Interesting symptoms

[LastDeadLast]

OK, so the other day, I was driving (calmly) about 45mph at part throttle and the car just stopped running. It felt like three cylinders just went out, but it wouldn't run at all unless you gave it 50% throttle or more. I managed to get it to the side of the road before it completely died. Once parked, I was able to get it running once, but it died again and I wasn't able to start it again. Thinking it was a fuel issue, I pulled one of the lines from the carbs and cranked it. No gas. Thank you AAA.

I brought it home, and checked everything: fuel line runs free, changed the fuel filter, checked the mixture, floats, check valve, the dizzy, plugs and wires. I couldn't find anything that really pointed to a problem. I also took the fuel pump apart, but didn't find anything wrong, however, it seemed that the longer the engine ran the worse it got.

I honestly thought the problem might be the fuel lines getting too hot, but today I got an in-line fuel pressure gauge installed and fired it up. At first I was hitting right at 2 psi. But as I left the car idle for a while, the pressure went down to less then 1 psi. I shut the car down and manually primed the pump, and the gauge goes up to 2 psi as I pump it.

Thinking I had a bad pump, I replaced it with the pump that originally came on the car when I bought it (a non-AC pump made in Canada). I fired it up again to find that I was back at 2 psi. However once the car idled for about 15 minutes, the same thing happened again to the fuel pressure. Interesting though, it never started running bad like the other day.

Do I have something wrong with my pump here? Could the gauge be bad? It's a brand new Earl's Plumbing (Holley) gauge that is oil filled.

Thanks for any assistance!

-s

 

[TR3driver]

My guess would be something restricting fuel flow that didn't show up in your test. Try looking into the fuel tank and see if there is any FOD.

Another possibility might be the soft fuel line(s) between the tank and pump. They can sometimes fail internally such that a flap of material can get sucked into the opening and clog it sometimes. IMO it's worth just replacing them, if you don't know they've been changed in the last decade or so.

 

[Moseso]

Gas tank vent plugged? Works for a while and then vacuum in the tank eventually overcomes the fuel pump...

 

[Brosky]

To add to Randall's point, if that line has become weak, the suction can actually close it up. Even the new lines of today, though better in rubber material, may not have the amount of reinforcement braiding inside to prevent the collapse.

 

[LastDeadLast]

All the rubber fuel lines are less than a year old, so I would doubt that as an issue.

Although the gas tank vent and clogged tank ideas have me intrigued. Moseso, are you talking about the long nylon tube that runs from the gas tank to the carbon canister in the engine bay? If not, where might it be?

Either way, should I be able to blow through the vent to the gas tank?

I dreading removing that gas tank. :crazy:

Thanks for all the good ideas.

-s

 

[Brosky]

You should be able to blow through the fuel line back into the tank, but only do so with VERY LOW air pressure. I think that would be the problem area, if any.

I don't know if there is a one way valve on the cannister line. I don't think so, but maybe someone who has had one off will know.

 

[Brosky]

Shannon, please don't take this wrong, but are you sure that they sold you reinforced fuel line and not vacuum line? I've ordered line at local stores and had to tell them to go back and get the fuel line with the white lines in the end when cut because the counter people either don't know better or just don't care.

 

[LastDeadLast]

You should be able to blow through the fuel line back into the tank, but only do so with VERY LOW air pressure. I think that would be the problem area, if any.

I tried that... I can't blow through with my mouth. I put 20 lbs of air pressure through it and I'm pretty sure I heard it come through the tank.. but like I said, I wasn't able to blow though with my mouth. Where does this thing connect to the tank?

-s

 

[LastDeadLast]

Shannon, please don't take this wrong, but are you sure that they sold you reinforced fuel line and not vacuum line? I've ordered line at local stores and had to tell them to go back and get the fuel line with the white lines in the end when cut because the counter people either don't know better or just don't care.

Paul,

Good point, it's been so long I don't remember. I'll check tomorrow. I usually fuel line for everything, including vacuum hose applications.

-s

 

[Brosky]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I tried that... I can't blow through with my mouth. I put 20 lbs of air pressure through it and I'm pretty sure I heard it come through the tank.. but like I said, I wasn't able to blow though with my mouth. Where does this thing connect to the tank?
[/QUOTE]

It connects to a metal line at the left rear of the car. The vent line should be beside it on the right. These pictures will show where the two lines are with everything else out of there.

20lbs psi is plenty. Remove the cap and have some listen for the gurgling sound in the tank as you slowly apply air to it.

And don't discount one of those lines back there being weak and collapsing either.

 

[LastDeadLast]

Paul,

Gotcha, I'll start tracing it down and see where it goes. I think my routing might be different than yours. My car seems to have 1971 emissions parts on it (not just in the engine, but everywhere), so hopefully this will be simple.

Thanks!

-s

 

[Brosky]

Good luck. Let us know what you find.

 

[davidk]

To test the vent line, you can crack the gas cap open and start the engine (car parked of course). If the pressure doesn't fade, you probably have a venting problem.

 

[poolboy]

All the rubber fuel lines are less than a year old, so I would doubt that as an issue.

Although the gas tank vent and clogged tank ideas have me intrigued. Moseso, are you talking about the long nylon tube that runs from the gas tank to the carbon canister in the engine bay? If not, where might it be?

Either way, should I be able to blow through the vent to the gas tank?

I dreading removing that gas tank. :crazy:

Thanks for all the good ideas.

-s

I got distracted while filling up and overflowed gas. Before I had driven 5 minutes, the engine wanted to cut out and die. I reached back and opened the gas cap. The engine caught and I was able to get about 7 miles before it happened again. I opened the cap again and drove home.
My intuition told me that I had flooded the fuel tank vent and caused the fuel to lock up in the tank.
I unplugged the vent line at the Carbon Cannister, and blew the gas back into the tank. No more problems and no more overfilling the tank. Might be worth a try.

 

[LastDeadLast]

OK, one more thing ruled out. It's not a vent problem. The reason that I couldn't blow through manually is that there's a restrictor in the engine bay just inches from where the line connects into the carbon canister. It's only a millimeter in diameter at best. I WAS blowing through it, but at a rate so slow I couldn't detect it. I took the end off the tank and removed the restrictor and was able to blow through just fine.

I slapped it back together and I'll test the fuel pressure again tomorrow to see if I still have the problem. I suppose I could have unclogged the restrictor without knowing it.

If that fails, I'm checking the fuel line.. and after that.. the dreaded gas tank removal.. after that.. anyone want a TR6? Cheap?

Thanks again for all the help.

-s

 

[TR3driver]

The reason that I couldn't blow through manually is that there's a restrictor in the engine bay just inches from where the line connects into the carbon canister. It's only a millimeter in diameter at best.

That doesn't sound right; I don't believe there should be a restrictor in the line between the canister and the tank. Some of the lines to the engine should have restrictors, but not that one.

And 20 psi is way, way too much, IMO. 4 psi is plenty.

 

[Brosky]

How cheap?

 

[TheSearcherMan]

As the fuel tank is higher than the fuel pump, why don't you just take the intlet line loose at the pump, and drain a couple gallons gas in a gas can, this will tell you if the filter is clogged or the tank is not vented. Also, when you have the problem, if it is a tank vent problem, just open the fuel filler cap, you should heard the vacuum let go if the tank is in a vacuum, and the car should run again. There should never be a vacuum on the supply line from the fuel tank as the pump is gravity fed. I don't see where you mentioned the fuel filter. Most of these cars probably leak enough air around the filler and your problem is elsewhere.

 

[LastDeadLast]

[That doesn't sound right; I don't believe there should be a restrictor in the line between the canister and the tank. Some of the lines to the engine should have restrictors, but not that one.

It's there from 1972 and up. Moss and TRF both list it:

https://www.zeni.net/trf/TR6bluebook/26.php - part number AS14

As the fuel tank is higher than the fuel pump, why don't you just take the intlet line loose at the pump, and drain a couple gallons gas in a gas can, this will tell you if the filter is clogged or the tank is not vented. Also, when you have the problem, if it is a tank vent problem, just open the fuel filler cap, you should heard the vacuum let go if the tank is in a vacuum, and the car should run again. There should never be a vacuum on the supply line from the fuel tank as the pump is gravity fed. I don't see where you mentioned the fuel filter. Most of these cars probably leak enough air around the filler and your problem is elsewhere.

I just didn't think about opening up the gas tank lid when the problem was occurring yesterday. I'll test again today, the problem is easy enough to replicate at least. When I changed out the fuel pump, I let the line run free for a bit. It's a full stream of gas.

I would have thought the gas tank lid leaked too, and just for kicks I put a little air pressure on the tank just to see. Nope. It's tight.

Just an aside: My wife "loves" it when I work on fuel systems. The fumes eventually work themselves up into the house and take days to dissipate.

How cheap?

You're supposed to be supporting not encouraging!!

 

[LastDeadLast]

Ok, the latest update.

I started the carand let it idle for a bit. The fuel pressure started out at 2.5 psi. Over a period of 10 minutes it slowly dropped to less than 1 psi. I opened up the gas tank lid to no effect.

I just don't get it. I guess it's time to lift it up and check the lines.

-s