Engine noise - Sounds like a diesel motor

[cook90]

1996 Explorer 4.0 (165,000 miles). Today I changed the spark plugs and wires and everything sounded great at first. I test drove the suv and after four miles of city driving the engine tone changed in an instant. It began to sound like a diesel motor. I assumed one or more cylinders weren't firing correctly so after limping home(1/4 mile) I visually checked the spark from each plug/wire and double-checked to make sure the wires were connected to the correct spark plug (they were). I reinstalled the plugs/wires and fired the engine back up and now it sounds even worse. Any ideas? Thanks. By the way, I also put a bottle of stp fuel treatment in the gas tank. Thanks, again.

Dan

-I used autolite platinum plugs (AP105) and duralast ignition wires (4144)

 

[cook90]

Also, could someone please confirm the order that the ignition wires attach to the ignition coil. Mine read 1-2-3 (front to rear) on the passenger's side and 5-6-4 (front to rear) on the driver's side. Right?

 

[2000StreetRod]

correct coil order

Also, could someone please confirm the order that the ignition wires attach to the ignition coil. Mine read 1-2-3 (front to rear) on the passenger's side and 5-6-4 (front to rear) on the driver's side. Right?

Correct

 

[my98nnj]

Which 4.0 do you have?
Have you checked the oil?
Where does the noise come from, top, bottom, front, side, rear???

 

[cook90]

Which 4.0 do you have?
Have you checked the oil?
Where does the noise come from, top, bottom, front, side, rear???

My vehicle is a 1996 xlt with 2wd. I'm guessing I have the 4.0L V6 OHV 12V FI Engine.

Oil checks ok. It was last changed 2000 miles ago in September (pennzoil 10w30).

Upon further inspection, it appears the noise is coming from the front, top of the motor. In fact, is it possible that the top, center pulley on the serpentine belt could make that much noise? It is wobbling, but the noise is SO loud it's hard to identify its location. It sounds like a deep-throaty rattle, just like a diesel engine. And it does change pitch periodically. FYI my serpentine belt hasn't been changed in a long time, if ever. It has cracks and needs replacement.

I should also mention that when I posted above that I "limped" home I wasn't really limping. There was no power loss and the car drove like normal except for the extreme noise. I've worked on a car in the past that had two out of four cylinders not firing and this was nothing like that.

Thanks,
Dan

 

[my98nnj]

I'm guessing I have the 4.0L V6 OHV 12V FI Engine.

Please don't guess, this is important information as one motor (SOHC) has very well known timing chain issues which can cause the noise your hearing if the guides fail.

is it possible that the top, center pulley on the serpentine belt could make that much noise? It is wobbling, but the noise is SO loud it's hard to identify its location.

Seems you have clearly identified an item needing attention.
Remove the serp belt and start the engine.

Noise still present? More troubleshooting needed.
Noise gone? You've found your problem.

 

[cook90]

update

Note: My engine is the 4.0 OHV (X in the vin#).

I removed the serpentine belt and started the engine......no noise. So I'm guessing that the idler pulley needs replacing (bearing failure?). Thanks for your help, everyone.

dan

 

[swetrid]

They didnt make SOHC in 1996 so its definitely a OHV.

 

[cook90]

serpentine belt size

The serpentine belt I removed from the engine is a Napa brand, size 5060870. Autozone and all the other companies I've searched recommend size 5060875 (1/2" longer). What size belt would you purchase/install? Thanks.

Edit: I installed the 5060875. It fits fine. No problems.

 

[cook90]

closing out this thread

Car is up and running. It was definitely the idler pulley bearing that failed. I also elected to change out the tensioner pulley while I was in there because I could tell it was starting to come apart, too. One thing I'd recommend for the 1996 OHV 4.0L is to replace the bearing inside the idler pulley with a similarly sized 6203 bearing (40mm o.d. x 17mm i.d. x 12mm thickness, approx $2-7). The reason I recommend this is because I had difficulty finding a similar idler pulley at the parts stores. I took the idler pulley and the new bearing to a machine shop and for $10 he installed the bearing inside the pulley. Very easy and inexpensive.

 

[96eb96]

Car is up and running. It was definitely the idler pulley bearing that failed. I also elected to change out the tensioner pulley while I was in there because I could tell it was starting to come apart, too. One thing I'd recommend for the 1996 OHV 4.0L is to replace the bearing inside the idler pulley with a similarly sized 6203 bearing (40mm o.d. x 17mm i.d. x 12mm thickness, approx $2-7). The reason I recommend this is because I had difficulty finding a similar idler pulley at the parts stores. I took the idler pulley and the new bearing to a machine shop and for $10 he installed the bearing inside the pulley. Very easy and inexpensive.

Lucky you caught it now. Everyone should change these two pulleys. They usually crap out on the road.

 

[cook90]

Very lucky. I'm also fortunate to have found this site. It's a wealth of information.

 

[Weapon]

similar sound

I replaced my plugs and wires today. When I started it up there was a rattle which seems to be coming from the ignition coil. What this gentleman has described is very similar but as I said I believe it to be coming from the coil terminal. Please help.