LM-2 O2 Sensor location

[pittwagen]

I intend to purchase an Innovate LM-2 3837 A/F meter to measure the air fuel ratios on my 79 Bus. I have the CA fuel injection system but somewhat modified. I removed all the left side exhaust, cat and crossover and have installed the federal left side heat exchanger with a 4 into 1 header and have the stock O2 sensor located in a collector in front of the muffler. Will I get accurate A?F readings if I use the Innovate 3728 tailpipe adapter or would I be better off finding a location to weld in a second O2 bung? Thanks for your thoughts. Here is the setup:

[telford dorr]

Weld in a bung. The tail pipe adapter is problematic at best (fall off, susceptible to air backflow). For best results, you want a lot of muffler and tailpipe between the bung and the outside atmosphere. (Somehow) put the bung in the collector, close to the factory location. Make sure it's located on the top of the pipe, not to exceed 45 degrees rotation from vertical.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[pittwagen]

I think I may be able to weld in a bung in the forward muffler pipe a few inches downstream from the existing O2 sensor bung. The muffler is a year old so the metal under the paint should be rust free for a nice clean weld. Thanks for the response.

[airschooled]

The LM-2 has analog outputs to simulate narrow-band oxygen sensors. Use the wide-band O2 sensor in your existing bung, and connect the L-jet green O2 wire to the corresponding outputs on the LM-2.

Page 39, section 6.7:
https://www.innovatemotorsports.com/support/manual/LM2_Manual_1.3.pdf

See you on the road,
Robbie
_________________
Learn how your vintage VW works. And why it doesn't!
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[telford dorr]

There you go - an even better (and easier) idea!
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[pittwagen]

Thank you Telford and Robbie. I ordered the LM-2 plus the 3889 18Ft cable and the 3811 analog cable. Shortly we will be able to see how an almost 42 (June 25) year old bus with CA emissions behaves. It has been running very well since the mods a year ago. Stay tuned.

[pittwagen]

Well here we are and 3 months have passed and i finally got the LM-2 installed on the bus.

First off I removed the CA O2 sensor and installed the LM-2 wide band sensor in the collector bung. See pic above. The sensor is about 26 inches from the tailpipe end. Set up the meter and calibrated the sensor before installing it. FYI fuel is 91 ethanol free and oil is Rotella T4 15/40.

So how does the CA system perform without the O2 sensor?

First off and once the engine was warm I noticed that the idle speed had dropped back to about 800 rpm so I adjusted that back to 900 or so.

With the oil temp around 180 (VDO gauge with dipstick temp sensor), CHT about 350 deg. (VDO), outside temp at 69F, I was seeing an A/F ratio of 15.7-1 at a steady 60kmph in 4th gear. Not much difference at 70kmph or at 80. Very light throttle. That the way I drive most of the time. Rarely do I exceed 90kmph.

If I shifted to 3rd gear and gave full throttle up to about 4000rpm the A/F ratio went down to 13.8 - 14.5. This indicates that the throttle valve wide open switch is working correctly. Did the same on a fairly steep hill for about 2km with the same results. CHT temps started to approach 400. Part throttle on the hill in 3rd and the A/F ratio would get back into the 15's. Back on the flat and the CHT's dropped back to just above 350.

I did a 5km run at 90kmph and the A/F ratio maybe dropped to 15.3 when on slight grades. Light throttle and back to 15.7. Oil temps went to 200deg with the higher speeds. CHT's were between 350 and 375.

Back to city street driving saw 15.7 and CHT's went back to around 350. Idle speed A/F ratio was between 15.8 and 16 on all the city stops.

So back home I adjusted the mixture screw on the A/F meter all the way in and the idle speed as well. Idle A/F ratio was now at 14.9.

The second run saw the A/F ratios drop to about 15.2 at steady 60 and 70kmph speeds and slightly higher at 80-90kmph. Traffic was heavy so it was difficult to maintain a steady speed. CHT's were slightly above 350 and outside temps were about 70-71deg.

The bus drives smooth with no hesitations, flat spots etc. Just like it did with the O2 sensor connected.

That's it for now. Thoughts and comments please.

[aeromech]

You removed an O2 sensor that was used by the ECU to control your air/fuel ratio. You installed an O2 sensor in its place to read the air/fuel ratio. Then you started fucking with adjustments. So you remove the brains and then play with things? How in the world does this seem like the correct path to take?

Get yourself a known good O2 sensor and install it in the original location. Then go to a muffler shop and have them weld in a bung for your LM2 sensor. When I bought my LM2 it came with a bung.

Then, go driving and use your LM2 to fine tune your engine plus keep track of your future air/fuel ratio
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
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VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
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Capable of leaping tall buildings in a single bound

[pittwagen]

So you honestly think you can fine tune a CA system with the O2 sensor in place and keep the CHT's in check. Dream on.

With the O2 sensor installed, (that was almost brand new) the engine engine ran hott and was obviously running lean. It was running as well as it was going to. Didn't need an LM-2 to tell me that. I just wanted a cooler running engine.

I knew exactly what I was doing. I keep exact records of what I do and the path back if need be. 50+ years of continuous ACVW ownership has taught me that. So don't tell me I was fucking around. I just wanted to see how the CA system performed (read cooler running engine) absent the O2 sensor.

Next step will likely include installing a 77 FI system to see how it performs and how much cooler the engine runs.

Oh, and by the way, I live in British Columbia, Canada. We do not have smog testing here. And yes, all the CA specific parts have been cleaned and put aside if there is any future need to reinstall them.

[aeromech]

You’ll need to manually adjust your enrichment as you drive. Go up a few thousand feet and your engine with run too rich. Jump down to sea level and it will run lean. You going to jump out and mess with adjustments to compensate? The original O2 would have done that automatically
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[skills@eurocarsplus]

hey gary can i borrow your LM and a screwdriver?

at least you know i'd get it back to you with a hundo taped to the side of it
_________________

[telford dorr]

Something doesn't make sense here.

A narrow band sensor (like your original sensor) is inherently stupid, and only knows if the mixture is either above or below stoichiometric (14.7) e.g. lean or rich. The FI controller varies the injector pulse width to keep the mixture around 14.7 (which oscillates the sensor output voltage between some low value and some higher value, the exact values a function of sensor temperature - except at full throttle, where it overrides the sensor and goes to a preset rich setting). Thus, with a properly operating system, one would expect the mixture to be consistently between 14 and 15 (except at full throttle or during warm-up).

One would expect the CHT to rise rapidly at any mixture > 15 (yes, if the mixture gets lean enough, the CHTs will start to fall again, but this has a low probability of occurring on a well running VW), but you say your measurements show leaner mixtures 15 -> 16, but cool CHTs. Don't understand this, unless your stock system was messed up to start with, or misadjusted.

I would have run the LM2 with the stock sensor installed, to establish a baseline, by either using a 2nd bung or using the LM2 simulated narrow-band output feature. Otherwise, it would seem hard to attribute the "improved" CHT readings to a disabled stock sensor (forcing the FI to run open loop), as opposed the to subsequent adjustments.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[aeromech]

Don,
I’d lend you tools anytime
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[airschooled]

A ‘79 CA-spec bus will run like a Federal bus with the O2 sensor disconnected, that’s it. Your AFM/ECU team will then be completely in charge of driving the mixture train. Some cars run nicely, slightly rich, others are undrivable. If you rarely drive above 90kph, why bother disconnecting the sensor at all? Let it run lean; your driving style seems safe enough for it.

The rest of y’all can show off your tools in private.
Robbie
_________________
Learn how your vintage VW works. And why it doesn't!
One-on-one tech help for your Volkswagen:
www.airschooled.com

[Wildthings]

When using an O2 sensor you might want to delay your timing another degree or two, say to 26 or 27° BTDC at 3800 rpms with the hoses removed and plugged. If you don't see power loss or a decrease in gas mileage by delaying the timing, you are hurting nothing.

If this doesn't get you where you want to be, then do as Robbie suggests and just disconnect the O2 sensor and if necessary readjust the AFM so it will run well without the input from the O2 sensor.

You need to remember is that part of the reason for having an O2 sensor is to supply the cat with sufficient oxygen to finish burning any fuel in the exhaust, so if you remove the cat then you remove a lot of the reason to have an O2 sensor.

[skills@eurocarsplus]

[pittwagen]

When I bought the bus 11 years ago we still had smog regs so I had the FI system properly set up to pass the test which it did until the testing was ended by the gov't 6 yrs ago. Never touched it since. When I removed the CA exhaust and tin a year ago I repositioned the O2 sensor location. I left the O2 sensor hooked up. Thats it.

I just wanted to see if the removal of the O2 sensor would affect the CHT's which it has by about 30 deg. I was going to weld in the bung which came with the kit but opted to just remove the original O2 sensor. I even bought the extra wiring harness to add the narrow band sensor feature to power the original O2 sensor.

Adjusting the mixture on the AF meter seems to have contributed to the lower CHTs. Bus seems to be running smoother as well. Next I will check the plugs and check the gas mileage.

[Wildthings]

Just so you understand, you can adjust the mixture using a wide band analyzer with the O2 sensor disconnected from the ECU, but if and when you hook the O2 back up to the ECU, the ECU will give you pretty close to a 14.7 A/F ration again.

[Clatter]

Whoo!

Down a road well-traveled by myself in the past..


The clamp-on O2 sender will read very close to one welded-in when sampling at cruise, where it matters.
It won’t work well at idle;
If you care about that, then weld in another bung.

If you have the ‘79 CA system working correctly and the wideband installed right,
You’ll see that 14.7 all day long driving everywhere.
Like was said, if you treat the thing gentle/well that’s OK.
It runs clean and efficient.
If you’re going to load it up and hit the highway hard, you risk frying the motor with your foot in it heavy at stoich like that.
Best to crank it down to a lower AFR at cruise - like mid/high thirteens.
Drive it by the CHT and shoot for as lean as you can without high head temps.

Un-plugging the factory O2 sender wire renders the system open-loop and it will function as any earlier L-Jet system.
I like to tune it a bit rich without the O2 sensor hooked up,
Then force the computer to lean it using the O2 sensor.

Had my sensor wire on a switch for a while.
Would leave it on during normal in-town driving,
But out loaded running hard during long-distance summer camping trips,
i’d flip the switch to disconnect the sensor, and run it open-loop using the slightly rich baseline tune setup earlier..

So,
In the end,
The latest type 4 permutation was actually the best,
If you’re willing to play the game right.
_________________
Bus Motor Build

What’s That Noise?!?

[pittwagen]

I mentioned previously that I had a very short and very open turbo exhaust. About 26" from sensor to end of tailpipe. I have read that short exhausts can provide false lean readings under light load which might account for the low to mid 15 AF reading but with reduced CHT's. Under load the AF ratio does drop. Maybe my numbers are some what lower than indicated. Plug reading may confirm that. Thanks Clatter for raising that issue.