Fuel Tank? Fuel Issue?

[67step100]

I've had my truck out a few times this spring already. Today I went for about a 30 mile drive and in the final stretch to my house doing about 50 mph I could feel the truck periodically hesitating, then it got worse and eventually died just before i got home. I was able to get it restarted and drove into the garage. This felt to me like a fuel delivery issue as I've had this happen with another vehicle in the past. I have 2 fuel filters before the carb and all of the fuel line I replaced last year except for the 6 inches coming out the bottom of the fuel tank. This is where I have my first fuel filter (under the truck) and it looked clear, even with the truck running back in the garage. I did notice an air pocket in the filter so maybe there was restricted flow from the tank to the filter (less than a foot from the tank outlet)?

Is it possible that there is crud in the fuel tank (I should mention the tank was near full) that is too large to enter the small fuel line leaving the tank and perhaps got sucked to the outlet, couldn't enter the line and plugged up the outlet? I don't know what is inside the tanks as far as baffles or even filters in the tank? Appreciate any guidance. Thanks.

[PwrWgnDrvr]

The fuel line does not come off the bottom of the tank. What you see under the cab is where it passes thru the floor, at the end of the tank behind the passenger seat. Look behind the seat and you will see where it comes out of the top center of the tank, runs along the top and down the right end to the floor. 2 filters in the line is unnecessary. Are they clear plastic? If so, and you see no crud, they are likely not plugged. The "air pocket" is normal and not a problem.
When it dies, start by determining if the float bowl is full of fuel. Or just install new filters and see what happens.

[67step100]

The fuel line does not come off the bottom of the tank. What you see under the cab is where it passes thru the floor, at the end of the tank behind the passenger seat. Look behind the seat and you will see where it comes out of the top center of the tank, runs along the top and down the right end to the floor. 2 filters in the line is unnecessary. Are they clear plastic? If so, and you see no crud, they are likely not plugged. The "air pocket" is normal and not a problem.
When it dies, start by determining if the float bowl is full of fuel. Or just install new filters and see what happens.

Thanks. Yes, the filters are clear plastic. I use 2 because I have had they fail in the past where the filter part inside the housing broke away from the plastic housing, effectively providing no filtration. I'm a little anal about getting debris in the carb since the orifices are so small. Doesn't take much to plug or clog them. I will replace the first filter regardless to see if that sorts it out. Problem is I don't want to be 30 or 40 miles from home if it happens again. I was lucky this time.

What does the pickup inside the tank look like? Is it possible for debris from inside the tank to collect from the suction at the intake to clog the pickup?

[PwrWgnDrvr]

Pickup is a 1/4" tube without a filter screen unless added aftermarket. Possible to plug it with crud, if its there. If that's the case, you need to clean out the tank. If you pull the sender out of the top, you can inspect the interior. The pickup tube is integral to the sender unit.

[wre805]

67step100, might be worth checking the fuel pump. Only saying because I just had fuel delivery issues in a 62 D200, thought it was bad gas or tank crud, and it ended up the arm of my pump was slowly failing. I was able to drive it but with odd symptoms coming and going - bumpy roads seem to play a part - finally the pump arm fell to bits.

[dodgeboykim]

Make sure tank venting is working properly. Either vented cap {or off top of tank up into cab corner and down under truck if it has that style.}

[67step100]

Thanks. I hadn't thought about the fuel pump but I did the venting. I assumed the gas cap was vented as I purchased it from a Dodge truck vendor. I am going to replace the short section of fuel line inside the cab as I had missed that previously. I'll check the venting as well as it should be simple enough. I assume there will be a vacuum when I open the gas cap after it has been running for awhile if it is not vented.

[BigBlockTrucks]

Thanks. I hadn't thought about the fuel pump but I did the venting. I assumed the gas cap was vented as I purchased it from a Dodge truck vendor. I am going to replace the short section of fuel line inside the cab as I had missed that previously. I'll check the venting as well as it should be simple enough. I assume there will be a vacuum when I open the gas cap after it has been running for awhile if it is not vented.

Without a vent it could be a vacuum created in the tank, but it could also be pressure. Gas expands with heat. It also expands when it moves around in the tank, both of which create pressure.

[ROD100]

I recently had a similar huge sputter issue while driving. Making the truck buck wildly in any gear from the engine surging. I parked it and haven't attempted to diagnose it yet. I have previously put on a new Holley one barrel carb, new fuel filter, pvc, air filter. It looks as if the fuel pump is fairly new as it appears to be rather shiny compared to the rest of the engine bay. Had previously ran through about 3 tanks of gas with no issues. Curious what fixes you all found with yours as I will likely start with them.

[martincom]

I recently had a similar huge sputter issue while driving. Making the truck buck wildly in any gear from the engine surging. I parked it and haven't attempted to diagnose it yet. I have previously put on a new Holley one barrel carb, new fuel filter, pvc, air filter. It looks as if the fuel pump is fairly new as it appears to be rather shiny compared to the rest of the engine bay. Had previously ran through about 3 tanks of gas with no issues. Curious what fixes you all found with yours as I will likely start with them.

How many miles on the engine? I'm somewhat suspicious of the timing chain, based on your symptoms.

[ROD100]

Big unknown on that. 4000 miles on odometer but was told when I bought it engine had been changed out, unknown about miles or where it came from. Slant 6. Just timing chain slop? probably have to pull cover to inspect it.

[martincom]

I have two methods I utilize to check the timing chain, without disassembling anything:

1. Timing light method Connect a timing light as you normally would. Bring the engine up to a very fast idle while observing the timing mark, on the dampener. (You may have to put another mark on the dampener if the factory mark becomes hidden, from the advance function.) The timing mark should be steady. If it is bouncing around a lot (1/2" or more); what you are seeing is the slop in the timing chain.

2. Measurement Method Utilizing a larger ratchet or breaker bar, rotate the crankshaft by the dampener bolt until the timing mark is at the far end from the rotational directional, without backing up rotation. Note the degree indication of the timing mark. Remove the distributor cap. Rotate the crankshaft in the opposite direction until the rotor just begins to move. Note the degree reading difference. As a rule of thumb, anything over 7 degrees is considered excessive wear of the timing chain.

The symptoms you reported would be indicative of severe timing chain wear and you would really see the timing mark jump around dramatically with the timing light and measure far more than 7 degrees of wear.

Passenger cars typically came equipped with a nylon toothed upper sprocket, for quieter operation. Larger trucks came equipped with all steel sprockets, which last younger, but are noisier. As your engine has been swapped out, who knows what you have. The nylon tooth sprockets began failing at 80,000 miles.

[ROD100]

I have two methods I utilize to check the timing chain, without disassembling anything:



Excellent knowledge and advice. I will definitely check on that. I have to admit it is not something that I would immediately thought of. Super busy this week with a house build, but hopefully will get to it next week. I have plans to swap in a 400 big block stroker. So if the slant six is bad off probably will look at speeding that up.

[PwrWgnDrvr]

....Super busy this week.....

But you have 20 hrs of daylight every day!

[Wildergarten]

Is it possible that there is crud in the fuel tank

I've had this problem on two trucks, both with big block engines. So I'm offering this post in the hope that you don't have this problem. The motor ran fine until it was under power when it lost fuel. Then it was a battle getting it back to fill the carb.

The fuel pump for the big block motor is driven by a push rod running on the camshaft. With the removal of zinc dithiophosphate (ZDDP) from the oils (thank you EPA) both the cam and the push rod can wear rapidly, thus shortening the stroke. So if all else fails, pull the pump and the push rod (it's behind a pipe plug) to get a read on that. I just removed the rod and put in an electric pump and the problem was solved. ZDDP is available as an additive.

[martincom]

With the removal of zinc dithiophosphate (ZDDP) from the oils (thank you EPA) both the cam and the push rod can wear rapidly, thus shortening the stroke. ZDDP is available as an additive.

There is a fair amount controversy and myth about ZDDP. First off, ZDDP is pretty old technology--dating back to the 1940s. Oil manufacturers are constantly tweaking and improving their additive packages. Most modern oils still contain ZDDP--just not as much. For example, nearly all Mobil oils contain 0.08%. Prior to the emission reduction, it was typically 0.12%.

If you have a non high performance classic car or truck, the off-the-shelf modern oils are fine, in my opinion and others who know far more about it than I do. If you are operating a high compression, high performance engine you'll want the higher level of ZDDP. Both Mobil and Valvoline's racing oils have the higher level. The Mobil 1 Race oil is a full synthetic. The Valvoline VR1 race oil is not. As a racing engine is typically not subject to high mileage between changes, the race oils are not formulated for high mileage and will require a more frequent change interval. This gets expensive.

A good choice for a '60s muscle car level of performance is Mobil 1 0-40w and 15-50w. They have 0.10% and 0.12% ZDDP respectively. They are easier to source, full synthetic and offer the extended change interval.

You need to be careful with ZDDP additives. They fall into the category of when is too much of a good thing not a good thing. Excessive levels of ZDDP can lead to corrosion and plugged/restricted oil passages.

https://www.sclegacy.valvoline.com/abou ... ng-oil-faq

https://www.mobil.com/lubricants/-/medi ... rev-31.pdf