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Post Info TOPIC: Fuel Gauge Issues


Poncho Master!

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Fuel Gauge Issues


We started to talk about this on another post (my 69 2+2)

You guys gave us some really good points and ideas of what to check.

A great rainy day project that I tackled today.

I ran new ground straps to the tank and the cluster.

Tested to make sure each were showing good ground.

No luck with the gauge.

Got out my voltage tester and got 5.7 volts on the lead wire from the tank.

Under the dash, I got the same on the back of the gauge.

The tank is 1/2 full.

I pulled out the cluster that Jerel sent me and rigged it up.

I connected it to ground/12 volts and the lead wire connection in the trunk.

Both gauges acted exactly the same.

013a.jpg

014a.jpg

Is it possible that the sending unit has lost ground ?

May be the sending unit after all.

I have been trying to find what the voltage would be for a full tank on that lead wire.

What would the voltage be for a full tank and what would it be for a 1/2 tank ?

All opinions welcomed biggrin

 



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Randy(Muttwood)



Poncho Master!

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If you ground the wire at to the sending unit the gas gauge should move to empty. This would eliminate any problems in the wiring to the dash and cluster.

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Canadian Poncho Superstar!

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Use an Ohm meter to check resistance between the fuel sending unit and ground.
You can do this in the trunk right by the latch receptacle as the sending unit wire comes into the trunk and joins the harness there.


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Poncho Master!

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It shows "open circuit"

Looks like I may have to pull the tank down to check the connections.

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Randy(Muttwood)



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While underneath, you should clearly see where the ground wire of the sending unit comes out and screws onto the driver side of the car. I don't specifically remember where it attaches.
A replacement sending unit is readily available, Spectra Premium FG105A.



-- Edited by seventy2plus2 on Friday 18th of June 2021 03:16:31 PM

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Can you see photos, damb can't post PDF's of complete wiring diagram, I even tried to zip it.



-- Edited by tramminc on Friday 18th of June 2021 03:47:02 PM



-- Edited by tramminc on Friday 18th of June 2021 03:47:40 PM

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Addicted!

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The following information is reprinted with the permission of Mr. Fred Aldrich, a.k.a. The Chevelle Engineer. Data presented are the same from his popular website with only minor changes to spelling and overall format. Mr. Aldrich passed away in 2011 and graciously allowed me to use some information from this website before his passing.

This process can be applied to all recent GM cars except those with computerized gauges.

1) Locate the fuel sender feed wire near the fuel tank. You're looking for a single tan colored wire. With the tan wire disconnected at the fuel tank, the fuel gauge should read past full with the ignition on. Wait a few moments as some fuel gauges take a long time to respond. Touch the tan wire from the body to any convenient ground and the gauge should read empty. If not, you have a wiring problem or a bad gauge.

2) If the gauge responds correctly, the gauge and wiring are OK. Next use a multi-meter to measure resistance to ground of the sender wire connection on the top of the fuel sender or the tan wire from the top of the fuel tank. Measurements should track the fuel in tank.

Full - 84-88 ohms
Half - 40 ohms, give or take
Empty - 0-2 ohms

If this doesn't check, then sender or wiring on top of the tank is bad or the sender not adequately grounded. Senders are typically grounded by a black wire which is welded to the sender and attached to the body with a sheet metal screw.

3) If the sender checks OK but gauge and wiring don't, clean the connections, reconnect the sender wiring and separate the Fisher connector (located just outboard of the fuse block under the dash). The gauge should then read past full. Ground the tan wire in the dash side of the Fisher connector and the gauge should read empty. If not, you probably have a bad gauge or possibly a dash wiring problem. Go to Step 5.

4) If the gauge checks OK, then make the same resistance checks to the tan wire in the body side of the Fisher connector. If the readings are different than those at the sender, body wiring has a problem and requires detailed inspection. If they look OK, then the Fisher connector is probably dirty.

5) Clean and reconnect Fisher connector, pull the connector off the back of the gauge and make the same resistance checks to the tan wire. If they don't check, you have a dash wiring problem. If they check OK, your gauge is bad. Gauges can be bench-checked but this is best left to a specialist.



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Poncho Master!

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Thanks for the input guys.

Checked the sending unit ground, right where Clint said it was.

It was good.

No ohms reading at all to the gauge wire.

No access to the sending unit on these cars, unless you drop the tank.

syphoned the gas out and decided to put a stop on everything.

Past experience tells me that once I drop that 52 year old tank, it could be a mess.

That sending unit ring could be a disaster and the tank could be brittle around there too.

I'm going to leave this one until fall.

Car is running so well right now, it needs to be enjoyed !

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Randy(Muttwood)



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ABC123 wrote:

syphoned the gas out and decided to put a stop on everything.

Past experience tells me that once I drop that 52 year old tank, it could be a mess.

That sending unit ring could be a disaster and the tank could be brittle around there too.

I'm going to leave this one until fall.

Car is running so well right now, it needs to be enjoyed !


 Great call!



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Get a wooden stick. Place it in a full tank. Mark where is stops. Periodically check the level with it.

Or get a CAA membership just in case you run dry.

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Canadian Poncho Superstar!

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Good call on holding off Randy. 

I've been without a fuel gauge in the 67 for years now, and simply pull in and top up before heading out. When I did a new tank, I figured I'd replace the sender at the same time...it lasted a year, and of course I chucked out the still working original. Big, big mistake. The original Delco senders are apparently 100x better than the offshore ones and are still worth repairing (and in demand). Remember this wisdom Randy.

Without a doubt it's a pain to drain and pull down the tank in these cars. You might be wise to just order a new spectra tank before you do it. The bonus on the 65-66 is the sender is accessible on the front of the tank.

I suspect the sender failed, but really should crawl under and check the grounds, but I'm too lazy.



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rockauto has stainless steal tank for 400 ca for our 69 fullsizs

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1969 2+2


A Poncho Legend!

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I can't find it on the Rock Auto site for a 1969 Parisienne. Is that what you looked under? I find for the US models but I'm not sure that will fit in under a Canadian car.



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I will try find the Canadian site that also sells the spectra tanks. They have free shipping over $100. They shipped exactly on time and were cheaper than Roc Auto because of the shipping. Think my truck tank was about $250 all in to the door.

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Jerel


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cdnpont wrote:
When I did a new tank, I figured I'd replace the sender at the same time...it lasted a year, and of course I chucked out the still working original. Big, big mistake. The original Delco senders are apparently 100x better than the offshore ones and are still worth repairing (and in demand). Remember this wisdom Randy.

 Ethanol tends to rot the plastic/rubber components of the newer sending units.



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Prince Edward Island

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Canadian Poncho Superstar!

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4SPEED427 wrote:

I can't find it on the Rock Auto site for a 1969 Parisienne. Is that what you looked under? I find for the US models but I'm not sure that will fit in under a Canadian car.


 Fuel tanks & sending units for the US cars are totally different.



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Guru

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US big car sending units are a major PITA. There are no replacements in the aftermarket and the originals can't be repaired. They are a canister design with a donut type float inside the canister. The only solution on them when they fail is to chop off the canister and weld to the mounting plate an arm style system. I think they used the canister system to prevent the gauge needle on the dash from moving up and down whenever you stop or turn, the American tank is quite large (26.5 gallons) but also very narrow and long with the sending unit up front. The canister has tiny holes to allow fuel in the canister to reflect the actual overall level in the tank but to ignore the sloshing about. The actual fuel supply doesn't draw from inside the canister but from a separate tube with a sock. A good design in principal but not so hot 50+ years later.

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Pontiacanada wrote:
cdnpont wrote:
When I did a new tank, I figured I'd replace the sender at the same time...it lasted a year, and of course I chucked out the still working original. Big, big mistake. The original Delco senders are apparently 100x better than the offshore ones and are still worth repairing (and in demand). Remember this wisdom Randy.

 Ethanol tends to rot the plastic/rubber components of the newer sending units.


 Thing is, my 67 has never had any E fuel inside that new tank. Only shell Nitro premium. I was filling up the tank with the new sender one day, and heard a strange clunk from inside. I think the float or something else fell off the sender. The gauge stopped working at that point.



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A Poncho Legend!

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I remember the replacement sending unit I got from GM for my 69 was nowhere near as robust as the original.

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Poncho Master!

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Canadian Poncho wrote:

I remember the replacement sending unit I got from GM for my 69 was nowhere near as robust as the original.


 This car was 43 years old when I bought it, Who's to say that the sending unit is original.



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Randy(Muttwood)



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4SPEED427 wrote:

I can't find it on the Rock Auto site for a 1969 Parisienne. Is that what you looked under? I find for the US models but I'm not sure that will fit in under a Canadian car.


 its under the 1969 impala same tank that is in are Canadian parisienne

{#3930952}



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Canadian Poncho Superstar!

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PartsAvatar is the Canadian supplier that I got my Spectra tank from. Free shipping for anything over $100. Looks like they are out of stock for yours but it would be about $325 all in if I have it sourced right.

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Jerel


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I wouldn't worry so much about replacing the tank, just focus on the sending unit. If I were you, I'd get a new one (and locking ring) and once I had it, I'd test it just by connecting the feed wire in the trunk where you checked for continuity last week. That way at least you can prove out the circuitry.

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