As part of my objective to increase power in my Jeep I knew I would eventually have to use a wideband O2 sensor to aid in tuning. I wasn't really interested in a display in the jeep, I just wanted to log it directly into VCM Scanner. I looked at the options, 2 of them looked really appealing, Innovate's little unit and this one from PLX. PLX does offer a nice digital gauge with this device for a bit more. I don't feel that I need it for my purposes. One of the reason these units appealed to me is that they could simultaneously output a narrowband analog signal and I thought that would be great to put this in place of one of the 2 upstream sensors which is the ideal point to measure. Unfortunately Chrysler is always looking for ways to technically meet a regulation while being cheap bastards. Every O2 sensor has a heater inside and the manufacturer is required to monitor the heater on startup. Most do it by monitoring the heater circuit directly which requires an extra wire going to the ECU. But Chrysler do it indirectly by putting a different voltage through the O2 sensor circuit at startup and looking for the resistance to drop in a specified time. The little Innovate or PLX boxes aren't going to support that. With HP Tuners I could disable one of the 4 factory O2 sensors and plug this device into that bung. However, I live in an area with emission testing and I'd rather not have the headaches if they for some reason reference all 4 sensors. It'll be at least another 11 years before I could switch to classic car status and possibly get an exemption. While I'm sure this jeep will still be kicking then, I'm not confident they wont move the goalposts again. It used to be 25 years.
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So with that in mind, a new bung was needed. Normally you want a wideband O2 sensor up in the header, but there really isn't a good option with the new shorty headers I installed to put it in a place where you could actually install it without interference while reading from 3 cylinders in a bank. While in open loop the O2 reading is only slightly lower below pre-cats with tests showing generally .2% variance, which is close enough for what I want to do with it. I could have gotten this done while the cats were disconnected, but in the end I think the location it ended up in is one of the better options anyways. Talking with the shop I used, we selected the 10 O'clock position on the pipe between precats and main cat just after it bends to the back after clearing the oil pan. This is clear of all suspension movement and clears the oil pan without issue.
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I routed the sensor pigtail up along side the existing wire looms, then hooked up the rest of it's harness around the junction of the cam position sensor with the rest of the passenger side harness. Brought it up along side the bridge over the valve cover and will probably tuck it into the bridge if I ever pull that damn thing again. Then into the grommet in the firewall just driver's side of the motor. I had to cut a rectangle into this for the interior plug, but I'll plug that extra space with RTV or black caulk I suppose.
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After considering various options I decided to mount the PLX module up in the firewall behind the glove box, which worked well with it's power leads. I decided to hop on fuse 6 (rear wiper). I also pulled the radio out for good access to the wiring routing through the upper center console. There is plenty of length with the sensor lead as well and I needed to wrap about 2-3 feet of extra cable up behind the glove box. I wanted it to feed into a HPT Prolink on the drivers door frame and decided to use some old Cat 5 cable for the job. At least a ground and single analog signal wire are needed, but I decided to send both wideband (0-5V) and narrowband (0-1V) signals. The current on these cables is minimal and 24awg cable is fine for the task. The ground I used for both the sensor feed and PLX power off the posts sitting above the fuse box with an extra 8x1.25mm nut to secure a ground terminal. I routed the orange Cat 5 wire to the red HPT Prolink input Analog 1 for 0-5V wideband signal and the blue Cat 5 wire to the blue HPT Prolink Analog 2 for the 0-1V narrowband signal. Once plugged into a HPT MPVI2+ or 3, you've got the analog voltage feed available in the VCM scanner.
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With a long term goal of deciding whether to go further with engine modifications, in the short term I'm going to start trying to lean the fuel a bit at higher RPM wide open throttle and seeing if I can get a bit more out of it as currently configured. Low speed pre-detonation still has to be prevented and this engine doesn't have knock sensors built in, so continuing to stay very rich below 2200 rpm as delivered from the factory is probably staying in the cards.
So with that in mind, a new bung was needed. Normally you want a wideband O2 sensor up in the header, but there really isn't a good option with the new shorty headers I installed to put it in a place where you could actually install it without interference while reading from 3 cylinders in a bank. While in open loop the O2 reading is only slightly lower below pre-cats with tests showing generally .2% variance, which is close enough for what I want to do with it. I could have gotten this done while the cats were disconnected, but in the end I think the location it ended up in is one of the better options anyways. Talking with the shop I used, we selected the 10 O'clock position on the pipe between precats and main cat just after it bends to the back after clearing the oil pan. This is clear of all suspension movement and clears the oil pan without issue.
I routed the sensor pigtail up along side the existing wire looms, then hooked up the rest of it's harness around the junction of the cam position sensor with the rest of the passenger side harness. Brought it up along side the bridge over the valve cover and will probably tuck it into the bridge if I ever pull that damn thing again. Then into the grommet in the firewall just driver's side of the motor. I had to cut a rectangle into this for the interior plug, but I'll plug that extra space with RTV or black caulk I suppose.
After considering various options I decided to mount the PLX module up in the firewall behind the glove box, which worked well with it's power leads. I decided to hop on fuse 6 (rear wiper). I also pulled the radio out for good access to the wiring routing through the upper center console. There is plenty of length with the sensor lead as well and I needed to wrap about 2-3 feet of extra cable up behind the glove box. I wanted it to feed into a HPT Prolink on the drivers door frame and decided to use some old Cat 5 cable for the job. At least a ground and single analog signal wire are needed, but I decided to send both wideband (0-5V) and narrowband (0-1V) signals. The current on these cables is minimal and 24awg cable is fine for the task. The ground I used for both the sensor feed and PLX power off the posts sitting above the fuse box with an extra 8x1.25mm nut to secure a ground terminal. I routed the orange Cat 5 wire to the red HPT Prolink input Analog 1 for 0-5V wideband signal and the blue Cat 5 wire to the blue HPT Prolink Analog 2 for the 0-1V narrowband signal. Once plugged into a HPT MPVI2+ or 3, you've got the analog voltage feed available in the VCM scanner.
With a long term goal of deciding whether to go further with engine modifications, in the short term I'm going to start trying to lean the fuel a bit at higher RPM wide open throttle and seeing if I can get a bit more out of it as currently configured. Low speed pre-detonation still has to be prevented and this engine doesn't have knock sensors built in, so continuing to stay very rich below 2200 rpm as delivered from the factory is probably staying in the cards.
