chykov's76doba

I am having a problem with filling my gas tank on my 76 Cordoba (gas cap behind rear license plate). I have only been able to put in about three or four gallons before it overflows. Does anyone know what the issue might be? And how I can fix it? Thanks

jacilynn_s

look underneath does it look like someone crushed the gastank with a jack?

Chryco Psycho

there has to be a vent line 1/4" or more going up to the filler neck to allow air out as it is filled , it may be blocked or pinched

chykov's76doba

No, there is no apparent damage to the tank or filler pipe. I will check the vent hose to see if there is an issue there.

Thanks for your help.

chykov's76doba

I can't seem to find the vent tube on the tank, and the service manual doesn't show it on their diagram either

Anyone know where it might be located on a 76 cordoba.

I am having a difficult time getting gas in the beast!

Thanks

TVLynn

Does the gas gauge work ? How much gas is in the tank ? It probably has several hoses for emissions, check on the front side of the tank

chykov's76doba

Yes, the gas guage appears to work. When I've got 4 or 5 gallons it shows just under a quarter tank (25 gallon tank) and the low fuel light comes on when it gets down to E.

It ran out of fuel, so I am pretty sure its not a guage issue. The only line I see coming out is the fuel line on the side of the tank.

440roadrunner

Fueling a tank has NOTHING to do with the tank vent. You should be able to easily inspect the tank underneath for damage.

The vents on any car made after about 70/71 does not actually "vent," anyway. The vent system is tied into the vapor recovery "smog" package, and vents through the carbon can. The fuel cap has a "pressure" and a "vacuum" relief valves, and is DESIGNED to run in a sealed position. What this all boils down to, is that there isn't really a "free" vent to the outside air.

Even my old Dart only has a 1/4" tube AT THE TOP OF THE FILLER neck. So once again, the point is that the vent does nothing in regard to the fill process. Filling generates a LOT of airflow. It all has to come back up the neck as the fuel goes down.

1--You are already at a disadvantage because of the low tank filler

2--Modern fuel stations seem to tend to "up" the fill pressure excessively

3--If you live in an area that has the fuel filler vapor recover boots, these add to the problem

4--Experiment with different stations, and try to find one which has an "end" pump where you can drive the front of the car "downhill" heading off the apron slightly.

5--If you have not done so, figure a way to safely carry some fuel, and if you can get the tank down to where you "know" it's low, try to siphon it low, and then intentionally run it out. Keep track of what you put back in, and what the gauge reads

chykov's76doba

Thanks that's a good idea.

The more I look into this it appears you are right. I need a better handle on how the system works.

I am reviewing the 1976 service manual and there is a great deal of information, but it assumes I already know a lot (wrong). So I will be asking lots of questions here and doing a bit of trial and error.

How difficult is it to change out the filter in that carbon can?

chykov's76doba

I got home from work today and checked the fuel filler pipe. There was still gas in the fill pipe. it hadn't slowly drained into the tank. Now I'm wondering if the tank is full (I was told it only had a couple gallons in it) and the guage is not working.

Any thoughts?

Thanks

440roadrunner

I'd say the tank is full. Have you taken a very good look underneath for damage?

chykov's76doba

yes, there doesn't appear to be any damage. the tank looks to be in good shape

Chryco Psycho

often the filler neck will have a baffle inside to allow air up as the fuel runs down , it might be worth pulling the filler neck out to take a look

chykov's76doba

Another problem, don't know if it's related or not. The fuel filter looked pretty bad so I replaced it, now I can't get the car to turn over. Any thoughts?

TVLynn

also back in the 70's they had a spring that was installed in the filler neck to stop people from stealing gas !!! worth a look

Chryco Psycho

Maybe I missed it but what engine ?

chykov's76doba

400 4bl

the car started right up last night before I replaced the filter

chykov's76doba

Well, the more I look into this, the more it's looking like the sending unit! Another question, will I need to drop the tank to replace it?

440roadrunner

No, but if you can clean and save the old one use it. The modern "repop" senders are well documented as "not being accurate."

You can "play" and find out where you are with the gauge, buy some resistors at Radio Shack

You can also check the temp gauge which has the same range as the fuel gauge.

Get enough "resistor" to total at least 1/2 watt, better 1 watt. For example, 1/2 scale is 23-25 ohms. So buy 4 x 100 ohm, 1/2 watt resistors and wire all four in parallel. This will make a 25 ohm, 2 watt resistor

"Full" scale is 10-13 ohms

"Empty" is 70-75 ohms.

Substitute them for the sender, leave the key on for a minute for the gauge to stabilize, and you can check gauge accuracy.

Drain the tank and check resistance of the sender, should be 70-75 ohms.

chykov's76doba

Thanks I will try this.

chykov's76doba

There was no problem with the tank, it was the sending unit. The float had a pinhole in it and the unit always showed empty, when it was actually nearly full. I fixed the unit and all is working well with the guage and refueling.

Thanks everyone for your help.