Zeitronix ZT-2 A/F Ratio Meter

ZEITRONIX A/F RATIO METER FAQ

The following are some questions I had about installing the Zeitronix A/F ratio meter on the S4. Thanks to Mike2kS4 & SLPRS4 from the Audiworld forum for providing the answers.

Q. Do the downpipes need to be removed for the O2 sensor bung install?
A. Nope, you can weld it on from under the car. Just drill a hole and weld on the bung.

Q. What’s a good location to mount the O2 sensor bung?
A. I mounted the sensor on the passenger’s side downpipe a few inches forward of the cat. I pointed the sensor wire outlet sort-of towards the driver’s front wheel.

Q. How far back from the turbo is the sensor?
A. I’ve always heard keep it minimum 12″ from the turbo housing to avoid hot exhausted air affecting the reading. Mine is ~18″.

Q. How is the wiring routed?
A. I ran the wire up and in-between the two firewalls and placed the logic box in the ECU tub along with the ECU. I then followed the ECU wiring diagram for the RPM and TPS taps.

Q. Any other tips on the wiring?
A. Wrap the cord in heat shield because one burned in the engine bay.

Q. How is the RPM pickup attached?
A. You have to solder it in.

Q. Did the bung come with a plug for when the sensor is out?
A. I never took mine out, but I purchased a bung plug with my bung to seal it up.

Q. How hard is the software to use?
A. The software is pretty easy to use, but you have to set it up for a 6cyl ignition pulse and that’s about it. You can even calibrate boost with regards to altitude.

Q. Where else could the logic box mounted?
A. The data logger hookup is in my glove box – I look at the display once in a while and then leave it in the glove box out of sight.

Q. Does it matter which Bank (downpipe) the wideband O2 sensor is mounted on?
A. I think that mounting in the passenger side is that way to go… that bank (1) typically runs a tad leaner. This is not always the case and there are many theories as to why this is. Tuning to the typically leaner bank would be safer IMO.


Lessons learned from my installation of the ZT-2

O2 bung install:

I had the installation of the O2 bung done at a local Midas shop. I was fortunate to have a technician working on my car who was very professional. He took great car with the car in general, and thought about what was required before cutting. Cost was $45, which included the cost of an O2 bung plug. The work took about 45 minutes.

After pointing out where I wanted the bung to be installed he set to work. It would have been helpful if I had brought the O2 sensor along with so that he could have checked the location to verify that the sensor would fit. He ended up using an O2 sensor from a Toyota to check that there wouldn’t be any obstructions when I installed the wideband O2 sensor.

Due to the location and angle he was not able to use a drill bit, he tried and couldn’t get it to work, so he used a grinder to make the initial hole and then expanded it to the size of the O2 bung. He mentioned that using a torch to create the hole would be a bad idea due to the affect on the rear O2 sensors of having acetone in the catalytic converter. So beware if your shop wants to torch the hole.

He used an arc welder to attach the O2 bung and then used a mirror to inspect the top part of the piece to verify the weld up there was good. Lastly he applied a coat of primer paint so that the weld would not corrode over time. While running the car to verify there weren’t any leaks he noted that the primer was burning off, so he applied a body filler paste to protect the weld.

Initially they could not find a plug at the shop to cover the O2 bung with, so a part had to be ordered from a parts shop down the street. You may want to ensure a plug is available if you are having this procedure done. While waiting on the part the technician started hunting around the shop and came across a plug that would work. Turns out it is an oil drain plug that fits the O2 bung.

ZT-2 Controller install lessons learned:

The steps required for wiring up the ZT-2 were not intuitively obvious. The directions that are supplied provide information about the ZT-2 and the associated wires, but understandably there aren’t specific directions for installing the unit in an S4.

There are a few questions to concern oneself with when installing the ZT-2.

1. Where will the control box be located? Due to the short length of the wires on the 12-pin signal connector it made sense to mount the controller in with the ECU, since that is where some of the input wires (rpm, throttle position) would be tapped into.
2. The box fits neatly under the ECU as can be seen here:

3. Where to attach the power connector and grounding wire? I chose to use the switched 12v terminal located under the lower dash, and attached the grounding wire to a bolt that helps to attach the hood release latch mechanism to the interior side of the vehicle. See the arrows in the picture below:

4. Determining which wires carried the rpm and throttle position required assistance. With the help of Mike2kS4 and Ah10 from the Audiworld forum I learned that the RPM used ECU Pin 37, a (green/blue) wire, Speed came from ECU Pin 54, a (white/blue) wire, and Throttle Position could be gotten from ECU Pin 36, a (brown/red) wire.

5. With that information I was able to solder (badly), the appropriate wires from the ZT-2 signal connector. See picture below.

6. The next step involves routing the 8-pin Oxygen sensor harness to the wideband sensor. I have not yet progressed this far.


Day 1 concluded with a test run of the system with the O2 sensor hanging in free air. Everything checked well except for the data from the throttle plate. The reading was very low and did not increase when the throttle was depressed. After some conferring with Mike2kS4 I used an ohmmeter to check the connections along with two other (brown/red) wires that I considered candidates to be the wire I was looking for. None of the wires showed a good connection to the throttle plate.

The next option was to tap into the accelerator pedal position. This would be very similar to the throttle plate position. This was ECU pin 34, a yellow/blue wire. After attaching the ZT-2 to this wire I tried again, this time the reading was all over the place.

Day 2

I had the bright idea to take and connect the wire from the ZT-2 directly to the throttle plate sensor. I found a wire to route through the engine compartment, from the ZT-2 connector (gray wire)

to the wire that came out of the adapter at the throttle plate.

I checked the connections with the ohmmeter and had a good connection. When I ran the car I got a signal on the Throttle Plate, but it was pegged at 99-100, even when the car was at idle. At this point I’m giving up for the time being trying to get the throttle plate information.

I routed the laptop cable into the cabin and behind the dash to the passenger side.

For the 8-pin Oxygen sensor I ran it through the rubber plug nearby the front of the battery.

For the time being the extra cord is routed to the passenger side and behind the firewall near the pollen filter.

Sometime in the next couple of days I will finish routing the wire down to the DP.


Completing the project

For the final stage of the project I took my car to a lift. After removing the plug in the bung I connected the wideband O2 sensor. It quickly became apparent how close the fit was and how lucky I had been. If the wiring out the sensor was just a little longer I probably would not have been able to get the sensor into the bung. All the more reason to bring the O2 sensor along with when you get the bung welded on.

After screwing the O2 sensor in I began to work on routing the rest of the wiring. The easiest way would seem to be to lower the adapter end of the 8-pin connector down in front of the firewall and to the side of the transmission. Then by going underneath the car you can pull it the rest of the way through.

I was advised to zip tie the cord away from the DP, but this proved to be more difficult than I expected since I could not reach my hands far enough up to attach the cord to anything. After attaching the two ends together I went back to the topside and pulled the slack out of the cord. It turned out that there was a well-placed part that formed a small ridge that kept the cord from falling to the side near the DP.

I was surprised to find that the short cord running from the O2 sensor to the connector was nearly long enough to reach the rubber part in the firewall.

I decided to zip tie the cord to the hose protruding from the firewall. This was a convenient location to change the direction of the connector, and would hopefully do a good job of keeping the cord from going anywhere it shouldn’t and coming into contact with a hot part. Considering that there is very little slack in the cord it is unlikely that it will fall some place that it should not be.

Finally, with all of the extra cord, I decided to route the wiring to the passenger side of the firewall and then behind the firewall, back over to the ECU.

After starting the car up and booting my computer the sensor appeared to be functioning properly.

Audi B5 S4