Evap routing on 4.2l with mopar efi

[kauaiman]

I have just installed a 4.2l with the Mopar EFI system. engine runs pretty good, but don't know where to hook up evaporations canister. I have a line that goes from valve cover to cone type air cleaner then to evaporations canister. have another line that goes to gas tank. have two other fittings on canister, not sure where they go? any help would be appreciated. As background info, I have a 1985 cj7 that came with the 4 cylinder. removed engine and found used vehicle with 4.2l with mopar efi and T-176 transmision. Fairly easy install using the used jeep parts.

[Moses Ludel]

kauaiman...I did a similar swap and documented the steps in my Jeep® CJ Rebuilder's Manual:  1972-86 (Bentley Publishers).  In the book, I address the concerns you have with your Jeep's EVAP hookup.

At the magazine website, I provided a bit of material on that swap, which may be helpful here.  These articles provide additional links to articles that will be helpful:

https://www.4wdmechanix.com/Carburetion-Versus-EFI-Conversion-for-the-4.2L-Jeep-Inline-Six?r=1

https://www.4wdmechanix.com/How-to-Tuning-the-Fuel-Injected-Jeep-Inline-Six-Stroker-Motor?r=1

There are two distinct Mopar EFI Conversion kits:  The earlier kit with 60-Way (60 pin) computer (1994-95 YJ 4.0L style) uses a two-rail system with a fuel return line to the tank.  A later kit patterns off the 1997 TJ Wrangler 4.0L system and has a single rail EFI design without a fuel return line to the tank.  The earlier (two-rail) kit uses an inline Walbro type fuel pump;  the later kit has a pressure regulator derived from the TJ Wrangler's top of tank regulator.  Identify which system you have and follow the correct guidelines. 

A possible resource for the instructions that came with the Mopar EFI Conversion you inherited would be HESCO.  Contact the HESCO tech staff and see whether a download PDF is available for the kit's original instruction sheet.  The instructions included hose routings for the vapor canister and air cleaner hookup.

Moses

[kauaiman]

thanks for the info, I have the earlier 60 pin computer with two rail fuel system. I did find a Hesco pdf that says to take one line off the intake manifold to the canister. I guess it needs vacuum to work?

[Moses Ludel]

kauaiman...My book covers the installation and also refers to the "vacuum source line and vapor hose to the engine as described in the Mopar kit instructions."  Sounds like you have these instructions.  If the kit instructions are for the two-rail system, you have it.  The kit's EVAP and other pieces make for a clean installation and eliminate a lot of OEM clutter on these models.

Your original 4.2L EVAP system also had a hose to the intake manifold (near the carburetor base).  This was on the PCV feed line, and the EVAP canister received continuous vacuum from the intake manifold.  The Mopar EFI kit has you doing the same thing. 

If you need to know how each of the vacuum circuits function on the EFI kit, the kit is a knock-off of the 1994-95 Jeep YJ Wrangler, including the EVAP system.  Here are some useful exchanges here at the forums, including PDFs that I provided on both CJ and YJ Wrangler EVAP vacuum hose routings:

https://forums.4wdmechanix.com/topic/988-mopar-mpfi-canister-connections/?tab=comments#comment-6634

https://forums.4wdmechanix.com/topic/755-jeep-42l-with-mopar-efi-conversion%E2%80%94runs-well-but-nox-is-too-high/?tab=comments#comment-5307

Moses

 

[kauaiman]

Thank you so much for the diagrams!! I still have the 4.2l canister, so it will be easy to apply a vacuum source from the manifold to complete the system. Thanks again. on a side note, does .035 gap for plugs sound right? I will need to buy a manual for the 1994/95 wrangler for tune up info. Thanks

[Moses Ludel]

You're welcome, kauaiman...A used factory service manual could be found on eBay or through used automotive book outlets.  I have the '94 Mopar XJ/YJ edition, which is the source for PDFs.  Pleased that the diagrams and information helped.  The great feature of your Mopar EFI kit (early version) is the use of stock, off-the-shelf 1994-95 YJ Wrangler 4.0L components.  You can order replacement parts accordingly. 

Many do this conversion with recycled YJ or XJ Cherokee parts, but the Mopar kit is made simple with its wiring harnesses.  Otherwise, the job is a slice and splice, stripping out OEM wires from a donor vehicle's harnesses.  The Mopar kit boasts four key wires that interface with your CJ chassis plus some wiring to the inline fuel pump.  I trust you got the kit's vehicle speed sensor (VSS) for the transfer case.  The kit's harness reaches that sensor as well. 

From what I recall, the Mopar kit's VSS looks like the 1990-91 YJ Wrangler style (photo below).  Your Mopar EFI Conversion Kit requires a vehicle speed sensor signal (VSS) from the speedometer drive at the transfer case...Here is an image of the 1990-91 YJ Wrangler 2-pin "adapter" that fits between the Dana 300's gear pinion speedometer drive and the speedometer cable.  This adapter picks up vehicle speed and sends this signal to the PCM.  The original CJ speedometer and cable continue to work while the PCM picks up the signal at the adapter's pin connector:

The Mopar EFI kit instructions were decent.  Backed with these factory diagrams and details, you should have it!

Yes, the spark plug gap for both the 4.2L and 4.0L engines is 0.035".  Convenient...

Moses

[kauaiman]

Thanks again, yes my donor vehicle has the speed sensor that you talk about. 
stay safe and look me up if ever visiting Kauai Hawai. 

[Moses Ludel]

kauaiman...You're at a great part of the world!  Thanks for the offer. 

Enjoy your Jeep, the Mopar EFI makes a tremendous difference.  The 4.2L engine bursts to life with MPI/EFI, the fuel mileage is better, the bottom end torque of this engine is legendary...Have safe fun!

Moses