Help with fuel guage problems

[75k20]

i’ve been having problems with my fuel guage for a while now and im not sure if i have it figured out yet.

with the intellitronix electric guage set i have, i made sure to set the switches to the 0-90ohm setting even though they previously were set differently. The right hand side tank seems like it’s always stuck on empty and the left hand side reads full.

i found old receipts saying that a shop said the fuel guage wasn’t working because the fuel level sender in tank was bad. they replaced only one sending unit with part number “DOR-692-079” i looked it up and it came up as the driver side mounted sending unit.

would i only need to replace the passenger in-tank sending unit to get my gauges working again? any help is appreciated, not knowing how much fuel i have drives me crazy. especially with 6mpg..

 

[SirRobyn0]

i’ve been having problems with my fuel guage for a while now and im not sure if i have it figured out yet.

with the intellitronix electric guage set i have, i made sure to set the switches to the 0-90ohm setting even though they previously were set differently. The right hand side tank seems like it’s always stuck on empty and the left hand side reads full.

i found old receipts saying that a shop said the fuel guage wasn’t working because the fuel level sender in tank was bad. they replaced only one sending unit with part number “DOR-692-079” i looked it up and it came up as the driver side mounted sending unit.

would i only need to replace the passenger in-tank sending unit to get my gauges working again? any help is appreciated, not knowing how much fuel i have drives me crazy. especially with 6mpg..

I cannot help you with the intellitronix part of it, but. I'll give you these clues which hopefully will help.

#1. The right side sending units have gotten harder to find in the last few years, they need to be ordered and often cost more. It is not uncommon for guys (and shops) to put a left side sending unit in the right tank. The only difference is the orientation of the fuel outlets which can be compensated for with slightly longer rubber hoses. It's not bad or wrong to do that and my truck has had a left sending unit in the right tank for years. So I would not rely on the part number alone to know which one has been changed.

#2. If one of the two tanks reads accurately, then suspect the other sending unit. If both tanks read false reading, whether it's the same reading or two totally different readings tank to tank then suspect the switch. Depending on the year of the truck and whether or not changes have been made to the switching unit, the gas gauge reading maybe be switched by the actually switch on the dash or the switching valve under the truck. If there is one wire leading to the switching valve then it's handled by the dash switch, if there are a bunch of wires going to the switching valve then the switching valve handles it.

 

[Dmack]

The general rule is if it reads below empty (9 oclock) the unit is grounded out. If it reads last full (3 oclock), it is an open circuit.

 

[75k20]

I cannot help you with the intellitronix part of it, but. I'll give you these clues which hopefully will help.

#1. The right side sending units have gotten harder to find in the last few years, they need to be ordered and often cost more. It is not uncommon for guys (and shops) to put a left side sending unit in the right tank. The only difference is the orientation of the fuel outlets which can be compensated for with slightly longer rubber hoses. It's not bad or wrong to do that and my truck has had a left sending unit in the right tank for years. So I would not rely on the part number alone to know which one has been changed.

#2. If one of the two tanks reads accurately, then suspect the other sending unit. If both tanks read false reading, whether it's the same reading or two totally different readings tank to tank then suspect the switch. Depending on the year of the truck and whether or not changes have been made to the switching unit, the gas gauge reading maybe be switched by the actually switch on the dash or the switching valve under the truck. If there is one wire leading to the switching valve then it's handled by the dash switch, if there are a bunch of wires going to the switching valve then the switching valve handles it.

are you talking about the switch inside the cab that changes the left and right tanks? or the one under the truck that actually switches the fuel? i just replaced the switch under the truck and i’m able to run it on either tank the guage just doesn’t show a correct reading.

 

[SirRobyn0]

are you talking about the switch inside the cab that changes the left and right tanks? or the one under the truck that actually switches the fuel? i just replaced the switch under the truck and i’m able to run it on either tank the guage just doesn’t show a correct reading.

Ok so the switch on the dash is the switch or tank switch. The thing under the truck is call the switching valve.

It doesn't matter if you can draw gas out of both tanks, there can still be an issue with the switch system that prevents the gas from reading correctly, even if the level changes when you change tanks.

I'll phase it differently to be clear. So if the valve under the truck has a bunch of wires running into it IDK, I think 7, at any rate more than one, then the valve under the truck handles the gauge changing. If the valve under the truck has only one wire running to it then the switch on the dash handles the gauge change.

As an additional note the valves with the 7 wires are more reliable than the single wire units were, so much so that some guys have switch systems. One thing that is good about those systems, is if the valve fails in such a way that it won't change tanks, the gauge won't change either, where as with the 1 wire system the gauge will change anyway and you won't know you have a problem until your on the side of the road. Also other differences simply made the multi-wire valves more reliable in general.

Hopefully that helps and is a little more clear, but the switch on the dash is the switch or tank switch. The thing under the truck is call the switching valve.

 

[75k20]

Ok so the switch on the dash is the switch or tank switch. The thing under the truck is call the switching valve.

It doesn't matter if you can draw gas out of both tanks, there can still be an issue with the switch system that prevents the gas from reading correctly, even if the level changes when you change tanks.

I'll phase it differently to be clear. So if the valve under the truck has a bunch of wires running into it IDK, I think 7, at any rate more than one, then the valve under the truck handles the gauge changing. If the valve under the truck has only one wire running to it then the switch on the dash handles the gauge change.

As an additional note the valves with the 7 wires are more reliable than the single wire units were, so much so that some guys have switch systems. One thing that is good about those systems, is if the valve fails in such a way that it won't change tanks, the gauge won't change either, where as with the 1 wire system the gauge will change anyway and you won't know you have a problem until your on the side of the road. Also other differences simply made the multi-wire valves more reliable in general.

Hopefully that helps and is a little more clear, but the switch on the dash is the switch or tank switch. The thing under the truck is call the switching valve.

got it. i have the one wire switching valve so i’m suppose that i can replace the switch in the cab and see what happens.

 

[AuroraGirl]

got it. i have the one wire switching valve so i’m suppose that i can replace the switch in the cab and see what happens.

Find the wire running from the senders to your switch
What are they both doing

 

[SirRobyn0]

got it. i have the one wire switching valve so i’m suppose that i can replace the switch in the cab and see what happens.

Well before you spend money on a switch and wait for it to arrive you could get in there and test. What I would do is to look at a wiring diagram and see what color the wires are for each tanks sending unit and the gauge. You can simply jump those terminals on the switch and see if the gauge reads accurately.

It'll take you all of about 10 minutes to do that and find out if that is the problem. You can find a wiring diagram for your truck by following this link. p://forum.73-87chevytrucks.com/smforum/index.php?topic=11766.0

If you find that the switch is bad you really should consider converting to the multiple wire valve under the tank. It's a fair bit of work to convert it over but in the long run will be more reliable.

 

[75k20]

Well before you spend money on a switch and wait for it to arrive you could get in there and test. What I would do is to look at a wiring diagram and see what color the wires are for each tanks sending unit and the gauge. You can simply jump those terminals on the switch and see if the gauge reads accurately.

It'll take you all of about 10 minutes to do that and find out if that is the problem. You can find a wiring diagram for your truck by following this link. p://forum.73-87chevytrucks.com/smforum/index.php?topic=11766.0

If you find that the switch is bad you really should consider converting to the multiple wire valve under the tank. It's a fair bit of work to convert it over but in the long run will be more reliable.

forgive me but i’m new to a lot of this stuff. could you walk me through how i would jump the terminals on the switch? writing drives me crazy

 

[SirRobyn0]

forgive me but i’m new to a lot of this stuff. could you walk me through how i would jump the terminals on the switch? writing drives me crazy

Ok, so you'll take the gauge wire that goes from the switch to the fuel gauge and jump it with one of the sending unit wires, and try it for both tanks noting if either or both of them seem to read accurately that way. That would be done using the wires on the connector for the tank selector switch on the dash. IDK which wires. You'll need to know the color of those wires which will be in the diagram link I posted. I'm sorry but I don't have the time to pick though the diagram to see what wire does what and write the colors down for out for you. Other than being tedious to look at those diagrams I'll bet you can find that info ok.

Someone that knows off hand the wiring color might come in as say too.

 

[75k20]

Ok, so you'll take the gauge wire that goes from the switch to the fuel gauge and jump it with one of the sending unit wires, and try it for both tanks noting if either or both of them seem to read accurately that way. That would be done using the wires on the connector for the tank selector switch on the dash. IDK which wires. You'll need to know the color of those wires which will be in the diagram link I posted. I'm sorry but I don't have the time to pick though the diagram to see what wire does what and write the colors down for out for you. Other than being tedious to look at those diagrams I'll bet you can find that info ok.

Someone that knows off hand the wiring color might come in as say too.

i believe i have it figured out. i’ll try to attach the photo. if i have it correct i take the “18TAN-30A” wire and wire it to “18TAN-30C” and see if the guage changes. and then also attach 30A to 18LT BLU-30B” and see what the guage reads?

 

[SirRobyn0]

i believe i have it figured out. i’ll try to attach the photo. if i have it correct i take the “18TAN-30A” wire and wire it to “18TAN-30C” and see if the guage changes. and then also attach 30A to 18LT BLU-30B” and see what the guage reads?

Yes, but to be clear you want to swap circuit 30C & 30B not attach the two to 30A at the same time.

 

[75k20]

Yes, but to be clear you want to swap circuit 30C & 30B not attach the two to 30A at the same time.

got it, i appreciate all the help. i can’t work on the truck right now because i lost my keys so i’m waiting for a new ignition switch before i can do anything. once i do i’ll post the results

 

[AuroraGirl]

got it, i appreciate all the help. i can’t work on the truck right now because i lost my keys so i’m waiting for a new ignition switch before i can do anything. once i do i’ll post the results

if it wasnt easy enough to just do a new cylinder, id say it would be better to get a new key even from a locksmith but that point you would pay more in labor than the cost and nice function of a new cylinder

 

[75k20]

Yes, but to be clear you want to swap circuit 30C & 30B not attach the two to 30A at the same time.

so i pulled the switch out of the harness and tested the wiring harness by jumping it. While it was unplugged the guage went to full im guessing because the circuit was open. when i tested them it seemed like it would show the correct guage reading only sometimes and other times it would get pegged to zero. do you think the switch is what needs to be replaced?