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Pushrods too long??
Okay guys, been awhile since I have worked on the "pit" or posted anything due to recovering from surgery.
It's been driving me crazy thinking what is wrong with the truck.
After installing the new cam it runs good when cold. Once it warms up good, it doesn't idle as good and makes a rattle/knock sound. This sound is only when the rpm's are up. or revved. not at idle.
Acceleration and steady cruise above 40 is great. Low speed (0-30) cruise isn't very smooth but only after it warms up. When still cold it runs great.
This rattle/knock sounds as if it is coming from the lower intake area, if that makes sense and have been told it was a rod knock but it isn't a deep metal sound at all.
What has been done;
1)Every sensor has been replaced
2)Rechecked pushrods for proper tightness and to make sure they weren't bent.
3)Intake manifold and TB cleaned and new gaskets - checked for vacuum leaks.
4)New - distributor and module (thought the noise was coming from this at first), distributor cap/rotor, ignition wires and plugs.
5)Ignition coil tested good.
6)Water temp normal
7)Oil pressure normal
8)Fresh gas (91 oct. )
9)After running with new plugs they look very good
What this is not;
Not an exhaust leak
Not valvetrain noise (lifters/rocker clatter etc.)
The strangest things I have found;
1)When attaching a vacuum guage to the vacuum "tree" on top of intake the motor instantly dies. Remove guage before it actually dies (attached for only 1 second or less) it stays running. Whith the vacuum line disconnected for these attempted test's the idle smooths out but dies when you plug the vacuum leak?????
2)The compression check;
120 across the board (hot or cold). Unfortunately I do not know what it was before the cam swap.
Where I left it before my surgery I had tried to pull the oil pan to inspect the lower end but found I need to move the AOD back at least 1/2". I have the pan resting on the K-member with the oil pump and pickup removed, well the pump is out and the pickup tube is at the bottom of the pan.
What bothers me is the compression - The motor only has 40K miles since a rebuild. When I did the cam swap I didn't think about pushrod length. Could too long of a pushrod cause the low compression readings from leaving the valves open a hair and possibly cause some kind of ignition knock or rattle (not a ping) and that is what I am hearing after it warms up and causing it to run a bit rough at low rpm?
What's up with the vacuum causing it to die? This is just too wierd!
Also, I've never had a burnt valve before so I have no idea what kind of symptoms they produce. Are my symptoms (the knock/rattle after warm up), the same for a burnt valve or two?
SORRY FOR THE LONG POST! But I have been down rocovering and thinking alot about it and hopefully I'll be able to wrench on it soon.
Thanks for any thoughts on this crazy truck. At least you know a Ford man when you see him - He'll be the determined one!
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'90 F-150 Super Cab - 5.0/AOD/3.55
275/60/15 BFG's / AR Wheels
Latest mod - 204/214 Cam
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Linear Mode
