I pulled my bed off and started the process of turning the rear tank into a water ballast tank and found some really hanky stuff. I had previously tried to find the location of the switching valve and HP fuel pump to no avail and figured I just couldn't see it. I was wrong. There is no switching valve on the fuel system, there is no rail mounted HP fuel pump, there is no evidence of a plug or lines that ever went to these items. There is however a switch in the dash and there are clearly 2 tanks. Anyone ever seen this goofyness before?


The real reason I'm posting however is to ask about my fuel gauge. Before I pulled the bed off, the front tank gauge didn't work at all (turned out to be a bad float), and the rear tank had a full brand new sending unit that worked fine on the dash. So I took the unit and float off and put it in the front tank. The problem is now my gauge is pegged full. I do still have the bed off the truck and from what I can tell the ground circuits for the tail light system are tied in with the ground system for the pumps? Also what, if anything, do I need to do with the plug for the rear tank. I tested everything out and it seems as though with the switch set to the front tank that whole circuit goes dead? Ive also read some things regarding a Instrument Cluster Voltage Regulator (IVR) but cant seem to find a location on the part? I took the cluster apart thinking that it must be in there but... it wasn't. Thanks for any help you can give me!

 

You must have a 92 or newer truck then. They don't use an external pump or selector valve, it is all done within each tank's FDM (Fuel Delivery Module).

The sensors are different between tanks if I remember right but if the gauge is pegged full then you have an open circuit.

Your truck also does not use an IVR.

 

Dixie460 is right^

Water just for ballast, or for camping use or something? I had considered mounting a decommissioned keg in the bed for such a purpose, but never thought to use the rear tank.

 

just for ballast actually im working on making it a drag truck. Its definitely a 91, front end, vin and title and match for 91. Thanks for the quick response guys ill get to chasing wires.

 

As far as I know the switch was made to 1 in tank pump in 1990.

 

X2... gas engine F-series trucks went to tanks with internal high pressure pumps in 1990.

 

well I got the truck all back together but still no fuel gauge. I traced all the wires and couldn't find any problem there. I do have the rear pump in the tank but without a sending unit on it and it is plugged in. Could this cause the problem? Or is it more likely that there is just still a problem with the unit?

 

Dang it... that's incorrect advice #2 for me today!

Good to know though, I'll be sure to store this info in NVRAM.

 

You have the front tank selected and the gauge still pegs at full? I don't have a schematic for you but if you ground the signal return from the level sensor (the one that goes TO the gauge) then it should drive the gauge empty. If it does that then you likely have a problem with the float or sensor itself.

 

Ok yeah I probed that wire and the gauge dives empty when switched to ground. Looks like the beds coming back off.

 

Why, a lot of work and loss of fuel capacity for 38lbs of ballast?

 

Why are you assuming he'll only have 4 3/4 gallons of water? Even a 19 gallon tank will hold 152 lbs.

 

You removed the tees where the lines from the 2 tanks come together, or have the lines to the rear tank disconnected & plugged, correct?

I think BF typo'ed his calcs.
18.2 gal at 8.3 lbs/gal is about 151 pounds.

edit: I see you beat me to it, NS

 

Not at all, it's the weight difference between a full tank of fuel and a full tank of water. A full tank of fuel is ballast as well. Yeah 18.2 x 8.3 = 151 but 18.2 x 6.3 pounds is about 115 pounds, a 36lb difference.


One better/easier/cheaper idea is to leave the fuel tank alone and useful as a fuel tank and fill the spare tire with water.


Edit..


Or replace the 18 gallon tank with the 38 gallon bronco tank. Full of fuel it would be 126lbs heavier. It would also allow for the removal of the mid-ship tank using the rear tank instead. Both removing total weight and removing weight in front of the rear axle.

 

If he's making a drag truck (as opposed to a truck that he intends to street drag with) he probably has a lot of rules about fuel cells to worry about, so having gas in that tank might not be an option. But if it is, yeah, water's not much heavier than gas. Of course steel is heavier yet, so bolting some extra weight in wouldn't be hard either.