Dumb Question - Can you test the sending unit without dropping the fuel tank?

[Jeff7]

I posted this in the stupid electronics thread but figured I might be better getting an answer in the engine section, this is what I posted...

So after seeing the thread about the hummingbird fuel gauge fix I decided to try and fix my fuel gauge. It reads over full when it's first filled, and sometimes (not when full) it will sporadically jump around anywhere from 1/4 to past full, otherwise it stays on full. I think it may be the sending unit but I would like to confirm that. From what I've been able to find (I have a 98 K1500 350) the sending unit is supposed to read 0-90 Ohms and it is the thinner ground wire and a purple wire (I'm guessing the purple one is the second from the left since that's beside the thinner ground wire), a shorted wire would always read empty and a broken wire/circuit being infinite Ohms would read over full.

So this is my stupid question, can you test the sending unit without dropping the tank? I tried sticking my multi-meter needles into where the wires meet the plug but didn't have any luck. Is there somewhere under the hood I can test (had a hard time following the wires), or should I try unplugging it maybe? If it is the sending unit I won't bother replacing it until my pump goes again so I'm not going to drop the tank out, but I'd like to confirm that so I'm not driving around with useless fuel gauge that could have been easily fix due to some other reason.

Thanks.

(This picture uploaded upside down, so were looking at the 4 pin connector, I'm pretty sure I want the 2 wires closest to the inside since the wire furthest out is thicker than the rest)

 

[Supercharged111]

Why not tap in farther upstream and have the multimeter in the cab so you can watch it fluctuate with the fuel gauge? I've wondered if you could just clean the thing, but that's a lot of work to experiment with.

 

[Jeff7]

Well I was thinking under the hood but there's a bunch of wires (7 for fuel and some for lights) that come up together and it's all under the ECU and some go in different directions so I was hoping someone could let me know exactly where to go.

 

[Supercharged111]

Oh yeah, 98+. I may have a pinout at home. I could get you the wire locations from that.

 

[Jeff7]

Yea lol. That would be really helpful. No rush, I'm actually taking off for a week tomorrow anyway, thanks.

 

[CrustyJunker]

I put a new sending unit in my truck when I did my build because of the bouncing needle on my fuel gauge, and still have the same issue. I tested my original sending unit outside the tank (since I had to put a high-flow pump in anyway) and found some dead spots when I slid the float up and down, but it appears that wasn't entirely the problem. My next try is to follow that sticky and see if silicone dampening the gauge itself will fix it. Here's why in my personal experience:

When I turned the key on in my old '96, the gauge smoothly drifted up from E and eased to the current fuel level...Taking maybe two seconds. -This truck never had the bouncy needle problem.

When I turn the key on in my '95...****! Whips from E to the current fuel level in a split second. Again, the gauge doesn't bounce around until I start driving, or physically move the truck in a way that causes the fuel to slosh. That makes me wonder if they did have some kind of physical dampening in the gauges from the factory.

Also... The oil pressure gauge in my '95 moves around accurately, but aggressively. My '96 had a slower, smoother movement there, too.

 

[Coveman]

i have a burb and let my mechanic tackle the fuel pump. the first two replacement pumps gave me totally erroneous readings(like stayed on full till the tank was actually 3/4 empty), the third was a delphi brand and was much more acurate, but has a little shaking in the needle that i didnt have before with oem.

the sender is part of the fuel pump and my mechanic thought it might be in the gage cluster...but that was fine before with the oem pump and im in no hurry to tear that apart. i think the electronics on the newer senders are just a bit tweaky

 

[98BlackSierra]

Every one of my trucks did the same thing. I'm pretty sure its the stepper motor in the instrument cluster.

 

[Jeff7]

Every one of my trucks did the same thing. I'm pretty sure its the stepper motor in the instrument cluster.

Any way to test that?

 

[Blackwater]

If you ever need to replace it, replace the whole unit. Also, Its a good idea to have a large friend to help you cause it is easier to replace it by taking the bed off. Especially if its full like most of the ones I had to replace. Hos and Burbs are out of luck on this.