Infamous 4.0 Diesel -
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Unread 08-13-2011, 07:17 PM   #1
Registered User
1998 ZJ 
Join Date: Apr 2007
Location: Northern, New Hampshire
Posts: 438
Infamous 4.0 Diesel

So my 4.0 has that infamous engine ticking/tapping that makes it sound somewhat like a diesel. Its got over 200k miles on it (I just got it though). Seems to run pretty good but I'm planning a tune up and wanted some feedback from everyone on how to prolong this engine. First, does anyone know what causes this ticking tapping sound on these engines....I tried pulling the wire off each injector to see if any cylinder quieted down but it made no difference.

Specifically is there a certain weight oil I should use? Temps range -30 to 100F here in NH. What about spark plugs? Thought about trying a screamin demon coil and opening the spark plug gap but will that have ill effects on this engine?

Looking for input and opinions about this!! I want to max my usable engine power and efficiency but also want to keep it running as long as I can!

-2013 JKU Sport, bone stock, Auto with 3.73's
-1998 ZJ Laredo, 4.0 42RE Selec-Track, 30" M/T tires
Skydmark1 is offline   Reply With Quote Quick reply to this message
Unread 08-13-2011, 07:42 PM   #2
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YJ Wrangler 
Join Date: Oct 2010
Location: Hamilton, Ontario
Posts: 742
My best luck with killing tapping noises from lifters (which is usually the cause of tapping from 4.0's) is Seafoam engine treatment in the crank case. I replace 1/4 of the engine oil with seafoam, up to a max of 1L, and go drive it for 20-30 minutes. Then with everything nice and hot (and crap is suspended in the oil) I change the oil and filter.

Oil weight, 10w30 in the summer, 5w30 in the winter, but you'll get a lot of opinions on that. That's what I run. A good tune up (plugs, wires, cap and rotor, coil if needed, set timing) will provide max power and fuel efficiency. Proper maintenance, oil changes and air filters will provide maximum life.
'91 Frankenheep YJ. 4.0, 4" BDS, Richmond 8.8, Titan 12k, 35" KM2's, rust.
'88 YJ, 4.2/4.0 head, +4½" & shackles, BFG 33's (sold)
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Unread 08-13-2011, 09:26 PM   #3
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1993 YJ Wrangler 
Join Date: May 2008
Location: Fresno, CA - California
Posts: 561
I replaced one quart of oil with a quart of Marvel Mystery Oil. I use 10w-30 high mileage all year. That quieted my engine substantially. I also use the Bosch copper plugs in it. No platinum.
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