4.2L to 4.0L Engine Swap
When doing any kind of engine swap, the best course of action is to buy
everything you might need at the same time. It's both easier and cheaper
than making a return trip. Tip: the '91 and newer 4.0L motors have less
plumbing and use the superior Mopar EFI system.
In this case, you'll need the:
- motor and all its accessories (any Jeep 4.0L should do
- auto or manual tranny makes no difference)
- Crank Position Sensor (CPS) - get a CPS that matches the
transmission to which you will be bolting the 4.0L,
either automatic or manual.
- flywheel or flex plate
- computer (type will depend on your transmission)
- exhaust manifold and O2 sensor
- charcoal cannister
- maybe the catalytic converter, depending on your local
motor vehicle regulations
- fuel tank & pump
Fuel injection systems utilize high pressures so make sure you use fuel
lines and clamps rated for foel injection use. The fuel rail input is
at the rear, near the firewall. The return is at the front.
The 4.2L motor mounts will work fine with the 4.0L although the 4.0L
block's rear motor mount hole on the driver's side is metric (it's
best to take all the motor mount bits when you buy the motor).
The expensive add-on you'll need for this swap is related to the
Crank Position Sensor (CPS). It is mounted on top of the bellhousing.
You have three options:
Speaking of sensors, you will also need a vehicle speed sensor (VSS).
This attaches to the speedometer output on your transfer case. Both Hesco
and Mopar can supply this.
Note: this information has been collected through various sources. None
of it is guaranteed. It is simply presented to give you a good idea of
what would be required to do a 4.0L swap in a 4.2L-equipped Jeep. As with
any swap, unexpected problems will crop-up.
- Do It Yourself
Cut a hole in your bellhousing so that you can bolt in the CPS. This
is the cheapest way to do it and the possibility of screwing up the job
is very high.
- Buy an Advance Adapters Bellhousing
It will have the CPS hole built-in to it and can bolt up to the
transmission of your choice, although some of these adapters do not
support the CPS. For these, AA suggests choice 3.
Note: the 4.2L bellhousing (YJ or CJ) will bolt up to the 4.0L.
- Buy a Hesco or Mopar CPS
Their sensor mounts to the harmonic damper at the front of the engine.
You must specify auto or manual tranny.