Wiring Help

[Larrythedog]

I was thinning the wiring harness on my 97 XJ 4.0. I marked every wire coming out of the PCM. Then starting removing wires one at a time. I came across three issues.

1. The 97 has two O2 sensors. Do I really need two sensors since Im not running a cat. Can I just loop the output of the upstrem O2 sensor to to the downstream O2 senser?

2. I came across a battery temp sensor. I was ready to cut this loop out but when I followed it back to the plug I noticed somebody installed a resistor between the two wires at the plug. Why? Does this affect the charging circuit?

3. Do I need the speed sensor?

Any help would be great.

 

[silverslk]

Larry I'm no expert.

From my understanding the 2nd O2 sensor only monitors the CAT condition. It would trigger a check engine light but not affect performance. The import guys run a "O2 sensor simulator" to keep the check engine light away if it matters.

The resistor simulates a temperature sensor. Not sure what temp it simulates but if the charging system works, I wouldn't worry or mess with it.

Speed sensor......I don't know. On Broncos the trans won't shift without one but don't know jeep.

 

[J Money]

Look up an "mil eliminator" to fool the ecu into thinking you have cats. I used to run them on my mustang because the computer threw codes and lights. It also ran like crap until I got those.

 

[Skullver]

After talking with Benny from Hesco he said the VSS signal actually retards timing as you slow down as well as a few other functions, he said you do need it. Good luck!

 

[Larrythedog]

Larry I'm no expert.

From my understanding the 2nd O2 sensor only monitors the CAT condition. It would trigger a check engine light but not affect performance. The import guys run a "O2 sensor simulator" to keep the check engine light away if it matters.

The resistor simulates a temperature sensor. Not sure what temp it simulates but if the charging system works, I wouldn't worry or mess with it.

Speed sensor......I don't know. On Broncos the trans won't shift without one but don't know jeep.

I going to remove the downstream o2 sensor. Ill just jumper the upstream o2 sensor PCM input to the downstream o2 input on the PCM.

As for the battery temp sensor, i did a little search on this. Ill keep the resistor in. It does affect charging.

 

[Larrythedog]

After talking with Benny from Hesco he said the VSS signal actually retards timing as you slow down as well as a few other functions, he said you do need it. Good luck!

Your the third person that tells me about the timing issues. It looks like Ill be keeping the speed sensor. The only question I have is can I use the 88 vss? Or do I need a 97 vss?

 

[CherBear]

I was thinning the wiring harness on my 97 XJ 4.0. I marked every wire coming out of the PCM. Then starting removing wires one at a time. I came across three issues.

1. The 97 has two O2 sensors. Do I really need two sensors since Im not running a cat. Can I just loop the output of the upstrem O2 sensor to to the downstream O2 senser?



Any help would be great.

If you don't have a cat, then why even bother... If you jumper them together it should throw a CEL because basically what you are telling the computer is the cat is doing absolutely nothing. The cat is supposed to oxidize most of the emissions, if oxygen is being used, then the after-cat sensor should read a lower oxygen level than the pre-cat sensor.

May I suggest adding a resistor between the first sensor and the second one, it might be able to trick the computer into not throwing a CEL.

OR you could replace the O2 sensor with a resistor which is exactly what the "O2 fooler" sort of kits they sell on the internet do. Except you save money by using radioshack parts VS ebay kits.