Fuel delivery problem - Keep it Simple, Stupid story

[patrino]

Posting this story in case it helps some folks down the road ...

Truck is a 1966 D200, with a 318 poly engine out of a '64 Belvedere. After The Old Carb Doctor overhauled and improved the carb, and after I installed a Chrysler electronic ignition, the truck has been running GREAT. 16+ months of no problems (and very few problems before that!)

A few weeks ago, while climbing a fairly good grade at around 55 mph, the truck started bucking & running poorly. Felt like either a fueling problem or an ignition problem. I killed the heater fan to take some load off the electrical system, no change. Lights didn't flicker at all either, so my gut said fueling problem.

At some points the truck was pulling so poorly I'd pull over to the shoulder. I'd blip the throttle once or twice, count to ten, and the truck would accelerate at full throttle all the way up to 60 mph. More evidence ... when you put a load on the carb, it was running out of fuel.

Monitoring performance for a while, signs continued to point at a fuel-delivery problem. Truck would cruise at 55 mph all day on a flat road, but after a couple / few miles of a grade, it'd buck and drop cylinders, losing power. As soon as I crested the grade, I could resume cruising at 55-60 mph. Around town, the truck ran perfectly, no problems.

So I started sleuthing ...

Replaced the fuel filter. There was some crud in the filter but it didn't appear clogged. Visually inspecting the filter at idle (and holding onto it, to feel the fuel pump working), the pump was working. No change, the problem didn't go away.

Replaced the fuel pump. Took about a half-hour, in the parking lot of the local NAPA. Cost about $35. (As an aside, most of my machines are motorcycles and I'm always BLOWN AWAY by how cheap automotive parts are, relative to motorcycle parts. I get the reasons, but still ...) No change, the problem didn't go away.

After limping the truck home, working with a couple friends, disconnected the pipe leading from the fuel pump to the carburetor. Pointed it at a container and fired the truck up. The pump barely filled the container. Noted - so a fuel delivery problem. But what was causing the problem? Probably not the fuel pump, since it was new, but ...

Disconnected the feed line to the fuel pump (the line from the tank to the pump). Lying under the truck, took a big pull on the hose to start a siphon, and just a trickle came out. Tried a few times, with the same result. So the problem seemed to lie between the fuel tank and the fuel pump.

I inspected the ~6" hose between the two hardlines, under the truck, on the passenger side. Looked good. I then inspected the 3" hose inside the cab, connecting the fuel tank pipe to the first hardline. BINGO! The hose had a split in it. I pulled the hose, and saw that it had collapsed almost completely. You could barely blow through it.

SO ... replaced that 3" section of hose. While I was there, I opened the fuel filler cap and shot some compressed air into the tank, via the siphon hardline at the top of the tank. I could hear the bubbles in the tank, so knew that the line was clear. Also shot some compressed air through the fuel line FROM the end of the fuel line feeding into the fuel pump TO the disconnected fuel line at the top of the fuel tank. The air passed through cleanly.

I test-drove the truck on the same grade where the problem first appeared, and the problem was solved! Truck is back to running great.

Not sure what the moral of the story is, but it's probably something along the lines of "start simple". :)

[712edf]

I probably need to replace all the soft lines on my fuel system too, a few a likely original (1975).
Same for brake lines too. They can look good on the outside & have cracks along the inner lining.

Glad you fixed it. Nothing more disheartening than having an engine lay down when you need the power the most.

Bucky

[PwrWgnDrvr]

I've seen plenty of rubber fuel line and brake hose that after a few decades the rubber deteriorates from exposure to the fuel/fluid and swells up, eventually shutting off the hose completely. Rarely cracks all the way thru before this happens. Seen this on lawnmower engines all the way up to brake hoses on my 5 yard dump truck.