How to tell difference between 4.2 and 4.0 engines? - Page 2 - JeepForum.com
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post #16 of 24 Old 05-09-2019, 09:34 AM
KLG79
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On a 4.2 the intake and exhaust ports are on the same plane. Inline.

On a 4.0 the intake ports are higher than the exhaust ports.


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post #17 of 24 Old 05-09-2019, 11:01 AM
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Quote:
Originally Posted by JoonHoss View Post
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Originally Posted by StrippedTorx View Post
Does it have a carb
A 4.0 can have/ run a carb too. They didn't come that way, but can relatively (and easily) be converted to run a carb

Hoss
I agree but that would be out of the ordinary. He has a 7. Somebody swapped in a 258 from a yj. If it was fi I would assume he has a 4.0. Not to many people around here running a 258 with fi.
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post #18 of 24 Old 05-09-2019, 11:08 AM
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The OP indicated his fuel pump is on the block, in front of the distributor. If it is still functioning, then I do not believe he could run FI on the lower pressure the mechanical pump generates.

Conclusion: his engine has a carb.

Tim

87 Comanche, 4.0, AX15 (formerly BA10/5), D44
84 CJ7, 4.0 (93 XJ) AX15 (Formerly T5)
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post #19 of 24 Old 05-09-2019, 12:35 PM
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The OP indicated his fuel pump is on the block, in front of the distributor. If it is still functioning, then I do not believe he could run FI on the lower pressure the mechanical pump generates.

Conclusion: his engine has a carb.
Better yet, he has a 4.2. The 4.0 casting didn't allow for mounting of a mechanical fuel pump (which was already stated in this thread).
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post #20 of 24 Old 05-09-2019, 01:17 PM Thread Starter
Joncure
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I'd say good work detectives! Yes my intake and exhaust manifolds are in line. It is carb'd (Weber 38), and the fuel pump location!
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post #21 of 24 Old 05-09-2019, 01:22 PM Thread Starter
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And manifold date stamp says '88
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post #22 of 24 Old 05-09-2019, 01:22 PM Thread Starter
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4.2!
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post #23 of 24 Old 05-16-2019, 03:51 AM
zouaveherb
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Disclaimer: Now I'm quoting here from Wikipedia but...….

"The 4.0 engine, which was introduced in 1986 for the 1987 model year, was a further evolution of AMC's 258 six.[16] It had a 3.875 in (98.4 mm) bore and a 3.414 in (86.7 mm) stroke giving it a displacement of 241.6 cu in (4.0 L).[17] Connecting rod length was 6.125" - similar to the discontinued 199 which was phased out in 1970."
It was introduced in 1986 for the 1987 model year on the Cherokee/XJ. It was not used on the YJ until 1990 for the 1991 model year. Also, the YJ 4.2 had a 2-barrel Carter BBD carburetor while the 4.0 is fuel injected. I know this because I had a 1987 YJ and a 1990 YJ. My friend's sister had a 1991 YJ.

/herb
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post #24 of 24 Old 05-17-2019, 07:13 PM
ShadowsPapa
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My 87 Comanche Sportruck had the 4.0 - also had uneven idle issues the dealership said "welcome to renix"...........

By the way - pictures

Black engine - 4.0 or 242, blue engine - 258 or 4.2
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