gas gage not reading correct

[Perry C]

okay I've pulled the bed where I can get to the sending units. If I unplug the connection to the selector valve the gage goes to full if I ground the main sending unit wire it goes to empty. I also checked when I press and hold the tank selector switch the correct wire gets 12 volts. so I plugged the selector vale back up selected the left tank I also pulled the sender out of the left tank cleaned connections. If i unplug the sender the gage goes full if I ground it , it goes empty. If I raise the float to what should be full I only get almost half a tank. I tried checking the ohms on the sender , float all the way down 0. all the way up I get about 91.3 I have my meter set on 200 not 200k my meter goes 200, 2k, 20k, 200k 2m 20m Which should I have it set on to check it?
Thanks

 

[philjafo]

0 to 90 ohms is what the sender is supposed to read IIRC. Female spade terminals are really hard to get clean, just replace them. Maybe there's a poor connection somewhere else, like at the guage.

 

[89Suburban]

I found out tonight that when I hit an eighth of a tank in Silvy I run out of gas.

 

[Perry C]

well I bought a new sender and still 3/8 of a tank is as good as it gets. I the main pink wire and plugged the new sending unit up eliminating the other sending unit still all I get is 3/8 of a tank on full. I unplug it gage goes to full ground it and it goes to empty. Could it still be the gage in the dash?
Help!

 

[89Suburban]

See if any of these troubleshooting helps:


http://www.gmsquarebody.com/forum/showthread.php?p=152865&highlight=fuel#post152865

 

[89Suburban]

More:

http://www.gmsquarebody.com/forum/showthread.php?p=97197&highlight=fuel#post97197

 

[HotRodPC]

I found out tonight that when I hit an eighth of a tank in Silvy I run out of gas.

Is there by any chance and dent in the tank? The pick up is prolly lifted in the tank, OR the bottom potion of the sock is very dirty and can't suck enough fuel pressure thru it. Prolly need to drop the tank for inspection. And while you have the tank down, be prepared to clean the underbody behind the tank and treat it with rust prevention before you put the tank back up.

 

[89Suburban]

Is there by any chance and dent in the tank? The pick up is prolly lifted in the tank, OR the bottom potion of the sock is very dirty and can't suck enough fuel pressure thru it. Prolly need to drop the tank for inspection. And while you have the tank down, be prepared to clean the underbody behind the tank and treat it with rust prevention before you put the tank back up.

Tank looks unmolested and no dents. I was on a steep hill facing forward at a light, when I hit the gas it shut off. Once the truck leveled out I stopped and turned the key on to let it prime back up and it fired up fine but I know when that gauge gets close to an 1/8 tank it's time for gas. I'll be pulling the tank out of the '89 and cleaning it and POR15 it and install it in the '90 at some point later on. Remember that has a brand new sending unit and pump in it.

Also in that process I am going to make the measurements and do a write up on making a thru floor pan access door for the Burb sending units with measurements etc.

 

[HotRodPC]

Also in that process I am going to make the measurements and do a write up on making a thru floor pan access door for the Burb sending units with measurements etc.

That would be cool. Maybe we can get someone to do this on the long and shortbed pick ups and Blazer too and put all these access panel maps in one thread. Sure makes it alot easier for fuel pump and sender replacement.

 

[smurph20]

Long bed 20 gallon tank senders are right in the break of the cab and bed cant cut a door for them youd be cutting the front panel of the bed not the floor.

 

[Perry C]

problem solved

Well I took the gage out of the dash. Went to pull a part bought 2 gages one out of a half ton truck and one out of a suburban. tried the one out of a truck and it read fine and the one out of the surban read fine also. I could move the float level and watch the needle move. swap tanks and it registered on the gage also. Just wish I had of checked the gage before pulling the bed and dropping the tank. But you could unplug the sending unit and the gage go full ground the gage wire and it go empty.

 

[89Suburban]

Well I took the gage out of the dash. Went to pull a part bought 2 gages one out of a half ton truck and one out of a suburban. tried the one out of a truck and it read fine and the one out of the surban read fine also. I could move the float level and watch the needle move. swap tanks and it registered on the gage also. Just wish I had of checked the gage before pulling the bed and dropping the tank. But you could unplug the sending unit and the gage go full ground the gage wire and it go empty.

Hey man, it's great you fixed it and reported back. And although you did a lot of extra work you still went over other parts of the system and learned new things looking under the bed and that mental picture stays in your mind in the future when something else goes wrong you know what the stuff looks like.

 

[HotRodPC]

Well I took the gage out of the dash. Went to pull a part bought 2 gages one out of a half ton truck and one out of a suburban. tried the one out of a truck and it read fine and the one out of the surban read fine also. I could move the float level and watch the needle move. swap tanks and it registered on the gage also. Just wish I had of checked the gage before pulling the bed and dropping the tank. But you could unplug the sending unit and the gage go full ground the gage wire and it go empty.

Good news. So it's considered accurate enough to trust now???

I wouldn't be to upset about the dropping the tank and all that work. Normally, that is where you start and find the problem. The only clue you really had that it was the gauge was that both tanks were reading wrong, and that could have even been in the switch. And weird things happen. Like my back up lights on my 84 not working. Come to find out, it was both bulbs burned out. They work just fine. That's what happens when things go wrong 1 at a time, and people don't fix them.

 

[chengny]

I tried checking the ohms on the sender , float all the way down 0. all the way up I get about 91.3

Do this same test, but this time check the resistance value after the signal has passed through the Pollak valve.

There are two circuits in a 6-port valve.

One is a reversible power power supply - to change the valve position.

And the other is a switch - to change which gauge level is sensed. The switch is mounted on the shaft of the valve plug and the contacts move along with the shaft.

Although it appears that the valve plug is operating properly, there may be a problem with the tank level swich.

Two pink leads come into the valve (one for each tank) but there is only one stab connector on the outlet side.

Pull the lead that heads up to the dash from the body of the valve. Manually stroke the sensing linkage and check the resistance at the connection you just pulled - the one that leads to the dash gauge.

If you get a nice variable 0-90 ohm resistance out of the sender mounted on the tank, but different reading when measured at the "downstream" side of the valve - there is an internal problem with the valve.

If it looks good at that point, plug the wire back on. There is another plug connector at the engine side of the firewall. Break that open and check the resistence again at that point. If the readings are screwy there - there is a ground in the pink wire somwhere between the firewall and the Pollak valve.

You must be registered for see images attach

You got it - good. Disregard this post.

I'll leave it up in case anyone in the future is trouble shooting a Pollak valve for improper tank level indication.

 

[chambo83]

My 87 at a full tank only shows about 1/4. I'm thinking of pulling the bed to check everything. Let me kno if the sending unit is ur problem