Point me in the right direction (guage problems)

[FarmerFrank]

OK fellas, long time listener, First time caller.

I have an 88' 7.3 CC long bed in my sig with 190k that i purchased back in July from a negectant owner. I drove it home from Harrisburgh (150 miles) and tore it apart and just today got it back on the road but it still has a few minnor issues i was hoping to be pointed in the right direction with.

The fuel guage does not work on both tanks (switch ? selector? dash? both sending units?) the ampmeter does not work, the tach does not work, and the speedo seems jumpy. i did not see any kinks in the cable. i have done zero troubleshooting on any of these issues.

Since i bought it i replace the pump and injectors with a used lower miles set (did not start hot). got the transmission rebuilt (still have spongy shifts). all new Dynomax exhaust system, new champion radiator and water pump, new shocks, patched rusty doors, replaced tires, window motors. good thing it was cheap.

i was never a diesel pick-up guy untill i bought my 86 with all intentions of parting it out and scrapping the rest, but then i fell in love with the simplicity, rugged, rusty, cheap oil burning heap that it is.

 

[franklin2]

On the fuel gauge. 99% of the time the sending unit is bad in the tank. But to make sure, switch it to the front tank(it's the one easiest to get to) and get under the truck and take the wires off the sending unit on the front tank. You should be able to stick your head up beside the driveshaft and get to it.

Once you get the plug off, turn the key to run but do not start the engine, and while someone is watching the fuel gauge, take a piece of wire that is hooked to a good ground, and touch it to the darkblue/yellow wire. The gauge should swing full scale empty or full(I forget which one). Then take the ground wire off and just let it hang open, and the fuel gauge should swing full scale the opposite direction. If it passes this test, then the wiring, the switching valve(which has the job of switching the sending wires) and the fuel gauge are good, and the sending unit is bad.

On your tach, check the sensor and the wires going to it. It's mounted up high on the rounded guard on front of the engine, near where the oil spout is. It reads the teeth on the gear under the guard.

 

[FarmerFrank]

Right. but like i said its both tanks, maybe coincedence but i've seen stranger things. they are both currently at way past full. my bronco is the same way and ive checked the sending unit on it a few times but never cared enough to fix it since im the only driver of it.

 

[The Warden]

FWIW "way past full" is where fuel gauges on a bricknose or OBS truck will sit if the sending unit's bad. The sending units should be 22.5 ohms at empty, and 145 ohms at full, so infinite resistance would peg the gauge past the "full" mark. The fuel sending units on these trucks aren't the best, so it's a very real possibility that they have both failed. At the same time, if it happened suddenly and to both at the same time, I would be looking elsewhere.

Do you get any readings from your oil pressure or water temp gauges? The gauges are glorified idiot lights, but you should still get SOMETHING.

Tach sensor failures aren't uncommon; you'll do well to get a new one and see if that helps things.

I have a jumpy speedo on my '84...it bounces around up to 35 mph, then smooths out. I'm pretty sure it's in the gauge itself; my cable's in great shape. You could swap gauges (and have a different odometer reading), or if it's not too bad, it might be easier to just live with it.

Welcome aboard

 

[FarmerFrank]

I suppose its possible that both are bad. Hard to say with no troubleshooting done. and yes the only two that work, not that they are wonderful, are my oil pressure and water temp. it will be getting manual of both. the Speedo seems to get jumpy around 55-65 but ill probably just live with that one. i just hate seeing dead guages in my dash, sends off all the wrong message in my head when i glance down if you know what i mean

 

[The Warden]

I hear you I was mainly asking about the oil pressure and water temp gauges to make sure that your entire cluster wasn't dead...which could indicate that the plug on the back of the cluster is messed up. I would still recommend pulling the plug and checking the terminals, just to be safe, but it's probably safe to rule that out...

 

[laserjock]

This screams electrical problem to me. If high resistance is full, I'd guess broken wire or something not plugged in?? Can't be coincidence all these problems happened at once can it?


Sent from my iPhone using Tapatalk - now Free

 

[bbjordan]

Ain't love grand

but then i fell in love with the simplicity, rugged, rusty, cheap oil burning heap that it is.

Ain't love grand? I know how it is...

 

[The Warden]

This screams electrical problem to me. If high resistance is full, I'd guess broken wire or something not plugged in?? Can't be coincidence all these problems happened at once can it?

I don't think the problems all happened at once...the impression I get is that he got the truck with these issues, plus a bunch of more major issues, and now that the major problems are taken care of, he's getting to the nit-picky stuff.

If the fuel gauge stopped reading for both gauges at exactly the same time, I'd agree with you...something got unplugged, the fuse for the fuel switchover valve failed, or the switchover valve itself failed...but, at least to me, it doesn't sound like that's what happened. At the same time, it would be worth checking the fuse, then switch the fuel from one tank to the other with the engine not running so you can hear the valve moving...

 

[typ4]

Check the fuse box for loose fuses, ign switch and ground wires, my 88 is doing this exact thing and it is a combination of the ign switch and a loose blade fuse socket.

 

[FarmerFrank]

You guys are amazing. anywhooo.
Yes i bought it like this and exactly what The Warden said, now that its running again im trying sort out the small stuff.
Now that you mention it the key switch is messed up, you turn it the whole way then hit a push buttion to jump the solenoid. it has the tilt wheel with a good tilting mechanicism but a bad switch and i have anouther tilt with a bad tilt mechanism and a good switch, just havent gotten to that project of making 2 into 1yet. i wouldnt mind putting a straight coloum in it but i dont want to loose my cruise controll that somehow still works! Hard to tell when ill get a chance to rip into it again, harvest season puts my trucks on the back burner.

Also after the wait to start light goes off the glow plug soleniod keeps clicking rappidly. i know all the plus are good and it fires right up after the light goes off but that soleiod just keeps ticking for 30 seconds or more. ill probably just put a momentary switch in it like i did on the 86 but it still makes me currious.

 

[FarmerFrank]

oh and i know the fuel selctor valve and switch is in working order becuase i ran the rear tank out of fuel on the way home with it and it switched to the front tank with no troubles

 

[typ4]

The gp solenoid is working fine , that after clicking is normal.

 

[FarmerFrank]

Thank you, didnt want to fry another set

 

[FarmerFrank]

Just in case anyone cares i finally tore the dash apart and here is what i found.
Both sending units are bad, guage and wiring are fine.
The volt gauge gets suck down below 8 volts and statys there until you bump it, wiring is fine.
The tach was tricky but where it mounts in the dash cluster there are 4 little prongs that were not making contact. i took it out, re-bent the tabs and it works fine now.
I was really hoping for a loose plug or ground somewhere but maybe next time.