Oxygen Sensor/EGR important?

[ncheney320]

So I have a 1976 bus with California emission and I am trying to set it up to be federal emissions. I had to put a engine in it so I am wondering does deleting the EGR and oxygen sensor will effect performance of the bus? I did purchased a federal emission ECU to replace the original California emission ECU. I replaced the whole heater boxes/exhaust with federal emissions as well. any advice would help. the bus hasn't been running in 35 years
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1971 VW Super Beetle (Merlin)
1976 VW Type 2 (Kermitt)
2002 VW Jetta (Jacob)

Click to view image

[airkooledchris]

The engine won't care that they are gone. The 79 California just had an O2 sensor without an EGR at all. The first thing anyone should do is unplug the O2 sensor, as it just leans out the mixture.

[sjbartnik]

The federal emissions Buses did not have oxygen sensors so the federal ECU you have won't have the bits to deal with the oxygen sensor anyway.

Deleting EGR also likewise won't negatively effect the performance, though it will negatively effect the emission of oxides of nitrogen. Just make sure that you block off the EGR pipe that runs into the intake plenum or else you will create a big vacuum leak.
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1965 Volkswagen 1500 Variant S
2000 Kawasaki W650

[SGKent]

There is some evidence that if the engine is running hot then the EGR will reduce temps and richen the mixture, helping to prevent detonation. I base this statement on Karl's (RIP) posted experiences with overheated pistons on engines that lacked EGR. The original purpose of EGR was to introduce inert gasses into the cylinders thus lowering the amount of oxygen available to burn. This only happens at part throttle. It is turned off at wide open throttle and at idle so there is no power loss. The downside is that the part is not available new and used ones are getting scarce so maintaining it can be a PITA, especially if one uses it as a daily driver and puts 12,000 - 15,000 miles a year on it. EGR service was something like every 30,000 miles.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wasted youth]

If you have an EGR odometer/clock on your bus, be sure to disable that, too. Unless you are looking forward to an unnecessary 'red light on!' experience.

[raygreenwood]

[Wasted youth]

I thought Lamda calculations (O2 sensor) include the premise of altered exhaust Air/fuel ratio from EGR valve function. Given that the EGR functions during a prescribed RPM range, and the ECU is calculating RPM, it seems counterintuitive to assume removing any part of that arrangement through component alteration could be anything but good.

So I would agree you would need to change the ECU to a model that does not support EGR, but I have no real idea how all this works at that level... just contemplating. If you do change the ECU in that vein, which ECU would be best? Would you then contemplate a different distributor or spark plug heat range?

[Silverboot]

not sure how relevant this is to the discussion, but i just smogged my 79 CA model with FI. I had Colin visit on his 2016 journey, and during that visit he unplugged the Oxygen Sensor. Everything ran well, and sort of forgot about it.

This past weekend during my smog test, once hooked up, the operator said she was running really rich. Hooked it back up, and passed.
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79 FI CA Riviera
74 Smallframe Vespa

[Wildthings]

The ECU has no way of knowing if you have a working EGR or not. The air flow through the AFM is going to be pretty much identical for a given engine output whether there is an EGR or no EGR. As stated above the EGR does not affect mixture as the exhaust gas is inert and doesn't pass through the AFM.

[Wasted youth]

[SGKent]

if you look at an air to fuel trace (LM1 or LM2 etc) on my bus the 1977 with EGR and FI, the A/F trace is up and down as conditions change - headwind, minor hill etc. If you look at a trace on a 1979 bus with O2 sensor the trace is almost a flat line at 14.7:1.

The advantage of the O2 sensor is that it keeps the mixture constant so the catalytic converter operates at it peak performance. The disadvantage is that at 14.7:1 one has a complete burn with the right amount of air to the right amount of fuel, and that raises the temperature which means more power - the side effect being greater potential for a 2.0 liter air cooled engine to scuff pistons, crack heads, drop seats, etc. The extra heat is not as easily carried away in the air like it is in most water cooled engines. Most racing engines that burn gasoline run just a tad rich of 14.7:1 because they want max heat for max expansion for max power. VW detuned your engine because it can't take heat like a water cooled engine can.

The O2 sensor is reading residual oxygen in the system then on the L-jet adding duration to the injector pulse when the mixture goes above a set point. This means that the engine can be say programed to run at 15.0:1 or whatever and then the ECU knows to add more fuel to bring it back to 14.7:1. If the AFM is set to say 13.5:1 with the O2 disconnected the ECU cannot remove time from the baseline pulse. Whether the EGR is tossing in lots of inert gas or not the O2 sensor is still only reading Oxygen in the system.

The coil sends a wave thru the electrical system that the ECU reads. It uses that to make a baseline pulse. Then length is added for:

TS1 cold
TS2 cold
AFM flap further open
O2 sensor reading lean

The speed at which the AFM door moves and the direction also tells the ECU when the car is accelerating and decelerating.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

[SGKent]

here is an air to fuel trace on a 1977 bus with FI and EGR smog legal at 70 mph. Someone posted their 1979 and the top line was 14.7 just a flat line all the time.

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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wasted youth]

[Wildthings]

[Abscate]

I'll bet the ECU map on an EGR equipped and a EGR-less car are different, as designed by VW.
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.ssS!

[busdaddy]

[SGKent]

[Wasted youth]

Okay, I will take that with a grain of salt. Unclear how Oxygen can move through layers of coating material... osmosis? And how is it done evenly?

More information...

https://www.thesamba.com/vw/forum/viewtopic.php?t=669667

And some more thoughts... last third of brief article talks about voltage difference based on temperature.

http://www.wellsve.com/sft503/counterp_v2_i3_1998.pdf

Finally, here is a sales brochure for thermocouples that introduced me to the concept awhile back. The idea as I recall is the thermocouple signal changed due to heat. Heat differences were a reflection of air/fuel ratios or engine load. That's about a 25 year old memory, but I think Aeromech would be well qualified to correct me on this.

http://www.avensyssolutions.com/data_AS/File/Solutions/AmetekPI/AMTLM2500.pdf

[telford dorr]

Here's my understanding of how EGR and the O2 sensor work:

1) EGR adds "inert" gas to the fuel-air mixture. By inert, I mean gas which does not have either fuel or oxygen. The gas could be argon, CO2, etc. However, the engine is making all of the CO2 you need, and it doesn't cost anything (extra), so they use exhaust gas. What this gas does is add space between the fuel and oxygen molecules, and when they burn, absorbs some of the heat. This reduces the combustion temperature, thus reducing NOx emissions. It also dumps that absorbed heat right out the exhaust valve. Thus, that burned fuel-air contributes nothing to the engine power output. As such, you should see a drop in fuel mileage. Can't say how much.

2) The O2 sensor is a voltage generator. The voltage is a function of the differential of oxygen on either side of the sensing cell. With O2 on both sides of the cell (atmosphere on the outside, exhaust on the inside), the cell produces no voltage. If the gas on the inside of the cell has less O2 and more hydrocarbons, the cell produces a voltage (up to around 1 volt). The magnitude of the voltage varies with temperature, but we don't care about that. The controller dithers the fuel mixture rich or lean, looking for that transition from no voltage to voltage. When it sees this transition, it dithers the mixture the other way, etc. This dithering keeps the mixture right around stoichiometric. This is where there's just enough fuel for the air available. Unfortunately, it's not the ideal mixture for minimizing NOx production.

In vehicles which have wide-band sensors, the voltage varies with the mixture ratio. This is done by using a second sensing cell. By applying a voltage to this cell, oxygen is forced to diffuse from the outside atmosphere through the cell walls into the sensing chamber. This oxygen reacts with the excess fuel in the sensing cell. The controller fiddles with this drive voltage until the primary sensing cell detects a stoichiometric mixture. The controller uses this drive voltage to determine just how rich the exhaust gas really is. [Or in the case of an LM2, display the mixture ratio on a display] The upshot of all of this is wide-band systems can run the mixture a bit on the rich side, thus reducing the combustion temperature and thus the NOx level, while keeping the mixture within the range the catalytic converter can handle.
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'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
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Same thing happens when you're stupid. - Philippe Geluck
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