My daughter's boyfriend is squirting his old mercedes. He wants to add an O2 sensor to make it easier to tune megasquirt. This old car never had an O2 sensor. What is the best location for the sensor, and what orientation? Wires up / sideways ? I told him I'd weld in a bung in the exhaust for him, if he could find a good location for the sensor.
So, it really doesn't matter too much. Put it where it is easy to get to. Orientation doesn't matter. The one on my 22R is about 12 inches from the head in #3 runner. The one on my 4AGE is well past the collector, probably 3 ft from the head. On the Sportster, it is maybe 16 inches from the head on the front cylinder.
For a wideband, it has to be oriented with the wires up. I expect the same is true for narrowband sensors. It should be mounted after the collector unless you're only interested in how one cylinder is working. It should actually be as far back as you can get it, but pre-cat (if there is one).
Pre-cat, of course, but on narrow bands sideways is fine. That's how Toyota mounts them. One runner is going to be OK too, because if you have one cylinder that is acting different than the other 3 or 7, you have more problems than can be corrected with the ECU adjusting it based on O2 content and you need to fix your motor.
It's possible that an old mercedes does not have the perfect idealized airflow found in Toyotas and Harleys, and that some cylinders will run slightly differently than others. That's why high-end ECUs offer individual cylinder trim.
As for orientation, you want to avoid condensation in the tip. Sideways - preferably with a slight downward angle - will work, but ideally the sensor will be pointing up.
"Squirting his old Mercedes" implies MegaSquirt and that one, while an excellent system for the home mechanic, does not have the capability to adjust fuel flow for individual cylinders. I know of no OEM systems that do this, at least not on any commonly available (non-exotic) vehicle. I saw a picture once of a Toyota NASCAR motor with a carb and 8 EGT sensors, though.
Thus my specification of "high end ECUs", as opposed to MegaSquirt. I have two cars with the ability to adjust fuel and ignition trim on individual cylinders.
On a carb'd car, I can see the usefulness of individual EGT sensors. Fuel distribution might be a little funky.
I added mine about 18 inches downstream of the valves.
More importantly, mount it in the upper half of the pipe. You do not want condensation running onto it, either during shut down and especially during the first few minutes of running, before everything is dry inside. Water on a hot O2 sensor is a good way to kill it.
Jack
I would jump straight to a wb02 system, like the Innovate LC1 for an MS car. On naturally aspirated cars make sure you place the sensor at least 18" from the head flange to keep from over heating the sensor.
I have to say it......
In a 02 bunghole?
I thought there might be a slew of opinions. The sensor will be a NB 3 wire sensor because that is what he scrounged. It looks like wherever it fits will be where it ends up. I figured that would be the real answer... I'll try to get it to point wires up.
Thanks!
Wires up is always good - as it's heated I would still keep it between 9 and 3 o'clock whatever you do.
Not many people have access to the right equipment to get individual cylinder trim correctly tuned, or the budget for the dyno time that sort of thing takes. Megasquirt does let you configure two separate outputs for each bank of cylinders differently, but not many Megasquirt owners even do that.
MadScientistMatt wrote: Megasquirt does let you configure two separate outputs for each bank of cylinders differently, but not many Megasquirt owners even do that.
I added bung holes on both sides of my TR8 Megasquirt installation, figuring on having the two halves of the engine running individually on seperate WBO2's, but after swapping the sensor back and forth, it's the same on both sides, so why bother?
jack
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