I am experiencing almost exactly the same symptoms. 2000 Ram 1500 5.9L. When less than 1/2 tank it codes misfires on 1 and 3 and random multiple cylinders, loss of power, chugging on acceleration. When tank is full or close to full it runs fine, no misfires & no codes. Problems started after replacing blown head gasket about a month ago. While apart, replaced both head gaskets, plenum gasket, valve stem seals, plugs, wires, dist cap, rotor, belt. Took a while to realize that the quantity of gas in the tank is related to the way it runs.

 

I just experienced this last week as well, exactly the same issue. The flashing CEL indicates missfires, as you probably already know by scanning the truck. I filled up to 3/4 tank, and the issue went away within a few minutes. I bought a fuel pressure gauge, and pressure was perfect with engine off, key on, and when running. I am down to 1/4 tank again today, and waiting for it to start the issue again. I have my fuel pressure gauge with me, and will test it when it is doing it.

My idle was a little unstable, but not horrible, how about you guys?

I am pretty sure that there is a crack, or a hole in the pickup tube of the fuel pump, and once the fuel level gets below a certain point, it starts sucking air, which is why we are seeing the missfires. The fuel pressure should be all over the place or at least fluctuating when this is happening.

I will hopefully have some data to post later today or tomorrow.

Anyone else experience this at a certain fuel levels?

 

my truck has been shaking for about a month now did a full tune up and no difference in the truck i have low compression in cyclinder 4 so could water in the tank or cheap fuel really cause low compression and could it be the injectors?????

 

I ran into the issue again tonight, as expected, but this time, the gas leve had to get below 1/8 tank before it really started bogging and missfiring. I checked the fuel pressure right when it was happening, and noticed it was about 48 psi, and under load, when missfiring, the needle was vibrating between 45 and 49psi, but I think that was just due to the missfiring causing the gauge to vibrate. If I had a longer hose that connects to the fuel rail, I would drive around with it connected, but I can't.

After that, I filled the tank to 3/4 tank, and drove around. My issue continued for about a mile or so before clearing up, and then was fine.

I think with these symptoms, and the fact that the fuel pressure seems to be within spec, I think my issue is water in the tank. If it were a broken pickup, or issue with the filter, etc., the issue would immediately go away once I filled the tank.

I'll try some fuel treatment, run it to close to empty and report back.

 

picked up some Gumout full system fuel treatment that says on it that it helps with water in the tank so i'll see how it does and keep u guys updated

 

Pulling my trailer home tonight gas gauge fell below 1/2 and as expected threw a pending code misfire on cylinder 3. Have been using Seafoam in the tank with the last two fill-ups, and was using Lucas fuel injector cleaner before that, the additives don't seem to make a difference in my circumstance. I expect over the next couple of days it will misfire more and more as the gas gets lower, especially pulling the trailer (7x14 full of tools).

 

If you fill your tank, or get it to 3/4 at least, does the problem go away immediately, or do you have to drive it for a bit to clear it up? If it goes away immediately, I would say you have something cracked in the fuel pump, that is allowing air/cavitation of the pump. That is what I thought mine was doing, but it took almost a mile before mine cleared up, after filling the tank.

So, I am pretty sure my issue is some water in the tank....

 

Even if it doesn't go away immediately, that may indeed be the trouble. We do not have a return style fuel system, so, even after you remove the source of the air, any air that is currently in the system, post-pump, will have to work it's way out via the injectors.

 

Good point.... I'd like to hear from others if the issue goes away immediately, or if you needed to drive a mile or so before the symptoms went away.

 

I think your issue in a fuel pump. They are coold by the fuel in the tank. When the tanks gets low they heat up. Had the same issue in two Dodges and a new pump corrected the issue both times !

Brian