My fuel sender resistor (88GT) was burnt through and through. The end (can't remember if it was top or bottom) was blackened completely around and the wound wires frayed.
I was gently cleaning it (laid out flat and fully supported) and checking for proper resistance and getting very inconsistent readings which I was afraid of, given the frayed wire conditions.
I inspected it and determined that the heat that blackened it burnt the wound wires had burnt through the backing. It felt flimsy and with a very slight sideways pressure on the thin edge let go. The material in the center was completely black, it had cooked right through.
[img]https://lh6.googleusercontent.com/-XE-FTurHmDw/URhBtgcf6yI/AAAAAAAACkE/XiQ857BqnwI/w721-h541-p-k/13%2B-%2B1[/img]

SUCK AN ELF!

So, looking for various alternatives... Advance Auto parts says a SunPro CP7583 fits. But I'm not sure about the resistance. I read that it should be 0 to 90. The description for this one says "For use with fuel level gauges and 5" - 26" deep tanks. Includes gasket and mounting hardware. Resistance specifications: Empty: 240 ohms. 1/2: 130 ohms. Full: 33 ohms."
This won't work right, will it?

You do need a sender with the 90-0 ohm rating as that is what the gauge needs.
There are many other senders like the one shown that have that rating (standard for GM).
I did mine 2 months ago and it works great now.
Had to figure a way to mount it to the supply tube in the tank and allow the whole unit to be inserted thorugh the tank hole but it was not too bad.
Mount the sender 1/2 way up the tank dimension and allow for the float travel.
Also, I had a grounding problem and solved it by drilling a small hole in the mounting flange and installing a brass #8 bolt with
a nut then another nut to secure a ground lead to the frame. I was getting a back feed from the fuel pump when it was running.
I was baffled for a while trying to figure out why the gauge worked until the engine was running then it showed 3/4 full with 1/8 tank of fuel.
I used the hole to test the unit prior to installing the bolt. Tied a string to the float. pulled it through the hole, installed the unit and pulled on the string.

That part should not get enough power to burn out like that. Likely has problems is the gauge or dash.
Metal likes to break off plastic board cause shorts when 2 plugs go into, etc...

You must fix whatever before you replace the sender.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

I will look into the dash then, as well as inspect the cut and splice job by a lazy mechanic who did not want to remove the harness through the little hole.

[ appendage ]
So, thinking about testing the gauge and wiring, I should be able to test from the gauge to the firewall for voltage and short, right? Between the purple and the black. That should be a sufficient test?

[This message has been edited by kjc88gt (edited 02-11-2013).]

If you want to be adventurous and make your own. You could try to estimate and figure out how much wire is used on the unit. Find a suitable material for the base and wind you own.

http://www.nichromewire.biz/index.html

Guessing the strip is about 2" long and 3/8 wide using 6.75 ohms/ft wound very tight together 12.5 feet should get you very close to 90ohm.
If you go with the 10.6 ohms/ft you could wind it a little looser using 9 feet.

Just have to do a little math.

[This message has been edited by Dodgerunner (edited 02-11-2013).]

Interesting thought - wind my own. What material would be suitable (survive in fuel and not pollute the fuel) for the solid backing?

Moot point possibly, I have ordered the VP unit from Summit. However, if getting it to fit is as difficult as some have said I may have to revisit this.
It's a spendy sucker when compared to the Sunsomething units, but cheap compared some units for other cars. I did not see the one on the FieroStore that I had read about in the forums.

But to bump up my question in response to TheOgre, is testing for shorts or voltage at the firewall connector suitable for locating problems in the dash/gauge? Or will have to pull the gauge out of the cluster? I do need to pull the tach out and fix the diode that puked and adds about 1900 extra RPMs.

I did some forensics on the fuel resistor today.

This was pulled from an 88 Coupe that has been sitting outside for last 8 years. My first plan of attack was to drop the fuel tank, and get it cleaned and repaired by a radiator shop that deals with this on regular basis.

I tested the fuel sender after cleaning all the black gummed up fuel off of it, with denatured alcohol and a soft paint brush. The readings were erratic and at one point went to infinity no matter what. After close examination of the resistor, some of the nichrome wires were broken on the resistor.



I did some checking on the wire, and it is 0.005" in diameter. Checked with 4 decimal place micrometer. Checking numbers for Nichrome 60 (I have no idea if this is what GM used), it turns out that this wire has 27 ohms/ft of resistance.



The substrate measured with calipers (not over the wire wraps) was 2.61" long x 0.4" wide x 0.030" thick.

One wrap would be .4 + .4 +.030 +.030 = .860"

It looks like about 3.5 feet of wire is wrapped around the substrate. 90 ohms/ 27 ohms/ft= 3.33 ft. 3.33ft x 12=39.96"

39.96"/.860"~46.5 wraps. Later on, I'll do a bit of counting on the wraps, but my 57 year old eyes will need serious magnification to do that.

At any rate, I went ahead and ordered one of the SN38 universal senders from Classic Instruments, described in another thread on the forum. The adaptation of that to the current sender/pump unit looked to be more viable than trying to rewind the resistor at this time.

However, early next year I may order some of the 0.005" nichrome wire in an experiment to see if the resistor can be repaired. Then to see if the current sending system can be made to work again. Probably not, but curiosity will build.

quote Originally posted by theogre: That part should not get enough power to burn out like that. Likely has problems is the gauge or dash. Metal likes to break off plastic board cause shorts when 2 plugs go into, etc... You must fix whatever before you replace the sender.

I believe it is inherent of the design and why the present sending units have resistance in the 200 + range. It's basically a variable short and 90 ohms results in a lot more heat build up than 200, I have a few variable resistance boards from sending units in the salvage yard from 90s model cars I pulled some years back and everyone shows varying degrees of heat stress at one end of the board. It's probably safe to say that keeping a full, or nearly full tank also helps to keep the sending unit filament cool and the fact that few maintain at least 3/4 of a tank continuously being why only one end of the board tends to show the heat stress.

Apparently, one person has gone to the trouble of rebuilding the resistor. Not a GM, but same principle.

http://www.thesamba.com/vw/...ewtopic.php?t=380693

$30 for a replacement unit - https://www.fiero.nl/forum/A...090219-2-078597.html

^^^^^^^^ That's what I did.

quote Originally posted by tesmith66: ^^^^^^^^ That's what I did.

Looks like the perfect solution even more so than what I came up with. The only thing I would do different than what was done in that thread is locate the sender in the OE position further down and bend the float arm to position the float as close to the stock location as possible. If 0 ohms can't be achieved simply remove the needle from the gauge and reinstall at the desired empty point which for me is a little below "E" as in stock form the gauge needle already overshoots above full if you put enough gas in the tank.