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Old 05-17-2018, 09:09 PM
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Help me ID my engine please

I can't seem to locate any remaining engine IDs on my 4.2L YJ. To-date I haven't really been concerned with the exact year of the engine, but the more I work on and learn about the rig, the more it bugs me that I don't know. The shell is a '91, I know that much--but the 4.2 was phased out by then, right?

The stamp between the 2nd and 3rd plugs is smooth as a baby's butt. I heard there was another ID spot on the drivers side of the block somewhere, but I can't find anything.

Is there yet another place that provides engine ID info? If not, are there any notable attributes that changed between years? In the case of the latter, maybe I can 'flowchart' my way to narrowing it down...

Thanks much!

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Old 05-17-2018, 10:23 PM   #2
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post a picture of it

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Old 05-18-2018, 02:12 PM   #3
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Yeah, a picture! I have a '91: that was the first year of the 4.0 *and* fuel injection. So that's an easy tell if you don't see a carburetor.
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Old 05-18-2018, 05:49 PM   #4
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Post your pics like this. The first shows the right side of the engine (passenger side) and the second pic clearly shows the alphanumeric code on the boss.
The boss is just below the head, between #2 and #3 cylinders. You seem to be aware of this, but I'm posting this for other jeepers that may not be aware of the build date location.

These pics are of a motor that I bought to rebuild in my leisure time.


1st digit = year (in my case 1981). If it was a 1991 it would be a 4.0.

2-3 digits = month (in my case, December)


4th digit = engine type (in my case 4.2)


5-6 digits = day (in my case, the 14th)

So, according to the information on my used motor, I have a 4.2CI, built on December 14, 1981.

If you don't have an alphanumeric code stamped on that boss, perhaps it's a rebuilt engine and the rebuilder ground off that information.

Look at the freeze plugs on the right side of the block to see if there's something like in the third pic. It's a disc held in place with a heat sensitive adhesive. If the motor is overheated, the glue becomes liquid and the disc falls out. Then the warranty is void. Rebuilders do this to protect themselves if the installer or driver runs the engine with low coolant or some other reason for overheating.


The dead giveaway is if there is an opening in the side of the block for a fuel pump. 4.2 uses a mechanical fuel pump bolted to the right side of the motor and a 4.0 (and 2.5) uses an electric fuel pump in the gas tank.
If I knew how to circle an item in a pic, I'd do so. In pic 1, the fuel pump opening is center bottom with two bolts still in place. Very obviously a 4.2.

As far as I can determine, any part that's designed for a 4.2 will fit the entire series of 4.2 motors, regardless of the year. If your research turns up anything any different, please let us all know.

Good Luck, L.M.
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"Wrangler....It's not just a vehicle, It's a lifestyle".
.................................................. ........................
1987 YJ-4.2L-Standard Shift- Re-manufactured Carter Carb-2" body Lift-31X10.5X15 BFG KOs-190K Miles No back seat.
HEI distributor with computer and all related relays and wiring removed.
12K Badlands winch with dual batteries.
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Old 05-18-2018, 07:49 PM   #5
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Sounds like you already cleaned off the boss and don't see any thing. It's hard to see. I once had a 650 Bonneville Triumph without any serial numbers stamped into the boss and went to DMV to get tags for it, DMV tried to raise the numbers with a acid
test with no luck and they gave me a little plate with serial numbers to attach to the frame. Turned out this 650cc was a flat track experimental model and never had serial numbers. So Lucky might have the right idea about the motor block numbers.
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Old 05-20-2018, 05:05 PM
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Ok, thanks for all this. I’ll have a chance to post a photo later this evening. All for now, more later when I get to my computer. Thanks again!
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Old 05-21-2018, 12:10 AM
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Quote:
Originally Posted by Luckymac View Post
Post your pics like this. The first shows the right side of the engine (passenger side) and the second pic clearly shows the alphanumeric code on the boss.
The boss is just below the head, between #2 and #3 cylinders. You seem to be aware of this, but I'm posting this for other jeepers that may not be aware of the build date location.

These pics are of a motor that I bought to rebuild in my leisure time.


1st digit = year (in my case 1981). If it was a 1991 it would be a 4.0.

2-3 digits = month (in my case, December)


4th digit = engine type (in my case 4.2)


5-6 digits = day (in my case, the 14th)

So, according to the information on my used motor, I have a 4.2CI, built on December 14, 1981.

If you don't have an alphanumeric code stamped on that boss, perhaps it's a rebuilt engine and the rebuilder ground off that information.

Look at the freeze plugs on the right side of the block to see if there's something like in the third pic. It's a disc held in place with a heat sensitive adhesive. If the motor is overheated, the glue becomes liquid and the disc falls out. Then the warranty is void. Rebuilders do this to protect themselves if the installer or driver runs the engine with low coolant or some other reason for overheating.


The dead giveaway is if there is an opening in the side of the block for a fuel pump. 4.2 uses a mechanical fuel pump bolted to the right side of the motor and a 4.0 (and 2.5) uses an electric fuel pump in the gas tank.
If I knew how to circle an item in a pic, I'd do so. In pic 1, the fuel pump opening is center bottom with two bolts still in place. Very obviously a 4.2.

As far as I can determine, any part that's designed for a 4.2 will fit the entire series of 4.2 motors, regardless of the year. If your research turns up anything any different, please let us all know.

Good Luck, L.M.
Thanks LM,

Right, no alphanumeric code. No 'heat sensitive disc' either (very interesting to learn about this though). Yes, mechanical fuel pump.

I'm attaching an image of the engine bay now. Forgive the mess, I took it while I had all of the wiring 'un-loomed' today as I was working on getting rid of the rats nest of wires that I inherited from the previous owner over 7 years ago!! (My own fault for waiting this long )

I can take photos of specific areas if that will help date the engine, but from the replies so far, I'm kind of getting the feeling that I might not be able to get an exact year nailed down (if all year in the 4.2L series are the same)... And that's ok with me. If they all have interchangeable parts, that's all I really have to know I guess.
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Old 05-21-2018, 12:27 PM   #8
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Cleaning up the POs rats nest and removing the computer and related emissions controls.
Installed a HEI distributor.
Also took the heater core to be repaired and painted the dash.

Took me two days of steady work. Time well spent.

I strongly advise against doing this without a schematic and a fair understanding of automotive electrics. Plus you need a clear head and a lot of patience.
Last pic is what it looks like now. Pic 4 is all the stuff I removed.

Good Luck, L.M.
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__________________
"Wrangler....It's not just a vehicle, It's a lifestyle".
.................................................. ........................
1987 YJ-4.2L-Standard Shift- Re-manufactured Carter Carb-2" body Lift-31X10.5X15 BFG KOs-190K Miles No back seat.
HEI distributor with computer and all related relays and wiring removed.
12K Badlands winch with dual batteries.
Warn front bumper. Matching imitation Warn bumper on the rear.
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Old 06-08-2018, 11:38 AM
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Time and time again when trying to diagnose something on my Jeep, I find something that leaves me even more confused than when I started (as I'm sure many of you can probably relate). This time I just had to laugh.

Embarrassingly, I was wrong initially when I said that nothing was engraved in the engine ID plate. Yesterday when I was working under the hood I took a bit of engine oil on a rag and rubbed it on the plate. I still didn't see anything. Then about an hour or so later I saw what looked a letter or a number! After wiping it off dry and hitting it with some compressed air, I found this (see image).

I found the plate, managed to see the characters engraved on it, but still have no idea what they mean! ha! It doesn't seem to fit the format of any ID resources that I've found online!

In other news, I did a little detective work and tracked down the previous owners email address. He said he was "100% sure the engine was a 90 or a 91" but didn't know which year. Since it's carbureted, that means that it must be a 90. So at least I guess I have figured out the engine date mystery. Thanks for the help, and maybe if someone else finds this thread with an odd looking code like this stamped on their engine, they'll at least know they're not alone.
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