Fuel sending unit does not work in 72 - Chevelle Tech
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  #1  
Old Mar 8th, 10, 11:40 AM
jerryjayssr jerryjayssr is offline
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JJ
 
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Default Fuel sending unit does not work in 72

I had someone put a new fuel sending unit in my 4 door (350) 1972 and it does not work. He checked the gauge and worked fine. The older one only worked below 1/4 tank and the one does not work at all. I spent $100 to put it in for it not to work. I wish i would have left the older one atleast that worked below 1/4 tank.
Any solutions?? The box said 1972 chevelle. The guy got it from Ground Up and we thought it was the right one?

My guess it wasnt though. Any way to get this one working?
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  #2  
Old Mar 8th, 10, 12:00 PM
GenPac GenPac is offline
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Default Re: Fuel sending unit does not work in 72

Does the gauge read full or empty?
Did you verify the sending unit worked with a DMM before installing?
Is the ground lead secured to a metal on metal body contact?

There is something to be said about DIY...
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Being politically correct is kinda like trying to pick up a turd by the clean end.
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  #3  
Old Mar 8th, 10, 12:19 PM
jerryjayssr jerryjayssr is offline
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Default Re: Fuel sending unit does not work in 72

The gage reads about alittle lower than 1/4 tank now. Not sure if it will work. I have yet to use all the gas in it.

I am waiting for an email back from the guy who checked it. But I know he definetly checked the gauge and he explained how it worked and that it read perfect when checked. I am not sure if he checked the sending unit, we assumed it was the right one and worked since it was new.

I do know the unit cost $45. Some other guy ordered it. The guy I got the car from. I remember looking in the cataloge and it said for 72 but I cant remember the model number. Is there anyway I can find it by looking under the car or do I need to pull the tank.

I'll get more details about the unit when he gets back to me. I was not there when he put it in. And I just emailed him a couple of questions.
Can I check the ground now??


Quote:
Originally Posted by GenPac View Post
Does the gauge read full or empty?
Did you verify the sending unit worked with a DMM before installing?
Is the ground lead secured to a metal on metal body contact?

There is something to be said about DIY...
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  #4  
Old Mar 8th, 10, 1:44 PM
GenPac GenPac is offline
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Default Re: Fuel sending unit does not work in 72

The sending unit should be grounded just behind the axle, on the bracket that is attached to the floor pan and has the driver's side fuel tank strap mounting boss on it.
Ensure there is a clean electrical connection there.
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'69 SS396 -Build Thread A mishmash of American made suspension components and Australian brakes.

Quote:
Originally Posted by Busted Knuckles View Post
Being politically correct is kinda like trying to pick up a turd by the clean end.
Lurking around again after a long hiatus...
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  #5  
Old Mar 8th, 10, 1:58 PM
GenPac GenPac is offline
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Default Re: Fuel sending unit does not work in 72

There should be a connector just behind the rear bumper that is the lead from the sending unit to the gauge up front. Take an ohmmeter and ground one end to the frame and the other lead to the wire coming from the tank. Take a reading. If possible, have someone bounce the fuel around and see where the unit reads. It should read between 1-90 ohms. A little over 110ish is OK on a full tank, if you show infinate resistance or 0 resistance, your sender is shot.
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'69 SS396 -Build Thread A mishmash of American made suspension components and Australian brakes.

Quote:
Originally Posted by Busted Knuckles View Post
Being politically correct is kinda like trying to pick up a turd by the clean end.
Lurking around again after a long hiatus...
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  #6  
Old Mar 9th, 10, 9:39 PM
jerryjayssr jerryjayssr is offline
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Default Re: Fuel sending unit does not work in 72

I'll check out the unit tomorrow then, I just found out that the original one had one line and the new one had 2.

I'll also reconnect the old one and see what that one reads.

My guess is the old one was bad, the new one was the wrong one since it had 2 lines and I dont have a return line. The guy was hoping they would have the same impedence. He did test the gauge and said that was good. He also said If I get the right unit, also get the extra wire.

I'll look into that too.
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  #7  
Old Mar 10th, 10, 1:16 AM
Geo71 Geo71 is offline
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Default Re: Fuel sending unit does not work in 72

I just got done replacing the one in my 71 (it was also a single line ordered it at the local NAPA)....guage was stuck on full when I bought the car. It's not that bad dropping the tank to get to it....and I found the build sheet while doing it!
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  #8  
Old Mar 10th, 10, 8:58 PM
jerryjayssr jerryjayssr is offline
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Default Re: Fuel sending unit does not work in 72

The old sensor just checked out at 50 to 150 ohms. Too dark now to check the new one that was just installed.

The fuel gage is the only gauge I have the rest are the idiot lights,
So the sensor should read 0-100 ohms then??



Quote:
Originally Posted by Geo71 View Post
I just got done replacing the one in my 71 (it was also a single line ordered it at the local NAPA)....guage was stuck on full when I bought the car. It's not that bad dropping the tank to get to it....and I found the build sheet while doing it!
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  #9  
Old Mar 10th, 10, 9:09 PM
Coppertop Coppertop is offline
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Default Re: Fuel sending unit does not work in 72

I think you guys are making this more difficult than it has to be....

The very basics on troubleshooting.

Flip down the rear license plate/gas filler door. Looks towards the driver's side. You should see a tan wire, there is a rubber "boot" that splits the wire between the sending unit on top of the tank, and the rear harness in the trunk.

Pull the boot apart. Now stick a piece of wire in the end that lead up into the trunk. Touch the other end of your test wire to a GOOD CLEAN METAL GROUND.

Have an assistant in the car turn the key to "ON". The gauge should go to "E".

Now have them watch the gauge as you disconnect the wire. The needle should quickly move to way past "F".

If it does this, the gauge is GOOD and the related wiring in the car is good.

At this point you must check the sender's black ground wire that is held in with a sheet metal screw to the trunk pan support brace roughly above the differential on the driver's side.

If that looks good, looks like it's tank-dropping time.

IMHO, you need a better service tech/mechanic if you are not going to work on your own car. Someone that just orders what they can get (even though it's wrong), is not someone you really want to deal with. (IE buying a sender with the wrong # of fuel connections).
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  #10  
Old Mar 10th, 10, 9:39 PM
tristatechevelle tristatechevelle is offline
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Default Re: Fuel sending unit does not work in 72

Yep.. what he says.
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  #11  
Old Mar 12th, 10, 11:54 AM
jerryjayssr jerryjayssr is offline
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Default Re: Fuel sending unit does not work in 72

just checked it.

Gauge reads full when disconnected

Empty when shorted

Right now the sender reads 1 ohm and tank is almost empty, gauge reads zero.
Last week tank read 1/8 tank when full. So it must be the new sender is wrong (had a return line).

I will check impedence of sensor when I fill tank today.
Old sensor read 50 to 150 ohms when out . checked that one


Quote:
Originally Posted by Coppertop View Post
I think you guys are making this more difficult than it has to be....

The very basics on troubleshooting.

Flip down the rear license plate/gas filler door. Looks towards the driver's side. You should see a tan wire, there is a rubber "boot" that splits the wire between the sending unit on top of the tank, and the rear harness in the trunk.

Pull the boot apart. Now stick a piece of wire in the end that lead up into the trunk. Touch the other end of your test wire to a GOOD CLEAN METAL GROUND.

Have an assistant in the car turn the key to "ON". The gauge should go to "E".

Now have them watch the gauge as you disconnect the wire. The needle should quickly move to way past "F".

If it does this, the gauge is GOOD and the related wiring in the car is good.

At this point you must check the sender's black ground wire that is held in with a sheet metal screw to the trunk pan support brace roughly above the differential on the driver's side.

If that looks good, looks like it's tank-dropping time.

IMHO, you need a better service tech/mechanic if you are not going to work on your own car. Someone that just orders what they can get (even though it's wrong), is not someone you really want to deal with. (IE buying a sender with the wrong # of fuel connections).
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  #12  
Old Mar 12th, 10, 1:18 PM
redrocket1953 redrocket1953 is offline
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Default Re: Fuel sending unit does not work in 72

I had this problem in my 70SS. I put 3 new ones in before I got one that worked. The problem was the float wouldn't float in the gas once in the tank. I took the sender out and left it hooked up, raised the float up and down and had someone in the car to look at the gauge and it worked fine but the float stayed down when in the tank with the gas. Nothing was hitting or rubbing on the float arm. I sent that one back and got another one and it did the same thing. Sent it back and got one from NAPA and it works fine and it was about half the price of the OEM ones that didn't work. Good luck
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  #13  
Old Mar 14th, 10, 9:58 AM
jerryjayssr jerryjayssr is offline
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Default Re: Fuel sending unit does not work in 72

well.

According to the above directions, the gauge is good.
And I checked the sensor and it read o-100 ohms,
so according to here that is good also.

But when I connected the gauge and moved it to empty the gauge reads empty whiich is good. But when I move the sensor to full it, the gauge only reads 1/4 tank. So I am not sure which one is right.

So, the real answer is what is the gauge impedence and the and the sensor. Seems the companies selling these wont tell me???

If I knew that then that I could tell which one was bad.









Quote:
Originally Posted by redrocket1953 View Post
I had this problem in my 70SS. I put 3 new ones in before I got one that worked. The problem was the float wouldn't float in the gas once in the tank. I took the sender out and left it hooked up, raised the float up and down and had someone in the car to look at the gauge and it worked fine but the float stayed down when in the tank with the gas. Nothing was hitting or rubbing on the float arm. I sent that one back and got another one and it did the same thing. Sent it back and got one from NAPA and it works fine and it was about half the price of the OEM ones that didn't work. Good luck
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  #14  
Old Mar 14th, 10, 6:46 PM
Professor_SS Professor_SS is offline
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Default Re: Fuel sending unit does not work in 72

Quote:
Originally Posted by jerryjayssr View Post
well.

According to the above directions, the gauge is good.
And I checked the sensor and it read o-100 ohms,
so according to here that is good also.

But when I connected the gauge and moved it to empty the gauge reads empty whiich is good. But when I move the sensor to full it, the gauge only reads 1/4 tank. So I am not sure which one is right.

So, the real answer is what is the gauge impedence and the and the sensor. Seems the companies selling these wont tell me???

If I knew that then that I could tell which one was bad.
i have the same problem with mine, i even replaced the wire from the sender to the gauge and it still reads e when empty and a quarter when full. never did get it to work so i learned to live with it. it will be interesting if someone has a solution for this.
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  #15  
Old Mar 14th, 10, 7:47 PM
Bill Rose Bill Rose is offline
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Default Re: Fuel sending unit does not work in 72

I never buy the cheap repro Chinese fuel sending unit. You can get the AC sender. It cost 3 times as much, but if you don't have to keep dropping the tank to replace the piece of junk you saved a few bucks on, it's worth it.

I've restored a number of cars, and I've never had a problem with the AC sender working.

It's a very simple system. There's no reason why it shouldn't work properly.
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