jfw432

I have a 2000 S10 with the V6. Before I get into it, I want to say that I've had this exact same problem on my 91 Jeep Cherokee (now sold). Both engines run clean under very light or heavy acceleration. High rpms are no problem as well. Idle is also clean.

The issue seems to come with very low loading on the engine. I'll give two examples when the engine will tap. First case; If I'm cruising at any highway speed (45mph+) and let off the gas there will be a faint tap that is dependent on engine rpms. The second I put the slightest load back on the engine by going up hill or by touching the gas pedal again, the tap will stop. The second case is; When I accelerate normally just before a shift. Let's say I accelerate on a level road and the engine shifts at 2900rpms. Between approximately 2700rpms and 2900rpms, just before the transmission shifts, I'll get a loud tap until it actually shifts. This tap is also dependent on engine rpms. If I give it more gas right before the shift when I first hear the tap, it'll go away and come back at a higher rpms just before it shifts.

I drove my jeep like this for 5-6 years and probably 50k miles before selling it. I pulled apart the valve train a few times looking for various things that could be wrong but never replaced any parts and never found any problems. I tried using a thicker oil at 20w50 and it made the tap a little deeper sounding and raised the oil pressure by a lot but the issue was still there.

It doesn't seem to hurt the engine but it can't be good. The first mechanic that heard the noise said he thought it was a broken wrist pin and he recommended I just continue driving it until it blows up. I've also heard that it could be piston slap. I'm at a loss and would really like to know if this is a serious issue or just a nuisance.

jfw432

Anyone? I almost never hear this when I first start up the engine but after 2-3 minutes it comes back.

jfw432

bump.

EinST

It's really hard to tell except the piston slap should be most noticeable after a cold soak. One thing you could try is to get your used oil analyzed, e.g., at blackstone-labs.com. Look for high levels of certain wear metals?

jfw432

Good idea on the oil analysis. I just ordered a test kit so maybe that will come back with something. Obviously, it'll be a while before I get any results but at least I can get some information on the issue to hopefully tell me if it's a big problem or something that can be fixed in a weekend.