ericwade381
Full Access Member
I'll give it one more try could my cluster be bad?
bad ground
- Thread starter ericwade381
- Start date
LCAM-01XA
Full Access Member
Oil pressure gauge on these trucks is random, that '88 should still have the real gauge with a real sender as opposed to just a switch that makes it read normal anywhere between 8 psi and 80 psi, but still they can be quite moody sometimes. Ours drops to nearly nothing from time to time, mechanical gauge hooked up to the same port shows now issues, sender's been replaced twice, so it's gotta be the gauge.
On the question about grounding the fuel gauge, no it does not have its own ground, instead it shares one with the temperature gauge and the electronic module that turns on the red "engine" light when either the oil pressure drops too low or the coolant temp gets too high. It also lacks its own power supply, it shares the 12V key-on again with the temp gauge and the warning module but also with the oil pressure gauge and the voltmeter. By the way the oil pressure gauge and the voltmeter ground together via separate ground wire, they share that one with the tach also. Why not ground everything together idk, but knowing the shared powers and grounds makes it easier to troubleshoot the gauges - for example if fuel and coolant temp are both acting up suspect their ground, if oil pressure and voltmeter are acting up suspect their ground, and if they're all going bananas then suspect the key-on power.
In any case it's possible the gauge seized up, wouldn't be a very common issue but these things are getting old so anything is possible. The cluster is of modular construction, the small gauges come out in vertical pairs and the speedometer and tachometer are their own units as well, so you don't need a whole new cluster - just hit a U-Pull-It yard for the block that contains the fuel and whatever gauge is right above it, it will drop right into your cluster.
On the question about grounding the fuel gauge, no it does not have its own ground, instead it shares one with the temperature gauge and the electronic module that turns on the red "engine" light when either the oil pressure drops too low or the coolant temp gets too high. It also lacks its own power supply, it shares the 12V key-on again with the temp gauge and the warning module but also with the oil pressure gauge and the voltmeter. By the way the oil pressure gauge and the voltmeter ground together via separate ground wire, they share that one with the tach also. Why not ground everything together idk, but knowing the shared powers and grounds makes it easier to troubleshoot the gauges - for example if fuel and coolant temp are both acting up suspect their ground, if oil pressure and voltmeter are acting up suspect their ground, and if they're all going bananas then suspect the key-on power.
In any case it's possible the gauge seized up, wouldn't be a very common issue but these things are getting old so anything is possible. The cluster is of modular construction, the small gauges come out in vertical pairs and the speedometer and tachometer are their own units as well, so you don't need a whole new cluster - just hit a U-Pull-It yard for the block that contains the fuel and whatever gauge is right above it, it will drop right into your cluster.
ericwade381
Full Access Member
Thanks! I'm going to go and pull a cluster today I really hope that's the issue!
idowreckin94
Registered User
help me out guys i see this is for reading empty mine reads way past full on the rear tank front tank works fine
welcome to the forum.
first posts warrant an introduction,
and then a complete read of the tech forum.
then theres an awesome new invention on this site called "search"
with that being said, check the resistance on your gauge, could be a ground problem, could be a sender issue, or operator malfunction.
good luck!
idowreckin94
Registered User
if you notice ive been on this forum since 2011 and i can normally find all my answers with the search button or tech articles but im lost on this situation but i don't mind the introduction i have a 93 f-superduty with a vulcan wrecker body with only 133k on it runs like a top looking to trade it in on a newer wrecker and want to get all the little nicknack things fixed like this
ifrythings
Full Access Member
The resistor part of your sending unit is wore out, when that happens the wiper stops contacting the resistive element and goes open circuit causing the gauge to read way past full, either find a new sending unit (good luck) or replace the resistor on your current one, you can use a gasser one for parts as long as it's after 87
idowreckin94
Registered User
thank you for the help its in a bad spot and i can't get the tank to drop without torching a bolt because i can't get to it so i guess shes sol
madpogue
Full Access Member
No reason to assume it's the sending unit itself. ANY break in the circuit to the sending unit will create infinite resistance, which shows up as the gauge ******* past full. Check the connector right at the tank, and IIRC there's also a connector where that little harness connects to the main front-to-back harness on the frame. Also check the connector at the FSV. Finally, you can measure the resistance reported by the sending unit at any of those places, provided you have a good circuit upstream.
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