First - I am new to this site, but have lurked for several years. I love the info on these threads.

I have a 1990 F-150 4WD with the 4.9L

I let a "friend" borrow my truck for a few months while he was getting back on his feet. The truck was not returned in the best of shape (tail gate broken, interior lights not working, flat tire and spare on the truck). But the biggest bugaboo was that there was a dead miss on the #4 cylinder.

He claimed it had just started.

After trying all the simple things i dug in thinking it was an injector.

Much to my surprise, when i removed the valve cover, the #4 intake push rod was lodged to the outside of the rocker.

I removed the rocker, checked the push rod for straightness, then reinstalled and checked compression, spring bind and cam lobe travel (at the rocker).

My question is two fold.

The only time I have ever seen anything similar was when a buddy and I over revved an old chevy 350 until the valves floated - would this be possible on my 4.9L?

I tore into it thinking I was going to have to remove the head (once the injectors checked out I removed intake and exhaust manifolds ... gah!) should I go ahead an remove the head and check it out?

Compression checks good across the board now ...

Thanks!

 

Is this a manual trans truck? If you can't find anything wrong...loose rocker, broken spring, etc, then an over rev scenario is possible due to a ridiculous downshift.

Weak springs could be the culprit also, but I've never seen that in a factory application.

 

My '93 4.9 was like that when I bought it. I put the rocker back and never had a bit of trouble. 265,000 miles and never burned a speck of oil after that. Ran smooth as silk.
PO said it developed the dead cylinder when he tried to use some old gas. He probably over revved it trying to get it to smooth out.

 

Possible but highly, highly unlikely. The stock 300 head can barely move enough air to spin fast enough to hurt itself. In stock form the engine is good for sustained operation up to about 5000rpm. People over on FSP commonly reuse stock springs with hotter cams (and I mean reuse the originals, not buy a new set of stock springs). The stock cam probably won't get the engine spinning fast enough to have problems and the head doesn't stop you before you get there anyway. I've never had reason to floor it in neutral for extended periods of time so I can't say for certain


I'd just run it. Just the gasket set to take the head off and put it back on costs about as much as a pick-n pull head. If you want to take the head off wait until you've got a ported and polished JY head to put on.


Your friend didn't **** up the engine by accident. He had to rev the crap out of it in neutral or intentionally downshift into 1st or 2nd at highway speed to do that. It's possible he did it by accident but when you've got some guy who's otherwise treated the truck like crap telling you that the engine that's known for not having problems with company drivers revving it out it on every shift just randomly spit out a pushrod when he was driving it. There's lottery winning or getting bit by a shark odds he's telling the truth.

 

thank you very much for the info.

I have not had the opportunity to get it all back together to check it out.

He won't admit to anything - said it happened while driving on the highway - I don't even know how this is remotely possible.

the spring is not broken and compression is at 140 (all cylinders are between 135-140)

Once I get it back together Ill repost something.