Do I have a rod knock? | Ford Explorer Forums - Serious Explorations

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Do I have a rod knock?

sd_iconoclast

Active Member
Joined
February 17, 2012
Messages
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City, State
San Diego, CA
Year, Model & Trim Level
1991 Explorer
I have a 91 EB with about 183K miles.
I have just replaced both heads with new ones as both of them cracked around 135K and 150K.
Yes, it did run that long with cracked heads.
Apparently, I had alot of sludge because (on the advice of some smart guys on this forum) I recently used SeaFoam and saw my oil pressure at Idle go from about 8 to about 20.
Along the way, my engine has developed a noticeable "clacking noise" and I am worried that it is a rod knock.
The noise seems to start pretty consistently around 3000 RPM, but it will generally start at lower RPM under heavier load, higher under lower load.
It seems to happen much less when the engine is cold.
I dont think it is lifter noise because I recently changed out all my lifters and I heard no difference.
Is there a good way to tell if this is a rod knock?
Does anyone have a rebuild short block they would like to sell?
Or a short block core in socal that they would like me to haul away?
 






The way you explained it, sounds to me like it's pinging, not rod knock. Rod knock would be MUCH more pronounced, even at idle, and get much louder when barely tapping the throttle or revving the engine. Try filling with $10 worth of 91 octane and see if it goes away. Another thing that helps is by using Techron Complete Fuel System Cleaner regularly, like with each oil change. The higher octane from premium gas will help stop the pre-detonation which is actually what you are hearing, if it's pinging of course. If it is however, you won't hear it anymore after you put the premium gas in, until you put 87 back in it. The pinging would be due to carbon build up, and possibly fouled plugs from the recent seafoam treatment. Also, the one treatment of seafoam I am sure didn't get all the carbon buildup out..the Ford TSB has you go through and repeat the process a total of 3 times I believe, through the vacuum underneath the throttle body. That same TSB also says to ensure the engine gets revved to above 3k rpm every so often even with regular driving, just to facilitate the carbon burning process, if I remember correctly. Hope this helps!
 






Funny you should say this...
Yesterday morning was rainy and misty and it seemed to me that the "clacking" was better.
This got me thinking that this might be preignition. I am just waiting to finish this tank of gas to try premium.
But I am mystified as to what could cause it. The heads have just recently been replaced, so they are perfectly clean.
They had both cracked so the coolant in the combustion chamber had stem cleaned the pistons to be pretty darn clean.
And of course, the plugs were new.
I used Seafoam in the oil, not the gas so I just dont see why it should ping at this point.
Was gas somehow better back in 1991?
 






Vacuum leaks and intake leaks can cause pinging. Double check everything you took apart when changing the heads. Its easy to forget or miss something on a big job like that. Does it do it mostly accelerating or under load?
 






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