Fuel Gauge and Ground

I've got a good part of my dash out and while I have it out I've got to figure out why my fuel gauge is not working. I think it may be a ground issue but not for certain. A few years back when I painted the truck, I pulled the bed and replaced the floats in both tanks, as the gauge was not working then. It's been awhile and things are a little foggy in my recollection but it seems that I recall grounding the float assembly with a piece of wire and moving the float assembly and watching the fuel gauge move. Thinking I fixed it, I put it all back together to later realize that, in fact, I did not fix it. That gauge lays on empty and never moves. This is the same with both tanks....no reading either tank. No problem switching tanks though.

Interestingly, just a few months ago, I happen to look down and noted that my gauge was on a quarter tank. First time I'd seen it off the E in years. Didn't last long before it dropped back down to E. This of course makes me think again that I have a ground issue.

I pulled my radio yesterday as there is supposedly a ground back behind it. I've still not found it and thinking it may be down lower, perhaps below the HVAC control unit. Also, it appears I have a firewall pad back there that may also be obstructing my view of it. Regardless, I read somewhere that there is a grounding stud that runs through the firewall. The ground wire for my fuel gauge is attached to this stud on the cab side. Same stud runs through to the engine bay side where there is supposedly a ground wire that should run from this stud to the engine. I've attached a picture of said stud. Can anyone confirm this for me? Is there suppose to be a ground off this stud to my engine? Aside from my fuel gauge, I don't have any other electrical problems.

No, I don't think that is a ground stud on both sides.  I think that is one of the HVAC bolts.

My remembrance is that the engine side ground goes to a screw by the windshield wiper, but we have a page on that (Documentation/Electrical/Grounds/Engine To Firewall Ground) and it differs a bit from my memory.

And on the inside I think G701 is just a screw going into the firewall.

But, let's talk about your fuel gauge because if everything else works it is not likely to be G701 that's the problem.  There's a troubleshooting procedure in the EVTM, but if you ground the wire from the sender at the tank the gauge should slowly go past Full.  If it doesn't, then you need to move your testing back to the Fuel Tank Selector Switch.

If you can get on the Y/W wire coming out of the switch then the gauge should go to Full.  If so, then try to get on the DB/Y and put the switch in Front and the gauge should go to Full.  If not then the switch appears to be bad.  If so, then you need to check C127, which is a gray 4-pin connector sorta under the master cylinder.

That is the dash support stay.
The ground stud is up just beneath the wiper motor and would ground to an intake manifold bolt between #7 & 8 cylinders.

Doesn't power pass through the ICVR, through the gauge, through the sender, to ground?
While I suppose you could bring ground all the way back to the firewall, ground (should be) ground.
A reference to zero potential throughout the system.

Machspeed wrote

I've attached a picture of said stud. Can anyone confirm this for me? Is there suppose to be a ground off this stud to my engine?

That stud is just bare, no ground attached. The engine ground attaches to the firewall just below the throttle cable and next to the large black oval plug. See below. It is attached to the firewall with a hex head sheet metal screw.



PS: Depending on the year of your truck, you may not have the large black oval plug. On the feedback carb and EFI trucks, the main harness passes through this hole. The earlier trucks had no hole there at all. My '84 is DSII, so just a plug. My '80 has no hole there.

Thank you gentlemen, this helps a lot.

Jim is right - that's the bolt for right hand side lower dash support arm.

G701/G106 screws to the dash support just to the right of the radio.



That bolt (lower dash support arm) is what I used to beef my ground path up. Ran a heavy (2 or 4awg, can't recall at the moment) cable from the battery to that bolt. Then on the interior side I ran a cable from the same bolt to a ground bar behind the dash. From there I ran a 10awg wire to the dash support. The ground bar could be ignored and a wire ran directly from the interior side of the bolt to G701/G106.

Not a modification that's really needed for most but if adding things like an amp, it's an easy way to add a reliable ground path.

Well that explains a lot, I've been looking on the firewall for that ground....sheez! Thanks Scott!

I'm going to test from front to back and hope I find the issue up front of the tanks somewhere. Really dreading dropping those tanks. Keep going back and forth on lifting the bed vs. dropping the tanks.

Lifting (tilting) the bed worked better for me, having done it both ways. Both are a pain in the butt, but if you're not looking to clean out/inspect the tank, tilting the bed was easier. Just beware that the rearmost bed bolts like to round out and spin... the LH rear one did that to me, and I had to wedge the head to get the nut off (and wrap/jam it with electrical tape to get it to re-install).

In the past I've just tack welded the bolt head to the bed.
They won't turn then, and it saves turning the lozenge shaped hole in the bed round.

Those bolts can get expensive. So if you can get them off without cutting them it's worth it.

I think I have 7/16 stainless carriage bolts in there now.  

That too... If I had a welder that wasn't a junky Harbor Freight wonder, I'd have done that.

The middle bolts are different (bigger keying boss) and don't seem to have this problem... only the back (and front?) ones with carriage squares were trouble for me.

ratdude747 wrote

Lifting (tilting) the bed worked better for me, having done it both ways. Both are a pain in the butt, but if you're not looking to clean out/inspect the tank, tilting the bed was easier. Just beware that the rearmost bed bolts like to round out and spin... the LH rear one did that to me, and I had to wedge the head to get the nut off (and wrap/jam it with electrical tape to get it to re-install).

Yeah, I think lifting the bed will be the route I'm going to take. I've had the bed off before so I'm hopeful those bolts will release without difficulty. Thank you!  

Hey!  I've got a junkyard $160 Horrid Fate welder.  

It would work just fine for tracking a bolt head down.

If fact, I'm about to go out and weld up some bed frames into storage shelf brackets.

Hopefully yours come apart easily as they are very frustrating when they spin (just like the front bumper bolts)

Similar to tacking the head to the bed, we tacked a nut to the top of a couple on mine. A little more difficult to cleanup if reusing the bolt though.

Tacking it to the bed means you don't need someone else, with another wrench, to get it undone.

That's true. For me, the condition of the bolt and bed would be the determining factor.
Fingers crossed that John doesn't even have to cross that bridge :)

Yes, fingers crossed.  But my hope is that he doesn't have to pull the bed and finds the problem in an easier/cheaper place to fix.  After all, it appears to be common to both tanks.

But, if he does have to pull the senders hopefully he'll use anti-seize so the bolts come off later if he needs to do so.

Thanks fellas. I pulled the bed 7-8 years ago when I had the truck painted. I don't recall the bolts giving me a lot of grief at that time. After I had the truck painted I had a spray in bedliner put in it and the liner is covering the tops of those bolts. If need be, I'll just cut them out.

Aside from the nonworking fuel gage, I really need to access the tanks. When the truck is parked in my garage, the place smells like gas. Also, in the hot Summer months, I have noted some pretty good pressure release when I pull the fuel caps for refueling. Not sure that is normal and I certainly don't like the gas smell. When I de-smogged my truck all those years ago, wasn't thinking much in how some things might be affected.

The rollover valves should be venting to the charcoal canisters.
Those lines may be pinched or clogged.

Gary said he just brought the line up and put a filter on it.
That vent should be working, but it won't absorb the fumes.

Right, you have a clogged or closed-off vent, John.  No way it should build up pressure.

As Jim said, I just routed the vent line, after the two merged, way up the side of the bed, turned it back down, and put a filter on it.  And it does vent out of it as when I filled the tanks yesterday I could smell gas over there, slightly.

Gary, you have pictures of how you routed those lines?