Tony72Cutlass'S'

Hello All,

I've been having some trouble trying to diagnose why my fuel gauge is not showing full when my tank is full.

So i filled up my tank with gas, and consequently. It does not register as "F" on my gauge, but rather empty.

I have been follwing this chart.



I disconnected the TAN wire in the trunk of my car. Went to the dash, and the gauge registered as Full.

Does this mean that perhaps my float has gone bad? and it's not registering?

Any ideas/comments would be great!

Thanks all,

-Tony

jaunty75

The sending unit is just a variable resistor with resistances between zero ohms (reads "E") and 90 ohms (reads "F"). When you pulled the tan wire, you opened the circuit, which means infinite resistance. Many gauges will go way past the F mark maybe all the way around to the 3 o'clock position with an open circuit and the key on, but maybe yours has a restrictor of some kind in place to prevent the gauge needle from going past the F mark no matter how high the resistance is.

In any event, if you ground the side of that tan wire connection coming from the gauge with the key on, the gauge should go to E. If it does this as well, your gauge on the dash is fine as is the wiring between the gauge and the back of the car where you pulled that connector apart.

You say that when you fill the tank the gauge stays on empty. I presume from this that your gauge doesn't move at all no matter how much fuel is in the tank?

If your gauge tests ok based on the procedure above but goes to empty and stays there as soon as you reconnect that tan wire, that suggests you either have a short in the section of that tan wire between where you pulled the connector apart and the sending unit OR the sending is stuck in the fully-down (empty) position. You need to check that tan wire. I don't know where the sending unit is mounted on the tank of a '72 Cutlass, but it's possible you may have to drop the tank to get the end of the tan wire that attaches to the sending unit. On my full-size '67 Delta the tank has to be dropped to get at the unit.

With luck, you'll find a short in that tan wire, correct it, and your gauge will start working properly. If not, you'll probably have to replace the sending unit, or at least find out why it's stuck and fix it.

Tony72Cutlass'S'

Hey there,

Thanks for the reply!

That's exactly what happened just now. I tested the gauge again and here's what went on.

1) Sufficient fuel in tank, tan wire connected --> Gauge reads right around empty

2) disconnect tan wire in trunk --> Gauge reads way past Full. like around 2pm.

So there might perhaps be a short between my fuel sender and where i was disconnecting the wire? Or it might be the sender went bad?

What i was thinking that perhaps my gasoline float doesn't float anymore.. Is that possible? :S

Looking at the CSM, it looks like i'm definitely going to have to drop my tank in order to get to the fuel sender..

jaunty75

Yes on all counts. It sounds like your gauge is ok and that you have either a short in the line coming off the sending unit before it connects at the back of the car or (and my money is on this) the sending unit itself is bad.

If you drop the tank and discover a short in the line, then you can put the tank right back up without opening it up. But if ends up that the sending unit itself is the problem, regardless of whether it's a bad float or something electrical, you might just want to go ahead and put a new one in.

Sending units are not that much money in the grand scheme of things ($70 for one for my car), and the one that it's in there, even if it is fixable, is still almost 40 years old. You'd hate to fix it only to have it break down again six months later. After all, the only thing worse than having to drop the tank once is having to drop it twice!

Tony72Cutlass'S'

Awesome, sounds like a good plan to me!

I definitely don't want to have to do this more than once.. They dont have any senders locally where i'm from. But the zone seems to have them about an hours drive away in northern NY state for around 50 dollars.

This might be a good opportunity to inspect those rubber lines above the tank and change whatever is cracked and easily repairable.

Is there a rule of thumb to determine if my sender has a return line? Originally my cutlass was bone stock 2bbl 350ci. (Now with performer intake and ebrock 1405).

MDchanic

From what you've said, you'll have to drop the tank to see what's going on and fix it.

Empty it first - gas weighs 6½ pounds a gallon, so over 120 pounds if you've got 20 gal in it.

You may have to destroy the straps to get it out, but they ARE available.

Good luck!

- Eric

MDchanic

Oh, yeah, Baby.

Just look at the fuel pump:
One in / One out = no return.
One in / One out / One more = return.

- Eric

Tony72Cutlass'S'

Awesome, Thanks Eric.

I'll check out the fuel pump and see what type it is. I find it a little weird that Autozone has the standard sender and Rockauto only has the sender With return..

I'm guessing the hoses back there are probably 3/8'' just like the ones that i have hooked up to my carb up front? I might as well pick up a good couple feet of hose so i dont have to run back and forth while getting the job done.. On my bicycle..

Tony72Cutlass'S'

Hey All,

So i crawled under my car last night to inspect and see if i could see any visible signs of grounding. Nothing, looks like i'm going to drop the tank this weekend.

Eric, Would you happen to know of a good supplier where i could get some good straps?? Last thing i need is my tank falling out..

On a completely unrelated side note.

Could someone help me make the distinction in between these 3 settings on my engine.

SOLENOID SCREW (RPM) = 750
CARBURETOR SCREW (RPM) = 550
FAST IDLE SCREW (RPM) = 1100

Is fast idle the setting when initially fire up the car and my choke is engaged, or just when the car is hot, choke is off, and car is in park?? I have a 1405 EBrock and i'm wondering how to set it up properly to match my factory specs.

MDchanic

I can't say for sure where you can get the straps, but I believe you should be able to get them at any auto parts store.

The idle speed screw is the one that opens the throttle when the choke is off.

The Fast idle screw is the one that bears on the fast idle cam when the choke is on.
The instructions usually tell you which step it needs to be on to adjust it (not always the top one). You do it with the engine warmed up and the choke off (open the throttle and push the cam so that it's under the screw).

The idle solenoid screw is the shaft of the idle solenoid - it's got a hex head.

- Eric

Tony72Cutlass'S'

Cool, Thanks! Looks like i'm taking a trip down to the states! You guys have awesome parts stores down there. I can't even get a wheel cylinder for my front drums without the store clerk looking at my funny up here..

It seems that i only have two screws i can adjust on the edelbrock.

The first one, (Above) as you said, that adjusts my throttle when the choke is disengaged.

But I also have this one, when i screw it in, it gives me a higher idle when the choke is on..



How many RPM's should i have my car set at when it's in Gear?

Right now.. Choke off and car in park = 1100 RPM

Also, Choke off and car in gear = 750 RPM.

Is that too much. My transmission kinda gives a little THUMP when i drop it into D from Neutral..

MDchanic

Well, you can look up the exact tune-up specs for your car in your Chassis Service Manual, but they're generally 550 RPM, sometimes 500, always in Drive (with the emergency brake on ). Your speed in Park is WAY too high - usually settles around 750-800.

As for the high idle, you'll have to look that up too, but what's right for the OEM carb. may not be right for your aftermarket carb, so you may need to fiddle around with it to get it "right."

- Eric

Tony72Cutlass'S'

Great! Thanks, I'll definitely tune down my idle settings..

Tony72Cutlass'S'

So this may have taken me a couple months BUT i finally got to working on my gas tank!

Eric, based on what you said, i think i'll have to destroy the bolts that hold the straps on. The straps appear to be in good servicable condition, but the bolts are COMPLETELY fused in place..

Should i even try unscrewing the bolts with 2 box wrenches? Or just cut them and get new ones. I'm sure if i used grade 5 bolts from my local hardware store with lock nuts it should be okay?

jaunty75

This is exactly what I did when I dropped the tank on my '67 Delta. The straps were fine, but the bolts were rusted solid. Some cutting and tapping with a hammer got them out, and then some nice new bolts from Lowe's did the job nicely.

Tony72Cutlass'S'

Awesome!

I think i'll do just that! i'm excited to take out the gas tank, i dont think its ever moved, maybe there's the world's first lansing build sheet underneath

Hey, how did you lower down your gas tank without squashing yourself? I remember eric saying that a full tank can weight 120 pounds..

Since my gauge doesnt work i could have as little as 1 gallon and as much as 2 or 3..

MDchanic

As Jaunty said, by all means cut the bolts, just don't use a torch .

You should be able to get the original bolts from GM if you want, but anything from the hardware store should be fine.

As far as lowering it, you can either bench press it (careful - it sloshes!), have a friend help, or use a floor jack and a board to stabilize it, and give you a chance to cut the hoses (be ready for a shower!)

Good luck!

- Eric

Tony72Cutlass'S'

I think i'll definitely try the jack with a nice board that i have lying around the house.

So i'm assuming there's probably a couple ounces of gasoline in these lines?? I guess i could optimistically catch it in a bucket but knowing my luck it'll spray all over my face..

In your opinions, should i use fuel injection hose or just regular fuel line? I was leaning towards regular rubber hose since these are vent and syphon hoses and not under a huge amount of pressure?

jaunty75

I first siphoned as much gas out as I could, but there was still perhaps 2 or 3 gallons in it. I then put stuff piled up underneath and gently lowered the tank onto the pile. The tank is actually not that heavy when it's empty. Once I had it off the car, I poured out the remaining gas through the filler neck into a large bucket.

MDchanic

That's pretty much what I did, too.

Once it's free, you can tip the filler into a low tub and dump the gas.

As for the lines - jeez, regular fuel hose - this ain't a Maseratti!

- Eric

Tony72Cutlass'S'

It's as close as i'll probably ever get to one!

Thanks for the tips guys, i'll hopefully post some pictures this evening of my progress.

hookem horns

Replace ALL rubber lines while under there, old ones will likely be cracking and don't like ethanol. Regular is more flexible than FI and is OK IMO. Siphon out most of the gas and you can manhandle the tank pretty easily. I used an old low table to hold it up while reconnecting hoses/wires before strapping in place.

frankr442

When adjusting the carb, keep in mind the specs and instructions you're looking at are for the OE Rochester carb. Who knows how close the A/M carb is as far as air flow, choke angle or a hundred other possible variables. Was any info available from Ebrock?

Tony72Cutlass'S'

Frank,

The carb is working great now! After many many conversations with edelbrock, i ended up ripping the carb apart and to my surprise, the floats were bottomed out from the factory!

I had to reset the float height to 3/8'' and to my surprise, the carb ran like a champ thereafter.

Moral of the story: Never trust any part you buy

oldsguybry

I also have a issue with my gas guage.... when it gets close to empty it sticks right above the empty mark and then I run out of gas ... happened a couple of times , when its cold out the gas guage goes way above full and stays there until the car warms up overnight via my underground parking garage.... and if I fill the tank past half full the tank leaks

Tony72Cutlass'S'

I got my new fuel sending unit from RA for around 40 bucks. I figured that if I was already going to check the wiring out there I MAW replace the sender. It'll give me piece of mind that the stupid gauge will work properly.

I actually tested the new sender with the tan coloured wire in my trunk. Works great so far!

Were you able to isolate the leak in your tank?? Apparently you might be able to patch it with some Jb weld ( I read somewhere that it doesn't dissolve in gasoline)

oldsguybry

cool on the availability of the sending unit , and yes the tank replacement/repair is on my list of many things to do

Allan R

That's exactly what happened to mine! Check the brazing around the filler neck. That was the problem with mine. Easy way to check that is park on a hill so the fuel level is higher at the neck.

Allan R

Tony, your fuel pump should be identical to mine. That means you should have only one line in and one line out. 3/8" hose, but at the back of the car you will find a combination of 3/8 and 5/16.
The sender is listed at ILT

Pn# - INL12269 - 1971-72 $55.00 Ea.

1971-72 Cutlass Fuel Sending Unit - 3/8" Fuel , No Return Line

Tony72Cutlass'S'

Cool! I think i have that exact same one (Rockauto shipment already came in!)

So i actually went ahead and tested the resistance of the fuel sending unit. It is exactly per spec to what it should be. One outlet, and i'm quite excited to assess the tank situation and install it. I just finished draining the last 1 1/2 gallons of gas from the boom-mobile.

Allan R

I hope it's the right one Tony. Too bad you didn't order the straps and mounting hardware at the same time. Did you use the tank drain method from the CSM or just suck on a tube till you got gas in your mouth?

Rootin' for ya to get those stubborn bolts undone. Remember to use 6 point sockets or box end wrenches so you don't strip down the points. I know those suckers will break loose. FWIW they're only torqued to 18 ft/lbs at the factory.

DONT FORGET to disconnect the 3 vent lines at the back of the tank and the rear ground strap connection before you drop your tank. It could get ugly.....be prepared to get some gas on you or the floor. Just to be on the safe side, I plan to keep a fire extinguisher close by......

Tony72Cutlass'S'

Gentlemen,

Choise of weapons for removing gas tank bolts

1) angle grinder

2) hacksaw (don't have a saws all)

For anything else I'd use the grinder in a second flat. But worries about sparks and ka-boom happening...

Opinions?? This damn tank is coming out tonight!

MDchanic

Eh. I wouldn't worry about sparks if it isn't leaking.

Just make sure the cap is on it and the gas you siphoned out isn't located anywhere near where you're working (as in: in the same building - gas fumes hug the floor and can cause unfortunate events).

- Eric

Tony72Cutlass'S'

Cool Eric,

Good info, I actually siphoned the gas directly into my sentra to burn it. Figured is put fresh gas in the olds in the spring.

It seems like the tank isint leaking, it's more covered in undercoating and crud.

Allan R

Hack saw is waaay to slow and awkward.
Angle grinder or bolt cutter. If you're worried about fumes, run a fan so you get constant air circulation. Angle grinders faster, makes lots of cool sparks, sounds good and makes it look like you're working hard if someone is watching.

Did you look at any of those sockets that CT sells? They have a reverse bite that tightens even more as you torque them? I'll be watching for your results.

.......Breaking News. Global Montreal has the exclusive story on a giant warehouse fire near the airport tonight. Apparently a car enthusiast trying to remove the gas tank from a restoration car project caused the blaze, which broke out around 9:00pm.

Witnesses near the scene say the night sky was lit up like a bomb going off. Firefighters arriving on the scene initially described the fire as 'likely set by an arsonist'. The warehouse structure was widely believed to be abandoned. Firefighters gained control very quickly, but remain on scene sifting through debris and looking for hot spots.

Jacques Muskelunge, a fire invesitgator said the whole thing 'smelled fishy'. Bystander Sandra Brighteyes, still in a daze, said there were a 'lot of sparks flying just before it exploded'.

Emergency crews entered the building to find a dazed and shaken young man standing next to a car he had been working on. 'It's like I was on a bad fishing trip' he said, still reeling from effects of the blast. "Oh well", he continued "It's not like I need a haircut anymore".

More on this breaking story later. In other news tonight QC MP Julienne Pomme de Terres tabled a new bill to ban Potatoes from Ireland......

Tony72Cutlass'S'

You couldn't be more right! Took me WAY too long to get that stupid bolt outta there. But i did it!

So true! I'm so close to the airport i think it would definitely make breaking news...

BAHAHAHAHAHAAAA too funny, because we actually have people that sound like that out here :roll eyes:

Hey Al,

Speaking of gas tanks, did you ever hear back from spectra?? those guys never answer me! and the plant is so close to my house, its ridiculous...


But on the bright side... TANK IS OUT.... on the down side... TANK IS SCRAP lol

I shall now post pictures..

Allan R

I don't know if I'd write the tank off just yet Tony. I'd try to take off that locking ring first. The metal underneath might still be decent. I kind of figured you might be looking at something like this when you posted pics of the front suspension parts. That car was sitting for way to long in the trees. Your new sender should have come with a new locking ring, didn't it?


Have you poked around the frame to see how solid it is? Reason I'm asking is I know where there's a good solid one here in AB. All you'd need to do is a body off resto...

(bang!) Sounded like you were shooting at me.... (kapow! biff! whack! Sock!) I love old Batman re-runs

Looks like you also need some rear suspension work too. Guess what I'm doing this spring??? Yup same thing.

re: Spectra. I'll call them tommorrow and ask. I keep forgetting about that because my hands aren't doing that project right now. I hope the local office wont' have any problem answering the phone. IIRC the tank is GM34R

Tony72Cutlass'S'

Thats the one! GM34R, i just sent them ANOTHER email saying id really like to buy one from them directly. I really hope they answer... If you could call in parallel that'd be a huge help!

I'll have to shoot the sender with penetrating oil and see if i can get the sender out. the new one definitely came with the lock ring as well as gasket.

The frame seems solid, just UGLY. i bought a wire brush for my grinder and I'm going to put on some glasses and go wild on it. My rear suspension absolutely has to be done. I brought my grinder home so i can chop out my lower shock mounts. they're completely finished. I figured why waste my time if I'm using all new fasteners anyway??

car_designer

That is a good one.

Good to hear you are making progress.

Allan R

I had fun writing it. Must watch too much news. That's how they talk. I also am looking forward to Tony's progress.