Help please - fuel problem

[Crosshairs]

I have an 81 vette with a 350 4-speed and I love it but I have a problem that has me stumped. A few weeks back the car died on me and I traced the problem to a fuel issue… it wasn’t getting any. The filter was clean but I wasn’t getting any flow so I assumed the fuel pump was bad. Rather than mess with replacing the mechanical fuel pump I replaced it with an electronic pump and it ran like a champ for a week or so then it acted the same way… the pump wasn’t pumping any fuel so I replaced it and it worked like a champ… for another week. The problem seems to be intermittent and I do not know what to do next. Could it have something to do with the return line that I did not do anything with (it’s still hooked up to the mechanical pump)? What am I missing?

 

[GerryLP]

I have an 81 vette with a 350 4-speed and I love it but I have a problem that has me stumped. A few weeks back the car died on me and I traced the problem to a fuel issue… it wasn’t getting any. The filter was clean but I wasn’t getting any flow so I assumed the fuel pump was bad. Rather than mess with replacing the mechanical fuel pump I replaced it with an electronic pump and it ran like a champ for a week or so then it acted the same way… the pump wasn’t pumping any fuel so I replaced it and it worked like a champ… for another week. The problem seems to be intermittent and I do not know what to do next. Could it have something to do with the return line that I did not do anything with (it’s still hooked up to the mechanical pump)? What am I missing?

If your fuel pump inlet and outlet lines are capped-off, then the return line should not be causing this problem. I have a Holly fuel pump, and it does not have provisions for the fuel return line. I keep it capped with a rubber cap and clamp, and I have not problems either.

There is a filter (is more like a strainer) made of plastic, and it is mounted to the fuel pick-up of the sending unit in the fuel tank. After 20 years, it's probably decayed, and perhaps blocking the fuel, but that would be an extreme situation. Before messing with the fuel tank sending unit, detach the return line from the mechanical fuel pump and cap-off both ends (the pump and the return line itself).

Also, does the electric fuel pump has a built-in pressure regulator? If memory serves, 9 psi is the max a Rochester carb can take. I use a 4150 Holly, and it also cannot use more than 7 PSI.

If you solve your problem, then consider removing the mechanical fuel pump altogether.

GerryLP:cool

 

[gkurtz]

I had a 350 chevy with a rochester carb doing the same thing. After changing the fuel pump, and swapping out a spare carb the engine would run for a while then starve out. It was the new stone filter I bought. It was new and clogged. Who would figure a new filter would cause so much confusion.

 

[bossvette]

a pin hole in the suction side of the fuel line can cause a problem. Where did you mount your electric pump?

 

[Crosshairs]

Thanks guys.

Gerry, I don't know about the pressure. It's just the generic type of pump that I got a Auto Zone. I didn't see any specs on it.

gkurtz, I did replace the filter but I used one with a paper element.

One other thing I might mention is that I got a see thru filter and placed it inline before the pump to see if there was junk in the line. It actually looks pretty clean but it does go "dry" sometimes and then gas sorta surges into it or sometimes it has like air bubbles coming from the gas line.

Sounds like it could be the strainer, huh? Man I hate to pull the tank...

 

[Bob Chadwick]

You don't want two filters on a mechanical pump. It can create the problem you are experiencing. I don't know if the same problem will occur with an electric pump.

 

[Crosshairs]

bossvette,

I disconnected the rubber line that goes to the mechanical fuel pump and put a new rubber line from the metal gas line to the elect pump. I mounted it inside the fender well in the engine compartment.

A pin hole would explain the "air bubbles" huh?

 

[bossvette]

Thanks guys.



One other thing I might mention is that I got a see thru filter and placed it inline before the pump to see if there was junk in the line. It actually looks pretty clean but it does go "dry" sometimes and then gas sorta surges into it or sometimes it has like air bubbles coming from the gas line.

Sounds like it could be the strainer, huh? Man I hate to pull the tank...

Its not that bad a job just empty it as much as you can and while you are at it replace the rubber line to the tank sounds like you have a hole somewhere.

 

[Crosshairs]

Bob,

I had the problem before I put the in line filter in. I was hoping I would be able to see something in the filter that would explain the problem.

 

[bossvette]

a better way to do it would be to mount the pump in the rear closer to the tank so it "pushes" the fuel rather then "pulls" it replace all rubber lines with new hose and clamps.

 

[Crosshairs]

Bossvette,

Yeah I know that but it isn't obvious to me there is a place to install the pump closer to the tank. Am I missing something obvious?

 

[bossvette]

I can't say for sure, I don't run a spare tire carrier and I have an in tank pump. I will look later and try to guesstimate :L (my 76 is up on the lift)
later

 

[JohnZ]

Electric fuel pumps are lousy "pullers", and great "pushers"; the instructions should have indicated that it needs to be mounted immediately adjacent to the fuel tank, below the level of the bottom of the tank.

 

[bossvette]

you shouldn't have any trouble finding a spot to put the pump in the back

 

[ernie d]

Crosshairs -

If you decide to go after the fuel tank strainer on the sending unit (I just replaced mine), you do NOT have to pull the tank. You just have to remove the sending unit from the tank to swap out the strainer.

First, lower spare tire cover and tire. Then put a clamp on the hose where it attaches to the steel inlet line on the tank. Disconnect hose, place hose end into a drain tank, remove the clamp and fully drain the tank. Then disconnect the positive and ground leads at the sending unit.

Now to remove the sending unit, using a tap hammer, rotate the cam locking ring CCW until the slots are aligned and the cam will come right off. Now you can carefully pull the sending unit out from the tank. Be careful to twist the unit so that the float, rheostat, swing arm and strainer clear through the hole (it's much easier than it sounds.

With the sending unit out, remove the strainer by twisting off the tube with pliers. Install the new strainer on the sending unit tube, and reassemble everything in reverse order.

You will need to buy 3 inexpensive parts. I got mine from The Last Detail, for a total of $12 plus shipping. Locking cam ($2), O-Ring Gasket ($2) and Strainer ($8).

Ernie

 

[Crosshairs]

Thanks guys... Guess I know what I'll be doing this weekend....

 

[garywcook]

Crosshairs -

If you decide to go after the fuel tank strainer on the sending unit (I just replaced mine), you do NOT have to pull the tank. You just have to remove the sending unit from the tank to swap out the strainer.

First, lower spare tire cover and tire. Then put a clamp on the hose where it attaches to the steel inlet line on the tank. Disconnect hose, place hose end into a drain tank, remove the clamp and fully drain the tank. Then disconnect the positive and ground leads at the sending unit.

Now to remove the sending unit, using a tap hammer, rotate the cam locking ring CCW until the slots are aligned and the cam will come right off. Now you can carefully pull the sending unit out from the tank. Be careful to twist the unit so that the float, rheostat, swing arm and strainer clear through the hole (it's much easier than it sounds.

With the sending unit out, remove the strainer by twisting off the tube with pliers. Install the new strainer on the sending unit tube, and reassemble everything in reverse order.

You will need to buy 3 inexpensive parts. I got mine from The Last Detail, for a total of $12 plus shipping. Locking cam ($2), O-Ring Gasket ($2) and Strainer ($8).

Ernie

The pickup on later model Vette's are different. It's secured by bolts and is larger than the gas cap opening. The tank has to drop.

I had some fuel starvation problems. I think the primary problem was caused by a clogged strainer on the fuel pickup. The other problem was probably caused by a collapsed fuel tank bladder. Cleaned out the tank, replaced vent hoses to the tank, new charcoal canister, and replaced the strainer.

Lots of pictures of the tank removal and pickup on my web site..

 

[Mr. Chuck]

I had a similar problem with a 1970 Mavrick after replacing a bad fuel line (rubber hose), which as it turned out had a slightly under size inside diameter and when I push the hose over the mating stainless piping, I caused a shaving of some of inside of the rubber to pile up and reduce the volume of fuel that the line could carry to the pump. In my case the car would run at low speed, but would falter and quite running once the bowl in the carb would run low. You mite also insure if the car has been idle for some time that fuel left in the lines has not turned to varnish and blocked the fuel line; a problem I had with my 73 Opel GT years ago.

 

[jdp6000]

Crosshairs -

If you decide to go after the fuel tank strainer on the sending unit (I just replaced mine), you do NOT have to pull the tank. You just have to remove the sending unit from the tank to swap out the strainer.

First, lower spare tire cover and tire. Then put a clamp on the hose where it attaches to the steel inlet line on the tank. Disconnect hose, place hose end into a drain tank, remove the clamp and fully drain the tank. Then disconnect the positive and ground leads at the sending unit.

Now to remove the sending unit, using a tap hammer, rotate the cam locking ring CCW until the slots are aligned and the cam will come right off. Now you can carefully pull the sending unit out from the tank. Be careful to twist the unit so that the float, rheostat, swing arm and strainer clear through the hole (it's much easier than it sounds.

With the sending unit out, remove the strainer by twisting off the tube with pliers. Install the new strainer on the sending unit tube, and reassemble everything in reverse order.

You will need to buy 3 inexpensive parts. I got mine from The Last Detail, for a total of $12 plus shipping. Locking cam ($2), O-Ring Gasket ($2) and Strainer ($8).

Ernie

Just a suggestion. If you are going to remove the sending unit why not put an intank fuel pump? They are quit cheap. I think the one out of an 82 or 84 Vette pumps 9-13 psi.

Jim

 

[GerryLP]

Just a suggestion. If you are going to remove the sending unit why not put an intank fuel pump? They are quit cheap. I think the one out of an 82 or 84 Vette pumps 9-13 psi.

Jim

Jim,

I have spoken with some people that have done a FI switch, and I think that a fuel tank swap is neded. FI fuel tanks have a sump built into them to minimize the splashing of the fuel from movement of the car. I believe that your L83's fuel tank is different in this way to the L81.

Anyone else Is this Correct?

GerryLP:cool