1998 Jeep Cherokee XJ Distributor Ignition Conversion to Coil Over Plug/Coil Pack Ignition

[WiscoJeep]

Hey I was looking to upgrade my 1998 Jeep Cherokee SE’s ignition system. My intent is to drop the distributor and replace it with a camshaft synchronizer (https://www.morris4x4center.com/dorman-camshaft-synchronizer-oil-pump-drive-includes-sensor-dor-689200.html?gclid=Cj0KCQjwn7j2BRDrARIsAHJkxmw1PJPPvcy8YpgleZmsRNOW_q9zw78_4IXXuvfIbh7uufSEW3rMaaEaAtSzEALw_wcB)

, and a RIPP 3.8 High Performance Coil Pack (https://rippmods.com/collections/jeep-wrangler/products/ripp-3-8-high-performance-coil-pack). “Viper Coil Kit”

Will this work with my current wiring harness and PCM?

or will I have to grab a 99-01 wiring harness and PCM to make this work?

[Moses Ludel]

WiscoJeep...The issue gets complicated:  Jeep OEM 4.0L engines with coil-on-plug systems do use a different PCM plus a wiring harness(es) to accommodate the later PCM and distributor-less engine.  The RIPP kit, which I checked out, is for the later JK Wrangler 3.8L "Caravan" V-6 (2007-11 engines, pre-Pentastar V-6 era). 

Below are Mopar part numbers for the SBEC (PCM or Single Board Engine Controller) for 1999 and 2000 model year XJ Cherokees.  1999 4.0L engines (ERO) have a distributor like yours.  2000 model year is coil-on-plug.  Note that the PCMs (SBECs) are different between 1999 and 2000 4.0L engines/chassis:

 EP0=2.5L Engine
ER0=4.0L Engine
EN0=4-Cylinder Turbo Engine
DG0=Automatic Transmission
DBB=Manual Transmission 5 Speed

1999 XJ Cherokee SBEC:

 1 MODULE, Powertrain Control
56041336AB 1 EN0 DBB
56041480AC 1 EP0 DBB Federal
56041481AC 1 EP0 DBB California
56041482AC 1 EP0 DBB European
56041483AC 1 EP0 DBB Leaded Fuel
56041484AC 1 EP0 DG0 Federal
56041485AC 1 EP0 DG0 California
56041488AC 1 ER0 DBB Federal
56041489AC 1 ER0 DBB California
56041490AC 1 ER0 DBB European
56041491AC 1 ER0 DBB Leaded Fuel
56041492AC 1 ER0 DG0 Federal
56041493AC 1 ER0 DG0 California
56041494AC 1 ER0 DG0 European
56041495AC 1 ER0 DG0 Leaded Fuel

2000 XJ Cherokee SBEC:

1 MODULE, Powertrain Control
56041632AD 1 ER0 DBB 4.0L Engine w/Export Emission
56041633AD 1 ER0 DBB 4.0L Engine w/Leaded Fuel
Emission
56041634AE 1 ER0 DG0 4.0L Engine w/Federal Emission
56041635AE 1 ER0 DG0 4.0L Engine w/California
Emission
56041636AD 1 ER0 DG0 4.0L Engine w/Export Emission
56041639AD 1 ER0 DG0 4.0L Engine w/Leaded Fuel
Emission
56041640AB 1 EN0 DBB Diesel Engine
56041661AD 1 EP0 DBB 2.5L Engine w/Federal Emission
56041662AD 1 EP0 DBB 2.5L Engine w/California
Emission
56041663AD 1 EP0 DBB 2.5L Engine w/Export Emission
56041664AD 1 EP0 DBB 2.5L Engine w/Leaded Fuel
Emission
56041665AD 1 EP0 DG0 2.5L Engine w/Federal Emission
56041666AD 1 EP0 DG0 2.5L Engine w/Califonia Emission
56041667AD 1 ER0 DBB 4.0L Engine w/Federal Emission
56041668AD 1 ER0 DBB 4.0L Engine w/California
Emission
56041672AD 1 ER0 DBB 4.0L Engine w/European III
Emission
56041673AD 1 ER0 DG0 4.0L Engine w/European III
Emission

Noteworthy, the camshaft synchronizer that you found at Morris 4x4 Center is an OEM replacement (Dorman) and likely a decent off-shore part.  The OEM 4.0L synchronizer/oil pump drives for Jeep 2000-up 4.0L engines are notorious for failing.  This is the reason that Dorman offers the aftermarket part;  there is a strong market for 1999 WJ Grand Cherokee through 2006 4.0L inline six synchronizer/oil pump drive assemblies.

The distributor in your engine is not a "conventional" type.  There are no centrifugal or vacuum advance mechanisms.  Its purpose is to simply distribute spark from the coil to individual cylinders in the firing order.  When the distributor is properly indexed in the block and the rotor synchronized, the distributor and coil rely on the PCM to provide spark signals.  The PCM gets the TDC reading from the CPS (crankshaft position sensor).  Once TDC is established, the entire spark timing curve is controlled by the PCM.  Feedback sensors on the engine and in the engine bay provide the PCM with signals to indicate where the spark timing should be at any given time—spark timing adjustments can be made in milliseconds.

There is little to condemn about your ignition.  Yes, it's more involved with a distributor that also drives the oil pump from the shaft's bottom end.  (The later distributor-less synchronizer assembly also must drive the 4.0L's oil pump.)  The distributor drive and rotor direct coil spark to each cylinder:  there is a rotor, cap and spark leads.  This arrangement has been an engine standard for stock to all-out racing engines for over a century.  True, coil-on-plug or "distributor-less" ignition can deliver a high output spark at each spark plug's own coil.  This is a great arrangement when each of the six coils are functioning properly, which is another issue.  Six coils are more costly to replace than one.

MSD, Accel, J&S Electronics (SafeGuard, notably) and others make enhancements for distributor type ignitions.   Be aware that even though it "fits", you cannot install a conventional distributor (OEM, MSD, DUI or other aftermarket) designed for the 1990-back Jeep 4.2L engine into your '98 XJ engine;  1991-up Mopar MPI/EFI requires electronic interplay between the fuel-and-spark systems. 

However, you can make your existing distributor ignition do a better job.  You can bolster coil output, enhance spark cables (8 or 8.5mm) and upgrade the rotor and cap quality.  If you need spark enhancement, see what the aftermarket has to offer for your existing distributor type ignition.

One thing that has worked very well for our 1999 XJ Cherokee 4.0L is reprogramming the PCM.  I chose Hypertech's MaxEnergy software several years ago, and that tuning changed engine response substantially.  If you're curious, here are the details in a video and lengthy article:

https://www.4wdmechanix.com/Hypertech-Max-Energy-Power-Programmers-for-Jeep-4.0L-and-Dodge-Cummins?r=1

Moses