EFI, MPI and TBI Upgrade Options for 1987-90 Jeep YJ Wrangler 4.2L

[Juan Grande]

Moses,

I have an '87 Wrangler YJ that I'm looking to refurbish.  I would like to replace the Carter BBD carbureted system.  I have two questions:

1. I have seen your articles on the Mopar MPI Conversion Kit and the MSD Atomic EFI kit.  I'm leaning towards the Mopar kit but would like to see if you can provide a compare/contrast.  My YJ will be much more of a Daily Driver with modest off road use.
2. I would like to do a Cat Forward replacement at the same time that I upgrade to a new fuel system (I recently did a Muffler Back replacement).  Do you suggest upgrading to a header application for performance improvement?  If so, is there a header that requires no/minimum customization (i.e. can share bolt pattern with intake manifold and will follow the factory exhaust path configuration)?  If you are suggesting a header upgrade, how choosy should I be with the cat selection?

Many thanks.

[Moses Ludel]

Hi, Juan Grande...The main and significant difference is that the Mopar EFI provides port injection and uniform air-fuel ratios at each cylinder.  Horsepower is generally better with MPI, though a quick torque rise engine like the 4.2L inline six would perform well with TBI, even using the stock BBD intake manifold.  The time honored weakness of an inline six is disparate A/F ratios at the cylinders.  The intake plenum is long, and the interior cylinders tend to charge better than the end cylinders.  Hence the popularity of a Clifford or Offenhauser "ram" intake manifold.

We took the Atomic EFI to its limit on the 4.2L application, it's really a higher displacement design for V-8s up to 600 horsepower.  The air-fuel ratio did trim properly, and with a stock BBD intake manifold, the MSD system worked impressively and reliably.  The system is spendy and uses proprietary MSD parts.

Given parts availability and overall cost of the MSD Atomic EFI, I would opt for the Howell Engineering TBI conversion for the 4.2L Jeep six;  it patterns off the 4.3L G.M. Vortec TBI system and offers the advantage of common off the shelf parts availability—anywhere.  Either TBI approach uses a conventional distributor, while the Mopar EFI/MPI uses the 4.0L Mopar MPI/EFI distributor with a custom crankshaft sensor and pulley.  The PCM is a factory 64-pin type, and the currently available system is otherwise off-the-shelf Mopar parts with a custom wiring harness and fuel pump with regulator: 1997-up TJ Wrangler single rail EFI equivalent.  The Mopar EFI kit includes a factory exhaust manifold (tubular) and EFI port injection intake assembly.  This is a nice setup with the factory "header"/manifold. 

Borla and Gale Banks Engineering offer replacement headers.  Mating the header to a performance cat is a regular chore for any muffler shop that builds complete systems.  Weigh the expense of Howell TBI with one of these headers versus the Mopar MPI conversion package.  The Mopar package was once a cost effective solution, but the price has crept up considerably.

Off-pavement, both Howell TBI or Mopar MPI would work nicely.  Owners of both systems are happy.  I'm personally familiar with the Mopar EFI/MPI conversion, which is 4.0L based...Howell's package costs less though the conventional distributor is arguably not as precise as Mopar's electronic fuel-and-spark management system and PCM.  Howell kit owners seem happy, though.  

Perhaps owners of each system would like to share their experiences...

Moses 

[Juan Grande]

Moses, many thanks for the quick reply.

You mention above that the "Mopar EFI kit incudes a factory exhaust manifold (tubular) and EFI port injection intake assembly."  My research on the Mopar kit doesn't show any exhaust/header components.  How am I mis-interpreting you?

My interest remains with the Mopar MPI.  Yes, the cost has crept up.  Also, it appears that suppliers are becoming sparse, especially for a manual transmission application.  I'm curious if anyone has any experience of getting some/most of the components from the junk yard and completing this kit through Mopar, HESCO, or other?  Can the be a more cost effective route without adding undue risk?

[Moses Ludel]

Juan Grande, they've either eliminated the factory head pipe, or I was getting the OE header as a separate item when installing these systems.  (My first Mopar EFI Conversion Kit installation was twenty years ago!)  Sorry about that.  Use of a stock iron manifold would make little sense, I'd upgrade to either a factory header or quality aftermarket header pipe.  You need the O2 sensor provision, which is in a better location on the tubular 4.0L header than the factory iron exhaust manifold...For Howell TBI, there would be little gain from a header, though many do it anyway...

Yes, many have done the "Mopar" conversion with stock 4.0L parts.  The intake manifold from a 4.0L will fit the 4.2L head and work okay, but it does not port align perfectly.  (You can port match if desired.)  

The original Mopar EFI kit was patterned after the '94-'95 Jeep YJ Wrangler with two-rail EFI/MPI.  The kit placed the fuel pump inline (an aftermarket pump of correct pressure) and used the OE fuel regulator at the fuel rail.  You can do your own Mopar EFI system with recycled 1991-95 Jeep 4.0L parts, including the complete intake, MAP, sensors and 60-way PCM with wiring harness; the biggest obstacle will be wiring.  Here, Mopar made a wiring harness to hook a '94-'95 YJ MPI system directly to the 1981-90 Jeep 4.2L OE chassis harness.  I've installed the Mopar kit, as you know, and the marvel is the 4-wire or so hook-up to either a 1981-86 CJ or 1987-90 YJ Wrangler.  You might see if that wiring harness from Mopar is available separately from HESCO.  Please update us and share price...

If you're good with electrical wiring and schematics, you can consider doing this conversion with the recycled OE engine harness spliced to your original Jeep chassis harness.  I have a good friend who pinned out his 1989 YJ Wrangler 4.2L chassis harness and paired it successfully with a recycled 4.0L engine harness.  This has been done by many.  For a CJ chassis (1981-86), the task would be different, as the YJ Wrangler electrics differ somewhat from the CJ chassis electrical system.  The Jeep YJ Wrangler happens to use a 60-way chassis plug before and after the 4.0L EFI intro in 1991.  

Note: Pins differ some, and wires need tracing and careful identification.  I can provide the Jeep YJ Wrangler 4.2L and 4.0L wiring schematics if anyone needs them for a 1987-90 YJ Wrangler 4.2L to 1991-95 YJ Wrangler 4.0L EFI conversion.  This conversion can also be done with later 1997-up TJ Wrangler single rail EFI parts, which is what HESCO/Mopar now sells in the "Conversion Kit".  Mopar kits still use the 60-way PCM, 1994-95 style, which obviously works with the later EFI/MPI.

With your own conversion, if you use the 4.0L intake, tubular header and wiring, you still need a crankshaft position sensor.  Here, you can turn to HESCO (official source for Mopar conversion kit, too).  They list the pulley/damper and remote mount CPS as components.  Without this approach, you'd need a flywheel from a 4.0L engine that has the CPS teeth plus a bellhousing that will work.  That's the catch:  You can get a bellhousing for an AX15 or NV3550 transmission from Advance Adapters, but there is no CPS bellhousing available for the T-5, T176/177 or other late Jeep CJ era transmissions.

For conversions, we can discuss transmission options, AA makes a housing to install a G.M. 700R/4 automatic, though you need to see whether this has the CPS mounting provision.  You'd need the correct flex plate for a CPS signal.  Research this.

We can kick the subject around further...Howell's TBI is looking better all the time...However, the cost of the Mopar EFI Kit reflects current parts cost for the single-rail EFI 4.0L entire intake system plus the increase in prices overall.  Keep in mind that the complete Mopar EFI system consists of all new parts:  intake, throttle body, all sensors, a PCM, complete interfacing wire harnesses, fuel pump, air intake filtration (E.O. legal if smog inspected), etc. 

Moses

[Juan Grande]

OK, I'm getting smarter by the day on this topic.  Here is what I learned since Moses' response above.  A good deal of my education came from a call to HESCO and some browsing on their forum site.

1. The PCMs are no longer being manufactured.  This is why HESCO no longer has the MPI Kit for Manual Transmission; they ran out of supply of the MTX PCM.  They still have kits for ATX but they are running out of PCM for this application as well.  You can still find MTX kits on the Internet but you can tell supplies are low.  I would think this also explains why the price has gone up.
2. I have attached the parts list for a MPI Kit.  This shows all of the parts needed if one tried to scrape together the parts from donor vehicles.  It has the MOPAR parts numbers and many of these items you can still be found new, including from HESCO.  Note that this list is for an MTX MPI kit.
3. I'm making the decision to go MPI for my rebuild.  From many sources that I have consulted (including Moses above) it is the consensus best fuel system option withstanding cost.  Fortunately, budget is not that tight and the approximately $1K premium for MPI over TBI is worth it to me.  I'm looking to have fun with my YJ for at least another 10 years after the rebuild and the amortization of $1K over that period works.  Additionally, I'm going to go the 'new kit' route.  The swinger for me is the availability of the PCM; even if I can scrape up everything else, I can't get a new PCM due to lack of availability and I would think there is a comfort in having a new PCM
4. Some of what Moses has been talking about above related to headers wasn't jibbing with me.  I wasn't seeing the availability of stock header products for the 4.2L engine, in particular I wasn't seeing any 'factory' options.  And then it dawned on me that perhaps his experience was with a 4.0L head on a 4.2L engine.  (Moses, might this be true?)  HESCO confirmed with me that there are plenty more options, including a 'factory' option, for headers on the 4.0L head.  I'm now strongly leaning towards a 4.0L cylinder head swap with my MPI upgrade.

So that leads me to this: what are the strong, do-it-yourself sources on doing a 4.0L swap?  I know about the water jacket issue.  What are the most proven techniques to closing these by a weekend warrior like me?  Is this something that should be best left to a shop?  I know HESCO has cylinder heads that are for sale that take care of this (including an aluminum option) but that may be something that breaks the budget.  Anyone have experience on this that they would like to pass on?

MOPAR MPI Kit Parts List.pdf

[Moses Ludel]

Juan Grande...Sorry for any confusion created around the header comment, the 4.0L header will not fit the 4.2L head.  I've installed 4.0L engines in earlier CJ/YJ 4.2L chassis using the Mopar EFI Conversion Kit, and in those cases, as you guessed, the later OE header fits a 4.0L head.  

I devote an entire section of my Jeep CJ Rebuilder's Manual: 1972-86 (Bentley Publishers, available from a variety of sources including Amazon and 4WD parts retailers) to the Mopar EFI Conversion Kit (two-rail at that time) into a 1981-90 Jeep CJ or YJ Wrangler, a virtual "texbook" install that also works for your chassis.  (You'd have the later single rail EFI if using the current Mopar/HESCO parts.)  In my book, Figure 9-134, readers see that I use a new cast iron 1987-90 OE type exhaust manifold that has the O2 sensor mounting provision like the 1981-86 CJ manifolds with the feedback BBD two-barrel carburetor.  This is your current exhaust manifold which works with the Mopar/HESCO intake manifold.

Note:  The intake manifold for the 4.0L in stock form will not fit the 4.2L head, the manifold in the Mopar EFI kit has been modified to fit.  Installers need to make that modification if using a stock (unmodified) 1991-up 4.0L MPI intake manifold on a 4.2L head.  Avoid the 1987-90 4.0L Renix cylinder head and manifolds.

The 4.0L head needs to be post-Renix.  This means 1991-up, and there are various castings and opinions about their pluses and minuses.  Without going into that issue, there is the problem you describe of two cooling passageways on the 4.0L head that overlap the 4.2L block and require filling them.  If you do use the 4.0L head on a 4.2L block, this step has been performed with 1) high temp epoxy or a combination filler and epoxy, 2) with a drill-and-tap approach using tapered pipe plugs with recessed heads and a sealant like Loctite 592 on the threads and 3) filling with a suitable welding method.  Any of the three methods have up and down sides.

The welding method can be done with TIG and Weld Mold Company 700 series cast iron filler rod.  I have considerable practice with this technique and illustrate it at the magazine under cast iron repair.  If I filled these two port openings using the Weld Mold iron welding method and a lengthy cool down within a heat blanket to prevent cracking.  Cylinder head resurfacing afterward would be mandatory, which might already be in the cards if a 4.0L head is being rebuilt.

Warning:  I would caution that the expansion and contraction of parts under heat cycling increases the long term risks on any of the repair methods described.  I use Weld Mold filler like 750 to provide a greater range of expansion and contraction than standard iron castings will normally provide.  This helps resist heat cycling challenges.  Coolant, heat, cold and heat cycling are the risks to success.

Note:  There is also a technique called "spray metal welding" that produces positive results with cast iron.  It is an oxy-acetylene process with a special torque and filler powder hopper.  I've looked at the technique many times and would like to experiment with it.  Many machine shops have positive results repairing iron cracks, filling holes and fixing valve seat areas using the spray metal welding technique.  See this third party video for a quick overview, there is much more material online:  

This is an example of a spray metal welding kit:

http://www.globalindustrial.com/p/metalworking-tools/welding/torches-handles/powder-spray-torch-outfit?infoParam.campaignId=T9F&gclid=CPj2172LhtICFQ2TaQodTLMLKQ

Frankly, I think this 4.0L head conversion on a 4.2L is impractical, although I respect those who pursue this performance enhancement and the promise of improved combustion and reduced risk of detonation/ping.  The gain is a better combustion chamber design and reducing detonation on lower octane fuel; however, the 4.2L stroke is long, and the torque rises quickly in these engines.  Driven within a normal rpm range for its design, idle to 4000 maximum rpm, the 4.0L head swap is not an earth shattering gain.  If you have a detonation issue with the stock head, you can retard the timing on the 60-way 1991-95 PCM with the use of a DRB scan tool or equivalent.  Some simply move the Mopar/HESCO CPS pickup at the Mopar/HESCO front crankshaft damper slightly to retard the base timing by relocating the TDC index point.

My preference would be to use the entire 4.0L long block with a 4.2L crankshaft.  This is the 4.6L stroker build that I discuss at length in the magazine and at these forums.  You could do just a 4.0L swap, but the added stroke of the 4.2L crankshaft is the single most significant gain possible with these Jeep inline six engines.  Using the 4.0L long block as a starting point, you can use a 1991-up 4.0L MPI OEM intake that matches the head design, and other 4.0L MPI parts, without any reservations or footnotes.  You would have a bulletproof, high torque engine good for 4,500-5000 rpm or more with a milder (higher lift and normal duration) camshaft and tuning, which I also discuss at length.  

If you don't do the 4.0L head swap and stay with your 4.2L long block (head and block assembly), there are aftermarket headers available from Clifford Performance and others for the 4.2L engine.  Make sure you get a header with a bung for the O2 sensor, or you will need to have a competent muffler shop install a common bung.  Pattern the bung's location as a match for the OEM header on a 4.0L MPI engine.  This will be the right heat and reading for O2.

Moses

[Juan Grande]

Moses,

OK, I've decided to just do a 4.0L swap into my 4.2L YJ.  Since the YJ will essentially be a Daily Driver, I'm not going the 4.6L stroker option.  After analysis, it is more economical to simply source a used 4.0L engine with EFI than it is to retrofit MPI onto the 4.2L engine.  As you might have guessed, my research shows that XJ 4.0L engines are more plentiful and cheaper than trying to find a 91-95 YJ 4.0L.

My question: Can you point me towards any resources that show how to do an XJ 4.0L swap into a 4.2L YJ?  I'm thinking a 92-95 XL engine (I have already found a 95 XL engine with harness, sensors, and computer for $450).  I'll be doing a full rebuild on the 4.0L engine.  I will also be swapping in AX15/NP231 gearing.  I'm fairly comfortable on tackling the harness issue by using schematics.  I will most likely change out my YJ fuel tank/sender with a tank that takes the appropriate in-tank pump/sender.  I want to be sure I understand the issues with 1) engine mounts, 2) XJ 4.0L serpentine belt reconfiguration for mechanical fan, and 3) what else to be sure to grab when sourcing the engine beyond harness, sensors, computer, and 4) anything else.

Many thanks.

Juan Grande

[Moses Ludel]

See my replies to your comments, Juan Grande:

3 hours ago, Juan Grande said:

Moses,

OK, I've decided to just do a 4.0L swap into my 4.2L YJ.  Since the YJ will essentially be a Daily Driver, I'm not going the 4.6L stroker option.  After analysis, it is more economical to simply source a used 4.0L engine with EFI than it is to retrofit MPI onto the 4.2L engine.  As you might have guessed, my research shows that XJ 4.0L engines are more plentiful and cheaper than trying to find a 91-95 YJ 4.0L.

My question: Can you point me towards any resources that show how to do an XJ 4.0L swap into a 4.2L YJ?  I'm thinking a 92-95 XL engine (I have already found a 95 XL engine with harness, sensors, and computer for $450). 

The engine swap is straightforward.  You do need the 4.0L bellhousing, flywheel, crankshaft pilot bearing for the AX15, wiring harness, intake and exhaust manifolds and sensors.  This will provide a crankshaft position sensor signal.  Otherwise, you'll be buying a remote pickup and crankshaft damper from HESCO or an Advance Adapters bellhousing to accept the OEM crankshaft position sensor (which requires a 4.0L flywheel, too).  If you can find a 1991-95 YJ Wrangler or XJ Cherokee 4.0L with the complete NP231 and AX15 transmission, this would be very useful.  You would have the parts I'm describing plus mounts, a harness, computer/PCM and more.  Many prefer the 1994-up external slave cylinder clutch linkage, so the prime donor vehicle years would be 1994-95.  The external slave AX15 arrangement began with the extremely rare 1993 ZJ Grand Cherokee manual transmission models.  All 1994-up XJ and YJ/TJ Wrangler models use the AX15 with external slave cylinder.

I'll be doing a full rebuild on the 4.0L engine.  I will also be swapping in AX15/NP231 gearing.  I'm fairly comfortable on tackling the harness issue by using schematics.  I will most likely change out my YJ fuel tank/sender with a tank that takes the appropriate in-tank pump/sender. 

Your 4.2L YJ Wrangler fuel tank has the same sender and pump attachment pattern as the EFI models.  (This is thanks to the 2.5L TBI applications.  All tanks from 1987 up have the EFI sender/pump mounting pattern.)  You do need the correct 1991-95 fuel pump module with the gauge sender to match your tank's depth (determined by the 15 or 20 gallon tank type).  You also need to wire the fuel pump and sender like a 1991-95 4.0L harness.

I want to be sure I understand the issues with 1) engine mounts, 2) XJ 4.0L serpentine belt reconfiguration for mechanical fan, and 3) what else to be sure to grab when sourcing the engine beyond harness, sensors, computer, and 4) anything else.

If you use a complete 1991-95 4.0L engine, you will get the serpentine belt system and engine-driven accessories, another reason to buy the complete engine assembly.  Your 4.2L should be serpentine belt and pulleys, right?  If so, all of the 4.2L brackets and engine driven accessories should swap over to a 4.0L engine.  You already have a short snout (serpentine belt) crankshaft...Be aware of the water pump, fan and pump pulley differences between a 4.0L XJ and a YJ.  You should be able to use your existing 4.2L serpentine belt water pump, pulley and fan.  Or you can use YJ Wrangler 4.0L components.

4.2L engine mounts and 4.0L YJ Wrangler engine mounts are the same from 1987-95, there may be one engine bracket bolt hole that needs massaging.  If you get the engine brackets with the 4.0L engine, there should be no stigma.  The transfer case mount, skid plate and driveshaft lengths/splines should each be compared and matched up as required.

Note: Be aware that XJ oil filters mount differently/horizontally.  The YJ 4.0L oil filter mounts similarly to yours.  To simplify, use a 4.0L YJ oil filter mounting system and a 4.0L type oil filter (use a built-in bypass valve in the oil filter).  If your stock oil gauge sender will fit, use it to match your dash gauge.  

The sensors must include the coolant temp sensor for the 4.0L MPI harness.  This also requires the 4.0L thermostat housing to mount the coolant temp sensor.

There are other nuances, but this is the main set of concerns...The more complete your donor's powertrain, the easier this will go.  4.0L YJ Wrangler air filter pieces or emission legal aftermarket pieces will help with your installation and passing emissions tests.

Moses

Many thanks.

Juan Grande

 

[CoreyD]

I have an '89 yj 4.2l with mpi conversion although I am not certain if it is from the mopar kit or is a mix. The pcm is for the 4.2l mpi conversion and the intake is stamped as a 4.0l intake but I dont know if its been modified and if the mopar used the 4.0l intakes or modified 4.0l intake or something else. I would really apreciate the wiring diagram for the mopar kit because I'd like to be able to sort out how this should look. I am interested to compare the mopar conversion wiring with the 4.0l wiring and my own system to get a clear picture of how this thing is put together so I know it's done properly. Just to add, I didnt do the conversion. My father paid someone to do it 20 years ago and he said there were some hinky things about the work and that it didnt seem to gain power afterwards and in fact possibly lost a little power. He told me it first didnt run right at all, stalling out , and he took it back in and the guy added a "chip" and then it still wasnt running like he hoped. Well, i dont know what adding a chip means, and why it made the jeep functional. All i know about the system is what I've said. Oh, except that its a double rail mpi and that the first external fuel pump would fail in heat + altitude and the new pump is loud as hell and it still fails in heat + altitude. My guess is vapor lock or the pump is overheating. i checked and it's compatible with in in-tank pump so I figure I'd put that in and that it would solve the pump issue. And also, I figured I'd add all new sensors and whatnot to the efi to make sure the pcm has all the data it needs but I'd still like to wrap my head around the wiring so I know it's receiving the data and able to act on it correctly. 

[Moses Ludel]

Hi, Corey...The latest exchange with Jordan89oak will be useful.  I included a PDF copy of the Mopar EFI Conversion Kit installation at that exchange and also below.  This should help answer some of your concerns.  There were two Mopar EFI Conversion Kits for the 4.2L engine.  The original was a two-rail patterned directly from the 1995 YJ Wrangler 4.0L.  Later, due to parts availability, the 1997-99 (pre-coil-on-plug) 4.0L single rail fuel injection was offered.  The distinction is the single versus two-rail EFI. 

A later, single-rail kit should have the modified 1997 style fuel pressure regulator mounted near the tank.  Single rail will not have a fuel return line from the rail to the fuel tank.  Some confuse the fuel pressure damper on the single rail for a pressure regulator, and it is not the regulator.  Review the PDF at the jorgan89oak exchange to see the modified single rail fuel pressure regulator and single EFI rail.  The regulator is a 1997-up TJ/XJ OEM style with a machined housing that permits mounting the regulator inline.  In a stock TJ/XJ, the regulator would fit directly atop the fuel pump module.

If you have two fuel lines attached to the fuel rail, one should be a distinct return line to the fuel tank.  (This is a must for a two-rail system.)  If the conversion on your 4.2L was done twenty years ago, it could be either system.  Both of the conversion kits use the 60-way PCM, which is the 1991-95 style.  This is another tip-off. 

With some comparisons, you should be able to nail down which system you have and whether it is a Mopar EFI Conversion or not.  If you have a two-rail EFI, the return line to the fuel tank must be unrestricted and feed directly into the tank.  Otherwise, this could be the source for your "vapor lock".  Fuel lines should be routed away from exhaust heat.  If the return line is functioning properly, fuel is constantly circulating back to the tank, and vapor lock would be nearly impossible.  The 1987-90 YJ Wranglers did have a fuel return line to the tank for both the 2.5L TBI and 4.2L carbureted engines.

I did a 4.0L conversion into an '87 YJ Wrangler and did use the 1991-95 style higher pressure in-tank fuel module.  The 1987-90 tanks provide for a module, as these vehicles had the 2.5L TBI option.  Do not use a 1987-90 2.5L TBI fuel pump, however, as it is not the same pressure as the 1991-up MPI applications.  TBI operates at a much lower pressure than MPI.  When you select a pump module, be sure to get the right one for your tank's gallon capacity and depth.  I replaced the 1987 OE tank with a 20-gallon 1991-95 style, though your YJ Wrangler tank should work if in good condition and able to accept the correct depth, 1991-up fuel pump and gauge module.

Many performance issues related to the EFI conversion have to do with the crankshaft position sensor.  It must be indexed for TDC #1 piston, verified with a timing light.  The sensor must be spaced properly from the damper.  The Mopar EFI kit damper is for either an automatic or manual transmission:  There are two dampers available based upon the transmission type.  See the notes related to the crankshaft position sensor and damper in the kit installation instructions.

Mopar 4.2L Jeep EFI Conversion Installation Instructions.pdf

Moses

 

[CoreyD]

How would you index it to tdc of #1 piston?

[Moses Ludel]

Hi, Corey...This is a time honored issue with the conversion kit.  The pickup bracket attaches to the oil pan bolts and can be a somewhat inaccurate reference.  There is a way to verify or at least get a ballpark sense for the base ignition timing.

Before checking the unloaded idle or base spark timing, it is important to note that a stock 4.0L EFI engine does not have spark timing adjustment.  Spark timing advance degrees are controlled within the PCM in response to various engine sensor signals and the PCM's software programming.  Base timing is fixed and not adjustable.  Moving the distributor housing will not change the base spark timing degrees.  While this was how we timed pre-EFI engines, it is not possible to change the base timing on a Mopar EFI/MPI system by forcing the distributor housing to rotate.  The factory distributor position is assured by the notched tang ("hold-down ear") at the base of the distributor housing.  The distributor clamps at one position only.  The important issue is properly indexing/aligning the distributor shaft and rotor with the cap's spark lead terminals.

The distributor must be installed correctly in its fixed position with the drive teeth and rotor indexed properly.  This is done to the specifications and method described in the factory service manual or the Mopar EFI Conversion Kit installation instructions, which I furnished in our last exchange.  Moving the distributor housing by eliminating the fixed index position for the housing will not advance or retard the spark timing.  It will simply put the rotor and distributor cap's terminal alignment out of position, which reduces the spark efficiency when firing.

If/when the distributor has been installed properly and indexed for the rotor and #1 cylinder's cap terminal position, control of the spark timing is from the crankshaft position sensor (CPS).  The sensor on a stock 4.0L engine is in a fixed position at the rear of the engine, picking up a TDC signal from the flywheel.  This CPS signal tells the PCM that #1 piston is at TDC.  Once receiving that signal, the PCM sends spark trigger signals to each plug lead. 

Actual spark timing is controlled by the PCM, adjusted in milli-seconds to compensate for engine load, temperature, MAP (including altitude), O2 sensor readings, vehicle speed and throttle position signals.  Some engines have a knock sensor, which tells the PCM to retard the spark timing to eliminate knock.  The Mopar EFI Conversion is a 1995 YJ Wrangler 4.0L prototype, which does not use a knock sensor.  With a 4.2L cylinder head, the kit recommends 91-92 octane fuel.  A 4.0L head is able to resist knock with its improved combustion chamber design.  However, the EFI conversion is a hybrid kit, using 4.0L EFI/MPI/PCM with a 4.2L cylinder head.

So, when I suggest "verifying" spark timing and indexing for #1 cylinder at TDC, this is not something you can do readily with a Mopar EFI Conversion kit damper and pickup.  The pickup works under Hall Effect principle, receiving a signal from the kit's special crankshaft damper.  The damper must be rotating to generate the signal, so there is not an easy provision for aligning the pickup to the crankshaft damper and timing cover mark.  An added complication is which timing cover the engine has, as the 4.0L and some 4.2L covers do not place the timing marks at the same position.  We discussed this in a June 2020 exchange.  Those with a 4.2L Mopar EFI Conversion and planning to use a timing light for base/idle spark timing verification need to read this exchange:

To clarify my comment about verifying the spark timing with a timing light, you can get a ballpark reading.  First, confirm that your timing cover TDC mark is true TDC for the #1 piston at top-dead-center.  You need to check this by bringing the #1 piston to true TDC by observing the piston position through the spark plug hole.  Know where TDC matches up with the timing cover mark.  If it happens to coincide with the "TDC" mark on the timing cover, that's great.  If not, make a dot with yellow marker paint on the crankshaft damper.  Line up the damper mark with #1 piston at true top-dead-center.

Now, using a timing light, typically an induction type hooked to #1 spark plug lead, see where spark timing reads with the engine at an unloaded idle.  Understanding that timing can vary due to PCM programming, this reading is for general purpose only.  The timing will normally read 10-14 degrees before TDC (BTDC).  12 +/- a few degrees would be normal. 

There are three ways to change base timing on your engine:  1)  by minor reprogramming of the base timing in the PCM a few degrees maximum, usually in the retard direction, allowed to eliminate ping or knock and done with a factory scan tool and programmer available to dealerships, 2) changing/re-flashing the software in the PCM with an aftermarket program that alters the base timing and spark timing curve, or 3) changing the alignment of the CPS with the crankshaft/damper and, therefore, altering the #1 piston's relationship to the TDC or CPS signal.  On a stock 4.0L engine, the CPS mounts in one position.  On your EFI kit, the alignment is supposed to be accurate but depends upon the oil pan bolt hole alignment, the accuracy of the pick-up's bracket and (to a small degree) the gap between the pick-up sensor and the damper.  Most accept that the kit's pick-up mounting position is "close enough". 

When Edelbrock and others offer this kind of crankshaft trigger, there is provision for adjustment.  Your bracket is "fixed", although some installers do make alignment changes to provide desired base timing.  Again, the base timing and the indexing/alignment with #1 piston at true top dead center is all the control you have.  The spark timing algorithms are strictly part of the PCM's programming.  The only change would be software programming, and you mention that the shop installed a "chip".  On the 60-way engine management computer, this would be a re-flash of the PCM with a different software program or the use of a module like the Jet V-Force that allows altering the software algorithm for fuel flow and spark timing—electronically within the PCM.

For your purposes and the equipment installed on the engine, I would begin by confirming the timing cover marks with true #1 piston at TDC.  (Inexpensive TDC tools available at Summit, Amazon and elsewhere:  https://www.summitracing.com/parts/sum-900189 or TDC tool at Amazon.  I prefer the Amazon tool for its yielding contact with the piston.)  Mark the damper for correct TDC if necessary.  Next, make sure the distributor is indexed properly in the engine by noting the distributor cap and rotor positions.  Use the guidelines (below) from a 1994-95 YJ Wrangler factory shop manual.  Lastly, attach a timing light to #1 spark lead and warm the engine to operating/thermostat temperature.  At an idle with no load on the engine, you should get a ballpark 10-14 degrees advance or BTDC reading with the idle stable.  Keep in mind that sensor inputs to the PCM will vary the timing advance.  You need a steady, smooth and unloaded idle.  Here is how to verify whether the distributor was installed correctly:

Jeep 2.5L and 4.0L EFI Ignition Distributor Indexing.pdf

Let us know what you find...The chronic sluggishness and poor performance could be an improperly indexed distributor, incorrect base timing, a sensor signal input (MAP or O2 sensor in particular) problem or a software issue.  Separate and troubleshoot these possibilities.  Troubleshooting this system is much like a 1995 OBD-era YJ Wrangler 4.0L.  You can even retrieve stored Check Engine/DTC readings from the data lamp lead that is part of the EFI Conversion Kit's harness.  First things first...

Moses

[CoreyD]

I have some confusion about the harmonic dampener and cps. On the 4.2l efi conversion the cps should be installed to the right of (as you are looking down at) the harmonic dampener. In my service manual it actually has a section on the 4.2l with efi conversion and it shows the dampener as having many teeth that the cps unit reads magnetically to locate #1 tdc. However on my dampener I cant see any fine teeth. So I am confused because you mentioned that the kit comes with a 4.0 harmonic dampener but from what I've seen, the 4.0 engine's cps sensor is towards the back of the engine on the drivers side. So how do I know if I have the right harmonic dampener and what position marks tdc for the cps?

[CoreyD]

Opps. In rereading the manual I realize that it is describing the cps that is reading the position of the small teeth on the flywheel which is for the 4.0l. As far as the 4.2l conversion, I do see that there are notches cut into the side of the dampener closest to the engine. 

[Moses Ludel]

Hi, Corey...Yes, the kit comes with a custom damper for generating a magnetic signal that the crankshaft position sensor (Hall Effect) needs. 

All Mopar EFI Conversion Kit dampers are "special" and not stock 4.2L or 4.0L.  They create a Hall Effect magnetic signal for the CPS pick-up.  A stock 4.2L or 4.0L damper does not create a signal.  The 4.0L EFI engines have the CPS is at the back of the engine.

As a point of interest and not of any consequence for your 4.2L, the stock 4.0L crankshaft position sensor is at the back of the engine, specifically around 11 o'clock if you are looking from the rear.  That CPS is in a fixed, non-adjustable location and aligns with #1 piston at TDC.  The flywheel is the Hall Effect magnetic pulse for the CPS signal on a 4.0L engine.  A 4.0L engine must use a 4.0L flywheel for that reason.

The EFI kit damper does not have "teeth", which you realize.  It actually looks quite stock, though it is not a stock 4.0L damper.  Here is an ad for the kit's damper.  (They refer to a V-belt drive but say the damper fits 1981-90...There are many 4.2L engines in that year range with serpentine belts.  The only distinction I've seen for the Mopar EFI Kit damper is automatic versus manual transmission.  There was never a distinction for the belt drive type.)  The damper shown does have some notches at the back but not "teeth":

https://www.4wd.com/p/mopar-performance-multi-port-injection-vibration-damper-p5249687/_/R-FKQS-P5249687

Your  YJ 4.2L engine should be serpentine belt.  Right?  If the engine runs, you have a Mopar EFI Conversion Kit damper.

Moses