resistance range for oe fuel pickup?

What is the range of resistance for the oe fuel pickup?

What is empty? What is full?

I know chebbys are 0-90 ohms. What are the XJ/MJ's?

thanks.

I know that the 89's are 1 ohm =empty and 88 ohms =full, but I believe that it is reversed in the later years if memory serves me correctly.


Jerry

Thanks, that answers half of my confusion.

I think that the wire to my tank either isn't hooked up right, or is broken somewhere. My gauge worked like 3 times since I had the truck, and then only fleetingly. so, no connection = infinate resistance = damn thing pegged on full all the time, which it is.

Can anyone confirm/deny for this or other years?

What year is yours?

Jerry

Mine's an 88, so it "should" be the same, but can't hurt to make sure.

But I am trying to determine the feasibility of putting a later, electronic speedo cluster in it.

Reguardless of year if the ohms are out of the 1-88 range you have a bigger problem. That scale would be correct for the '88 also. If you are not in that range at the gauge cluster you have a sender or wire problem.HTH

'91 and newer are reverse.

105 ohms = empty

5 ohms = full.

With wire disconnected, gauge should read Empty. Short terminal A to terminal B on the body half of the sending unit connector by the tank. Gauge should read Full.

Source = 1994 FSM

Ah, wonderful...

So, that basically scratches a plug and play instrument cluster swap.

I've not measured the resistance at the cluster, as I didn't have the FSM, nor the forsight to ask...

The gas gauge is minor, so when I had the cluster out, I was more concerned about being able to drive it at night, and getting the parking lights to work.

Now that I've got an 88 FSM, I could find the wire color, and attempt to measure.

Or, go and jiggle the wires atop the tank.

The same diagnostic works for the '88, but in reverse. The wires from the fuel tank go into a 3-terminal connector about 15 inches forward from the tank. Unplug that and your gauge (with ignition ON, naturally) should read Full. The fat wire is the fuel pump. The other colored wire (violet?) is the sender. Jumper that to the black and the gauge should then read Empty.

The wires inside the tank are just push-on spade connectors. It's possible one of them isn't making contact. I worked on one a couple of years ago that had an inoperable gauge. The gauge checked out, so I pulled the fuel pump expecting to replace the sending unit. Previous owner had been there first. Both wires were hanging loose in the tank. Once I pressed them onto the terminals all was well.

I should have expected something like that. Why would anyone cut all three wires 6" away from a connector? (And then splice black to violet, and violet to black?)

yeah, I dunno bout PO's on this truck.

It's 7 years since it's been registered. Which is good cause the mileage is relatively low (91K or something). But bad because it's been god knows how many people's projects.

Wiring under the dash looks good, and only a few issues under the hood...

Dunno bout under the truck. Thing sits so low, I gotta put it on ramps to get around underneath it.

Good info though, thanks.

Well, I did this check finally

(yes, it took me two months to care enough)

and, it looks like it's the sending unit.

Odd thing is, when the tank is almost totally empty, or at least really low, the gauge will read E. Anytime else, it's pegged on F.

However, when I jump it, the gauges goes to E.

And, with gas in the tank (full) the resistance reads infinite.

Looks like I get to drop the tank.

You don't have to drop the tank. Some folks think it's easier if you do, other folks think it's easier if you don't You CAN remove the fuel pump and sender with the tank in place. It's retained by a metal lock ring. Use a BRASS punch to knock that around, and the entire unit comes out. Try to have less than half a tank of gas when you do this.

Also, the factory recommends always using a new O-ring when replacing the fuel pump. Coat it with Vaseline to help things slide into place.

The tricky part of reinstallation is getting the little "foot" (you'll know what I mean when you see it) back into the little recess in the bottom of the tank.