I've got a 300 that up until recently has not given me any major problems.


It's been sitting for the better part of the year, and I started it last weekend and drove it around the block and shut it off. It ran fine at this point.


After sitting for another week, this weekend I started it back up and as soon as I turned the ignition on, I heard what sounded like a snap or a pop from under the hood, but initially thought it was just the starter engaging. The engine fired right up, but with a noticeable misfire.


The plugs are brand new, replaced earlier in the year but the truck hasn't been driven at all. I pulled the plugs and #6 was wet, so I checked the wires and the #6 wire was rusty, so I picked up a new set of wires.


I also ran a compression test on it, and noticed #6 had 0 psi. A year ago it had compression, and was within range of all the other cylinders, so it's definitely a new issue. I tested with two different gauges and got the same result, and tested multiple cylinders to ensure the gauges were working, and they are. So it's clear that I now have 0 psi in the #6 cylinder. #5 is good.


I also have true dual exhaust with straight pipes, and the exhaust impulses for the rear three cylinders is noticeably different from the front three. The front three appears to be much more smokey (blue oil smoke, not white coolant) than it has been in the past, and I don't know if that's related or just oil residue in the cylinder from sitting for so long. There is very little, if any, smoke coming from the rear 3, but you can clearly hear something is wrong.


I am suspecting a broken or bent or stuck valve, a broken valve spring, or possibly a bent or broken pushrod for the exhaust on #6. I can hear the typical ticking of the lifters from these engines, but there is no rod knock that I can hear. I don't see any metal flakes on the oil on the dipstick, but plan to drain the oil to check for anything metallic. I also plan to open everything up and check for myself, but I am more or less interested to know if anyone else has had any similar issue, and can share any experiences that might relate. Or if there are any other checks or things I can do to verify my suspicions.


The engine's got over 220k on mostly all original parts, so if it's time for an overhaul, then that's what I'll do...

 

Lots of things could be the cause, and I probably won't be much help but if you can pull the valve cover watch the valvetrain. And that will give you an idea of what is going on. Maybe it broke a pushrod...

 

Hopefully it's just a bent pushrod. It's not uncommon for the valves to get a little stuck after sitting.

 

This. Valves stuck after sitting, started ok the first time, got really stuck after that (kinda like a shifter that goes into 4 just fine but breaks on the way back out), valve-train carnage ensued.

 

Do a leakdown test - turn the crank so that piston is at TDC at what SHOULD be between the compression and power strokes. At that point, both valves should be closed. Then you fab up some way to pump air into the chamber via the spark plug hole. Normally it would build pressure of course. But air will come out somewhere. Where it comes out tells you (sorta) what broke -
Air cleaner - intake valve (pushrod, etc)
Tailpipe - exhaust valve (pushrod, etc)
Crankcase - piston, compression ring, etc, or poss head gasket (chamber-to-oil, unlikely)
Radiator - head gasket chamber-to-coolant (unlikely)

Given that it's a big zero, one or the other valve seems the most likely.

 

That was actually a great idea. I hooked up the air compressor to it and it definitely sounded like I could hear some air coming through the intake, so that may be where the problem is.

I'll be pulling the valve cover off this week to confirm.

 

I think I found the problem


Is it as simple as ordering a new pushrod, removing the rocker arm, removing the bent rod, installing the new one, and torquing the rocker arm back to spec?

Or will there be anything else I'm missing?


Do I need to pull a straight rod to measure before ordering, or will a stock replacement be fine? Any suggestions on a place to order from, or would my local oreily's or autozone be sufficient?

I'll be doing all new gaskets, as well as a thorough cleaning of the engine while everything is accessible...

 

Get a stock replacement rod, make sure the rocker arm moves and the valve isn't stuck