Fuel Gauge issues

unoleisu · Dec 6, 2010

Hello everyone. On my 87 BII 2.9L M50D I'm still trying to figure out my fuel gauge issues.
Symptom: When I fill the tank, it shows full as it should. Reads fine until it gets down to half full, then below half full, it bottoms out. (shows completely empty)
I have varified that at half full, it is indeed half full.

So far I've replaced the in-tank sending unit with a whole new setup (everything eccept the pump) cleaned the wire terminals at that end, and attempted to replace the instrument voltage regulator. The IVR was first replaced with one from the salvage yard, it was bad. Then I ordered one from LMC truck (part # 47-o894 instrument voltage stabilizer) The part they sent me was incorrect. It looked exactly the same, except the mounting tab was exactly backwards of the original, and would not hook up. I called them, they checked their stock, and then sent me another incorrect one. Now I have to prove to them with pics that their stock item does not match the original, as their information says.

Any ideas?
Anybody know who else might carry the IVR?
Thanks for all the input!

n_grimm · Dec 7, 2010

I realize you have a new sending unit but have you tried unplugging it and testing it with an ohm meter to ground when it is below half? If it reads infinite resistance (open circuit), it has a problem. One place on line said 10 to 80 ohms full sweep but I'm not sure if that is correct but it should read something. The arm could have gotten bent at some time so one of the wipers doesn't make contact when the float gets closer to the bottom and of course any open circuit will make the gauge go to empty. Just a thought

unoleisu · Dec 8, 2010

I'm currently making an access door to get to the sending unit easier. I don't want to drop the tank to work on it any more. Using a panel I cut out of my 85 BII parts doner as the "door".
The old sending unit, and the new one both, don't seem likely to have the exact same problem, although I suppose it is possible. I plan to start testing it as soon as I finish the access door.
I'm wondering if possably the gauge itself could be at fault. It seems to be an issue with resistance in the circuit....I don't understand why it would be fine until under half full and then bottom out.

n_grimm · Dec 8, 2010

Good idea on the access hole. After I cut mine out I was wishing I would have slid a piece of plywood or metal over the tank first since I nicked the wires a little. At least when the sender is out you can check for voltages at the gauge as you move the float to different positions. Since the voltage regulator also powers the temp gauge, it seems like it would also drop at the same time as fuel gauge if that was the problem. I would check to see if the voltage from the output of the regulator is making it to the gauge and if it holds steady while the float is moved.

unoleisu · Dec 9, 2010

I replaced the temp gauge a few months ago with an after market one, because it wasn't working right. It had been showing it was over heating all the time. I didn't know the two gauges might have a related problem, back then. I was influenced by comments I had read back then about how BII gauges were junk in general.
Anyway, I'm trying to get my e-mail account to upload the pic I took comparing the two different Voltage stabilizers, so LMC will be convinced they are offering the wrong one for this application. (am I the only one who has had this problem?)

On the access door cutting issue, I use an angle grinder with a 6" cut-off wheel to do all my fabrication cutting. It makes a nice clean straight cut quickly, (especially in sheet metal)and I can easily control how deep the wheel penetrates. If a guy is crafty, he can actually cut at an angle and do large radius cuts as well. (I.E. Fender cutting) Also, I just did a 2" body lift on my BII, so I had a little more clearance over my tank. I'm thinking there might be enough room over the tank to fab a little stowage compartment, maybe..... have to give that a little more thought.

unoleisu · Dec 9, 2010

I'm trying my hand at uploading pics. This should be the Gauge Voltage stabilizer comparison, in case any one wants to see. Can't seem to get my yahoo account to upload it for e-mail....hmmm

n_grimm · Dec 9, 2010

I would bend the metal tabs and pull the guts from one of the new ones and stick it into the old housing or maybe just turn it around. I'm probably more impatient than you though. Makes you wonder if they just messed up when they assembled them.

unoleisu · Dec 10, 2010

I have been tempted to do exactly that. But at 50bucks a pop, I want to be shure the guts are the right ones. It could be that this design is for a different application. I may try to test them and see if they function the same. As soon as I finish my new bumper mounted spare tire carrier, I think I'll start on that.
I finally had to use my wife's e-mail to get the pic sent to LMC. Now I'm waiting for their response. Still can't figure out what's up with my yahoo account. It just freezes up every time I try to upload an image.

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