Good afternoon I believe I have a pre ignition problem on my 2006 Ford ranger 4.0l xlt 4x4. As soon as I press the gas petal I get kinda a low pitch noise kinda sounds like a cow mooing and after I get moving that stops but comes back when I stop and go again, I also have a rattling noise coming from the engine it sounds like and that occurs as soon as your press the gas petal and never seems to go away, it's not super loud but very noticeable with the radio off, I just replaced spark plugs and that didn't help I have autolites double platinums in. Do any of you have any ideas? Thanks in advanced 😊

 

The 4.0l SOHC engines used in Rangers from 2001 to 2011 had 2 long timing chains that could get loose and then break the chain guides, and this causes a rattling sound
Ford did a redesign of the chain tensioners in 2003 so most 2004 and up didn't have this issue, but with long timing chains it can still happen if a tensions starts to fail

Google: ford 4.0 sohc timing chain problems

For more info on that

You can change tensioners, and that may help with the rattle, but............rattle comes AFTER guide is broken, so..........it will get worse over time
New tensioners are not a waste of money because they are needed regardless of when you change the guides

The original problem was that the tensioners springs were not lasting and they wouldn't hold the long chains tight at startup, oil pressure takes over after startup
So the long chains banging on the guides at each startup weakened and then broke them
The new tensioners have better springs, but, any part can fail over time, even with better design



Pinging/knocking, pre-ignition, shouldn't happen on the 4.0l SOHC engines because they have a Knock Sensor, it adjust the spark timing so this 9.7:1 compression ratio engine can run on Regular gasoline, 87 octane
I would try a tank of 93 or 94 octane gasoline and see if that noise goes away, if so then Knock Sensor is not working, which could be caused by the timing chain rattling????

I would stop by an auto parts store and have them read any codes from the computer, WRITE ANY CODES DOWN!!!!!
It may have a knock sensor code in history

 

Thanks for your reply! So I checked codes tonight and had none never has a code been thrown on that truck it only has 65,000 miles on it, but I'll throw some octane booster in my tank and see how it responds, but how hard of a job is a timing chain tensioner replacement on that truck
​truck?

 

Several videos and how-tos out there on changing the two long chain tensioners

Not that hard, just wrench work, no special tools, 27mm socket, is needed

Video here: youtube.com/watch?v=-5mI-ah4qRQ

Thermostat housing need to be removed, how-to here: https://howtoreplacefordthermostathousing.com/
The lower housing had a tendency to leak on this engine, so give it a close look