Engine knock/tick, only while in gear

[ETTsiAWD]

Hello, I recently picked up a '99 XL 4x4 with the 4.0 OHV motor and the 5sp auto. It has a mild knock that follows engine rpm, but only when the trans is in gear - in neutral or park the engine is quiet. The knock has the sound of a single sticky lifter, only one occurance per crank rev, only ticks maybe 75% of the revs "hit or miss". Holding the truck in place with the brakes and revving into the convertor, the tick does follow engine rpm - doesn't go away (thinking maybe low oil pressure due to the low rpms when stopped in gear). I can also hear it when driving at low speeds with the windows down, like around a neighborhood. Beyond about 2000rpm it either goes away or blends into road noise (I'm guessing the latter).

I should mention that the truck drives fine, no apparent engine or trans problems, and it only has 80K on the dial. However, I want to get this sorted out as I hate "unknown noises", especially ones that sound like knocking bearings.

Poking around with a stethoscope, it's clearest to hear low on the block from underneath, and on the passenger side valvecover. Being a sharp metallic rap though, it transmits pretty well to just about everything so it's hard to localize.

I already changed the oil, no metal bits to be found, and have tried both 5W-30 and 10W-40 in case it was oil thickness or lifter related. I'm wondering what this could be that sounds like a lifter or rod bearing but only when in gear.

With the trans in neutral or park, the noise goes away. I'm stumped as there shouldn't be any difference in what's moving between having the trans in park vs. in drive but the vehicle stopped. In both cases, you've got all the moving engine parts, the flexplate, the torque convertor, and the trans pump. Everthing else should be not moving - and that's the same for both park and drive-but-stopped. So I'm at a loss here.

I've heard of loose or busted flexplates (on other vehicles), but most descriptions of that indicate a noise when in park and neutral, and it quiets down once in gear due to some torque load "wedging" the flexplate together. That's the opposite of my issue. I've also heard that the crank thrust bearing is suspect in this sort of "noise when in gear" situation, but I'd really rather get some confirmation on that before tearing into the oilpan.

Also, I found a bunch of TSBs from Ford with the title "4.0 owner complains of "diesel" sound", which could easily be this problem, but I can't get the main body of the TSB without signing up (like for Alldata), just the titles. Anyone know what this TSB is referencing? I've got about a dozen TSB numbers with that title.

Any help would be appreciated. I'm a pretty decent shadetree mechanic so I don't mind getting dirty up to my elbows, but I didn't buy this truck with the intention of working on it all the time.

Thanks!
-Mark

 

[wyochimneysweep]

could be rod bearings my chysler 2.7 you could hear the rod knock till it was in gear and had a load on it. good luck

 

[thomdykas]

Hi Mark,

Your description of the "noise" is nearly identical to the one I have. My guess has been a failing lifter except that the sound really seems to come from low in the block at times. Some guess a lifter, and some guess a rod bearing.

This '93 had 125K on it when I freed it from the ivy that had been growing over it in my neighbor's driveway. It ran like a champ after I charged the battery, but the "klack" has been there off and on - mostly on, since. The previous owner says she never heard the noise before. It's quite noticeable, but doesn't seem to affect running, or driving - fuel economy is about right. My rig has about 127K on it now, and still runs good. Still has the noise.

What did you ever find out about what it was, and how hard to fix. I'm a competent shade tree - literally. I'd like to wait for better weather before tackling a top end review in my driveway in NW Washington.

Thanks,

Thom