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Installing Hesco MPFI on 4.2 Engine (1988)

Old 07-10-2019, 01:15 PM
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Default Installing Hesco MPFI on 4.2 Engine (1988)

Hi,

I'm in the middle of the MPFI install on an 88 YJ 4.2. I know this engine was used in the Cherokee and wanted to ask if anyone could offer some advice. I'm not the original owner of this jeep and have recently discovered that the wiring beneath the dash is a rats nest of madness. The HESCO kit says I can remove the carb computer beneath the coolant reservoir, and I've read that the wiring harness can also be removed....but haven't found any information on how to do so.

I'd love to clean up all the wiring, so am asking if anyone has pulled the original wiring harness and computer as most of the wires don't seem necessary. I pulled the harness through the firewall and see only a few wires that go back into the cabin through the drivers side plug.

Has anyone removed the OEM harness and successfully rewired the gauges on the dash? Is this a mess of a job?

Thanks,
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Old 07-11-2019, 01:17 AM
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Nope, XJs never came with a 4.2L. 84-86 was either the 2.5L I4 or the boat anchor GM 2.8L V6. 87-01 was the 4.0L I6 or the 2.5L I4, factory MPFI.
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Old 07-11-2019, 08:04 AM
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Originally Posted by vernors View Post
Hi,

I'm in the middle of the MPFI install on an 88 YJ 4.2. I know this engine was used in the Cherokee and wanted to ask if anyone could offer some advice. I'm not the original owner of this jeep and have recently discovered that the wiring beneath the dash is a rats nest of madness. The HESCO kit says I can remove the carb computer beneath the coolant reservoir, and I've read that the wiring harness can also be removed....but haven't found any information on how to do so.

I'd love to clean up all the wiring, so am asking if anyone has pulled the original wiring harness and computer as most of the wires don't seem necessary. I pulled the harness through the firewall and see only a few wires that go back into the cabin through the drivers side plug.

Has anyone removed the OEM harness and successfully rewired the gauges on the dash? Is this a mess of a job?

Thanks,

I installed the Mopar unit on a YJ years ago.

Your engine was not used in an XJ, but a close derivative of it was.

Don't let the wiring scare you. You may have to split the harness as cutting the tape off with a razor knife, but I think it's minimal.
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Old 07-11-2019, 11:13 AM
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Originally Posted by cruiser54 View Post
I installed the Mopar unit on a YJ years ago.

Your engine was not used in an XJ, but a close derivative of it was.

Don't let the wiring scare you. You may have to split the harness as cutting the tape off with a razor knife, but I think it's minimal.
Yes, I've pulled the harness through the firewall and started tracing the wires. Most of them go to engine control stuff, a few wires head back into the cabin through the drivers side bundle near the brake booster. I assume those wires are being used for something, but don't know if the PCM/ECU needs to be hooked up. I've heard that it doesn't, but am not yet sure. I'd like to pull the whole harness out as one piece, but that seems unlikely.
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Old 07-11-2019, 08:20 PM
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What I remember is exactly that. a bunch of wires but you still use a couple?
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