Jeep 4.0L cold start tapping

[curtjames37]

Vehicle: 1998 Jeep Cherokee 4.0L I6, 137,000mi.

I've been lurking here a while and this is my first post so bear with me. I'm experiencing a pretty noisy tapping sound when starting the engine cold. It sounds a lot like piston slap but I have never heard of this engine having that problem before. Ambient temp doesn't seem to matter. The noise won't start until oil pressure builds. It starts off faint and then gets more pronounced as oil pressure rises. After about 2-3 minutes of idling the noise is gone and won't return until the motor is shut off and restarted. Once the oil reaches operating temp the noise won't return until it cools off and is restarted. There's been no reduction in performance, idle quality, or fuel economy since this started. Current oil is 10w-30 Havoline conventional with a Wix filter.

I'm thinking it might be a lifter but I'm certainly no expert so I'd like to get a second opinion. Any ideas on what it might be? Thanks in advance!

 

[Merkava_4]

That sounds to me like a hydraulic lifter is bleeding off shortly after a few revolutions of the camshaft after initial start up. It could be bleeding off from a momentary interruption in oil flow, but as the oil pressure slowly builds, it finally gets pumped back up again. I'm thinking you need to get oil pressure sooner. Trying a different oil filter might work.

 

[curtjames37]

Thanks for the reply, Merkava_4. I have tried several different filters including the Wix that is on there now, a PureOne, and a Mobil 1, and none of them changed the sound or duration at all. One thing I noticed when I started it to go to work this morning was it actually took a few seconds (maybe 1-2 secs?) after oil pressure was up to start tapping. The oil light just blinks on and pressure is usually up within a second or two.

 

[Gary Allan]

I'd Auto-Rx it to assure that there's no imbalance in oil flow up top. You can pull the cover and see which one is the problem. The shame of it is that the 4.0 requires head removal if you wanted to change out lifters. The 2.5 does not. I don't know what the screw up was in the head redesign for the 4.2/4.0 head transition.


:welcome:

 

[curtjames37]

Thanks, Gary. I think I will order a couple bottles of ARX and do two treatments on it. I've only had the Jeep for 20k miles and I'm not sure how well the previous owner(s) took care of it so I'm sure the ARX will do some good. If it doesn't help my lifter noise then I'll pull the head and replace them.

 

[meep]

carbon build up can cause these noises too. Mine had a nasty piston slap/knock until mid-warm. Suspect the piston was actually contacting head carbon until heat expansion increased the gap. I did the water cleaning trick and it's been immediately more quiet. Less pinging too. But, I've lost some mpg in the process (lowered compression by clearing out the carbon).

Use oil cleaner, use fuel cleaner, clean the carbon, and if there's noise left you'll know it's just gonna be there. These engines can get pretty noisey as they age but I'm told that's fine and they'll just keep going.

M

 

[PT1]

Just go on Ebay and get a Vortec engine cover for it and nobody will question anything.

 

[JTK]

Curt, have you owned this Jeep long term? Did the noise just start? Reason I ask is, I've owned a 1994 4.0L Cherokee and a 1997 Wrangler 2.5L. Both clickedy-clacked like diesels from new. That was back when I ran PH8A's on them and any'ol brand of 10w-30 @ 3/3000 OCI's. Great vehicles. I miss them.

 

[BarkerMan]

If you can take off the valve cover and still start you engine push on each rocker carefully with your thumb or the palm of your hand. If you can change the noise you have your answer, it's a lifter.

With the engine off remove one spark plug wire. Short it to ground carefully. Start the engine for each cylinder, one at a time. If you can change the noise you also have your answer, it's a lifter.

 

[mechtech2]

Lifter noise doesn't change with the plug firing or not.

 

[BarkerMan]

It will if you have a damaged valve, valve seat or a sticking valve.

 

[curtjames37]

UPDATE:

The noise is still the same. I bought a stethoscope and I've ruled out the lifters. I can't pinpoint exactly where it's coming from but it seems to be somewhere near the rear of the engine. I will try to pinpoint it further but it's hard because it only does it for a short time at startup. Not enough time to really try to find it. It seems to be noisiest at the bell housing but I'm not convinced that's where it's at yet.

I'm a few hundred miles into an ARX rinse phase and the noise hasn't changed one bit. Any more ideas guys? I'll try to get a recording of it so you guys can hear it.