Guys,

Replaced my front tank sending unit yesterday that was a 4 wire plug and the orig. rotted one was a 2 wire. I briefly tried swapping wires around but either got way over full or nothing.............any advice?

Orig. 2 wires were black and blue/yellow stripe

4 wire is red/black stripe, gray/red strip, black and yellow/? stripe

Thanks

 

you need to find the proper sender for your truck. just popping anything that fits in the hole will not work.

 

the old sending units use resistance to move the gauge. You four wire sending unit is probably for an electric pump in the tank. two wires you don't need unless you want an electric pump in the tank. also if you left the pump on the sending unit it also won't work because you lift pump may struggle to pull fuel up through it.


oringal black wire should be black should be ground.
the best way to figure out the new one is to pull the sending unit back out and trace where the wires go. hook your black one to the wire that stops at the top of the unit. hook your other wire to the one that goes down to the float arm.

 

ALL sending units use resistance. Problem is, some generations are high resistance full, low resistance empty, whereas others are low resistance full, high resistance empty. OP's profile references a 2000 van and a '67 LeMans, neither of which are even remotely relevant to this section. So until we know what year truck we're dealing with, and what year vehicle the replacement is for, the above may or may not work. A confirmation of the above would be to ohm that pair of terminals and swing the float arm and see which way the resistance rises.

 

OK.....1993 IDI F350 and 1991 IDI F-Superduty......a good amount of posts about these 2 besides the van and OP's.......so I did know where I was posting....thanks

4 wire sender was put into the 2 wire ('93 F350) truck.

The replacement pickup was sourced by an IDI buddy, so it's within a couple of years (+ or -) of the 1993.....which has/had the 2 wire sender.

The 1991 F-Superduty, also IDI, has the 4 wire front and rear tanks.

There's no fuel pump assembly (IE, gas engine) attached to sending unit or a provision for it and wouldn't use it anyway if there.

So my assumption is that sometime in 1992 they changed.

Just thought maybe one of you had to source a different sender, since finding one is almost impossible, and run into this?

Thanks for your time.

 

the IDI fuel tank sending unit is only a 2 wire unit. the 4 wire unit is for the gas engines with in tank gas pump.

 

No IDI ever had an electric fuel pump, Again, there may be four terminals on the connector, but it is not, by definition, a "four-wire sender". Only two of the wires are actually used. The top plates on the sender/pickup assemblies on both my PSDs have four terminals on the connector, but the sender only uses two of them.

In any event, it's not the number of terminals/wires that's important, it's which type (see second sentence of post #4) of sender it is, and which type of gauge setup you have. Pretty sure a '93 would be the same as a '95 PSD, where Full is high resistance and Empty is low resistance. The '80-'86 trucks are just the opposite, and I **THINK** so are the '87-'91s.

So, a little exercise to determine compatibility. First, determine which way the gauge works. Switch the tank switcher to the tank in question, disconnect whatever sending unit might be connected, and turn the key to RUN. Observe the gauge. Then turn the key off, put a jumper wire between the terminals on the connector, and turn the key to RUN again, and observe the gauge again. One of two sets of things should have happened. Either:
(1) It read FULL (or pegged past full) when you first turned the key to RUN, and EMPTY when you used the jumper
-- or --
(2) It read EMPTY when you first turned the key to RUN, and FULL when you used the jumper.

My money's on it's a type 1.

Now, determine which type of sender you have. As mentioned above, look for a terminal that corresponds to a wire going from one of the terminals to the float arm pivot, and another terminal that connects to the top plate of the assembly itself (this would be a ground). Those two terminals should be the two that show varying resistance based on the float position. Connect an ohmmeter between the two, and swing the float arm up and down and look for the resistance reading to rise and fall. If you don't see that, keep trying different pairs of terminals (since we're only checking resistance, and don't really care about polarity at this point, there are only four possible combinations, mathematically). So once you're seeing resistance rise and fall on the meter with swinging the arm, you should see one of two things. Either:
(1) The resistance is higher when you swing the arm UP (140-ish ohms) and lower when you swing the arm DOWN (25-ish ohms).
-- or --
(2) The resistance is lower when you swing the arm UP and higher when you swing the arm DOWN.

If the "types" match, that is if both the gauge test and the sender test indicate type 1 -- or if they both indicate type 2 -- then the sender should work, provided you connect it using the two terminals you found to be effective for the sender test. If not, then the sender simply won't work; it's for the "other" type of gauge resistance logic.

Is there a wire harness permanently attached to the outside of the plate? If so, what colors are the wires?

 

Sender itself has only one yellow wire running (internally) to connector....so in theory it's 2 wire....1993 has a 2 wire top plate plug....1991 has a 4 wire top plate plug.

Saying that............after playing with it today, I noticed that I only got "over full" reading or empty and know I have a half tank (which was read/verified prior to replacing sending unit).

So my guess is that it's a non relating resistance logic.

Lastly.....orig. 2 wire was blue w/yellow stripe, and black

4 wire plug is yellow w/white, gray w/red, red w/black and black.

I tried my blue/yellow stripe wire to the yellow/white and read opposite of pinning to full......showed empty then.

Thanks for your time

 

Is the sender/pickup assembly already installed in the tank?

 

The 88 to at least 94 idi have the same resistance. I've taken 94 sending unit contact strip and put it in the 88. I didn't know that the bullnose was backwards, but even so with the wrong one the gauge would read backwards it would still tell you what you wanted to know.


to the op if your still not getting nothing take the sending unit out and pop off the plastic cover where the float arm pivots. your contact strip is in there. you can see if it is worn or not. you can also just swap the contact strip. I've done that before.

 

Just get a gas for the year of your truck. I got the 87 F250 5.0l Spectra. Ford change there resistance in their sending units. Fuel Tank Sending Unit Tech - FORDification.com Don't remember the where the 2 wires went on the 4 plug, but it's not that hard to figure out. I believe they both went to the rear. Let me know if you can't figure it out and I'll look the wiring diagram up.