Fuel Level Gauge No Longer Working

[franklin2]

This is a much better diagram. http://www.oilburners.net/forums/attachment.php?attachmentid=45682&d=1375563775

 

[MIDNIGHT RIDER]

Were it me, I would eliminate the gauge wiring from the FSV and route it through a SPDT toggle-switch, thus eliminating any problems with the FSV from the equation.

My switch is located beside the driver-seat, next to the manual fuel-valves.

Longer wires could be spliced on and the switch mounted somewhere on the dash if that were preferable.

Considering your information, I don't think you have a float or sender problem, nor do I think the problem is in the instrument panel.

My best guess is a problem either within the FSV itself, or in the plug-connections at the FSV.

Located down under the truck, those connections can get awfully corroded.

 

[Shadetreemechanic]

on my 85, my guage quit and about a week later fuel started pouring out of the rear tank. The FSV failed and was drawing from the front tank and returning to the rear. I replaced the FSV, but used one from an 89 which has a different plug. I expect that my guage will work again once I get the plug wired in. Until then the FSV seems to default to the front tank when it doesn't receive power.

 

[The Warden]

Were it me, I would eliminate the gauge wiring from the FSV and route it through a SPDT toggle-switch, thus eliminating any problems with the FSV from the equation.

My switch is located beside the driver-seat, next to the manual fuel-valves.

Longer wires could be spliced on and the switch mounted somewhere on the dash if that were preferable.

Considering your information, I don't think you have a float or sender problem, nor do I think the problem is in the instrument panel.

My best guess is a problem either within the FSV itself, or in the plug-connections at the FSV.

Located down under the truck, those connections can get awfully corroded.

With all due respect, if the FSV is bad (and see below; I'm about 85% sure it isn't), I'll replace it with another FSV before re-wiring and replumbing my truck. I don't think the FSV is the piece of junk that you make it out to be, but maybe I've just been inordinately lucky? This FSV was installed used in 2002 and has been working perfectly to date. I only replaced the OEM FSV because I thought it had failed...turned out the fuse had blown because I had switched it too many times, and the core problem was a bad injector pump.

With that said, you gave me an idea...and I'm now kicking myself for not thinking of this earlier I'll take a jumper wire and jump the wires in the plug to each sender in turn and to the instrument cluster, and see if I get anything. Surprisingly given the environment I live in, the FSV plug is completely clean on both ends.

Thank you for the idea

on my 85, my guage quit and about a week later fuel started pouring out of the rear tank. The FSV failed and was drawing from the front tank and returning to the rear. I replaced the FSV, but used one from an 89 which has a different plug. I expect that my guage will work again once I get the plug wired in. Until then the FSV seems to default to the front tank when it doesn't receive power.

I was worried that that might have been the problem, but I think I can fairly say that I've avoided the worst at least. I just came back from a 200 mile run, with topping off both fuel tanks before departure, and running the aft tank the whole way...and no fuel coming out of either fill neck like I'm draining from one tank and returning to the other. I won't know for 100% certain that I was drawing from the aft tank until I refuel again (I got maybe 2 hours of sleep last night; I need to take a nap before going to work this evening, so I'll refuel later), but when I fueled up yesterday, the aft tank was at about the level I thought it would be...so, I'm about 85% sure that my FSV is switching properly. OTOH, as Midnight pointed out, maybe there's an internal corrosion issue keeping the sender wires from properly making contact?

BTW, you said that the FSV off an '89 had a different plug...which of your trucks are you referring to, and what was the difference between them? I thought that all diesel FSV's were the same between '85 or so and '97? (I know that '83 and '84 trucks have a different FSV because they used metal and rubber hoses instead of the plastic fuel lines in '85+ trucks, although the FSV in my truck now came off an '85 or '86; the plug's identical)...

If I can get myself to a point where I'm functional tomorrow, I'll take a look...thank you guys again

 

[franklin2]

That other truck he got the valve from may have had a replacement valve from one of the chain stores. They sell the pollak valve, but there was a big write-up on here sometime back that showed these replacement pollak valves need some rework with the wiring, and the plumbing also, to make them fit up.

 

[Shadetreemechanic]

The plug on my 85 is just slightly narrower than the one that I took off my 89. They both appear to be factory valves. The plugs are very close, in fact I plugged my 85 harness into my 89 FSV and was disappointed that my guage didn't start working. It was only after further investigation I noticed they are not the same.
In looking at my sig, it would appear my parts truck is an 88, not an 89, anyway the FSV plugs are definitely different.

 

[The Warden]

Bringing this thread up from the dead...

After two years, I have an update!

I've been busier than a one-armed paperhanger with various other projects, so this problem went on the backburner. I replaced the FSV just to be safe, and while both the old FSV and the "new" one are working properly, I still didn't have any luck with my fuel gauge.

Fast-forward to tonight...I'm getting ready to tow a boat for the Scout group I work with, and when I replaced the bulb in one of my clearance lights, I found a few extra 194 bulbs to replace the turn signal indicators. At that point, I figured I may as well take a look at the back of my dash to see what shape the instrument cluster voltage regulator was in.

And, here's what I found:

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When I push the circuit board against the terminal on the IVR, my fuel gauge reading comes back!

I didn't want to risk damaging the circuit board, so I figured I'd be better off asking here first...is that disc attached to a pin that goes into the IVR and it's just a matter of gently prying it out, or how exactly does the IVR connect to the circuit board? Can I get a replacement pin (or whatever that is), or is my only choice buying a new IVR or getting a junkyard cluster?

Thank you again! And, here's proof-positive that an IVR DOES exist on '80-'86 trucks

 

[madpogue]

I've got two decommissioned clusters ('85, '86) in the basement; I'll check that part of the board out when I get home.

 

[The Warden]

Please do! Thank you

 

[madpogue]

Here's what mine look like:

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So yeah, looks like you lost one of the "rivets". I didn't try too hard to pull either one of those things off the regulator; didn't want to damage the board/film thing. But they were on fairly tight. I'm thinking if you were able to get it to function just by touching it, you could probably re-attach that contact point to the regulator with some pin, perhaps a toothpick or the like. Just something that would physically secure the film to the contact on the regulator.

 

[IDIoit]

Tim, ive been trying to find time to read this entire post.
its not working...
if you have issues with the system, why not just take the time and install the rear larger tank, and delete the front.
no FSV, no BS.
JM.02W

 

[The Warden]

Tim, ive been trying to find time to read this entire post.
its not working...
if you have issues with the system, why not just take the time and install the rear larger tank, and delete the front.
no FSV, no BS.
JM.02W

Hey Brian,

The FSV's not the problem...take a look at the last four posts before yours I have it figured out now; I'm just trying to figure out the proper way to repair the IVR in the dash.

Three reasons I don't want to do the tank swap:
1) I don't want to deal with relocating the spare tire,
2) The problem's been found and isn't related to the FSV or anything in the dual-tank system, and most importantly
3) This is on the extended-cab truck, who's days are sadly numbered...I'm just limping her along until the crew-cab's road-worthy.

Here's what mine look like:

You must be registered for see images attach

So yeah, looks like you lost one of the "rivets". I didn't try too hard to pull either one of those things off the regulator; didn't want to damage the board/film thing. But they were on fairly tight. I'm thinking if you were able to get it to function just by touching it, you could probably re-attach that contact point to the regulator with some pin, perhaps a toothpick or the like. Just something that would physically secure the film to the contact on the regulator.

Thank you so much! I suspected that the the two things were identical, but it's nice to get the confirmation. I finally pulled out and cracked open the factory shop manual. It's saying that the things (they're calling them "connector buttons") just snap on and off the IVR. So, it looks like I will be good shape if I can find another connector button. I'm finding replacement IVR's on LMC Truck, but no mention of the button...I may have to go junkyard diving on the other hand, the hole in the circuit board's so small that I'm wondering if the button's supposed to be a permanent part of the board...in which case I may have to solder it.

I actually tried just pushing the circuit board against the IVR and wrapping it in electrical tape, but that didn't get it to make electrical contact

 

[Shadetreemechanic]

You said above that you were limping this truck along. I have on a couple of occasions simply set an offending loose wire or connector in place and added a drop of superglue. I wouldn't do it if you are looking for a permanent fix because at some point you might have to clean it off, but it has worked flawlessly for me several times in the past.

 

[madpogue]

^^^^^^^ Hmmmm, come to think of it, look for something called wire glue. Glue that conducts. This would be a perfect application.