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OBD1 to OBD2 conversion


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I am planning to do this to my jeep. Currently I have a 1996 OBD2 engine and dash harness, 4.0L MT ECU, does anyone have the wiring diagrams for the 1991 and the 1996 engines? Additionally, does anyone know what sensors need to be changed? 

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How much do you want to integrate the obd2 system? You could just use a 91 obd1 harness and an adapter for an obd2 ecu. There is a guy that posted here once that I’ve kept in contact with who is making them. Or… if your just wanting obd2 for the tuning, consider that the 91+ sbec obd1 ecus can be fully reprogrammed for about $350 by THE Jeep 4.0 and stroker tuning guru. Option 3 is a nice Holley terminator x system. Self tuning and runs a 4.0 based engine beautifully. $1050 without timing control and $1350+ with. 

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I 100% want to fully integrate it. It has to be easier than getting modern OBD2 engines to run in a test cell. Additionally, the 1996 ECU is tunable with HPTuners now which is a HUGE plus. 

 

The terminator X system is more appealing to me than getting another canned tune ECU. The jeep has a locked "tuned" ecu and it still doesn't feel quite right. I am very familiar with HPT and tuning engines for various functions so being able to tune the engine for reliability and drivability I think will not be an issue. It would however be nice to have timing control... 

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I have seen that guys harness and although it is slick I don't really consider it a full conversion. More of a novelty that would allow me to pre-tune an ecu before doing the wiring conversion. Plus its kinda pricy (a little less than 1/2 of the terminator)

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Have you considere socketing the obd1 ecu and have Chris tune it? He can dial in that ecu and get it perfect. I’ve used HP tuners along with Holley and mega squirt. Chris can tune that obd1 to equal if not better results than most people get with a dyno tune. He tunes a lot of Russ Potengers builds

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8 hours ago, ghetdjc320 said:

Have you considere socketing the obd1 ecu and have Chris tune it? He can dial in that ecu and get it perfect. I’ve used HP tuners along with Holley and mega squirt. Chris can tune that obd1 to equal if not better results than most people get with a dyno tune. He tunes a lot of Russ Potengers builds

I have not considered that but if I convert to OBD2 there is no reason I can't have Chris or Ryan tune it still. I just downloaded a 2005 TJ 4.0L tune file to look at and it is fairly sparse. Still would like to see a 1996 tune file as I bet it is even more sparse (no/limited spark tables). However, it has enough tunability to get the fueling and engine fan stuff dialed in. 

The other nice thing about OBD2 with HPT would be for data logging. 

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Also, and this is a long shot, but if I did this conversion I may pigtail the pins listed in 2000-2001 models for COP in case I want to try converting to COP for ignition timing. It looks like you can do it without needing the 00-01 CAM pos sensor if you just leave the dizzy in place (which also runs the oil pump). 

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Hey I'm that guy! I won't get too sales pitchy but I will explain my reasoning for making such a time consuming (to build) harness. 

 

Once you factor in the low and high rough estimate for hardware changes with a full harness swap you are at 170-290 (depending on what quality sensors you purchase) plus whatever the harness cost. 

 

Socketing the ECU isnt impossible but it is time consuming and you need to know what you are doing.

 

Diagnostics are much easier. If you suspect the obd2 ecu has faulted you can simply unplug the conversion harness and install the stock ecu in about 5 minutes. The conversion harness also comes with a built in 8 foot long obd2 harness to reach into the cab and provides all live data that would normally be available in the 96 year. 

 

Trevor

 

 

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Hi That Guy!

 

Your harness is slick AF I just don't think it is quite right for my application. I already have the ECU and a 1996 dash and engine harness that I am in the process of striping, cleaning, re-wrapping (maybe add some pins) etc. I understand the pricing 100% as custom building harnesses takes a ton of time, I have a background in engine stand testing... 

 

With that being said if you want to sell some pins so I can add a pigtail or two to the harness I am rebuilding to experiment with COP and potentially trying to use the other unused O2 signal pins to send data back to ECU for OBD2 data logging of wideband and maybe a knock box if I get crazy enough... 

 

I have a loose 1991 Dash harness I am going to compare to the 1996 dash harness to see what the differences are when interfacing with the engine harness. I have also heard that the 00-01 ECUs don't play nice with the 1991-1996 Tachometer.  

 

In any case if you are willing to let me pick your brain a bit I am still in the research phase of doing this. Also curious on if my COP plan is even feasible with the 1991-1999 Cam Pos sensor in the distributor can be left in place and work with an 00-01 ECU. 

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1 hour ago, Cummins93 said:

Hey I'm that guy! I won't get too sales pitchy but I will explain my reasoning for making such a time consuming (to build) harness. 

 

Once you factor in the low and high rough estimate for hardware changes with a full harness swap you are at 170-290 (depending on what quality sensors you purchase) plus whatever the harness cost. 

 

Socketing the ECU isnt impossible but it is time consuming and you need to know what you are doing.

 

Diagnostics are much easier. If you suspect the obd2 ecu has faulted you can simply unplug the conversion harness and install the stock ecu in about 5 minutes. The conversion harness also comes with a built in 8 foot long obd2 harness to reach into the cab and provides all live data that would normally be available in the 96 year. 

 

Trevor

 

 

Hey Trevor, good to see your still on this forum. So what’s the status of the adapter and what products do you have available now? 

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11 minutes ago, ghetdjc320 said:

Any reason you don’t want to use the opda? Opda with the stock coil rail or a viper coil works very well. 

To be honest I had to google OPDA. For some reason I assumed they used a different oil pump drive method on the 00-01s. Did not realize they literally just made this =P 

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1 minute ago, Torq_Shep said:

To be honest I had to google OPDA. For some reason I assumed they used a different oil pump drive method on the 00-01s. Did not realize they literally just made this =P 


Yeah, it works great for cop or cnp setups. Just make sure to grab the Crown version instead of the oem Mopar one. There is a tsb on the Mopar one. It has a poor bushing design that doesn’t get good lubrication and fails. The Crown one is a revised design. 

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The 91 to 95 dash tach doesnt interpret anything but the 96 ecu tach signal. The 96 ecu is a one year PN. don't try to flash a 97 to 99 to the 96 cal. The harnesses are available with a week lead time. 

 

Ive been working on a piggybacked standalone that seems to work very well. 

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12 minutes ago, Cummins93 said:

The 91 to 95 dash tach doesnt interpret anything but the 96 ecu tach signal. The 96 ecu is a one year PN. don't try to flash a 97 to 99 to the 96 cal. The harnesses are available with a week lead time. 

 

Ive been working on a piggybacked standalone that seems to work very well. 


Pics and prices would be awesome! 

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