Erratic Fuel Gauge

[seth_95]

I have a 95 6.5 disel and my fuel guage is acting really weird. When it is below a half of tank it moves a lot when I stop and go and then I filled it up today and it reads way past full. Is it a gauge problem? or a sending unit? I just bought this truck so I am trying to get a few bugs out of it. Thanks!

[DmaxMaverick]

Sounds like every GM fuel gage I've had the privilege to monitor. As early as I can remember, to the latest models I own or have seen, that's how they work. If it is in true GM form the lower half will be a lot faster than the top half.

That said, just how much "way past full" are we talking about? Just want to make sure you don't have something "out of the norm". Normal is about the width of one section past full.

[oilburnertoo]

I also have a '95 6.5LTD, When I fill it up the gage reads about 1/8 tank past the full mark, when it gets down to 3/4 full I can fuel it up and put 19/20 gals in it, this is a 34 gal tank. This leaves 14 gals for the last 3/4 tank, I think most gages read about this accurate. I have a buddy that has a '96 6.5LTD and his reads pretty much the same as mine.

[c.d.ewen]

'98 GMC burb. Fill the 44 gal tank, and the needle pegs right, not more than a 1/4-tank's distance past the Full mark. Takes a lot of driving to drop to the Full mark, then as you travel, the needle goes faster and faster to the left. The last 1/4 of a tank, the needle drops like a rock. Go over a bump in the last 1/4, however, and it's (as a famous sportscaster would say), "Whoa Nellie!" - the needle bangs right, half-a-tank's distance past the Full mark, then comes back to a 1/4, then does it again and again.

Bottom line: you ain't alone. Some things you worry about, some things you don't - when I get down to a 1/4 tank, I put in more diesel and the problem goes away.

Charley

[seth_95]

Mine Reads about 1/4" past the full mark when full. I filled it up yesterday and it was between E and 1/4 and it took 27 gals.

[DmaxMaverick]

I'm wondering if you don't have more serious electrical problem going on, considering this and your other current issues. Were your wipers/blower operating at normal speed? Brighter/dimmer than normal lights?

Bad battery(ies)
Alternator/voltage regulator
Ground(s)
Short circuit
Corroded connector(s)
PCM

[seth_95]

Well my wipers were not on but my blower was on low and it seemed to be a normal speed of sound to me. In the morning when I start mt truck the speedo moves off 0 and if i give it throttle it moves up to 5. Doesnt do this when it is warm. Could this be a cluster situtation?

[DmaxMaverick]

Could be a cluster, but more likely a poor ground. Some speedo isn't really abnormal, but too much (like 1/4 over full on the gage) can indicate a problem. With that in mind, don't overlook the ign. switch. A poor contact there can cause all kinds of problems, like leaving you on the roadside. If you haven't gone through all the grounds on the truck, you should anyway, whether it's the cause or not. These animals are very sensitive to electrical continuity and clean juice. If you find yourself going through a lot of PMD/FSD's, LP's, OPS, wiper/blower motors, light bulbs, etc, you likely have dirty or inconsistent power.

[6.5 Detroit Diesel]

Just another confirmation. My '93 will fill up to about one section past full again. Also, when I push the throttle to the floor and it is below half tank it will rise slightly. When I hit the brakes, it drops down a substantial amount.
I seem to remember something about GM not having a baffle system in their tanks or if it is there, it's not very good. My 81' Firebird had the same problem with the gas gauge moving around under acceleration and braking.:cool:

[seth_95]

so what grounds should I be checking?

[seth_95]

also if you look at my other thread, my 6.5 left me stranded. Take a look and let me know, post if you have any ideads on that thread.

[DmaxMaverick]

Grounds?? All of them. Battery, intake manifold, body, frame, etc, etc.

I was refering to the other thread in my above post. You have too many issues at once to call it coincidence.

[damork]

Crawl under your truck and examine the grounds on the frame near the fuel tank. I had the symptoms you describe and after cleaning up a ground from the wiring harness to the frame by the fuel tank crossmember the problem was solved. If that is giving you problems, track down the rest - especially the grounds attached to the passenger head bolt - both where they connect to the engine, body, and frame, as well cleaning up battery connections.