Bad Fuel Gauge?

[gringoloco]

Starting form the top:

- The factory fuel gauge was pegged when I bought the truck (disconnected).

- Aftermarket oversize fuel tank. There was an aftermarket sender/gauge setup, that was inaccurate.

- I replaced the sender with a 0-90 ohm unit so I could use the factory gauge with the aftermarket tank. Tested sender before install w/ DMM 0 empty, 90 full, and smooth transition between.

- Double checked the readings post install, still good

- Re-installed tank, w/ new sender, wired an extra ground to be sure, trashed aftermarket gauge, reconnected brown wire to fuse box and went for a fill-up

-Filled tank about half full, but gauge reads less than 1/8th?

- Pulled brown wire at cluster, ohmmeter shows 42 ohms between wire and ground, which I figure should read just under half on the gauge.

Bad gauge? Never had one fail on me, so I'm not sure if this is how it would manifest...

Thanks for the help/ideas

[VetteVet]

-

I replaced the sender with a 0-90 ohm unit so I could use the factory gauge with the aftermarket tank. Tested sender before install w/ DMM 0 empty, 90 full, and smooth transition between.

Did you compare the sender float arms for length? A shorter float arm would require more gas to raise the float and the reading wouldn't start soon enough.

"also you should ground the fuel plug-in at the fuse panel and check for empty in order to make sure the resistor on the fuel gauge is the correct resistance.
key on of course.

[gringoloco]

Originally Posted by VetteVet

-

Did you compare the sender float arms for length? A shorter float arm would require more gas to raise the float and the reading wouldn't start soon enough.

Yes, I set up the new sender arm to be on the bottom of the tank at 0 and at the top at 90. Not sure if this is what you're asking?

Originally Posted by VetteVet

"also you should ground the fuel plug-in at the fuse panel and check for empty in order to make sure the resistor on the fuel gauge is the correct resistance.
key on of course.

Good idea- didn't think to do that. I'll give it a try and see what I get.

Thanks for the input
Posted via Mobile Device

[SCHRUMGMC]

Ah, Post a photo of it ?

[gringoloco]

Originally Posted by VetteVet

"also you should ground the fuel plug-in at the fuse panel and check for empty in order to make sure the resistor on the fuel gauge is the correct resistance.
key on of course.

Grounded the fuse panel. Gauge settled spot-on the 'E' mark. Remove the wire and it pegs past full. Seems normal to me...

Originally Posted by SCHRUMGMC

Ah, Post a photo of it ?

Photo of? Here's what the in-dash gauge reads at 42 ohms. The under-dash gauge in this pic is disconnected.

[SCHRUMGMC]

Well, I thought you had a Bad Fuel Gauge.I wanted to teach myself what things could go wrong for when I get a Truck

[VetteVet]

[quote=gringoloco;5813949]Yes, I set up the new sender arm to be on the bottom of the tank at 0 and at the top at 90. Not sure if this is what you're asking?

Yes that was what I was thinking.

Grounded the fuse panel. Gauge settled spot-on the 'E' mark. Remove the wire and it pegs past full. Seems normal to me..

Well that is the normal thing to happen. I am grasping but the float sometimes gets fuel inside it and being heavier it will read less fuel in the tank and the gauge will show less fuel than it actually has.

Being an oversized tank if it was longer than the stock tank then you would be able to put more fuel in it before the gauge registers. Do you have a vehicle with the stock tank you can use the sender in for comparison?

[gringoloco]

Originally Posted by SCHRUMGMC

Well, I thought you had a Bad Fuel Gauge.I wanted to teach myself what things could go wrong for when I get a Truck

I still think it may be...

Originally Posted by VetteVet

Well that is the normal thing to happen. I am grasping but the float sometimes gets fuel inside it and being heavier it will read less fuel in the tank and the gauge will show less fuel than it actually has.

Being an oversized tank if it was longer than the stock tank then you would be able to put more fuel in it before the gauge registers. Do you have a vehicle with the stock tank you can use the sender in for comparison?

You mean swap the gauge? Yeah, my truck has a stock style Blazer tank and sender w/ stock cluster. May have to do some comparison readings between the two trucks with the DMM then possibly swap clusters if I have to. Was hoping someone had seen a failure like this before, to save me the trouble of swapping everything around...

I'm still thinking 42 ohms at the fuse box should equate to somewhere around the halfway mark on the gauge?

[SCHRUMGMC]

alright just wondering

[Longhorn 70]

Are the gauge and sender linear on a properly working unit?
Is half a tank = half resistance?
Posted via Mobile Device

[SS Tim]

Did you try positioning the float arm "key on" to see if you could get the gauge to follow the float? Your numbers seem to be only the sender resistance. The gauge cycling is a good indicator. With everything buttoned up, can you reach the wiring to remove it and connect a test sender without dropping the tank? Did the float arm contact the bottom of the tank or is the sender the down limit with the float close to the bottom?

[gringoloco]

Originally Posted by Longhorn 70

Are the gauge and sender linear on a properly working unit?
Is half a tank = half resistance?
Posted via Mobile Device

Stock, I dunno. My aftermarket sender definitely is.