Cracked spark plugs

JEEPNKID71

MEMBER
FORD RANGER

I own a 1999 Ford Ranger XLT 4.0L. It has just turned over 98,000 miles. MY problem is this. It seems that roughly every 6 month's my truck ends up cracking a spark plug. This occurs in the same cylinder every time. I am not sure of the cylinder number, but it would be on the driver side closest to the radiator. Whn I pull the plug everything looks good but the insulator is cracked. I replace with a new plug and the truck will run fine for 5 or 6 month's until it does it again. I have noticed that sometimes at idle the engine will be at about 900 RPM's and drop a few hundred RPM's for bit than return back to normal idle. This does not happen all the time as it is speratic. On some occasions when slowing down from crusing speed to idle the engine will run at about 1500-2000RPMS when at a complete stop than return to normal idle speed. This also occurs every now and than and is not consistant. I do no think that is normal for this vehicle. Please let me know what it may possibly be.

1 Reply

MIKE H R

MECHANIC
3,094 POSTS

With reference to the spark plug check to see if there is anything touching it when the truck is off or running, also check the wires to make sure they are not too tight when the engine runs. Check and see if there is any movement when the engine is put in gear. To do this have someone start the truck and with the brakes on put the transmission in gear and see if the engine moves. That would be checking the motor mount. With the iratic ideling has the throttle body been cleaned out. There could be a little carbon build up.