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4.0L starting to sound like a diesel

9

93XJdude

NAXJA Forum User
Location
Colorado Springs,CO
for the past 4 months my engine has progresssively started to sound like a diesel. it really does it when up to operating temp and idling. could this be piston slap? i have searched a lot but all ive seen is them sounding like it on start-up. is the engine starting to die or is it something to not worry about? thanks for any help.
1993 sport 4.0L HO aw4
Tony
 
Same here, I also have a 93 sport 4.0L HO aw4. How coincidental.
I've been told by a mechanic my rods inside of the engine are loose and will eventually break and come through the block in which case I'd need a new engine. How many miles do you have? I've got 162,xxx.
 
Three years ago, I took my XJ into the dealer to replace the clutch and rear seal. When I picked it up a few days later, I thought someone mistakenly put a Kenworth motor in it. What a racket! In my case, the diesel sound continued on while driving - not just during start up. It did not make any noise prior to the dealer service. I took it back to the dealer and asked what was wrong with it. The diagnosis: "The engine is just tired". It had 174K on the clock.

The sticker shock on the clutch replacement along with the technical analysis of my motor dieseling prompted me to start doing my own maintenence. The first task was to drop a JDM engine into the XJ. I've kept the old one around so I could possibly do a re-build one day. Maybe then I will find out what was wrong with it.
 
Same here, when I pull into the parking garage at work' it's a little embarrassing. If anybody ever asks me I'll tell them it is a diesel. With mine

I'm told it's rod knock. I'm in the process of collecting new parts so when it does kick the bucket I'll just replace it.
 
i had that same problem 3 years ago i think its nothing but I was worried back then I changed the hydraulic valve lifters and tappets it fixed every thing but its a big job you need to take off the cylinder head not just the valve cover then there is this thin long tool to reach the lifters. but after this fix the first time i started the engine it felt very quiet and stable and didnt need to be cranked as much as before.
 
bewilderedbeast said:
My 96 has 127K and sounds as quiet as when it was new.
Click to expand...
x2

i had a tick and now its gone with some MMO. i have 172K miles and it sounds smooth. i do oil changes at 3k and use castrol 10/40.

maybe because i drive like a wuss.
 
165k on my '88. With the hood closed, it's very quiet. Open, I hear the injectors the loudest.

Frequent oil changes, good filters all around. I flog mine on the streets.
 
Could be piston slap or a number of other things. First, check your compression.

You can also get a "mechanics" stethoscope to help isolate the source of the clatter. Some use a long handle screwdriver and their ear to the handle. Place the tip around each of the injectors, on the valve cover by each cyl, even underneath. Also check your exhaust for leaks.
 
My moms xj started that knocking noise so found the rod that was nocking, dropped the pan and replaced the bearing(it was shot) fixed it for three days, then back to constant knock. took it to a dealer and they said it was a bent rod. That was 80,000 miles ago, now at 300,850 miles and it still runs just as strong rod knock and all.
 
Many XJ's of that vintage have piston slap, but you should beware, because it is almost exactly the same sound and frequency as a failing water pump, and if you have both you may not know it for a while. So check your water pump and other belt pulleys. If it's a pretty steady rattly sound, rather than a rhythmic knock or clack, and there is nothing loose, it's probably piston slap. It will often get quieter when the engine heats up, and will not be noticeably louder under load. My 95 has slapped quite audibly since I got it at 110K miles. It still slaps audibly and runs like a watch otherwise at over 260K miles.

Rod knock will usually be more regular, and slower, since not all the rods will knock at once, and will be noticeably worse under load. A bad bearing will usually compromise oil pressure too. If you have good oil pressure, you can probably relax a bit.
 
oil pressure is good, just recently replaced water pump. like i said it is only really noticeable at idle at operating temp (210) and it isnt steady the frequency fluctuates.
 
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