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Old 08-31-2010, 12:46 PM   #1
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6cyl engine I.D help needed

hi im new here and have a question,i have an 89 yj with a bad trans. the engine was swaped out and i cant tell if its a 4.0 or a 4.2 is there a way to tell the differance and do they use the same auto trans? thanks for any help! p.s the engine thats in there has a carb

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Old 08-31-2010, 05:36 PM   #2
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The 258 (4.2L) can be identified by the 4th character of the engine build date code ("A", "B", "C" or "M"), stamped into the engine block below and between the number 2 and 3 spark plugs. An engine stamped with "B" is an early 258 with a 7.6:1 compression ratio. "A" and "B" are engines with 1-barrel carburetors, while "C" and "M" are 2-barrel. "M" originated in Mexico.

Hope that helps.

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Old 08-31-2010, 05:43 PM   #3
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Jesus, 7.6:1 compression? Thats pretty low!

My turbo Eclipse ran 8.5:1 and I was pushing 30lbs of boost. Wonder what the bottom end of this motor can take!
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Old 09-04-2010, 05:55 PM   #4
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He can't use the engine code seeing as the engine was swapped out. Any other ideas that someone's got? I'd suggest getting a Haynes or a Chilton's, as they probably ahve pictures of the different engines, and its a pretty nice thing to have as a Jeep owner anyway.
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Old 09-04-2010, 06:03 PM   #5
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Well all 4.0L are fuel injected. all 4.2 are carbs.
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Old 09-04-2010, 09:39 PM   #6
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Quote:
Originally Posted by redneckpilot View Post
He can't use the engine code seeing as the engine was swapped out. Any other ideas that someone's got? I'd suggest getting a Haynes or a Chilton's, as they probably ahve pictures of the different engines, and its a pretty nice thing to have as a Jeep owner anyway.
The codes should still be there if it was an I6 that was put in his jeep, if they didn't put in an I6. The original question be answered here.
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Old 09-04-2010, 10:02 PM   #7
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Quote:
Originally Posted by redneckpilot View Post
He can't use the engine code seeing as the engine was swapped out. Any other ideas that someone's got? I'd suggest getting a Haynes or a Chilton's, as they probably ahve pictures of the different engines, and its a pretty nice thing to have as a Jeep owner anyway.
Actually, he is wanting to verify which engine was swapped in, so my information still stands as valid and useful.
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Old 09-05-2010, 09:48 AM   #8
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Ya Think?
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Old 09-05-2010, 11:53 PM   #9
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4.2 is the carbed engine
4.o fuel injected
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Old 09-05-2010, 11:59 PM   #10
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4.2 is the carbed engine
4.o fuel injected
Doesn't mean they couldn't have swapped heads. ID'ing the block is still important.
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Old 09-06-2010, 09:30 AM   #11
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I agree
ID the block

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