?

TIA.

NJTman

The straps are reusable unless rotted away. The fuel filler neck grommet and the fuel gauge seal. As well as the fuel sending unit are all still available from dodge. Once you get the fuel level low enough, you use a floor jack and a piece of 3/4" plywood under the tank, fitting in between the straps. Unscrew the bolts on the straps, disconnect the filler tube, and slowly lower the tank down a little bit to allow you to reach over the to to disconnect the fuel lines and electrical connector. Once that is done, lower the tank down all the way. Slide the tank off the jack, and pull it out from under the truck. Unscrew the fuel gauge retainer ring AFTER the area has been cleaned of dirt and debris. I use compressed air and a blow gun. You don't want dirt dropping in the tank from the retainer ring area.

Pump the fuel out of the tank into clean containers and inspect the tank, making sure nothing is in there but clean fuel

oliver foster

I do the same as T-man but use two jacks so it is more stable when lowering the tank.

james1

Thanks guys; that sounds like a plan.

Is my bouncing fuel gauge likely due to a faulty sending unit ? Why would my Low Fuel light continue to function properly?

Also note that my parts manual shows the sending unit as part number 5200 4932. My local Dodge dealer's computer showed that number as having been superseded with new number 5201 7992. Unfortunately, his computer lists the part as "backordered" with no delivery date known. He showed two dealers -- one in South Dakota and one in Colorado -- as having the part in stock. The dealer in South Dakota could not find the unit on his shelf and the dealer in Colorado shipped his unit out to me yesterday. Soooo, it's possible there are no more of these parts available from Ma Mopar. We're going to drive these old trucks as long as we can, but the parts problem is going to become acute...

edwinsmith

Going by others I've worked on in the past the sending unit is usually a wire wound rheostat. there is a wiper that rides on the coil of nichrome wire and the contact usually wears down and no longer makes good contact. These are sometimes repairable if you're handy enough.

The Low Fuel lamp is operated by a switch in the fuel sender unit. I don't know what it looks like since I haven't had one apart.

There is also a 5 Volt regulator module on the back of the instrument panel that could be causing problems. It's hard to tell from the FSM if it's directly involved in the fuel gauge but it seems probable.

The contact pins on the back of the gauge panel are NOT gold plated and they will corrode. Also they are simply crimped into the circuit board. I cleaned and soldered the joint where the pins crimp to make sure they are good. Clean the pins all the way up and tighten the plug connectors carefully.

My fuel gauge sort of works it goes to 3/4 when the tank is full and hovers around 1/2 tank forever and then goes down very slowly after that. My low fuel light has never come on because I'm to chicken to let it get that low.

When my lift pump went out I thought I was out of fuel because the truck wouldn't start after sitting with the nose up on a slight incline. Had to get a tow truck to get home. With the truck sitting in my driveway inclined nose down the truck started. I drove to the station and put in 19.5 gallons of fuel which means that I had 9.5 gallons left in the tank.

I'm now waiting on all the parts to put in a piston lift pump since my current pump had less than 10,000 miles on it.

NJTman

Precisely why I bought a spare sending unit for the shelf in the garage that dopey elf used to sit on. I stuck a screwdriver through his pointy little head, and shoved him in a bag of dog poop I cleaned up the yard with.

Stupid elf..... I hate elfs.....

edwinsmith

Did you need a gauge to tell you how many elf's you had on the shelf? Did the light come on when you got down to 1 elf?

james1

I've finally gotten around to completing this chore and am in the midst of it now. T-Man, your above advice was perfect; thank you. Fortunately both the fuel filler neck grommet and "fuel reservoir" seal are still available from Dodge -- both were shot on my truck. A couple of questions:
1. There are two fuel lines connected to the top of the of in-tank fuel reservoir -- one of which is marked with a piece of yellow tape reading "FUEL." Both lines connect to the tank with identical "quick connect horseshoe-type retainers." Does is matter which connector I hook which line to? That is, is it possible for me to get the two lines reversed or are they completely interchangeable?
2. My fuel tank straps both have a T-connector on one end which hooks into the frame and the other end is secured with a stud and nut rather than a bolt. Is this normal? (It is not what is showing in my Mopar parts manual for my 1993 D6 truck.)

TIA.

edwinsmith

Yes. It DOES matter which line goes where. One is the fuel suction line and the other is the return line.

You might consider replacing all of the rubber lines while you have the tank down.

Edwin

james1

Thanks Edwin.

1. How will I know which fuel line goes to which barbed connector?
2. My parts manual shows a bundle of three tubes going from the engine bay to the fuel tank. When I removed the tank from the truck, there were only two lines connected to the reservoir top on the tank. Am I missing a line?
3. I've run biodiesel in the truck and I agree that replacing the rubber fuel lines is probably prudent. Should I just fabricate myself some new lines (using Dorman 800-075 tubing and Dorman 800-082 clips for example)?

Again, TIA.

Angry Johnny

Yeah, you can't buy new sending units anymore but, you can still buy the gas fuel pump module assemblies and I believe the sender off of that would work just fine. It just costs more because you are buying an electric pump as well.

Disclaimer: I haven't tried this yet but my gauge gets hinkey at times so I may have to be the guinea pig for this soon.

james1

I purchased the last sending unit available in the US from the Dodge dealer in Colorado Springs; replacement of the sending unit is the reason I dropped the fuel tank...

edwinsmith

The one marked F or Fuel I assume goes to the lift pump on the engine. You could disconnect it from the lift pump and blow air through it to make sure. That line would go to the nipple which is the suction tube. You'd probably have to pull the fuel pickup assembly out of the tank to tell which. Unfortunately my FSM doesn't show it to be able to tell you. Somebody else may be able to chime in and give better information.

Edwin

oliver foster

The nipple that will go to the fuel line to the motor will be bigger .
The return line and nipple will be smaller.

If I am understanding the question at hand.

death row dave