Engine running rough

[Hammerhead]

For what it is worth, we were having trouble with the engine running rough in my CCKW .  It was especially bad when increasing the RPM's going from second to 3rd and even worse when shifting to 4th.  We tried cleaning the gas tank out, the fuel filter, rebuilding the fuel pump, rebuilding the Carb, adjusting the float level 2-3 times, checked the timing and rechecked it 2-3 times.  Of course we replaced the points, condenser, and rotor.  Replaced the spark plugs twice.  Compression and vacuum checked and double checked.  STILL couldn't find the gremlin causing it.  THEN, a friend suggested getting a rebuilt Distributer and DANG it fixed the problem!  She purrs like a kitten and smooth as can be.  The internals of the distributor must have been plain worn out.  It sure was a vexing problem that had us pulling our hair out but is sure taken care of now.

[emptyhead]

Thanks for the reply. Have run the engine with old distributor and new out of the box stil the same thing. Ran it with different intake but still running on three cylinders. The saga continues.

[Smadge]

Crazy!

[colkking]

not for nothing....might you have a vacuum leak somewhere that is causing it to run rough?
for what it's worth, I had that problem with my old Mopar...

[emptyhead]

Part of the vacuum leak was from the manifold but still hunting down problems will update. Thanks guys

[yd328]

I haven't read back in the post, have you tried blocking off the large vacuum line going to the brake booster?  The booster itself could be a source for a big leak.

Gary

[emptyhead]

Yeah just put a plug in the middle. The only silver lining in this whole thing is I’ve gotten to know a little more about the whole engine in general since I’ve basically taken part over half of it. Thanks guys

[Cleprechaun]

Pull the heat riser out of the manifold. Supply gas to the carb via elevated bottle of gas. Get new cheap coil and attach GOOD battery directly to it. Squirt SMALL amounts of gas into carb as it’s running. Make sure there are no vacuum leaks, an open hydrovac line will make it run crappy. Wiggle spark plug wires as it is running (funnier if you have a buddy do it). one of these tests should shed light on the problem.

[8683jb]

Wiggle spark plug wires as it is running (funnier if you have a buddy do it).

Soon-to-be former buddy! It would be funnier though.

[Cleprechaun]

Remove heat riser butterfly valve in exhaust manifold.  Replace ignition coil and hook a GOOD battery straight to it. Wiggle plug wires while it is running. Plug the hydrovac hole right at the carb, they run terrible if that leaks. Gravity feed gas to the carb

[HenryVIII]

Hi
I have a couple comments after reading about this problem. I cannot remember but I thought you said this is a rebuilt engine, so here goes. You have good compression on the leak down test which means the rings and valves are sealing and holding, because this test is done with the piston at TDC and the valves closed and will show OK even if you have a collapsed lifter. But you have low compression on 4,5,6 when it is running. But the valves are all moving/lifting when you check with the head removed. Also you have the correct valve lash when you checked it (.040-.080) correct? 1,2,3 are on one lifter body and 4,5,6 are on another lifter body. Each lifter block is hydraulic and fed oil from an internal oil galley. Is it possible an oil passage supplying the lifter galley is blocked or maybe a plug was left out when the engine was reassembled and the rear bank of lifters are not getting enough oil to open the valves completely and/or at the correct time. Do you have enough oil pressure when idling? 

Here is my suggestion. 1 Remove the rear lifter block and see if the gasket is damaged or missing or leaking. 2 If gasket was OK remove both the lifter blocks and see if they are both getting the same amount of oil when the engine is cranking over. If not you have a oil supply problem. 3 if they are both getting same amount of oil, switch lifter banks and see if the problem moves to the other 3 cylinders. If problem moves you have a bad lifter bank.

Is the cam timed correctly? I think so because this would affect all cylinders, not just 3. The only one thing that these 3 cylinders have in common is the rear lifter block.

I think the rear three cylinders are getting fuel and spark but they just do not have enough compression to do much.

Good luck. Please keep us posted as to what you discover.

Henry