Gas gauge troubles

[2059]

OK Gents, here ya go. My gas gage worked intermediately in the beginning and now it will pull off the "rest" position and go to empty and that's where it stays. Here is the trouble shoot list so far, all continuity tests:

1) Confirmed good ground from the sending unit body to car body not just the tank.
2) Confirmed continuity from the sending unit probe to ground. 75 ohms. (depends on how much is in the tank, my guess 3/4 to less than full. Topped it off ~40ish miles ago)
3) Confirmed continuity from the sending unit wire to the rear half block harness connection behind the drivers kick panel. 75 ohms.
4) Confirmed continuity from rear half harness block to dash harness block. Full continuity.
5) Confirmed continuity from harness side block to lugs at gas gauge in board. 75 ohms on one stud and full continuity on the other.
6) Confirmed continuity between the studs on the gauge. Don't remember the resistance but it was not an open circuit.

What the hell am I missing?!?! Don't want to just start changing parts.


Thanks in advance!!!

BTW: Have a great Labor Day Weekend!!!!

 

[bm02tj]

what voltage is applied to the gauge I believe it should be 5 vdc

 

[PUNKN8R]

Okay now that continuity has been confirmed (or basic grounds). I would check for voltage supply to gas tank sending unit. You should be reading about a 5v pulse. This 5v pulse is supplied by the voltage limiter which reduces a 12v supply to the 5v pulse and is mounted (plugged into) the back side of your gauge cluster. This voltage limiter also supplies the same 5v pulse to your temperature gauge. By the way does the temp. gauge work??

 

[2059]

what voltage is applied to the gauge I believe it should be 5 vdc

Not sure didn't check. But i will today after work.

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Okay now that continuity has been confirmed (or basic grounds). I would check for voltage supply to gas tank sending unit. You should be reading about a 5v pulse. This 5v pulse is supplied by the voltage limiter which reduces a 12v supply to the 5v pulse and is mounted (plugged into) the back side of your gauge cluster. This voltage limiter also supplies the same 5v pulse to your temperature gauge. By the way does the temp. gauge work??

Yup, temp works fine so does the ammeter/voltmeter. I checked the service manual and saw how the circuit runs in the cluster board.

Here’s one for ya, DW and I went out with some friends last night for pizza and on the way home pulled a decent hole shot and the gauge registered for a bit then went back to empty. It hit me, Is it possible to get the sending unit installed up-side-down? I don’t remember if it’s “keyed” since it’s been months since I put it in.

 

[okiemopar]

I think it would be hard to get in up side down because the the way the pick up tube is bent, but I guess any thing could happen

 

[Gpuller]

I know you said you checked all your grounds but have a feeling there is still problem there. I was chasing a intermittent tach problem this summer. Tach would work fine then read low then not at all, only worked when the headlights were on. It was driving me nuts, had the dash a part dozens of times. All grounds "seemed" to be fine with my multimeter. Ended up being a so-so ground between the actual tach housing and the gauge cluster frame. The tach attached to the frame with 4 screws, sanded all 4 points on tach housing and frame and bingo the tach works like it should. Good thing too, because I was about to drive over the SOB.
Check your grounds, check your grounds...especially on a car with lots of fresh paint like yours.

 

[2059]

I know you said you checked all your grounds but have a feeling there is still problem there. I was chasing a intermittent tach problem this summer. Tach would work fine then read low then not at all, only worked when the headlights were on. It was driving me nuts, had the dash a part dozens of times. All grounds "seemed" to be fine with my multimeter. Ended up being a so-so ground between the actual tach housing and the gauge cluster frame. The tach attached to the frame with 4 screws, sanded all 4 points on tach housing and frame and bingo the tach works like it should. Good thing too, because I was about to drive over the SOB.
Check your grounds, check your grounds...especially on a car with lots of fresh paint like yours.

if I was having problems with the other gauges on that circuit I would agree however; the temp and oil pressure work fine and they are in series off the voltage limiter. In fact, it goes oil gauge, fuel gauge and temp gauge, in that order, off the low side of the limiter and the oil and temp gauges work fine. Therefore, I must have a problem with the gauge itself or the sending unit in the tank.

I'm leaning toward the sending unit since it seems to be an intermediate problem. I know what your thinking; If it's intermediate then it must be a ground. I grounded the sending unit separately off the pick-up neck since the ground strap would do no good because the fuel line is isolated, using Stainless rubber sleeved P-Clamps in place of the std spring clips.

Gonna order a new sending unit and if I'm wrong then I'll call Shannon at Redline and get his input.

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one thing that hit me after i posted. I checked continuity from the posts and nuts on the gauge to the copper run on the circuit board and it was good, no resistance, not open. I'm gonna get under there and loosen/tighten those nuts a couple times just to make sure.

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just pulled the nuts off and wire wheeled them. reinstalled, tightened and..... nothing..... goin with the sending unit theory...

 

[2059]

OK. At the risk of looking like a complete dumb-a$$, I found the problem with the gas gauge yesterday. I had the damn sending unit/pick-up in up-side-down!! Yes it can be done. Like I tell the guys at work; "We can F#*!-UP ANYTHING if we try hard enough". Here's the reason; the flange is not "keyed" or indexed and I remembered when I installed the sending unit/pick up in the right way; the pick-up tube hit the bottom of the tank and wouldn't allow the flange to seal at the top. So I just assumed that it didn't go in that way. To install it correctly, I had to bend the pick-up tube about a 1/4" up, to get everything to fit and seal.

Anyway, the gauge, sending unit and pick-up works great and I discovered yesterday, that if I keep my foot out of it, I get about 12 MPG. (like I care) ...

 

[okiemopar]

Glad you got it. You never know on these old cars. I have put 3 different sending units in my car and haven't got one that will work right yet but one of these days maybe. Ronnie

 

[lynchroad]

Yeah, You never know about this aftermarket parts. I have saved the rosted out gastank and cut out a big hole near the pick up mounting Surface . With the new sender mounted,you can see if the pick up is correctly bent, and the float-arm moving freely. Connect some jumpers, and check the reading Full / Empty, and roughly Half. I have my instrument cluster out, but I used a separate battery.

 

[Dennis H]

Glad you got it. You never know on these old cars. I have put 3 different sending units in my car and haven't got one that will work right yet but one of these days maybe. Ronnie

Same here. Gave up. I can mess it up wothout trying. Wish I had the old tank and sending unit.