4.9 knocking/pinging?
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4.9 knocking/pinging?
Hello everyone! My Name is Chris. Im new to the forum. Anyways. I picked up a super clean 91 F150, 4×4, 5 speed, with the 4.9 big 6. It runs good, but it does have this issue where at idle its quite, and runs smoothly (sometimes it has what feels like a missfire). When it's revved (to about 1500-2000 RPM it makes a knocking/ticking sound. I've tried running 93 octane fuel with no change to the sound. While driving it doesn't make the sound unless I'm coasting and apply a little throttle then it ticks again. At 55+ MPH it stays constant... I've cleaned the fuel injectors. Checked the pistons /cylinders for access carbon build-up with a bore scope, and every piston was shiny clean (could see the machining tool marks). Would the wrong spark plugs make this noise occur? I'm just wondering if anyone has had this issue, and or a fix, or some diagnosing I could do. I appreciate it in advance.
Elder User
Joined: Sep 2018
Posts: 735
Likes: 8
From: NC
I am guessing lifter tick. Dump a quart of marvel mystery oil in it, let it idle for about 20 to 30 minutes and change oil and filter and see if that helps. You can also use seafoam and do the same thing. If that doesn't resolve it then you need to look deeper.
cost to try this first 4 to 10 bucks, it will clean out the inside of the engine, no harm done.
cost to try this first 4 to 10 bucks, it will clean out the inside of the engine, no harm done.
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Joined: Jul 2019
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So I actually did try the Seafoam in the engine trick, because I thought that was the issue at first too. It could still be. I pulled the valve cover off. Turned the motor over manually checking all of the pushrods while each rocker are was compressed, and not. None felt loose at all. I also am running Lucas oil stabilizer in the motor, because I've seen a bit of videos where that helped quiet lifter tick, or rod knock. Didn't do anything to quite my situation which kinda leads me to think it could be fuel related pinging, but idk...
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
It sounds like an exhaust leak from the way you describe it, Use a screwdriver or hose and put your ear to it and see if you can find the location.. You can also run codes and see if anything comes up. You can use a paperclip instead of the jumper he uses, You don't have to have a check engine light on to have codes. Sandy
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octaneforce
1987 - 1996 F150 & Larger F-Series Trucks
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Jan 19, 2011 09:13 AM
