Need some help here

[weasel609]

So I took my truck out middle of nowhere on a mushroom picking adventure and Murphy steps in and says nope your gonna have a bad time. Truck was running fine and then all of a sudden I'm getting no fuel and truck starts stalling out and every time I hit the throttle I can here this loud gasping sound. Well I figured my jets were finally fouled up from a previous incident in which the carb and air filter caught fire from getting way too vertical and the only thing I had to put out the fire was a Motts Caesar drink so all over the air filter and carb it went. New plugs, wires, distributor, rotor and she ran like a top again so was no real surprise when what I thought was the jets fouling caught up to me. So I got a ride back to civilization got a new carb and I'm off to the races. Unfortunately even after tuning the carb the issue is still there. The truck will run for as long as it decides then starts to starve for fuel. I unhooked the fuel line and tried turning it over after it died and getting lots of fuel so I think my pump is still good. Anyone have any input on what my problem might be?

 

[MadOgre]

I wouldn't doubt if it is the fuel pump still. I had one go that still pumped fuel just not an adequate amount at an adequate pressure.

On high mileage engines (Cams Specifically) the push rod or the cam lobe can wear giving insufficient stroke to the fuel pump.

Often times it seems like the pump is pumping but if you keep testing for a few minutes it quickly declines in volume of fuel being pumped. Due to the lines initially siphoning fuel from the tanks.

 

[chengny]

Rather than a low fuel flow condition (pinched gas line, fouled filter, tank venting issues, etc), another possibility is entrained air in the fuel supply.

You may be pulling air into the gas pump suction line. This can result in a reduction in gas pump capacity or, more frequently, an excess amount of air being delivered to the carburetor - in greater quantities than it is able to vent off.

This generally occurs due to split rubber hose sections or loose missing clamps (at the steel to rubber transitions). Specifically, on top of the gas tank.

When the pump is moving a lot of gas (high loads) or if the tank level is very low, an increased negative pressure is developed in the gas pump suction side as it lifts the fuel from the tank. If any of the conditions described above exist, air will be drawn in from the atmosphere and mix with the liquid fuel.

Don't assume that, because you don't see any evidence of a gas leak on the driveway, your pump suction line cannot be leaking - it can.

There are sections of the fuel system that are physically located above the pump. When the pump is running, the only leakage will be air going into the lines (because of the negative pressure). And when the pump is stopped, the gas that remains in the elevated sections (higher than the pump) will flow back down the pickup tube and go right back into the tank.

You didn't mention the conditions that typically exist when your gas flow is suddenly lost. But, if it is an air leakage/ingress issue, this would probably be most evident at high engine loads (or as above, if you tend to let your tank get fairly empty).


Just a thought, it isn't often that these hoses fail:

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[jetman]

Most excellent suggestions by MO & chengny. Recently I was having a similar issue, which seemed to typically come up when driving off-road on rough terrain.
Changed out a bunch of 30 year old fuel line (as much as I could easily get to), then placed two (2) clear WIX 10 micron fuel filters in series just before the carb. Have not been plagued with fuel issues since then, knocking on wood..

 

[weasel609]

Thanks guys I will see if I can check those lines. I thankfully have my tools with me. I was low on fuel when it happened so the air in the line is also a possibility. I'll see if I can get to the top of the tank without having to drop it to inspect the hoses and fill it up and try to purge the lines also.

 

[MadOgre]

Jerry always has good ****! I think we would be hooped with out him

Just one more thing to add is that a fuel pump has to work harder to pump fuel as the tank is emptied. Or is masked by a pressurized fuel tank. (I had that happen once) So sometimes a failing fuel pump will have no issues with a full tank but then has issues as the tank is emptied.

 

[chengny]

There is enough of a gap between the cab back and the bed front for you to at least do a decent visual inspection:

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A better leak test would be to release the gas line at the pump suction port and apply some (slight - maybe 2-3 psi) air pressure to the entire line. Then - with the tank to pump section pressurized - get under the truck and trace the line all the way back. Just feel/listen for air leakage. Use soap suds for hard to reach areas.

 

[weasel609]

So I tried topping off the fuel tank completely and unhooking the line to the carb and turning it over for a while (collecting the fuel into a container of course) and no luck on the avenue. Unfortunately where the cab and box meet up isn't where the lines go into the tank (PO disabled drivers side tank so I only have righty). So it looks like my next battle plan is to siphon the tank low and drop it to inspect the fittings etc. A minor detail I didn't include in the opening post is that this mushroom picking adventure takes place so far off the grid that the nearest place with electricity is Tumbler Ridge and that's about an hour and a half away. So any advice on fuel tank removal in the bush. I have sockets wrenches and some other odds and ends but my biggest worry is breaking a five dollar part that I can't just run to the local hardware store to replace

 

[MadOgre]

So I tried topping off the fuel tank completely and unhooking the line to the carb and turning it over for a while (collecting the fuel into a container of course) and no luck on the avenue. Unfortunately where the cab and box meet up isn't where the lines go into the tank (PO disabled drivers side tank so I only have righty). So it looks like my next battle plan is to siphon the tank low and drop it to inspect the fittings etc. A minor detail I didn't include in the opening post is that this mushroom picking adventure takes place so far off the grid that the nearest place with electricity is Tumbler Ridge and that's about an hour and a half away. So any advice on fuel tank removal in the bush. I have sockets wrenches and some other odds and ends but my biggest worry is breaking a five dollar part that I can't just run to the local hardware store to replace

Wait !

So you cranked the engine over and no fuel came out of the fuel pump with a full tank ?

If that is so then install a new fuel pump and try again.

 

[chengny]

This is key:

Unfortunately where the cab and box meet up isn't where the lines go into the tank (PO disabled drivers side tank so I only have righty).

Seems this - not so minor - detail was omitted in the OP. I was going to ask about dual tanks, but figured you would have mentioned that.

Is the tank switching valve still installed?

If so, how was the line that ran over to the removed (LH/production) tank decommissioned?


Is the dash mounted transfer switch still installed and wired up?

The reason I ask is because prior to 1981, the tank transfer valve was of the solenoid operated type. It defaulted to the production tank if no power was provided from the dash switch. If you wanted to switch over to the auxiliary tank, the switch was moved to the RH setting and power stayed on the entire time that the switch was in that position. Moving the switch to the LH position, secured the power to the actuating solenoid and the internal spring shuttled the valve to the production tank.

So if your lines are still in place (that used to service the LH tank) - and are not properly capped - a loss of power to the transfer valve would shift the valve and allow air to be sucked in. This could be the result of a failing dash switch, an intermittent break in the power lead from the switch to the valve, loss of power from the fuse block to the switch, a weak ground connection from the transfer switch to the frame - or even an internal problem within the valve actuator.

On the other hand, if the lines are capped tightly (and this loss of power scenario occurs) the truck would also stall - but this time it would be just due to lack of any fuel available to the pump.

If the entire system was properly converted to a single tank setup - and the transfer valve has been removed - you can disregard any of the above.

 

[weasel609]

Sorry for the lack of details guys. So when I topped of the tank the truck will fire up and run and until it gets the air pocket or whatever is happening and when I throttle it that's when the gasping occurs. So I turn the truck off crank it and it sputters for a sec burning whatever remaining fuel is there. The best method I have found for restarting it is to turn it on pump the pedal two or three times, turn it off then on pump again repeat two or three times the. Turn it over and it fires back up until the air bubble comes back into the system. As for how the primary tank was disabled the tank was removed wires cut and taped and the hoses were capped and plugged with the dash mount switch still installed. So it was not properly converted just cut and remove style. I will try toggling the switch to DS tank to see if it functions or not. The truck is a 79 short box reg cab 4wd.

 

[weasel609]

Well kinda good news. It's not the fuel pump. I bypassed the tank entirely routing a jerry can directly to the inlet on the pump and she runs fine. So I can at least get her home and tie into the issue completely in the proper work environment and wash off the two inches of mud that coats the body and the three coating the undercarriage. So the issue is definitely with the fuel supply route wether it's the wiring for the tank switch or a cracked line or whatever else it could be. I'll be sure to add to the post when I figure it out so that the trouble shooting is there for anyone else who runs into this issue

 

[weasel609]

Well I found out what the issue was. Anyone have an idiot of the year award they care to bestow? I guess somehow the tank selector switch got moved from RH where my only fuel tank is to LH where the original tank was chopped out. Someone can go ahead point and laugh cuz I sure have been. So if anyone ever has a similar problem; check and make sure you are trying to draw fuel from a tank that you actually have hahaha

 

[HotRodPC]

If you don't intend to put the left tank bank in, might be a good time to just bypass the switching valve. At least it's running and figured out. That's the important part. Some of us have done more stupid **** than that.

 

[MadOgre]

Well I found out what the issue was. Anyone have an idiot of the year award they care to bestow? I guess somehow the tank selector switch got moved from RH where my only fuel tank is to LH where the original tank was chopped out. Someone can go ahead point and laugh cuz I sure have been. So if anyone ever has a similar problem; check and make sure you are trying to draw fuel from a tank that you actually have hahaha

Ya I wouldn't beat your self up over that one! At least you got no issues now, which is very good!