Installing O2 sensor for Air Fuel gauge

[Graham]

Just bought a wideband A/F gauge. Will use this initially as an exhaust analyzer to set up mixture.

Some of you have installed sensors for your Megasquirt systems. From your experience, any suggestions as to where best to install the sensor bung and how to route cable? I am thinking of temporarily installing the gauge where the clock is on my '72 SL.

[Mike D]

Use a heated O2 sensor and mount it behind the "y" pipe connection. I'm running mine ('74 W114) up through the transmission hump and behind the center console. I suppose you could simply come up through the A/C drains as well.

[thorsen]

If you don't have an o2 sensor bung, the usual McParts stores carry a "spark plug no-foul adapter" that I have used to mount o2 sensors. Cut the non-threaded end off and weld it into your exhaust pipe.

[cadurning]

If you use a anti foul adaptor make sure that the threads fit the O2 sensor. The O2 sensors that I have used are 18mm. Also there is a bung made for the puropse that can be purchased at any exhaust shop or at an auto parts store like NAPA.

http://www.diyautotune.com/catalog/mild-steel-18x15-thread-bung-and-plug-kit-p-71.html

[Graham]

The AEM unit I purchased comes with a bung. Eventually I will permanently install it, but I think I will first turn it into a portable meter.

I found a pick up design from Daytona Sensors (pic below). I will probably buy another bung to make one of these. Might first install the gauge in a box and use it as a portable, using a cig lighter for power.

But eventually, I will permanently install it. Thinking of modifying ashtray so I can mount two gauges in that location and need to figure out how best to get O2 sensor cable from under car to that location.

For those like me who have been searching for a CO analyzer, this seems like a reasonable option. About $200 for the meter on eBay. Easy to convert A/F ratio to CO% for those of us setting up mixture on old MBs.

[ctaylor738]

This is a topic of great interest to the 113 crowd. Here is a thread, where toward the end, Jim Villers offers his recommendations.

http://www.sl113.org/forums/index.php?topic=10749.0

He brought his meter to Pagoda University Blacklick this summer and did a presentation. He also did a clinic and fixed some cars' chronic problems.

[Graham]

Originally Posted by ctaylor738

This is a topic of great interest to the 113 crowd. Here is a thread, where toward the end, Jim Villers offers his recommendations.

http://www.sl113.org/forums/index.php?topic=10749.0

He brought his meter to Pagoda University Blacklick this summer and did a presentation. He also did a clinic and fixed some cars' chronic problems.

Thanks Chuck.

I seem to be on the same track as Jim Villers. He says he would buy the Innovate unit if he was buying again. I did have a look at their units. They have a portable unit (LM-2) but it is a bit expensive. An earlier one (LM-1) can still be bought at slightly lower price. The LM units seem to be aimed at datalogging of AFR along with other variables like rpm etc. They also have units intended for permanent install (LC-1+gauge), and they are in the $200 range.

I read a number of reviews and chose to buy an AEM 30-5130 wideband unit with analogue readout. I chose the analogue unit because it is apparently hard to digest the digital readout when it is changing rapidly. I initially plan on making an exhaust probe and use the unit as a portable unit. I had no need for datalogging, so saw no reason to buy the more expensive Innovate units.

The wideband units will display AFR to one decimal place. It is easy to choose the required AFR using the CO-AFR conversion chart I posted earlier. For our early 107,s with M117 engine, MB says IDLE CO% should be 0.5-2.0%. This would translate to an AFR range of 14.28-13.77 or a lambda of 0.97-0.94.

I mention the lambda because the meters will read that out instead of AFR if desired. This could be useful if the fuel you are using is not straight gasoline (with the Stoichiometric ratio the meter assumes). Oxygen laden fuel additives like ethanol, MBTE and those added to winter fuels cause the gasolines stoic ratio to be lower.

I don't know what the idle, cruise and load CO% should be for the E5/E10 summer/winter gas we get at the pumps. The ethanol makes a big difference to the CO in the exhaust.

As you can see, I am still in learning stage . I think I will just set up on rich side and see how car runs.

[ctaylor738]

Sounds good.

I think that I am going to spring for one of the units with data logging. I found it really useful when I was diagnosing a problem with my 129 with one of the OBD2 programs that runs on my laptop. I have a course laid out so I can basically record a test run and know what the car was doing by looking at the elapsed time.

I have farted around A LOT with my DMM reading O2 sensor voltage which is what is really going on here, and the changing readout was not a problem.

And thanks for tracking down that link for the exhaust pipe adapter. That will make things a lot easier.

[Graham]

Originally Posted by ctaylor738

Sounds good.

I think that I am going to spring for one of the units with data logging. I found it really useful when I was diagnosing a problem with my 129 with one of the OBD2 programs that runs on my laptop. I have a course laid out so I can basically record a test run and know what the car was doing by looking at the elapsed time.

I have farted around A LOT with my DMM reading O2 sensor voltage which is what is really going on here, and the changing readout was not a problem.

And thanks for tracking down that link for the exhaust pipe adapter. That will make things a lot easier.

My AEM gauge arrived today. It does have an analogue 0-5v output that can be used for datalogging. But, I don't yet know how I would do that - need some type of software on the laptop (or my iPaq) I guess. But, I am mainly going to use it to setup and fine-tune so not going there yet.

I do have one of those OBD programs for my W210, but really have not used it. But, then those computer controlled cars don't really need tuning anyway!

BTW, Innovate SELL an exhaust pick up - Bit pricey though! Looks like they use the exhaust flow to suck the gas in and around a U-shaped pipe.

[Graham]

Originally Posted by ctaylor738

And thanks for tracking down that link for the exhaust pipe adapter. That will make things a lot easier.

I made one of those today, but it didn't work! I think problem may be that it was intended for a single exhaust. I got very high readings indicating I was measuring mostly air. I think the exhaust was going out the other pipe.

Doing some further testing - will add to this later OK Back!

I "solved" the problem by stuffing a sock up the open pipe! This forced the exhaust past the sensor. Once I did this, I obtained an A/F ratio of 14.0-14.1 or 1.6-1.4 %CO (at idle). Very steady - definitely useful for mixture adjustment.

I think I will now get bungs welded into the exhaust - Need to find a place where the sensor can be at about 45deg from vertical and from where I can run cable back safely.

[Bill Adkins]

Why do you want it installed at an angle. All that I have seen are 90 degrees to the exhaust stream.
Bill

[Graham]

Originally Posted by Bill Adkins

Why do you want it installed at an angle. All that I have seen are 90 degrees to the exhaust stream.
Bill

Hi Bill,

Just going by what the manual says - It say at least 10deg up from horizontal, preferably more.

I suspect that mine will be closer to horizontal than vertical!

Regards

graham

[Bill Adkins]

Cool, I was just curious as I have changed many in the past and always thought they were mounted at 90 degrees to the exhaust tube. Don't really know for sure..... the couple of bungs I have welded in were at 90 and they seemed to work but I'm not positive.
Bill

[Graham]

Originally Posted by Bill Adkins

Cool, I was just curious as I have changed many in the past and always thought they were mounted at 90 degrees to the exhaust tube. Don't really know for sure..... the couple of bungs I have welded in were at 90 and they seemed to work but I'm not positive.
Bill

Bill. It may be that the wideband sensors are different. What they say is "To prevent collection of liquids between the sensor housing and sensor element during cold start phase, the installation angle should be inclined at least 10deg from horizontal with electrical connection upwards."

Going to exhaust shop this morning - have to choose a spot for sensor - might put in two bosses, IF I can find a place on the downpipes, so I could switch between banks for trouble shooting. Otherwise, may put it further back after crossover pipe and just measure the partly mixed gases.

We will see how it goes. Still don't know where I am going to mount gauges permanently. I already have a fuel pressure gauge where the clock usually is, so need a place for two gauges if I re-install the clock.

[Bill Adkins]

Thanks for the info, all the factory locations have been in either the inner side wall or the top side of a tube. From what you said I would try for the upper side of a tube and even on the inside of a bend would most probably be optimal. I have an advantage as I am a welder so it's out to the garage for me for that type of project. The idea of a bung in either side is more to my liking as a diagnostic tool and that after all is why your doing this project. Good luck
Bill