The vehicle: 1984 Ram 318 4 speed.

Issue: In the top gears at low rpm (above idle to 1800 or so) if I put it down to 3/4 throttle the truck starts sputtering and wanting to quit like its' out of fuel. From a standing start I can hold it to the floor and row all the way through the gears, rev it to the moon, no problem. It has power to burn and the fuel mileage is very good. When I bought the truck a few weeks ago it had no such issue at all pulling itself at low rpm.

What has been done so far:

New fuel filter with the line to the tank blown out. All clear.
New fuel pump.
Checked needle and seat, no restrictions.
New cap, rotor, wires, and plugs. None of the plug wires are crossed.
New ECU.
New coil.
Checked vacuum advance and it is working properly.
Base timing calls for 12 degrees. It is set on 14 and starts with just a tap of the key. I moved the timing up to 16-no change, moved it down to 12-no change. Full mechanical advance is in the 32 range. Tried driving with the advance unhooked-no change.
The idle is rock steady at 750 with 19 inches vacuum and throttle response is good.
EGR valve is unhooked, but I took it apart anyway and made a block-off plate.
There is no catalytic converter.
PCV valve works.
The carb is a Holley 2280 with some emission stuff on it. I wired the choke open and drove it and it still coughs and sputters. Have a perfect working 2280 on my '71 so I pulled it off and put it on the truck. Amazingly, same thing, still coughing and sputtering.
I have covered the whole intake manifold, lines, and brake booster with ether and found no noticible rpm change.

So there you have it. I have tried everything I can think of over the last few weeks, replaced a bunch of parts and still have the same problem. It's getting worse.

Does anyone know what it could be?

Check that the gas tank is venting, and there are no cracks in the fuel line that can suck in air. I found mine was at the small rubber connection from the sending unit to the hard line.
If you suspect a fuel tank/line problem, just rig up an alternate setup, like a quart or gallon jug of fuel with a rubber fuel line connected to the inlet of the fuel pump.

That's a great idea, I'll give it a shot.

Thanks!

What a toughie . I'd clamp the pcv line shut & try it then clamp the booster line shut & try it (can do those 2 in minutes). next I'd consider replacing the intake manifold gaskets using composite side gaskets with Permatex "high tack" the red spray in a can, goes on light and seals very well. Holler what it ends up being

If you would please describe again how it's acting up, Is that in some or all gears & that's going to 3/4 throttle from an in gear rolling start at anywhere from idle to 1800 rpm it will sputter but WOT the same way is OK.

What plugs did you put in? I recently got a bad batch of Autolites, literally right out of the box.

What is the vacuum reading when the problem occurs?

If I had to guess it's a misfire due to a mild lean spot in the fuel curve, if it goes away at WOT at that same rpm it's probably not ignition related.

Has it by chance gotten colder lately where you're at?

I'm gonna try 451's fuel can on the fender first so we can eliminate water in the fuel, crap in the tank, or a cracked fuel line.

Blus and Robert: It's out on the highway cruising 60mph, top gear, 1500rpm, lean into it to climb a hill and it starts. At the same time I can downshift to 2nd, wind it out to 5 grand and no problem. So the way you worded it Robert is exactly right.

Yeah Blus, it's getting more noticible with the cold. Just an external vacuum gauge is all I have, nothing in the cab. Plugs are Champions. I know what you're saying about the Autolites, I put some colder ones in my 360 Magnum and man did they ever kill the bottom-end power. Went back to Champions. I'll be off-line until later tommorow Guys, thanks for the quick replies.

Ok, went back at it yesterday and put a fuel can on the fender and took it for a rip.

No change.

I clamped the PCV and booster hose and the idle rpm went up about 100rpm but still sputtering.

I have a '70 Carter 2bbl that's been sitting on the shelf for years so I'll blow it out and try it.

so it sounds like a fuel starvation problem at low rpm? i had one eat its into the fuel pump cam on the front of the camshaft. at low load or higher rpm it would pump enough but under load or lugging up a hill it would do the same thing it was on a 87 flat bed ram dumper used for constuction. not sure if it is the same problem but it sonds like it?

Put a carb kit into the Carter BBD.

It's an improvement, but still stumbling.

Put ANOTHER new set of Champions (hotter, 14's) in.

Floats were set dry. Re-checked them on the truck they are sitting in a level position with fuel in the bowl.

Been racking my brain every day but nothing yet

Just for grins and giggles, swap the fuel pump from your older truck onto the '84.

I would also check for vacuum leaks if you say you clamped off the PCV hose and the idle went UP.

fuel pressure???

how many miles are on the truck?
what gear ratio?

80,000 miles. Well kept vehicle, not beat on or abused. Just bought it a couple of months ago for the transmission and bellhousing; but the truck is fun to drive and too nice to rip apart.

2.94's

4 speed manual overdrive.

1500 rpm at 60 mph