Chasing Amy (if my dead fuel gauge was called Amy, that is)
 

So tonight was electrical night. My power antenna is working again, and I'm still baffled by my damn fuel gauge.


Here's the story so far...


- tightened all bolts on the gauge circuitboard. Inspected 'FUEL' bolt and lightly sanded around its screw hole.


- checked continuity of WG between the pump plug and the black dash socket (b3.) Failed.

- checked the wires I was using to do the continuity test. Passed.


- placed a jumper from the pump plug directly to the black socket (b3.) Failed. (Yes, I turned the key to ON.)

- removed jumper from black socket and applied jumper end directly to FUEL screwhead. No response from fuel gauge.


- reconnected all plugs, turned key to ON and checked voltage of WG on both sides of pump connector. Voltage jumped up and down between 0v and 9v, never slowing or settling.


So it seems that WG took some damage somewhere. I have a spare instrument cluster that I will install, and we'll see what the jumper does with it...

One more bit of info. Possibly the most important. I had the current pump out of the tank earlier this winter. I did the resistance test as per the FSM and got back some crazy numbers. Definitely not what I was told by the FSM to expect. I also had a spare pump on hand, leftover from my 1st FC. The fuel gauge and low fuel light in that car worked perfectly.
I did the same resistance test on this spare pump. I got the same results as with the first pump.

I'm not going to insist that my having two bitched pumps is an impossibility, but I'm thinking that it's a tad unlikely...

It's looking like I'll need a 3rd, absolutely positively 100% working normally pump before I can make any more progress with this.

Any comments?


With regards to the resistance test on 15-34/35 for the fuel gauge, if I was to connect my DMM directly to b3 at the gauge socket and then manually move the meter's needle through its range to at least try to find out if the meter is OK, would I risk damaging the meter's internals?

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ba-bump

It seems you found your problem. You said the WG wire did not ohm out from the plug at the combination meter to the fuel pump plug. There are two connectors b/t the meter and the fuel pump plug. One is open.

The other connector is C-03 (50:26/27.) I saw this connector while I had the instrument cluster out and it was connected and appeared to be both snug and undamaged...

I'm thinking that WG has been severed somewhere...


What I don't understand is, even if WG is severed, why didn't the meter respond to the jumper wire?

bump :)

Repair the WG wire first. It goes from C02, then a foot later to C03, then to the left foot well at X-13, then all the way back to the fuel pump plug.

Once fixed, disconnect the fuel pump plug. Put one end of a 32ohm resistor on the end of the WG wire and the other end of the resistor to a good ground. Turn the key to ON. The gauge should read approx halfway. Anything close to 32ohms is fine. Say five ohms on either side of 32, should get the meter to read close to halfway. You've seen the fsm, right?? Zero is approx 95ohms, middle 32ohms, full approx 7ohms?????

,,EDIT: SORRY. WRONG PLUG. I TRIED FIVE TIMES TO SEND THREE DIFFERENT PICTURES. ONE SCHEMATIC, ONE LOCATION DIAGRAM, ONE OF THE X13 PLUG. THIS SITE SUCKS BIG TIME.

I will get on this at my next opportunity - hopefully b4 the end of the week. Thanks. :bigthumb:

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I've restored continuity, but I keep forgetting to grab a resistor... :doh:


More to come. :D

Do I take my time or do I take my time? :D


In the interests of seeing threads with common questions seeing some kind of completion, here's an update. :)

I hit the gauge problem today. The fuel level arm is sending the right resistances, and I have continuity from the pump right to the socket going into the gauge cluster (C-02, I think.) So it has to be the friggin' gauge itself. It fails to respond to either the pump or a 33ohm resistor (they didn't have 32ohm resistors at the store I went to.)

I have a spare gauge cluster here, and I intend to transplant its fuel gauge into the current cluster. I'd rather not drop the entire spare cluster in as it would 'confuse' my mileage #s in my fuel log... :)

More to come as I hopefully wrap this up tomorrow...

Allright.


It was the gauge. I took it out and replaced it with my spare and the spare read normally, right about where it should be. :)


I took the faulty gauge to my electronics guru to check it out. When he checked the resistance on various bolts (the ones that connect the gauge to the circuit board) he got back some ridiculuosly high resistance readings (~ 190 ohms.) There was no sign of any physical damage/failure, but he did notice that one of the contact points, where the metal strip meets a hardpoint, was dirty. He sanded it with a long, narrow abrasive strip. I wasn't going to put it back in the car right then as I was heading home, so he quickly put 12 volts to two of the bolts on the back and -bingo- up went the gauge.

For now, I'll assume it's repaired. I'll put it back in the dash when I can, to make certain.


Now here's an important part, and something that I've noticed is commonly reported when the FC fuel gauge kicks out.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/fuel-gauge-whacked-but-low-fuel-warning-light-ok-38103/

I now take this incorrect reporting as an indication that the contact points *within* the gauge need to be cleaned. I'd venture that there are more than a few FC owners out there who pitched perfectly good fuel gauges b/c they didn't know any better... :( Maybe this will help end that.

To those who try to clean the gauge themselves: the gauge is very delicate - treat it accordingly. :)

Jesus Amur, it took you 9 months to figure this out? LoL :bigthumb:

What little free time I've had during all this had to be spent on other things, and in the grand scheme o' things the fuel gauge didn't rank all that high. Between the trip meter and the low fuel light I was able to cope just fine. :)

Lol, my trip meter IS my fuel gauge...

My problem is the sender, though (and it only took 1/2 a day to figure that one out :))

Thanks. :p:


How do you know it's the sender? Resistance test? On my spare fuel pump, the small metal tab that the level arm moves (the tab that moves across the filaments to send the signal to the gauge) is broken right off. Thus, no signal. :)

Just a possible explanation for you...

Couple of reasons- 1) the gauge works from full to just a bit above 1/2 tank, and 2) I took the pump/sender assy out of the tank and played with it. The wiper arm in the sender pot makes a very distinctive noise, and just by moving the float arm one can tell where the internal windings are shot...

It doesn't bother me enough to buy a new one one and change it out :)