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DanHoug
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Joined: December 05, 2016
Posts: 5919
Location: Bemidji, MN
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 Posted: Tue Nov 11, 2025 7:13 am Post subject: Re: Are cats required? |
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one factor in favor of retaining a cat on a Vanagon is the huge increase in your family's safety if you have an attached garage. my vanagon without a cat will spike the carbon monoxide level in the garage to the point of alarm by the simple act of starting, with the 16' door OPEN and quickly backing out. with my tight garage, the CO alarm level is still exceeded 8 hours later. no other car i have with a cat does that. you'd think the cat is too cold to have an effect on CO right at start up but it does trim CO that quickly.
a single cylinder small engine does the same thing, spike CO values extremely quickly. anything else with a cat does not including a V8 truck, a V6 truck, and numerous 4 cylinder econoboxes.
when my mother-in-law was entering senility, she parked her Buick Century in her attached townhome garage and forgot to turn the motor off. it was too long ago to recall if the townhome had a CO detector but the smoke detector in the garage went off concurrently as the garage temp went over 120F. she was too deaf to hear the alarm but my wife discovered it when she visited her the next day. no CO poisoning symptoms, would not have been the case if the car hadn't had a cat.
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-dan
60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
Past projects can be found at--
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do.dah
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Joined: August 27, 2015
Posts: 861
Location: Washington
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| Posted: Tue Nov 11, 2025 7:51 am Post subject: Re: Are cats required? |
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Ehh, I have a cat, and I regularly take my van into a shop to double check it's health. One of the things I have my mechanic do, is stick his sniffer into the tailpipe and check the emissions.
It always passes, but just a short amount of time running in my 2 car garage with the garage doors and side door open, but the house to garage door closed, and the CO alarms in the house start sounding their displeasure...
None of my other cars with cats, set off the alarms as quickly.
| DanHoug wrote: |
one factor in favor of retaining a cat on a Vanagon is the huge increase in your family's safety if you have an attached garage. my vanagon without a cat will spike the carbon monoxide level in the garage to the point of alarm by the simple act of starting, with the 16' door OPEN and quickly backing out. with my tight garage, the CO alarm level is still exceeded 8 hours later. no other car i have with a cat does that. you'd think the cat is too cold to have an effect on CO right at start up but it does trim CO that quickly.
a single cylinder small engine does the same thing, spike CO values extremely quickly. anything else with a cat does not including a V8 truck, a V6 truck, and numerous 4 cylinder econoboxes.
when my mother-in-law was entering senility, she parked her Buick Century in her attached townhome garage and forgot to turn the motor off. it was too long ago to recall if the townhome had a CO detector but the smoke detector in the garage went off concurrently as the garage temp went over 120F. she was too deaf to hear the alarm but my wife discovered it when she visited her the next day. no CO poisoning symptoms, would not have been the case if the car hadn't had a cat. |
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khughes
Samba Member
Joined: July 13, 2013
Posts: 914
Location: Phoenix AZ
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| Posted: Tue Nov 11, 2025 9:08 am Post subject: Re: Are cats required? |
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| Abscate wrote: |
| Stinky123 wrote: |
In the olden days (late 70s early 80s). The car magazines used to bitch about cats putting out a more dangerous chemical than the one that they control.
Modern engines run plenty clean w/o them. |
bitter old men who couldn’t buy 428 super jet V8s... anymore |
Hey! I resemble that remark!
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'86 Westy FAS GenV Turbo (Marvin) |
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?Waldo?
Samba Member
Joined: February 22, 2006
Posts: 10133
Location: Where?
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| Posted: Tue Nov 11, 2025 2:44 pm Post subject: Re: Are cats required? |
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| DanHoug wrote: |
one factor in favor of retaining a cat on a Vanagon is the huge increase in your family's safety if you have an attached garage. my vanagon without a cat will spike the carbon monoxide level in the garage to the point of alarm by the simple act of starting, with the 16' door OPEN and quickly backing out. with my tight garage, the CO alarm level is still exceeded 8 hours later. no other car i have with a cat does that. you'd think the cat is too cold to have an effect on CO right at start up but it does trim CO that quickly.
a single cylinder small engine does the same thing, spike CO values extremely quickly. anything else with a cat does not including a V8 truck, a V6 truck, and numerous 4 cylinder econoboxes.
when my mother-in-law was entering senility, she parked her Buick Century in her attached townhome garage and forgot to turn the motor off. it was too long ago to recall if the townhome had a CO detector but the smoke detector in the garage went off concurrently as the garage temp went over 120F. she was too deaf to hear the alarm but my wife discovered it when she visited her the next day. no CO poisoning symptoms, would not have been the case if the car hadn't had a cat. |
It is good to keep in mind that the bond of hemoglobin to CO is 200-250 TIMES stronger than the bond to oxygen. Even low levels of CO (well below when most alarms will go off) are retained in the blood and will build up over time causing various issues including chronic fatigue.
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I am a high-functioning autistic into VW diesels and Vanagons along with other things that are unrelated to this site. |
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E1
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Joined: January 21, 2013
Posts: 8752
Location: Westfalia, Earth
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| Posted: Tue Nov 11, 2025 7:14 pm Post subject: Re: Are cats required? |
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The CO connection you mention to Chronic Fatigue Syndrome is absolutely correct. Well done.
CFS is largely misunderstood and misdiagnosed — if not going untreated — for a simple and continuing lack of AMA protocol; not only that most doctors don’t know what to do with it, but also admins not knowing how to categorize and bill it for more profit.
Daily rush hour driving is a perfect recipe, for one — not to mention other “priorities” we’re just getting wrong.
_________________
If ever twice as rich, we’re gettin’ a double-wide
’84 “Westfailure”/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
The caveman’s first question to the headhunter: “Hey, you got any coffee?” |
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zerotofifty
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Joined: December 27, 2003
Posts: 4187
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| Posted: Tue Nov 11, 2025 11:20 pm Post subject: Re: Are cats required? |
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| E1 wrote: |
The CO connection you mention to Chronic Fatigue Syndrome is absolutely correct. Well done.
CFS is largely misunderstood and misdiagnosed — if not going untreated — for a simple and continuing lack of AMA protocol; not only that most doctors don’t know what to do with it, but also admins not knowing how to categorize and bill it for more profit.
Daily rush hour driving is a perfect recipe, for one — not to mention other “priorities” we’re just getting wrong. |
This is a very tiring subject, makes me sleepy.
At anyrate I routinely check my air cooled VW heaters for leaks with a CO detector. I had one car that had a cracked heat exchanger, it pumped exhaust into the cabin, really smelled bad.
All you air cooled Van folks should do periodic checks for CO when running the heater. Note that the heater uses exhaust gas upstream of the catalyst, so it dont matter if you got a catalyst or not. If the heat exchanger is cracked, leaks, you will get deadly gas into the cabin.
Use care, be safe.
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Sorry About That Chief.
Give Peace a Chance.
Words to live by. |
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Earl Bay
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Joined: October 26, 2015
Posts: 127
Location: France 38
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| Posted: Wed Nov 12, 2025 1:28 am Post subject: Re: Are cats required? |
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What does that mean technically?
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If you unplug the lambda (O2) sensor, your system will be running in constant open loop. |
because this still sounds like not having the OXS won't be a problem
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A well tuned wbx engine will run fine with the oxygen sensor disconnected
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It actually drives (or feels) better than before |
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jlrftype7
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Joined: July 24, 2018
Posts: 4768
Location: Chicago
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| Posted: Wed Nov 12, 2025 6:38 am Post subject: Re: Are cats required? |
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| Earl Bay wrote: |
What does that mean technically?
| Quote: |
If you unplug the lambda (O2) sensor, your system will be running in constant open loop. |
because this still sounds like not having the OXS won't be a problem
| Quote: |
A well tuned wbx engine will run fine with the oxygen sensor disconnected
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It actually drives (or feels) better than before |
Open Loop, no adjustment for running mixture by engine management system based on input from the O2 sensor or other sensors, since it's been disconnected. So, the MAP changes for engine fueling, typically gets richer than what the MAP would be for ideal emissions output from the tail pipe, and affects fuel economy as well.
A well tuned engine from the era of Fuel Injection systems of the '80s was designed to run well even with no input of an O2 sensor, since you needed a good baseline from what was, at the time, simple, non-complex controls on emissions and fuel consumption. It also meant, compared to the much Richer running engines of the 70s, saving life on a Catalytic Converter by having an engine that didn't need such a high CO setting just to idle well and give good power through the range.
I can remember dialing in MGs with an Exhaust Gas Tester, 5% CO/Rich setting for idle was normal spec for them , with their older CARB set -up, compared to a Fuel Injected European vehicle running a Bosch L-Jetronic system of 1.5% CO as max, adjusted downward to usually just under 1%. I seem to remember the MGs had some sort of emissions cleaning, like an Air Pump system and maybe EGR as well, but your base CO/Rich setting really was as high as 5% for a good idle, then the cleanup before the tail pipe was done with bolted on pollution controls. Very 70s.... 
The Fuel Injected Cars had cats, the older Carb'ed vehicles didn't.
This doesn't mean you are free to disregard the emissions control without consequences. It just means there is no 'electronic' hand to continually monitor, and tweak if needed, the fuel mixture. So, if things start to 'creep' out of spec from your tuned baseline, you'd never know it easily until it became more apparent .
_________________
'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto
Last edited by jlrftype7 on Wed Nov 12, 2025 6:53 am; edited 1 time in total |
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E1
Samba Member
Joined: January 21, 2013
Posts: 8752
Location: Westfalia, Earth
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| Posted: Wed Nov 12, 2025 6:46 am Post subject: Re: Are cats required? |
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| Earl Bay wrote: |
What does that mean technically?
| Quote: |
If you unplug the lambda (O2) sensor, your system will be running in constant open loop. |
because this still sounds like not having the OXS won't be a problem
| Quote: |
A well tuned wbx engine will run fine with the oxygen sensor disconnected
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It actually drives (or feels) better than before |
The first comment meant that fuel mixture will not be adjusted by the Digijet (pre-1986) or Digifant (‘86 and after) system, but remain in open loop as it is at startup before the O2 sensor and computer kick in.
This also means there would be no adjustments for altitude whatsoever.
The second comment means that someone very adept with tuning (like the guy who said it) can indeed tune without an oxygen sensor, but that’s a tiny percentage of owners.
Whenever a van runs better without an oxygen sensor, something is very, very wrong.
_________________
If ever twice as rich, we’re gettin’ a double-wide
’84 “Westfailure”/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
The caveman’s first question to the headhunter: “Hey, you got any coffee?” |
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khughes
Samba Member
Joined: July 13, 2013
Posts: 914
Location: Phoenix AZ
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| Posted: Wed Nov 12, 2025 12:25 pm Post subject: Re: Are cats required? |
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| E1 wrote: |
| Whenever a van runs better without an oxygen sensor, something is very, very wrong. |
Hmm, if you're running at sea level it seems entirely possible that under WOT conditions you could indeed see better performance (due to the richer mixture) than in closed loop mode. But that's the only exception I can think of. At altitude, forget it. And at pretty much any throttle position beside WOT it'll run "worse", even if you don't notice on the butt dyno, you'll definitely notice it at the gas pump. Unless "something is very, very wrong."
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'86 Westy FAS GenV Turbo (Marvin) |
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RawUmber
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Joined: June 23, 2019
Posts: 330
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| Posted: Wed Nov 12, 2025 12:57 pm Post subject: Re: Are cats required? |
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| khughes wrote: |
| Hmm, if you're running at sea level it seems entirely possible that under WOT conditions you could indeed see better performance (due to the richer mixture) than in closed loop mode. |
Digijet (like the OP's) exits closed-loop during WOT, likely for this reason. Same with early Digifant. |
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E1
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Joined: January 21, 2013
Posts: 8752
Location: Westfalia, Earth
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| Posted: Wed Nov 12, 2025 2:07 pm Post subject: Re: Are cats required? |
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Did not know that!
Is that controlled by the full-throttle switch? (Digijet)
So far as VW’s reasoning for this, my first guess would be to avoid *any chance* of being too lean at higher revs. That sure takes down other engines.
_________________
If ever twice as rich, we’re gettin’ a double-wide
’84 “Westfailure”/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
The caveman’s first question to the headhunter: “Hey, you got any coffee?”
Last edited by E1 on Wed Nov 12, 2025 2:09 pm; edited 1 time in total |
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GoEverywhere
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Joined: December 13, 2020
Posts: 1038
Location: Portland, OR
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| Posted: Wed Nov 12, 2025 2:09 pm Post subject: Re: Are cats required? |
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| cmyoch wrote: |
I can understand the dilemma. We do our part in Illinois with conservation, recycling, etc. If the worst I have is a 1600 DP Super Beetle and this van. We're still ahead of the majority. |
If it makes you feel any better I tell people all my vintage cars are 100% post consumer recycled product(Hells, I pulled my '66 Plymouth out of a field and its parts of at least 4 cars now...)
See? Now my rides are environmentally friendly!  |
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E1
Samba Member
Joined: January 21, 2013
Posts: 8752
Location: Westfalia, Earth
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| Posted: Wed Nov 12, 2025 2:10 pm Post subject: Re: Are cats required? |
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Then why not a green bus?
_________________
If ever twice as rich, we’re gettin’ a double-wide
’84 “Westfailure”/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
The caveman’s first question to the headhunter: “Hey, you got any coffee?” |
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RawUmber
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Joined: June 23, 2019
Posts: 330
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| Posted: Wed Nov 12, 2025 3:08 pm Post subject: Re: Are cats required? |
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| E1 wrote: |
| Is that controlled by the full-throttle switch? (Digijet) |
Partially. Idle and Full Throttle switches share the same input and signal to the ECU, so the ECU uses additional inputs (AFM being one) for its conditional reaction to their activation. |
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E1
Samba Member
Joined: January 21, 2013
Posts: 8752
Location: Westfalia, Earth
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| Posted: Wed Nov 12, 2025 3:20 pm Post subject: Re: Are cats required? |
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But the full-throttle switch is the first step that signals everything else that it’s at full-throttle, Right?
_________________
If ever twice as rich, we’re gettin’ a double-wide
’84 “Westfailure”/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
The caveman’s first question to the headhunter: “Hey, you got any coffee?” |
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RawUmber
Samba Member
Joined: June 23, 2019
Posts: 330
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| Posted: Wed Nov 12, 2025 4:35 pm Post subject: Re: Are cats required? |
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| Yes, throttle switch activation is the initial event that triggers the evaluation process that may result in the ECU concluding that it's at WOT. |
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Earl Bay
Samba Member
Joined: October 26, 2015
Posts: 127
Location: France 38
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| Posted: Thu Nov 13, 2025 3:49 am Post subject: Re: Are cats required? |
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| jlrftype7 wrote: |
| Earl Bay wrote: |
What does that mean technically?
| Quote: |
If you unplug the lambda (O2) sensor, your system will be running in constant open loop. |
because this still sounds like not having the OXS won't be a problem
| Quote: |
A well tuned wbx engine will run fine with the oxygen sensor disconnected
|
It actually drives (or feels) better than before |
Open Loop, no adjustment for running mixture by engine management system based on input from the O2 sensor or other sensors, since it's been disconnected. So, the MAP changes for engine fueling, typically gets richer than what the MAP would be for ideal emissions output from the tail pipe, and affects fuel economy as well.
A well tuned engine from the era of Fuel Injection systems of the '80s was designed to run well even with no input of an O2 sensor, since you needed a good baseline from what was, at the time, simple, non-complex controls on emissions and fuel consumption. It also meant, compared to the much Richer running engines of the 70s, saving life on a Catalytic Converter by having an engine that didn't need such a high CO setting just to idle well and give good power through the range.
I can remember dialing in MGs with an Exhaust Gas Tester, 5% CO/Rich setting for idle was normal spec for them , with their older CARB set -up, compared to a Fuel Injected European vehicle running a Bosch L-Jetronic system of 1.5% CO as max, adjusted downward to usually just under 1%. I seem to remember the MGs had some sort of emissions cleaning, like an Air Pump system and maybe EGR as well, but your base CO/Rich setting really was as high as 5% for a good idle, then the cleanup before the tail pipe was done with bolted on pollution controls. Very 70s....
The Fuel Injected Cars had cats, the older Carb'ed vehicles didn't.
This doesn't mean you are free to disregard the emissions control without consequences. It just means there is no 'electronic' hand to continually monitor, and tweak if needed, the fuel mixture. So, if things start to 'creep' out of spec from your tuned baseline, you'd never know it easily until it became more apparent . |
Thanks for clarifying. I tried to dig a bit deeper on this subject.
This might or might not be of interest for you but it appears (found one person stating that on a German forum) that the DJ engine (delivered in Germany, where this bus is registered) didn't come with an OX sensor from factory.
It also appears the DJ never came with a cat from factory. When looking at German online shops it seems the OX sensors they sell are only for G-Kat equipped busses which seem to be the SR, SS or MV engine codes.
What is certain is that the cat on the bus I'm talking about was a retrofitted cat from HJS that came with an HJS controller and cable set. This HJS retrofit kit isn't produced anymore.
The reason why somebody would have invested in that back in the day is a better emissions class and thus paying substantially less taxes.
Since the cat was retrofitted you can revert backwards without breaking any law, and since the bus is registered with historic plates now the emissions class is no longer required to save taxes.
Bottom line, if this engine never had an OX sensor to begin with there shouldn't be any problem removing it.
Which appears to be the case since the engine runs just fine from what I've experienced (admittedly I don't have a whole lot of experience with it, neither before or after cat removal, but the bus used to be my Dad's daily driver) |
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jlrftype7
Samba Member
Joined: July 24, 2018
Posts: 4768
Location: Chicago
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| Posted: Thu Nov 13, 2025 6:59 am Post subject: Re: Are cats required? |
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| Earl Bay wrote: |
| jlrftype7 wrote: |
| Earl Bay wrote: |
What does that mean technically?
| Quote: |
If you unplug the lambda (O2) sensor, your system will be running in constant open loop. |
because this still sounds like not having the OXS won't be a problem
| Quote: |
A well tuned wbx engine will run fine with the oxygen sensor disconnected
|
It actually drives (or feels) better than before |
Open Loop, no adjustment for running mixture by engine management system based on input from the O2 sensor or other sensors, since it's been disconnected. So, the MAP changes for engine fueling, typically gets richer than what the MAP would be for ideal emissions output from the tail pipe, and affects fuel economy as well.
A well tuned engine from the era of Fuel Injection systems of the '80s was designed to run well even with no input of an O2 sensor, since you needed a good baseline from what was, at the time, simple, non-complex controls on emissions and fuel consumption. It also meant, compared to the much Richer running engines of the 70s, saving life on a Catalytic Converter by having an engine that didn't need such a high CO setting just to idle well and give good power through the range.
I can remember dialing in MGs with an Exhaust Gas Tester, 5% CO/Rich setting for idle was normal spec for them , with their older CARB set -up, compared to a Fuel Injected European vehicle running a Bosch L-Jetronic system of 1.5% CO as max, adjusted downward to usually just under 1%. I seem to remember the MGs had some sort of emissions cleaning, like an Air Pump system and maybe EGR as well, but your base CO/Rich setting really was as high as 5% for a good idle, then the cleanup before the tail pipe was done with bolted on pollution controls. Very 70s....
The Fuel Injected Cars had cats, the older Carb'ed vehicles didn't.
This doesn't mean you are free to disregard the emissions control without consequences. It just means there is no 'electronic' hand to continually monitor, and tweak if needed, the fuel mixture. So, if things start to 'creep' out of spec from your tuned baseline, you'd never know it easily until it became more apparent . |
Thanks for clarifying. I tried to dig a bit deeper on this subject.
This might or might not be of interest for you but it appears (found one person stating that on a German forum) that the DJ engine (delivered in Germany, where this bus is registered) didn't come with an OX sensor from factory.
It also appears the DJ never came with a cat from factory. When looking at German online shops it seems the OX sensors they sell are only for G-Kat equipped busses which seem to be the SR, SS or MV engine codes.
What is certain is that the cat on the bus I'm talking about was a retrofitted cat from HJS that came with an HJS controller and cable set. This HJS retrofit kit isn't produced anymore.
The reason why somebody would have invested in that back in the day is a better emissions class and thus paying substantially less taxes.
Since the cat was retrofitted you can revert backwards without breaking any law, and since the bus is registered with historic plates now the emissions class is no longer required to save taxes.
Bottom line, if this engine never had an OX sensor to begin with there shouldn't be any problem removing it.
Which appears to be the case since the engine runs just fine from what I've experienced (admittedly I don't have a whole lot of experience with it, neither before or after cat removal, but the bus used to be my Dad's daily driver) |
Yes, back in the 80s, Europe was still getting NON Cat, non feedback fuel system versions for Certain Markets, while the USA had gone to feedback/O2 sensors by law, along with a Cat. Converter to meet emissions specs.
So yeah, it can be tricky with an older ECU, making sure what it was designed to do. I've seen O2 sensors back in the day with Grey Market Imported vehicles, that were """wired""" to the ECU, when in fact it was all for show to try and pass DOT inspection for being imported to the US under then current emissions requirements. They'd slap a cat onto the exhaust since you couldn't hide or fake that , but didn't have the right ECU/Fuel System in the vehicle to actually use the input from an added O2 sensor...
_________________
'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto |
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zerotofifty
Samba Member
Joined: December 27, 2003
Posts: 4187
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| Posted: Thu Nov 13, 2025 9:43 am Post subject: Re: Are cats required? |
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I tried to retrofit a cat on my Van, it fought me the whole time, I got scratches and bites all over my arms, It was really got bad when I put the wrench on the nuts. I gave up and let the cat go. I heard one can put a tiger in the gas tank, I wont even attempt that. 
_________________
Sorry About That Chief.
Give Peace a Chance.
Words to live by. |
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