Automotive Forums

This is a 2000 4.0L SOHC engine.  I have an engine noise that sounds like detonation, around 2400 rpm and up with the engine moderately to heavily loaded.  But it is not detonation, it is insensitive to gasoline octane level.  I have been told that it is one of the cam chains by a dealer.  Probably the rear chain tensioner.  They want $400+ to fix it.  Has anyone experienced this issue, and does anyone know how difficult it is to fix?  The vehicle has 140,000 miles on it and this noise has been there for over 80,000 miles.  

Hello,

I have a Ranger that does the exact same thing!  It is a 1999 Ford Ranger XLT 4x4 with the 4.0l OHC Engine and automatic trans.  No one can seem to pinpoint the problem and i fear causing damage to the engine.  The problem was present when i purchase this truck with 124,000 miles on it and it now has 135,000.  For me the problem is only present when it is warmed up and above say 2500rpms.  It is very audiable when backing off the gas petal after pulling out somewhere until it downshifts.  A Ford machanic rode with me one day and said rod bearings.  But, since that day others i have talked to about it or heard it claim it couldnt be the rod bearings.  So to be sure it was not the rod bearings i disconnected the spark from each cilinder one at a time and run it up to those rpms.  Every time the noise was present indicating it is not the rod bearings.  I have also seen TBS's about carbon build up causing this issue so i tried decarboning the engine, no improvement,  This has driven me crazy since the day i noticed it (shortly after purchasing the truck) and if anyone has figured it out i am eager to know what it is.  I have also heard about a timming chain causing noise at hard acceloration from www.auto.consumerguide.com.  

Thanks,
Geoff