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Unread 06-28-2013, 10:39 PM   #1
4everyoung
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yj 2.5L to 4.2L

im looking for a list of what parts im going to need to buy to put a 4.2L out of a 88 yj into my 95 2.5L yj before everyone says just do the v8 im not doing that because i dont want to replace my entire drivetrain the 4.2 i bought came with the ax-15 and a transfer case if anyone can give me a list of the parts i need for this swap that would be very helpful thanks!

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Unread 06-29-2013, 05:32 AM   #2
SeanB95YJ
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more common for 91+ 2.5s would be to upgrade to the 4.0 as it's (basically) swapping computers, moving mounts and adding a couple extra wires to your 2.5s harness (for the 4.0s #5 & #6 injectors) and I think extending the temp sensor wire.

but being you already have the 4.2, I believe if you do the Nutter bypass as part of the swap, the only thing you'd need is to relocate motor mounts and either remove your in-tank fuel pump to use the 4.2s mechanical (block mounted) pump.... or use your in-tank pump and get an adjustable pressure regulator to knock your PSI down from the high pressure pump to the low pressure required by the carb.

oh, and you MIGHT have to lengthen and/or shorten your drive shafts
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[FONT="Comic Sans MS"][COLOR="Blue"]Sean B. - Schenectady, NY - 95 YJ, 350/700r4/NP241, JB Shorty SYE, 8.8 rear, 2" BDS, 1" homebrew shackles, Daystar 1" BL, TJ flares, 35x12.50 General Grabber AT2 on 15x10 Bart D-Truckers, Polyshield polycarbonate windshield, HD over/under crossover steering
[/COLOR] [COLOR="Red"]swap/build thread: [url]http://www.jeepforum.com/forum/f22/after-almost-4-years-finally-my-own-build-swap-thread-1542284/[/url][/COLOR][/FONT]
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Unread 06-29-2013, 07:50 AM   #3
Tom95YJ
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If you have emissions inspections do not do it what you will be doing is commuting a federal felony. Federal law states an en engine must be from the same model year or newer.

Also the 88 YJ with 4.2l will have a BA10 trans not a Ax15 unless It was swapped


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Unread 06-29-2013, 07:57 AM   #4
Jeepsr4me
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Yeap what ^^^ he said. that trans is not a good one. You would be better off if you could sale that 88 YJ and buy a Cherokee of closer year to your Jeep.. Then do the swap. Not worth it, but a better idea than what you about to do.
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Unread 06-29-2013, 09:45 AM   #5
Tom95YJ
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Originally Posted by Jeepsr4me View Post
Yeap what ^^^ he said. that trans is not a good one. You would be better off if you could sale that 88 YJ and buy a Cherokee of closer year to your Jeep.. Then do the swap. Not worth it, but a better idea than what you about to do.
The BA10 is not as bad as its cracked up to be. I have 210k on mine and it shifts a hell of a lot better then my 98tj did with a ax5 48k on it


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Unread 06-29-2013, 10:38 AM   #6
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Originally Posted by Tom95YJ View Post
The BA10 is not as bad as its cracked up to be. I have 210k on mine and it shifts a hell of a lot better then my 98tj did with a ax5 48k on it


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Well the sun does shine on a dogs *** every now and then. So you got one of the only good ones.. rest of us got crapped on.
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Unread 06-29-2013, 01:07 PM   #7
1998zj
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You do realize the 2.5 has more horsepower than the 4.2? I have owned both and they both run the same speed on the interstate. Unless you do a bunch of work to the 4.2, the swap is not worth the effort.
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Unread 06-29-2013, 01:23 PM   #8
Tom95YJ
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You do realize the 2.5 has more horsepower than the 4.2? I have owned both and they both run the same speed on the interstate. Unless you do a bunch of work to the 4.2, the swap is not worth the effort.
Compare the torque. I had a Build up the 2.5L in my 97 Bored .40 over , Mopar Purple Cam TB Spacer 19# injectors, Eletric Fan, Full Exhaust, Yella terra roller rockers, 4.0 TB, CAI and it still didnt make any power in a useful RPM range and I maybay gained 20 hp and TQ but it still didnt come close to a Stock 4.2L's Torque

4.2L 258 ci I6 :

Bore x Stroke 3.75" x 3.90"
Displacement 258 (4.2L)
Compression Ratio 9.2:1
Horsepower (net) 112@3200
Torque (net) 210@2000
Main Bearings 7
Valve Configuration OHV
Fuel 2bbl Carter BBD



2.5L I4

Bore x Stroke 3.88” x 3.19”
Displacement 150.4 ci 2.5L
Main Bearings 5
Valve Configuration Overhead valve
Compression Ratio 9.2:1
Horsepower 123@5250 RPM
Torque 139@3250 RPM
Fuel DeliveryMulti Point Injection
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Unread 06-29-2013, 01:26 PM   #9
4everyoung
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im doing the swap for low end torque for chewin out in the bush im not planing on racin this on the pavement so top speed doesnt matter to me
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