4.2L MPI Conversion Kit Ignition Upgrades?

[my83andme]

Hey Moses, been searching through and utilizing your past information for a long time, first and foremost i want to just say thank you for sharing your knowledge. 

So, im finally getting close to starting for the first time in near a decade. The 1893 4.2 had seen better days and got a fresh rebuild which led to being bored over (no clue honestly by how much), port and polished, etc. Its got the older rendition Mopar MFPI.. 

All that said, i am contemplating  better ignition as the parts are already old worn and due for replacement. My question is looking for best recommendations for improved ignition module, distributor, spark plug gap advisement, etc. As the motor has been worked over, im also contemplating an adjustable fuel pressure regulator thinking it may be needed to cure any pre-detonation pinging and further tune everything if needed. 

Im by no means the most knowledgeable, but doing what i can and hope ya'll that know more can get me up to speed. I appreciate your help.

[Moses Ludel]

My83and me...You're welcome.  Upgrading the ignition distributor on either the two-rail or single-rail MPI kit would be a problem.  The 60-way PCM is programmed to work with the MPI kit's distributor.  That distributor (two-rail kit) is a 1994-95 off-the-shelf Mopar 4.0L unit.  So is the coil.

This distributor is generally reliable.  You may get some benefit from an aftermarket coil or possibly MSD upgrades.  However, the stock 4.0L prototype ignition is both reliable and adequate for your uses.  I'd save the money here and simply test the kit's components for reliability and wear.  This includes the MAP and throttle position sensor, the O2 sensor and so forth.  You're essentially working with a stock 1994-95 Mopar 4.0L system.  The exception is the crankshaft position sensor.

The crankshaft position sensor and damper are unique to the kit.  So is the fuel pump and filter.  Each of these components should be tested to confirm that they are reliable.  The crank position sensor should be cleaned and gapped properly.  The external fuel pump may be wearing out. 

The fuel filter requires periodic changing.  Spark plugs, the distributor cap/rotor and ignition cables are distinct wear points.  Service and tune the engine periodically.  You can get upgrade spark cables, which would be an improvement.  Use a quality distributor cap and rotor with brass contacts.  Fuel injectors may need attention at some point.

That would be my approach...Here are two videos and articles that will be helpful:

https://4wdmechanix.com/jeep-4-0l-ignition-tune-up-and-injector-cleaning/

https://4wdmechanix.com/road-ready-episode-8-testing-efi-fuel-pressure-and-volume-at-the-rail/

Moses  

 

[my83andme]

I appreciate your reply Moses. 

Keeping the distributor as changing it would be problematic; as i understand upgrading the coil should produce better spark in all RPM range possibly better compensating for the over-bored cylinders, am i correct? If so, what recommendations might you have in the options available? Currently the new spark plugs (Champion Copper Plus) are gapped at .35 (started there unsure of where to set them), Cap is topped off with old but good condition BWD supermag 7mm wires. Need to replace cap and rotor soon. 

Any recommendations for improvement regarding cap/ rotor, plug gap, and especially coil upgrades would be very much appreciated. 

Also, new issue is a wiring gremlin i may be starting a new thread on soon if you would graciously impart some wisdom there as i have zero knowledge when it comes to electrical. 

I appreciate you!

[Moses Ludel]

Hi, my83andme...Availability of an aftermarket replacement coil may be an issue.  I would check with MSD.  The OEM coil is not lacking in any way, especially if you are running 0.035" plug gaps.  You're in pretty good shape as you describe.  You might check the ohms resistance on the coil to make sure it's up to par, but I'd be surprised if it has fallen off.  A coil of this type (non-oil) generally either works or not.  Again, I would concentrate on the fuel pump and crankshaft position sensor.  Make sure the sensor's gap is correct and keep it clean.

As for the fuel pump, I'm a fan these days of testing the pump with an aftermarket oscilloscope like my Autel MP408.  There are inexpensive Hantek and other affordable types.  For one-time use, a scope would not be practical.  It would be practical to buy a new replacement spare fuel pump and carry it onboard.  Change the fuel filter at reasonable intervals.  That's about it. 

Your concern about the bore size and and an increase in spark demand is not a concern.  The bore is likely 0.030" over stock.  That's standard fare for machine shops purchasing 4.0L "engine rebuild kits".  Seldom do they go to 0.040" and very rarely to 0.060" on these blocks.  If you boosted the compression ratio or widened the spark gaps significantly, that would increase the coil's spark voltage demands and load.  The higher the compression, the higher the required voltage to fire across the gap.

Moses