Knocking (backfire) in Intake? I'm stumped! - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 12-04-2014
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Knocking (backfire) in Intake? I'm stumped!

I recently purchased a project 2000 Ranger with the 4.0 OHV engine. It has an odd problem that seems to be an extreme backfire through the intake plenum associated with cylinder number 1 - if I pull the plug wire, the backfire (loud pop or knock) stops. No other cylinders have the same effect. Compression test on cylinder 1 is good, so I am thinking it's not a valve, head or headgasket issue?

Oddly enough, I found this YouTube video showing the EXACT same symptom but no additional information:


I am stumped, any suggestion greatly appreciated! This is my first Ranger and my first post, although I have wrenched on British cars for many years. Looking forward to actively participating!

Last edited by jharrellh; 12-04-2014 at 08:29 PM.
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Old 12-04-2014
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Compression is good, i.e. 160-170 on all cylinders.

What does #1 spark plug look like?

Check firing order.


Could have a lifter that holds intake valve open only when running, pop valve cover off
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Old 12-05-2014
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Firing order confirmed, plug looks pretty normal, maybe a little light if anything. Compression on 1,2, and 3 is good - ran out of time last night but will check remaining cylinders and pull valve covers this weekend. Thanks for the suggestions, I am starting to think it has to valve/vavetrain related.
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Old 12-08-2014
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Kind of interesting, don't you think? Valve is free, shaft looks okay, pushrod is straight. Looks like it just sheared the pin and walked off. Anyone ever see this? With 160K mile would you put a pin in and see what happens? http://i122.photobucket.com/albums/o...psaf2abbb5.jpg
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Old 12-10-2014
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Just to wrap this up, replaced the rocker shaft assembly and all seems well so far.
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Old 12-10-2014
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Never seen that on this engine before, pin must have been made, or installed, on a Monday, or late afternoon on Thursday before a long weekend, lol
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