I have a 89 f350 crew cab 7.3 IDI with bad sending units. i was going to install universal sending unit in the fuel tank. Can anybody tell me what the operating ohms for the factory gauge is. Unless somebody can tell me where i can get new sending units for the front and rear 19 gal. tanks

 

Subcribing,

 

er... i "think" it is about 16-158ohms

don't take my word for it though

 

you can't buy new sending units anymore strangely.
you can have them rebuilt far cheaper than new replacements would be anyway though,so it doesn't matter:
Rebuilt Fuel Sending Unit Specialist

 

Also just asking because I don't have my tanks droped yet, the sending unit is in the tank correct?

Chet

 

yeah,the sending unit is part of the pickup in the tank and looks something like this random google image search pic:


just drop the tank,insure it's getting power.if so,remove it and follow the directions on sending it in for repair.they'll fix it up and ship it back like brand new again.insert and back in action.
you want to make sure it's not your gauge or a selector switch issue before paying to ship it off.so test the basics first......lots of threads on how to do that by searching here first.

 

Thanks Diesel Junkie. All I can go by is what the stealership said it was, the sending units many years ago. One tank registers 1/2 tank, and the other hardly any. And both tanks run out before there empty. Found that out when I put gas in years ago and drained them both. Got way more out then I thought was in there.

Chet

 

You might want to check your ground if you havent already done that,

1987 and below
73 Ohms empty
10 Ohms full

1988 up on most
22 Ohms empty
145 Ohms full

 

I'll give it a try. It will be a while but I'll let you know when done.

Chet

 

most common is bad or dirty grounds , both senders also go through the switching valve
and if you run out of fuel when there is till some showing the plastic pickup on the sender has disentigrated and it can no longer draw fuel from the bottom of the tank
usually it will die at 1/4 tank when this happens
the sender grounds the circuit to indicate an empty tank and high resistance at full tank
so an open circuit would read past full at all times and if the seding unit wire was shorted to ground it would be below empty

 

No my problem is it only registers 1/2 tank on one when full and not at all on the other one when full. I've been estimating fuel since new. Its an 86 van I bought new and they never really worked right. Took it back under warrinty and they said it wasn't cover. I use 12 mpg times number of gallons I put in. Once I started to fill one tank, and it was gas. I drained both tanks and got way more then I put in. Thanks,

Chet

 

I agree, check the grounds and tank switch. Try to get an Ohm reading from from the cluster area to the tank sender. Also, the gauge in the cluster could be bad.

Good luck, let us know.

 

"the sender grounds the circuit to indicate an empty tank and high resistance at full tank
so an open circuit would read past full at all times and if the seding unit wire was shorted to ground it would be below empty"

Does this work in the opposite direction on pre '87 vehicles with the 10-73 ohm sending unit? If I disconnect the wire to the sending unit on my 1978 F600 and touch it directly to Ground the gauge goes to Full.