Thedude584

So one of the valves on my 2000 4.2 is stuck open so my truck idles really rough and the amount of power is steadly decreasing. Any ideas on where i can get new heads for it? or should i try and find a motor to swap? I'm not looking to upgrade by putting an 8 in it i want the same motor. any helpfull info would be great.

transmaster

I don't know the the clearances are between the pistons and the valves so I don't know if the valve is hitting the piston crown or not the bottom line is stop driving it NOW!!!! before you have anymore damage. You will have to pull the head to see what has happened. In this case I would have both heads rebuilt so you have both heads with the same number of hours.

Good old Bill

Sound advice from Trans, am wondering why the valve has stuck open? Seen it happen before on the 460 engines, usually they would stick closed and bend the push rods. Any way, pull the heads and have the machine shop go through them. Might need a new valve and guide. Should be fixeable.

Fast Hampster

I have nothing to add to what Transmaaster and Bill said, but i wanted to ask about some pictures of a stuck valve if possible. I've seen a lot of different engine issues, but never even heard about this one.

transmaster

Have you looked to see if the engine valve is stuck open. There is no mention of valve problems in all of the forums I looked at but there are reports The 4.2L V6 has an occasional problem with the Intake manifold runner Control failing and this will cause all of the problems you are mentioning. This problem is reported by the OBD.

Good old Bill

Hi Ham, as we know valve action is due to the camshaft opening the valve, the valve valve spring closing it. When internal clearance between valve and valve guide get messed up the valve can stick in any position, open, closed, or in between. Carbon deposites are usually the cause, although with engines sitting over winter and not winterized, moisture is the problem. Boats and small garden equipment fall into this last catagory.

Good old Bill

Hi Trans, changed my intake seals a while back and seen the intake runners you mentioned. Can you tell me exactly what they do? This is new territory to this old coot?

transmaster

I don't know the 4.2L V6 well but as I understand it the ECM can switch between two intake runners according to the engine speed, load, etc. If the device that does the switch fails the truck will run real rough, not have much power, etc.

Good old Bill

Thanks Trans, so I guess its something like secondaries on a carb. Sure wish I would have paid more attention to it while apart. Do remember two different passages to each cylinder. The actuator being sandwiched between engine and firewall. They are sure changing these engines. Thanks again.

transmaster

This is the sort of things they do with engines these days to get high horse power and good gas mileage, proper emissions, etc.