alopeks
NAXJA Forum User
- Location
- D/FW Metromess
Sorry in advance for the long post. I'll start with the critical stats:
99 XJ
4.0, AW4, NP242 - basically bone stock.
221,000+ miles, and it's not just my daily, it's my only.
Engine-wise, in the last 3 years (since I bought it) I have replaced:
Radiator
Vapor Canister Purge Solenoid
Water Pump
Head Gasket (done by a professional shop)
Heater Core
A/C system (practically all of it)
Oil Pressure Sensor
Muffler (Thrush Turbo, stock size)
and as of last week, all 12 pushrods
So, about 3 weeks ago I noticed a sudden disturbingly loud engine noise. As I started the Jeep, it made a harsh scraping-like sound, that was consistent with engine RPMs. I had been driving at that point for well over an hour, with a couple brief stops (no more than 5 min each) and most of that time at highway speeds. The engine did NOT make the noise until I started it up the 3rd time, and yes, I would have noticed.
The sound at first was VERY similar to what I remember hearing years ago when my first XJ decided it was tired of having a straight 6, and wanted to see how well a straight 5 would function. Sadly, the answer is "not well." Thankfully, this time I did not have the same end result, as my first XJ was making the sound of a piston blowing a hole in itself right through the top, which resulted in a very brief trip and a very long wait for a tow truck. Instead, I have been able to keep driving, everyday, for almost 3 weeks. The sound never goes away, but usually gets a little quieter as the engine warms up. It is MOST disturbing (and LOUD) when I first start the engine, especially in the morning.
Oil pressure, temp, voltage were and still are all normal. I listened carefully and timed the sound to determine it was happening once every 2 revolutions, and at first thought it was valve related. Doing some research lead to me to believe it might be any number of things, including flexplate damage, a cracked exhaust manifold, a bent pushrod, cracked or otherwise damaged rocker arm, collapsed lifter, or even an issue with a valve. I also discovered the concept of the dreaded piston slap, which frankly sounds like a painful and cruel way for someone's older brother to pick on them.
Anyway, in trying to eliminate all of the easiest possible problems first, I confirmed that none of the bolts in the flexplate were loose, oil was being pumped consistently to all the rocker arms, and none of the pushrods were bent (though most of them has a good bit of sludge or carbon residue, thoroughly baked onto them. I also straightened out the rocker bridges (3 were somewhat tweaked) and of course replaced the valve cover gasket while I was in there. I was disappointed (but not very surprised) when this didn't solve the problem.
So, what do I try next? If it is piston slap, is there a reason the sound is only heard half as often as the RPMs? Are there (easy-ish) ways of confirming an engine is having piston slap? Your help is VERY MUCH appreciated.
-alopeks
99 XJ
4.0, AW4, NP242 - basically bone stock.
221,000+ miles, and it's not just my daily, it's my only.
Engine-wise, in the last 3 years (since I bought it) I have replaced:
Radiator
Vapor Canister Purge Solenoid
Water Pump
Head Gasket (done by a professional shop)
Heater Core
A/C system (practically all of it)
Oil Pressure Sensor
Muffler (Thrush Turbo, stock size)
and as of last week, all 12 pushrods
So, about 3 weeks ago I noticed a sudden disturbingly loud engine noise. As I started the Jeep, it made a harsh scraping-like sound, that was consistent with engine RPMs. I had been driving at that point for well over an hour, with a couple brief stops (no more than 5 min each) and most of that time at highway speeds. The engine did NOT make the noise until I started it up the 3rd time, and yes, I would have noticed.
The sound at first was VERY similar to what I remember hearing years ago when my first XJ decided it was tired of having a straight 6, and wanted to see how well a straight 5 would function. Sadly, the answer is "not well." Thankfully, this time I did not have the same end result, as my first XJ was making the sound of a piston blowing a hole in itself right through the top, which resulted in a very brief trip and a very long wait for a tow truck. Instead, I have been able to keep driving, everyday, for almost 3 weeks. The sound never goes away, but usually gets a little quieter as the engine warms up. It is MOST disturbing (and LOUD) when I first start the engine, especially in the morning.
Oil pressure, temp, voltage were and still are all normal. I listened carefully and timed the sound to determine it was happening once every 2 revolutions, and at first thought it was valve related. Doing some research lead to me to believe it might be any number of things, including flexplate damage, a cracked exhaust manifold, a bent pushrod, cracked or otherwise damaged rocker arm, collapsed lifter, or even an issue with a valve. I also discovered the concept of the dreaded piston slap, which frankly sounds like a painful and cruel way for someone's older brother to pick on them.
Anyway, in trying to eliminate all of the easiest possible problems first, I confirmed that none of the bolts in the flexplate were loose, oil was being pumped consistently to all the rocker arms, and none of the pushrods were bent (though most of them has a good bit of sludge or carbon residue, thoroughly baked onto them. I also straightened out the rocker bridges (3 were somewhat tweaked) and of course replaced the valve cover gasket while I was in there. I was disappointed (but not very surprised) when this didn't solve the problem.
So, what do I try next? If it is piston slap, is there a reason the sound is only heard half as often as the RPMs? Are there (easy-ish) ways of confirming an engine is having piston slap? Your help is VERY MUCH appreciated.
-alopeks