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96 OBD2 comment JP magazine

unclethumbtack

NAXJA Forum User
Location
Seneca MO
I was in my reading room and I was going over some old JPs and I was reading the article in the June '08 issue called XJ and MJ building pg 35. Now what caught my attention was that Christian Hazel said he would not have a '96 up because the OBD2 computer is just too unforgiving. What gives? I have built my trail rig using a 1996 with a 4.0l 9inch/44 blah blah blah but I wondering what computer problems he is talking about.
 
for a dedicated trail rig, the use of OBDll can get in the way of doing things "the way I've always done it before," but it is not a problem with the +96 computers. More often than not, it's a matter of the builder not understanding how to achieve the desired result while not interfering with the information flow to the computer.... and sometimes it's just a builder that's too lazy to research how to do something correctly. In this case, I've not seen the article, so I don't know where the author stands.
 
I plan on leaving the engine and tranny stock (maybe one of those manual shift kits), eventually run a doubler, I picked the cherokee because of the torque and durability of the 4.0 and the toughness of the aw4. I have found that if you build around a strong stock setup it is easier to find parts and answers on boards like NAXJA. So I guess I just misunderstood what he was saying.
 
OBD-II, while it makes more sense than OBD-I, is pickier about how things are done. You can get codes for things that don't cause a problem - a good example would be using a separate regulator for the alternator instead of the inbuilt PCM regulator circuit (not common, but some people do it that way in the course of a swap. Or, convert to an internally-regulated and/or "one-wire" Delco unit.)

Yep - throws a code. Nope - can't get rid of it. And yet, you don't have any driveability problems. The code doesn't so much come from low system voltage (that's not what's monitored,) but the fact that the PCM doesn't see anything happening with the regulator signal. Oops.

It takes a little more thinking to modify OBD-II systems than pre-OBD, but that's about it. I have a distinct preference for pre-OBD - simply because it's easier to modify and use "parts on hand" to effect repairs without the system going into "b**ch mode" or "limp home mode" just because it doesn't like what I did.

Hazel is probably going to go deeper into mods than you intend to - and OBD-II will likely get in his way. OBD-I is also likely to get in his way, and he'd be better off with a mid-1970's rig (beginnings of electronic controls, pre-OBD, easy to modify) instead of OBD control setups that check everything - whether you want them to or not.

The problem with persistent OBD codes is that the CEL/MIL stays lit, and that can result in a genuine problem being "covered" by the persistent non-problem that you know about (you won't see the CEL/MIL light up, because it's already lit for no good reason.) Since you can't programme OBD to "ignore" specific faults, that gets in the way of some modders.
 
The problem with persistent OBD codes is that the CEL/MIL stays lit, and that can result in a genuine problem being "covered" by the persistent non-problem that you know about (you won't see the CEL/MIL light up, because it's already lit for no good reason.) Since you can't programme OBD to "ignore" specific faults, that gets in the way of some modders.

My thoughts exactly...
 
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