ECU pin diagram / 96 OBDII

[mrtappan]

I've been back and forth all over looking for a a ECU connector pin diagram of which circuits are bare minimum for FI swap. I've seen some things here or there but nothing that makes me confident in the info. Does anyone have an ECU plug diagram of the wires required to make a 96 OBDII setup run?

I want to have a bare bones harness for the FI as the Jeep is already completely rewired for the body. I want to strip the ECU harness down to the bare minimum for the fuel injection to function.

If it matters:
donor harness/ECU from automatic 4.0 1996 cherokee
Jeep is a 85 CJ7 completely rewired with a Painless harness so the OEM bulkhead plug is long gone. Jeep has a very mild 4.6 stroker engine. VERY mild. Low compression with the mildest cam I could find. Not some hot rod power plant. So OEM injection should be fine from everything I read.

I know I can cut and remove all the automatic transmission stuff out but I'd also love to remove that huge bulky fuse block.

I had stripped down (and was confident) in an OBDI harness I had from a 91 cherokee BUT i ended up using an OBDII crank sensor. I don't want to cut the wires on it and splice it to the old plug. I definately don't want to pull the engine just to change sensors. So I want to switch to the spare OBDII setup I have.

Plan B: What company offers a service to just do it? I'd rather do it myself with the right info but I'm honestly getting tired of searching. If I just have to pay for a solution, I will if it's reasonable.

[mpgMike]

The OBD II ISO requirements make it difficult to simply eliminate "stuff". Attempts usually lead to "Limp Home" mode, where nothing works right. Since you are retrofitting to an older '85, a possibility is to use a stand-alone controller.

Pro's:
- You choose the inputs and outputs that you need.
- You can customize Fuel and Ignition tables, as well as Idle control, and Comp Tables.
- You can add electronic cooling fan and other peripherals through the generic I/Os, analog and digital.
> This could include a WB O2 sensor. The rusEFI UAEFI has a controller built in for a Bosch 4.9 LSU. (I have this on my '95 4.6 ZJ.)
- I am using rusEFI.com UAEFI that should also work for you. IT COSTS UNDER $300 US!! It uses Tuner Studio, which is also the IDE for MegaSquirt and several other stand-alone platforms. This means there is support for Tuner Studio beyond the rusEFI community.

Cons:
- You have to wire everything yourself.
- You may need to modify the stand-alone board for your application (with the rusEFI, "dumb" coils require removing a resistor and soldering in a surface mount IGBT; older MegaSquirt offerings had numerous mods for specific applications -- as an example).
- You are required to do the tuning to match your hardware. Fortunately, a "base tune" from a Megasquirt, rusEFI, or other can get you started; so long as it is Tuner Studio based.

The '96 OBD II is tough, as the ISO OBD II requirements mean you MUST have a down-stream oxygen sensor; you MUST have other feedback that you really don't need on your '85. If the stand-alone route sounds intimidating, consider converting the electronics to the older OBD I; '91-'95. There you can eliminate VSS, Tach Output, AC I/Os, CC I/Os, etc.

[mpgMike]

Appendix A:

I stated that I'm using the rusEFI.com UAEFI. I have a '95 ZJ with a 4.6 stroker (not typical by a long shot; high compression, custom ported head, many other custom things). Currently the factory ECU controls everything but ignition. My tach works and I have cruise control. I retrofitted 6 GM LS coils and replaced the stock distributor with a later model Cam Sensor. MY goal was fuel efficiency. I think I'm on the right track, as I went from mid-15's to over 24 MPG highway.

I have a vehicle build thread on JeepForums.com (https://www.jeepforum.com/threads/time- ... n.4480984/). The rusEFI stuff starts (I think) on page 8. The actual 4.6 stroker engine build is outlined on the same forum at https://www.jeepforum.com/threads/high- ... d.4467732/

To save you some time, I'm on my 4th UAEFI controller (read that as I had 3 failures and still kept trying). The rusEFI products are open source. You can download the PCB and get them made elsewhere. There is a Bill of Materials (BoM) so you can order the parts from Digi-Key or Mouser and build your own. The schematics and all of the software are posted on github.com.

My attempt at using GM LS ignition coils fried the UAEFI Smart Coil driver (U103 in the schematics) -- TWICE! After the 2nd failure I looked up the actual electronic component charged with driving a smart coil. I reviewed the data sheet, did my own search and found a much more robust pin-compatible replacement (both the old and my proposed replacements were Texas Instruments). That new part is now standard starting with UAEFI Rev E. I have one now that has lasted at least several hundred miles (couldn't make it out the driveway with the old one).

Open source means the developer (AndreB) can improve the product available to future customers based on feedback from current users. It also means you can steal/borrow ideas for your own project; in fact, many folks do -- and share their projects on rusEFI platforms! Believe it or not, AndreB actually helps those developing things on their own, as they are sharing their results open source. There is a rusEFI Forum, Facebook Group, and something else that I can never remember and is just too difficult for me to follow (yes, I'm old).

You might think this is sounding like an advertisement for rusEFI. It is not. In fact, for every 20 people that read this post, rusEFI (or other stand-alone offerings) may be something to look into for only 1 person (1/20). I am in no way affiliated with rusEFI (disclaimer). I have in the past cursed rusEFI publicly and sworn it off. After some thought, I came to my current conclusion:

Stand-alone ECUs are not for everyone. Open source stand-alone ECUs are a unique breed, and not for everyone that would otherwise go with an aftermarket stand-alone ECU. The rusEFI UAEFI is less than $300 US (with connectors and enclosure options). Today, good luck buying a stand-alone for less than $1500. I consider the rusEFI offerings to be the modern MegaSquirt offerings of the late 1990's and early 2000's. Both were/are low cost, and open source.