OBD1 vs OBD2

Hi guys I am seeking some knowledge regarding the the two systems in regards to how well a 95 OBD1 ecu will control an engine that was from a 96, I know I need to use my existing sensors but I would like to know if the ecu will handle the mapping required to work with the different cam that was used in the 96 model engine, ie can the OBD1 computer adjust to suit the new cam profile?
Also for performane mods which ecu is better OBD1 or OBD2 as I have the entire loom etc for both.....
Cheers, JJ

I'd stick with the ECU and harness that came with the vehicle. Lots of little things changes, like the instrument panels, etc. Plenty of people have done the swap with no ill effects. ODBII can give more detailed trouble codes, but on the flip side it can throw more codes - for example if you do the manual shifting mod for the tranny.

If I knew for certain that the OBD1 computer wouldn't work 100% with the 96 model engine to get it's full performance then I would do the swap as I have everything from a 96 xj....

OBDII will be less tolerant of mods.

If you have inspections there you may get CELs and/or codes that could give you issues at inspection time.

How much of the 96 engine are you going to be using? If you gave us more details on what exactly it is you are trying to accomplish you can get a better and much more explanatory response.

I am trying to gain back some fuel economy in my Xj, mine is a 95 OBD1 and I need to pull my motor out to do some repairs to it and I have a perfectly nice 96 ZG Grand Cherokee engine sitting next to the car so after some research I found that the 95 model engines torque peaks at 3950rpm where as the 96 ZG engine peaks at 2400rpm so my thought was with the much lower and broader torque curve it would be more closely matched to highway speeds especially when towing.
Now I have the entire loom, ecu, sensors and dash cluster from a 96 Xj as well as the loom, ecu, sensors from a 96 ZG so I can use as little or as much as I like but I will be using the alternator from the ZG (136A vs 90A) as well as most of the pulleys etc but I will be using my existing transmission.
The other thing I am finding in my searching is that the 96 Xj and 96 Zg engines are the same part number using the same cam etc but the peak torque on a 96 Xj is at 3000rpm compared to 2400rpm for the Zg so is there a difference in the mapping used in Grand Cherokees?

So in essence I can use as little or as much as I like from any of the 3 models but I want the best, most efficeint end result, I hope this makes sense....

Cheers, JJ

I'm with lawsoncl on this. Keep your wiring and harness. Use the later motor.

Something odd here: "research I found that the 95 model engines torque peaks at 3950rpm where as the 96 ZG engine peaks at 2400rpm"

Not sure I buy that statement?

Be sure to use the 95 torque converter with the 95 AW4!

Also might be transmission computers issues (confusing the ECU/PCM) since the ZJ does not come with an AW4 in 96!!!!

Just use the motor. Those HP and torque ratings are very suspicious and probably very wrong.

cruiser54 said:

Just use the motor. Those HP and torque ratings are very suspicious and probably very wrong.

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I'm wondering if that 2400 peak HP in the Grand is for the V8?

lawsoncl said:

I'm wondering if that 2400 peak HP in the Grand is for the V8?

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Could be. There's gotta be some misinformation here. The 4.0 didn't have that much of a variance in torque output between the years.

lawsoncl said:

I'm wondering if that 2400 peak HP in the Grand is for the V8?

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Sounds more like my diesel!!!

Those figures were quoted in a genuine Chrysler brochure and the 2400rpm was for peak torque not hp and were for the 4.0 litre as we never got the V8's here.
I find it odd that there was a 600rpm difference (peak torque) between the 96 ZG and the 96 XJ!!!
I have to change the plate between the engine and the auto due to the transmissions being a different shape in the bellhousing as well as fit my existing torque convertor so that means using my existing flexplate as well as they are different.
I am hoping that the OBD1 computer handles the different cam timing properly as it is by far the easiest to do but getting peak torque at 2400rpm is very appealing.....

Cheers, JJ

The computer isn't gonna have any problems with the different motor.

FWIW, those same numbers are posted over on JF in the ZJ specs section, but I don't see a mention of where they got those numbers.

http://www.jeepforum.com/forum/f13/zj-forum-faqs-read-before-you-post-880249/#post8113793

edit: 95 was the last year for OBDI; 96+ would be the newer electronics, and the peak numbers and RPMs are shown as having changed at the same time. Anyone familiar with all of the accompanying changes?

cruiser54 said:

The computer isn't gonna have any problems with the different motor.

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If he changes flex plates, and not the CPS and ECU/PCM I would be concerned about a miss match of FP teeth vs CPS?

I would also still be concerned about TCU to ECU/PCM comm differences between OBD-I and II, especially since the TCU's in those years get their data from the engine computers.

I remember reading a writeup about the Grand having a different intake manifold with a larger volume. THat might explain the 600 rpm torque peak difference. I think the OBDI flexplate ad CPS sensor are the same - have to double check part numbers to be sure though.

The TCU will also be OBDI or OBDII for the diagnostic wiring and will likely throw a P0700 is mismatched. On the OBDI (and probably the OBDII) the TPS signal is Tee'd off the sensor input that goes to the PCM.

lawsoncl said:

I remember reading a writeup about the Grand having a different intake manifold with a larger volume. THat might explain the 600 rpm torque peak difference. I think the OBDI flexplate ad CPS sensor are the same - have to double check part numbers to be sure though.

The TCU will also be OBDI or OBDII for the diagnostic wiring and will likely throw a P0700 is mismatched. On the OBDI (and probably the OBDII) the TPS signal is Tee'd off the sensor input that goes to the PCM.

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Sounded to me like he said the flex plates are different:

"I have to change the plate between the engine and the auto due to the transmissions being a different shape in the bellhousing as well as fit my existing torque convertor so that means using my existing flexplate as well as they are different".

I thought by OBD-II (if not OBD-I) that the ECU sent a separate TPS like signal to the TCU. So it is just a "Y" split?

hubs97xj said:

FWIW, those same numbers are posted over on JF in the ZJ specs section, but I don't see a mention of where they got those numbers.

http://www.jeepforum.com/forum/f13/zj-forum-faqs-read-before-you-post-880249/#post8113793

edit: 95 was the last year for OBDI; 96+ would be the newer electronics, and the peak numbers and RPMs are shown as having changed at the same time. Anyone familiar with all of the accompanying changes?

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As I mentioned above I got my figures from genuine Jeep brochures maybe they got their figures frm the same source....

Ecomike said:

Sounded to me like he said the flex plates are different:

"I have to change the plate between the engine and the auto due to the transmissions being a different shape in the bellhousing as well as fit my existing torque convertor so that means using my existing flexplate as well as they are different".

I thought by OBD-II (if not OBD-I) that the ECU sent a separate TPS like signal to the TCU. So it is just a "Y" split?

Click to expand...

Yes the flex plates are different but the difference as far as I can see is in the mounting of the torque convertor....