Fuel Sending Unit Fix

[3500GMC]

Here's the typical 'dead' sending unit. The fuel gauge swings all the way past the full mark. Common problem. Open circuit. The fuel level sensor is just a potentiometer, or a variable resistor, if you will. Your fuel gauge in the dash is basically an ohm-meter.

A fix of sorts is to get the contact radius of the 'arm' more to the inside of the contacts. The missing contacts can be seen in the photos.

Another fix is to buy a new sending unit if you are not adventurous. (or crazy)

The '93 has been nickel-diming me to the poor house lately and I just ran across this sketchy sending unit. It did work but when the tank got to around 1/4 full, the gauge went bonkers. Typically the gauge will swing past full and stay there if any part of the sending unit electrics becomes faulty. So the 'fix' may last a week, or it could last another 10 years...

You will need to drill out the two aluminum rivets. (#8 x 1/2 screws and locknuts will re-attach it perfectly). Then gently pry apart the hooks that hold the arm in. Get some looping pliers to tweak the arm. Small needle nose would work too. Easy does it. You can see the new shape of the arm now in the photos. Stretch out the little spring under the arm a little bit before assembly. Stretch it about an 1/8" longer free standing. Snap the arm with spring back into the housing. Re-attach the float. Bolt it to the bracket and you're done.

You can test your work by plugging in the sending unit with a ground outside the tank, switch the IGN key on, and slowly move the float.

 

[bison]

I fiddled with these FFen things before, I don't think its worth it,often the windings are worn so thin from the contact sliding over it that a week later you got to drop the tank again if it gives up the ghost a second time cause the winding broke.

Yours looks in good shape though.

 

[Burning oil]

I fiddled with these FFen things before, I don't think its worth it,often the windings are worn so thin from the contact sliding over it that a week later you got to drop the tank again if it gives up the ghost a second time cause the winding broke.

Yours looks in good shape though.

x2 been there to many times. I got tired of buying fsu's and or tring to repair them, so came up with the Metrum Rod FSU. Another big problem is the stock fsu's are exposed to the fuel. I have had a heavy tarnish almost like wax build up on the assembly.
In the pictures yours looks brand new. Completing your write up could buy some time though.

 

[jrsavoie]

Tell me more about this Metrum Rod FSU.

I was just about to order a new AC Delco or aftermarket when I found a referance to pmdcable.com on another forum.

 

[WarWagon]

Even ULSD has sulfur in it. Gasoline is just as dirty and both fuels attack the electric parts they are exposed to. It is said the sulfur builds up on the units and causes trouble. The sliding contacts for the resister are not as much trouble as the pivot contact. Concentrate your efforts on this and not the delicate resistor coils. Clean the while thing, of course, with brake cleaner or MAF sensor cleaner. Corrosion and arcing messed one sender of mine up in 85K and 2 years from brand new truck. I had to take it apart to clean the pivot point (bearing?) contacts out to get it to work again.

The 'knock off' tank sock pictured is missing the bypass valve and will stall out your engine when it starts to plug. I know this because I had to drop the Fing tank to remove it after crawling home with idle power only on the 93. This sock actually caused my lift pump to loose prime more than once!

I replace the units after not having much luck with them cleaned or new. I look for other more reliable technology than this 'cheap' model "T" technology... Like capacitive fuel sensing units for a jet boat or the FSU that Leroy sells using even different technology. The big difference with the new technology is the fuel doesn't touch the electronics.

The Metrum Rod FSU replaces the factory float and resister with a metal rod. So toss the sock, check the lines for rust and reuse the factory fuel pickup assembly with some modifications if it is rust free. The last 'hose the tank out' bugs in fuel slime problem I had would have ruined the factory float sender again. The Metrum Rod survived and was still working reading the slime level... The last time I dropped the tank the factory sensor gauge was reading 1/4, sock would not let any fuel through, and we took a bath from a full tank when we dropped it. Yeah thought it was near empty. (Note to self stick a hose in it and see what is left next time as the sock could be plugged solid.)

 

[crow]

Hey, thanks for the info! I have a 1994 Chevy c1500 v6 4.3L and after fulling it to the max, the needle got stock on the full position. I think I will use your info and mess with it.

Crow

 

[3500GMC]

Problem areas for sending unit access:

The two 'clip nuts' (dealer item) will usually break and spin where the tank strap bolts fasten. Total PITA.

Removal of the bed is all fine and dandy until you break off bed bolts or Spin the nuts in the cross braces too. Total PITA.

Dropping the tank bed on is doable but if you can drain the fuel and Con a friend into helping, things may.. MAY go smoother.

Slide the tank out towards the pass. side. The straps will get in your way otherwise.

Get all the rust and dirt off the FSU lock ring before you crack the seal- Be careful here.

 

[nealpellecchia]

I fiddled with these FFen things before, I don't think its worth it,often the windings are worn so thin from the contact sliding over it that a week later you got to drop the tank again if it gives up the ghost a second time cause the winding broke.

Yours looks in good shape though.

When the sock is clogged does it run through the bi-pass valve? picture anybody?

 

[dangerousdave]

I have to do this little job soon. The fsu is just starting to go flaky occaisionally.

 

[NVW]

When the sock is clogged does it run through the bi-pass valve? picture anybody?

On the diesel sock there is a small bypass that should allow fuel to flow.

 

[nealpellecchia]

On the diesel sock there is a small bypass that should allow fuel to flow.

What causes the increase in suction?

 

[NVW]

What causes the increase in suction?

When the sock is plugged the LP pulls a vacuum. The picture is blurry but this is the sock.

 

[nealpellecchia]

When the sock is plugged the LP pulls a vacuum. The picture is blurry but this is the sock.

so that little nub does the work of that big tube? vacume effects the tank more because it can't get enough out of the big tube and fuel?

 

[NVW]

I can't remember but the little nub goes into the pick up line. I don't even remember seeing that until I saw this pic. IIRC the bypass is near my thumb.

 

[NVW]

OK, this is a better pic of where the sock joins the pick up line. The first pic is deceiving.

 

[nealpellecchia]

OK, this is a better pic of where the sock joins the pick up line. The first pic is deceiving.

it's a part of the sock then. needs more gas in the tank cause it's on the top side only ? I'm having trouble syphoning the fuel out so I can drop the tank.

 

[NVW]

The sock is on the bottom of the pick up tube, it sits horizontal in the tank.

 

[nealpellecchia]

The sock is on the bottom of the pick up tube, it sits horizontal in the tank.

thanks. back to my starter troubles. the rebuilt solenoid finally failed. remote starter switch had been giving xtra voltage but ... Then One final screwdriver attempt worked. But I had to cross the B to the S terminal with the screwdriver tip touching the end of the stud to get cranking. It couldn't be that dirty a new terminal but maybe. New solenoid cap...contacts,,,new washer. Do the washers rotate around to use it equally on all spots?
Ridiculous continual problem.

 

[bison]

The washer seems to rotate judged by the burnmarks around on the ones i have taken apart but the stud contacts don't have that option and if the contact area is worn/burnt uneven then all one get is exessive sparking/burning and overheating and not enough juice makes it to the brushes.

 

[nealpellecchia]

The washer seems to rotate judged by the burnmarks around on the ones i have taken apart but the stud contacts don't have that option and if the contact area is worn/burnt uneven then all one get is exessive sparking/burning and overheating and not enough juice makes it to the brushes.

and all this happens in a year or much less! the dealer washer that I saw was silver in color. the new ones are copper "the cheap" ones. what to do?

fuel problem has gone into remission. even low on fuel truck has run perfectly with no cap...no bubbles in clear line I left on top. Parts store clear line. cap / tank will build up pressure just sitting overnight with no use since shut down on a cold day!!! I tighten cap next morning to keep thieves/ vandals out. I should install clear line piece before fuel mgr. and before lift pump. Then I'll know...