360 runs strange, lifters??

[MopaR&D]

I've been trying to figure out a weird issue with the 360 in my D200 pickup for years. Basically what happens is on rapid decel or when free-revving it, when the revs fall it sounds and feels like it's not running on a few cylinders for a few seconds. Does it worse when it's cold. I went through the ignition and upgraded some things, no change. I thought it might be a phantom vacuum leak, I just installed an Edelbrock 2732 adapter plate to make sure the carb was fully sealing to the Performer intake but it still does it. I recently replaced the timing chain which was badly worn, definitely runs better but still has the same issue. I did notice that if I shut it off while it's running funky then go to restart it kinda sounds like a few cylinders don't have compression. All I can think of now is maybe some of the lifters are pumping down on decel? Idk how the heck that would work but I'm stumped. It does still have the original cam and lifters afaik, according to the odometer the truck has 133k miles on it (had 122k when I got it). Runs like a champ otherwise but this annoys the heck out of me and keeps me up at night lol.

 

[mbaird]

Interesting… I have a similar issue on the 5.9 in my Barracuda. I am pretty sure it is due to collapsing lifters when revving past 4500 then decelerating. In my case it is my fault because I did the pushrod measurements wrong before ordering new Smith Bros. Pushrods…urgh…. So I used the stock ones which are a bit to long .
Your issue might just be dirty clogged lifters ? Take them apart and clean them .

 

[MopaR&D]

Interesting… I have a similar issue on the 5.9 in my Barracuda. I am pretty sure it is due to collapsing lifters when revving past 4500 then decelerating. In my case it is my fault because I did the pushrod measurements wrong before ordering new Smith Bros. Pushrods…urgh…. So I used the stock ones which are a bit to long .
Your issue might just be dirty clogged lifters ? Take them apart and clean them .

That's a good idea, they can be removed through the cylinder head on an LA engine right?

 

[junkyardhero]

That's a good idea, they can be removed through the cylinder head on an LA engine right?

yes.

i'm wracking my brain right now, because i want to say there's *some* aftermarket headgaskets that inhibit this but i'm coming up empty. but that's something you'd realize straight away.

 

[MopaR&D]

It's about time for an oil change, I might dump some Marvel Mystery Oil in it and see what happens. The truck sat without running for 10+ years according to the seller when I bought it, might have some gunk in the lifters that never worked its way out.

I have some new valve cover gaskets to put in, I'll check if the new head gaskets I installed back when I put freshened heads on it block the lifters from being able to be removed. They were the standard Fel-Pros that come in the full engine gasket set, 8553PT is the part number??

 

[Bewy]

If you had collapsing lifters, I would expect a noisy valvetrain that you would hear. Tap, tap, tap. Collapsing would be noisier than bleed down, tap/tap versus tick tick.

 

[Oldmanmopar]

Have the heads rebuilt your valves are not sealing. Exhaust seats are not sealing do to the valves sinking in the seats causing the springs to lose seat pressure. You could try and shim the springs to extend the life of the engine but this would just be a temporary bandage. I know that sound very well.

The fast way to check is remove the rockers put a straight edge across the tops of the valve stems. The exhaust valve stems will be higher then the intakes due to wear from the fuel not having lead to prevent exhaust seat and valve wear . Use a feeler gauge and measure the difference on the tops of the intake valve under the straight edge.

A quick and cheap way to temporarily fix this is to air up the cylinders one at a time and throw a .020 - .025 shim under the springs with the engine still in the truck. Get new valve seals and also replace them while your in there. You'll see a big difference.