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LM-2 O2 Sensor location
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Clatter
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PostPosted: Thu Jun 17, 2021 4:41 pm    Post subject: Re: LM-2 O2 Sensor location Reply with quote

Why go backwards putting an earlier system on?
Switch the O2 sensor wire and enjoy the best of both worlds.

The ‘79 also had the WOT switch like a ‘76.
They brought it back after none in ‘77 and ‘78..
Why?
They weren’t dumb.
After the system gets it’s inevitable air leaks and starts running lean,
It’ll get lean on hard hill pulls when it needs the fuel most.

Those air leaks make for running lean around town if you don’t have closed-loop watching out for you.
We all know that 45+ years later air leaks are inevitable.
Tell me your throttle body bushes are fresh.


I can hear the switch activate on my ‘79..
On the switch, babay. Bitch Switch. Fuel ON! Twisted Evil



Why waste time/money on an inferior system?
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Clatter
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PostPosted: Thu Jun 17, 2021 4:44 pm    Post subject: Re: LM-2 O2 Sensor location Reply with quote

Don’t bother trying to read plugs anymore unless you’re running race gas.
Too much crap in the fuel nowadays to make plug reading worthwhile..
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airkooledchris
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PostPosted: Fri Jun 18, 2021 12:14 pm    Post subject: Re: LM-2 O2 Sensor location Reply with quote

Clatter wrote:
Don’t bother trying to read plugs anymore unless you’re running race gas.
Too much crap in the fuel nowadays to make plug reading worthwhile..


He mentioned he has access to 91 non-ethanol fuel in his area, it's still worth reading plugs, if nothing else for the big obvious things it might show.

I played with the factory O2 sensor for a little while, but eventually just left it unplugged all the time. The switch on the dash now toggles between the factory TSII signal and a potentiometer. Flip the switch and dial up some fuel if your climbing hills or powering down the highway at 75, then toggle back when in town.
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PostPosted: Fri Jun 18, 2021 1:16 pm    Post subject: Re: LM-2 O2 Sensor location Reply with quote

airkooledchris wrote:
Clatter wrote:
Don’t bother trying to read plugs anymore unless you’re running race gas.
Too much crap in the fuel nowadays to make plug reading worthwhile..


He mentioned he has access to 91 non-ethanol fuel in his area, it's still worth reading plugs, if nothing else for the big obvious things it might show.

I played with the factory O2 sensor for a little while, but eventually just left it unplugged all the time. The switch on the dash now toggles between the factory TSII signal and a potentiometer. Flip the switch and dial up some fuel if your climbing hills or powering down the highway at 75, then toggle back when in town.


One of our good members burned up his engine trying to manually adjust on the fly. He climbed up in altitude and forgot. Expensive mistake.
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PostPosted: Fri Jun 18, 2021 10:54 pm    Post subject: Re: LM-2 O2 Sensor location Reply with quote

We actually have access to 91 ethanol free and Chevron 94 ethanol free. The Chevron 94 is a dedicated hose so no hose contamination with 87 and 89 which have some ethanol.

Think I will fill up with 94 and go for a trip up the valley and maybe a bit beyond. Highway covid travel restrictions have been lifted so we can now travel out of our health area.
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PostPosted: Sun Jun 20, 2021 8:29 am    Post subject: Re: LM-2 O2 Sensor location Reply with quote

General rule of mountain motoring: elevation goes up, octane goes down.
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PostPosted: Sun Jun 20, 2021 7:55 pm    Post subject: Re: LM-2 O2 Sensor location Reply with quote

really hard to read plugs and tailpipes since lead went out. Used to do it at the track all the time, Air fuel meter is easier. Also you are tuning a heavy bus with an ancient air cooled engine. Tune it for optimal without knowing what optimal is and you'll create problems. There is a reason VW went to square port heads in 1979 when they were forced to run 14.7:1 on California buses. It is also the reason air cooled bus engines went away - heat. Once you get between 13.5 and 14.7 the combustion temps start to really climb. Makes lots of power by making extra heat.
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Wildthings
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PostPosted: Sun Jun 20, 2021 9:16 pm    Post subject: Re: LM-2 O2 Sensor location Reply with quote

Here is mine with a 72-74 exhaust, seems to work just fine.

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metahacker
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PostPosted: Sat Jul 09, 2022 9:34 am    Post subject: Re: LM-2 O2 Sensor location Reply with quote

the output of the CA 79 system sensor is using a standard narrowband analog 0 - 1V input (well, technically i believe it's 0 - 0.9V) ..

"How to Tune & Modify Bosch Fuel Injection" covers this ... in detail , specific to the lambda & L-Jet in Chapter 5 & 7, respectively.

anyways.. this means, as Robbie says, you can connect the analog simulated output of the LM-2 to the stock ECU.

this actually allows the 79 CA system to do some great stuff, since the LM-2 output is programmable. you can remap the LM-2 analog output around your own lambda target.

normally, that O2 sensor can only really tell you ... if you are above/below target lambda (1.0 aka stoic aka 14.7 on gas) .. it doesn't provide any meaningful resolution to say "how much" you are off .. it just lets the computer hunt it's only known target - stoichiometric. That's why the 79 CA bus loves to sit at 14.7

Image may have been reduced in size. Click image to view fullscreen.


and well, stoichiometric is the ideal convergence point of your CO / NOx and HC emissions being at the lowest combo ... and that's cool. but it also will be near the point of an air-cooled engine running at it's highest temperature

do understand that ACVW temperature is a direct product of your AFR and timing......hence why dudes in airplanes are watching their EGT/CHT gauges and adjusting mixture vs altitude/throttle...air cooled fan speed = RPM - you can't change that and your thermostat flaps are always wide open once the motor is warm - so your temperature is literally a product of only your tuning....unlike water cooled where you have a thermostat regulating things during normal operation (not just warmup), and the cooling system capacity typically has a meaningful safety margin...thus coolant temp = thermo temp...ACVW dont work that way...your tuning determines temp directly).

anyways. if you look at your LM-2 manual, section 4.3.1...
you will see there is a configuration screen to deal with analog output...
Image may have been reduced in size. Click image to view fullscreen.
...and the narrowband should already be configured for 0 - 1.0V with Lambda 1.0 in the middle.

the VW ECU is trying to hit that middle value (1.0 Lambda, 0.5V, aka 14.7:1 AFR on gas).

I would suggest that you consider using the O2 input to the ECU to your advantage, and recurve the LM-2 output so that you have a more "reasonable" (e.g. chosen for engine temp minimum value, not emissions minimum output) target in the middle (at 0.5V) - something like 0.89 Lambda

I am not clear on how VW implemented the WOT, so you may need to adjust your cog wheel position to dial that in mechanically. I would shoot for 0.85 Lambda on that.

IMO the CA system would be the ideal way to run any stock-like T4 Bus engine, with a wideband like the LM-2 doing a puppet job on its O2 input... then you could reach some degree of altitude compensation through the O2 input... which is, IMO, the biggest weakness of the Jetronic... without closed loop O2 input there is no altitude compensation.... hence why there is input on the ECU to wire up an altitude compensation switch via pin 12)... otherwise it's a pretty amazing system and so easy to tune perfectly.

If you tune the Jetronic "perfectly" for ideal temp at Death Valley (without any O2 input), and then drive to top of a huge mountain in Colorado and be so rich that you kill your rings... or do the reverse, and melt your heads from being too lean. I know one of our favorite posters here has a line about driving from the Sierras to Death Valley and how great the Jetronic works....well, the physics of that notion are just not possible without a closed loop system. I just drove across America twice (with a '78 2.0 L-Jet) and datalogged most of the time... the AFR swings a lot from the beach to the big mountains. I wish I had the CA 79 EFI system (sans exhaust:) ) - it would have done much better, particularly being instructed to keep things about 10-20% richer than 1.0 Lambda.

Bad tuning is what kills Bus engines. They came from the factory with it, too. Fuel ain't the same as it was back then either. And the shit in the books is wrong. Dudes like Raby (who know what they're talking about through actual R&D) sound like broken records with regards to that. Timing should be MBT and AFR should be specific Lambda targets based on load and intended goals. That's just how engines work. But, that's a tangent... we're talking about CA O2.

And with regards to sensor placement, tailpipe works ok. Upstream is technically more ideal but I've ran it several different ways (on the same engine even) and it's okay as long as there is ABSOLUTELY NO leakage at all in the system - it will totally send your readings into super lean BS territory with even just the slightest flange, fitting or pinhole leak. Keep in mind, a wideband is heated. A narrowband generally wants to be where it can hit ~660F. That's likely where O2 sensor placement lore comes from. Your LM-2 wideband definitely won't care as much as your stock O2 narrowband sensor did, where placement is crucial. Hell, if you follow all the typical forum advice to retard your timing 9º under max spec on a lazy dog 7:1 CR motor, you might even get your EGTs high enough to throw code 08 (sensor overheat) on a LM-2 if you place it far enough upstream :-)
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PostPosted: Sat Jul 09, 2022 10:24 am    Post subject: Re: LM-2 O2 Sensor location Reply with quote

you want your sensor to be in a spot where there is no dilution.

14.7 is an ideal AFR on a water cooled engine. It is the most efficient ratio not only because it is where CO and NOX slopes cross at a minimum, hence less smog and the catalytic works best, but the temperature gives more expansion and hence more power. Before 02 sensors we used to lean an engine (watercooled) at the track until the glue on the plug porcelain bubbled, which gave us the best power without melting the engine.

If one knows the history of the VW AC type 4 engine, VW had to change the exhaust manifold flanges in 1979 so they had more contact area, and they went back to the 72-74 style heat exchangers to pull the excess heat from the heads - that 14.7:1 created. Unfortunately because AC engines run hotter than water cooled, NOX was higher, and about 1980 VWOG announced that the AC engines could never meet new EPA standards because of NOX so they were abandoning AC engines. Then when the warranties were up on all the AC engines, and the last ones 7-8 years old, VW recalled all the AC parts from dealers and took them back to Germany. People here, now gone RIP, were a part of that recall.

In my own experience on my 1977, 14,7 at lite cruise works fine and passes smog with flying colots, but as soon as the bus gets over about 45 mph the amount of wind resistance starts to build, the throttle begins to transition to WOT, and the mixture will begins to fall closer to 13.2 - 13.3, I stay below 13.5 because at 13.5 the head temps are similar to 14.7. This slightly richer mixture shortens the catalytic life some but the alternative is scored pistons. High ZDDP will also shorten the cat life. At full WOT the AFR is closer to 12.5:1. FWIW I have a good friend who bought a 1981 AC Vanagon camper new. He never got to use it on a real camping vacation because the engine seized from overheating at 55 mph the first long day out each time. He spent more time camped at VW dealerships than in parks. VW put 4 or 5 engines in it over three years. It was finally determined that the AFM was set too lean at the factory, which was melting pistons. He traded it in on a conventional water cooled car and move on to car and backpack camping rather than fight with AC engines. Ironically he told me that the reason he bought the camper to begin with was because I had such great luck with my 1971 bus, (which has a mixture of about 12:1 to 13:1). The 1971 would get about 16 - 17 mpg while my 1977 gets 18 - 20 mpg. I would not go leaner. Smog laws will not allow me to tune any richer than I am now.
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metahacker
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PostPosted: Sat Jul 09, 2022 12:11 pm    Post subject: Re: LM-2 O2 Sensor location Reply with quote

Yeah Steve, I concur.. pretty spot on

the stock tune on any late bus is setup to run around max possible engine temp

the factory AFM tune for a Bus sucks bad at sea level, its an engine melter

i bought a NOS AFM to compare to the "rebuilt to factory specs" one i had - both did the same shit - engine ran in the 15's at the beach, hot AF

a Vanagon T4 stock tune at sea level IMO would be a huge nightmare, i could see it killing an engine very quickly if you drove it like VW intended (floor it and steer)

14.7 is not a good choice for an air cooled engine except when u sniff for smog, that's the only time it's worthwhile... best rule of thumb is to jump on either side of it.. it's a "reasonable" compromise of all factors for a water-cooled engine, particularly with a cat... but not ideal in any way, particularly for ACVW

it isnt usually what you end up with for best idle quality (it's typically happiest mid 13's to low 14's .. ~13.8 +/- 0.2 on a normal ACVW would be what i would expect),

it's not ideal for very light throttle cruise (better is 15's for mpg, or 13's for temp over efficiency...or 17-18 if you want both and you really know what you're doing - GLWT on Jetronic w/o lots of EGR, a 123 distributor and AFM mastery)..

stoich is not ideal for accel power (better 12's so your engine doesnt die) but technically the leanest side of rich (like 14.1) is usually where an engine will actually make the most torque...but it will be at its almost hottest possible tune (which can be pretty gnarly at WOT), hence why people say to target no leaner than 12.5 to 13.2-13.6 ish NA and even 10's and 11's for Turbo (and many people would say air cooled should tune similarly to Turbo... but too rich can ruin your rings)

bottom line --
friends dont let friends drive acvw stoich
(yet this is how later VWs all came set up)

air cooled and water cooled engines don't necessarily respond to AFR tuning any differently .. but with air cooled engines, the tune directly dictates the engine temperature ... the cooling system is a fixed size fan with fan RPM a direct product of engine RPM - there isn't a massively overspec cooling system on your bus being regulated by a thermostat (like a water cooled system) - it's like an airplane - you are cruising, the prop is spinning and the only variable to dictate final temp is engine tune (not a thermostat). so, you have additional consideration dictating choices.... the water cooled engine will like similar AFRs, but i would gladly tune a water cooled engine much closer to stoich on WOT than i would an air cooled (or a Turbo) .. the intake fuel charge is a drastically important component in managing air-cooled engine temperatures when they are being run at maximum torque output ...

and of course these AFR numbers are totally bullshit since Lambda is the only number that really matters. the 12 13 14 stuff is just a gauge trying to show lambda values assuming that the fuel is 100% gasoline. E10 will show 14.7 at stoich on a gauge but it's actually just the sensor saying lambda 1.0 and the gauge displaying a gasoline AFR. the sensor always reads stoich as 1.0 lamba...whether it's 14.7 (100% petrol) or 14.1 (E10) or ~9:1 (E100).

another reason the CA bus is so cool, that sensor will not only help with elevation but also fuel mix differences.

79 CA Jetronic is pretty high tech shit for an old bus IMO and adding a LM2 to drive the narrowband output makes it pretty freaking awesome.
I'd consider that with a 123 distributor (and a little time spent on the map....) to be as good as any modern car. I think with a good target AFR, a Bus engine could live a LOOOOOONG time with that setup.

the L-Jet was on nice european cars into the 1990s (although later with barometric and oxygen sensors)... for a reason. It's really quite good
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PostPosted: Sat Jul 09, 2022 12:33 pm    Post subject: Re: LM-2 O2 Sensor location Reply with quote

I don't differ with anything you said. The VW bus is really a truck being pushed by a 1930's designed aircraft engine designed to be cooled by air over fins and an oil cooler at much colder temps than sea level temps in CA.

That said, we do agree that anyone who tries to tune a late 2L bus by ear is tossing dice. Where they run best they are too hot. My NOS AFM was about 17:1 out of the box. All I used it for was to get the spring tension on the door. The engine showed cooler (obviously less fuel) and the heater really cooked, but any attempt to accelerate suddenly was flat and unresponsive. My guess is that if I would have taken it out onto the freeway, the WOT would have been around 14 - 15 and the pistons would have scuffed. I only tested it under 40 mph. Then I used the slider to adjust the mixture and it works great across all RPM ranges. It is a non-O2 bus, and not a 79 O2 bus. It smogs as clean as my 1990's Acura Legends did.
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