How To: Set CO Dwell

[Ron]

Corrected:
54508
If The Anti-Tamper Plug Is In Place, See:
How To: Remove CO Anti-Tamper Plug Here (http://dmctalk.org/showthread.php?8362-Removing-the-anti-tamper-plug-covering-the-mixture-adjustment-screw)

[Michael]

What is the breather hose? Is that the big hose on the other side where the oil fill chamber is or is there a smaller one? The pic is pointing to something but I can't make it out.

[Bitsyncmaster]

Your text in the photo should say "=20 deg. on eight cylinder scale".

If you mean the large hose that goes to the air cleaner, That hose is just open in the air cleaner so blocking it does not simulate if the air cleaner was on.

[Ron]

What is the breather hose? Is that the big hose on the other side where the oil fill chamber is or is there a smaller one? The pic is pointing to something but I can't make it out.The "Oil Fill Tube/Hose":
38507

[Ron]

Your text in the photo should say "=20 deg. on eight cylinder scale".

Yep! Will fix shortly...

THANKS!


If you mean the large hose that goes to the air cleaner, That hose is just open in the air cleaner so blocking it does not simulate if the air cleaner was on.No. To be clear:

The Large Breather Hose goes to the atmosphere (eventually). The Small Breather Hose goes to the Oil Fill Cap.
The Oil Fill Cap has two hoses going to it. Both supply vacuum! [This puts the crankcase under vacuum.] Removing the breather creates a vacuum leak, because instead of having vacuum from the air fuel unit, the breather and thus the Small Breather Hose, would be open to the atmosphere...
So, you have to plug the Oil Fill Cap Tube/Small Breather Hose connected to it (depending on where you separate it).

You can see this if you remove the hose from the cap and place your finger over the tube then seal the bottom of the cap with your palm.
( It is quite strong ;-)

Technically, the CO should be set with everything in place as it will be ran during normal operation, but it can be hard to get to with the breather in place.
This is why it should be double checked and readjusted if necessary, while in place.

[Michael]

Thanks, with my cams the mixture is hard to dial in, but I have never set it with the hose blocked off. However on my car the vent hose has it's own filter since I use the stainless cleaner. Should I remove that line and plug it at he cap?

38517

[Ron]

I can't make out how it is plumed in the pic...

As I mentioned, the best way is to set the CO with everything in place as it will be ran during normal operation (if you can get to it ;-)

One thing- It seems you have the the Oil Fill Cap connect to the "extra" filter instead of the Small Breather Hose. If that is the case, note that the crankcase is normally under vacuum (closed system). This would make it an open system (like a lot of early model vehicles/defeated PCV system), which ALL of the settings etc do not expect and prone to throw things off..., no longer clearing/burning blow by gases as intended (Gains v/s keeping it clean is debated endlessly ;-).

But non-stock cams change things too...
So FWIW- Personally, I'd add a tube to the breather and use a CO analyzer to set it.

(There is something bugging me about that cap I want to check out, but not get into and confuse things now...I'll post up if it turns out to be anything)

[DMCMW Dave]

Thanks, with my cams the mixture is hard to dial in, but I have never set it with the hose blocked off. However on my car the vent hose has it's own filter since I use the stainless cleaner. Should I remove that line and plug it at he cap?

38517

NO. That must be open. If the car is operating correctly there is no reason to disconnect anything. If the car isn't operating correctly, fix that first.

[Ron]

I corrected information in the pic (Post #1) that was causing some confusion.

NOTE- If your D's plumbing is not stock (closed system), this How To Does Not Apply.

[dmcnc]

This PDF is one of the better how-to's I've come across for setting CO
57912


EDIT:
The WS Manual calls for the dwell to be pulsing 35°-45°, NOT 45°!
-R

[Domi]

This PDF is one of the better how-to's I've come across for setting CO
57912

Thank you for sharing this PDF :thumbup:

[Ron]

This PDF is one of the better how-to's I've come across for setting CO
57912
It's very well done but some of the settings and procedures are different for a D...

[Ron]

The manual says to "switch dwell operation for 6 Cylinder engine....dwell operation for duty cycle is 50%" +/- 3.0%"
(WSM D:04:01, CO EMISSION ADJUSTMENT, 2, 11) [Open Loop]

The Specification section says "Normal Operation (Sensor connected and CO properly adjusted) 35-45° (reading pulsates)" (WSM D:04:01, A) [Closed Loop]
Here, they give Dwell values with the meter switched to 4 Cylinder (w/o mentioning it, anywhere)!
AND people have been using these checking values as a setting value by averaging 35-45 = 40° and selecting 4 Cyl on the meter instead (or 20° on 8 Cyl). This is supposed to be for checking the closed loop operation, not setting CO while in closed loop! [Note IF the system is OK, it would not matter.]

Closed Loop Setting Values:
O2 Sensor Connected
Duty Cycle of 44.444% OR Dwell of 40°, switch in 4 Cyl mode = (26.666° in 6 Cyl mode, 20° in 8 Cyl); Pulsing.

The section continues with "Oxygen sensor disconnected - 40-50° (steady reading)" (WSM D:04:01, B)
This is correct, if your meter is switched to 4 Cyl instead. [Closed Loop!]
This is the same as the CO EMISSION ADJUSTMENT section (above).

Open Loop Checking Values:
O2 Sensor Disconnected
Duty Cycle of 50% OR Dwell of 45°, switch in 4 Cyl mode = (20° in 8 Cyl mode, 22.5° in 6 Cyl mode); Pulsing.

We have: the manual using a 6 Cyl setting and then 4 Cyl later (w/o mentioning it anywhere), setting the CO in closed loop and checking in open loop (that's backwards), and meters that don't have 4 Cyl so it is converted to 8 Cyl. Made for a lot of confusion and questions for years...

Why they don't use 6 Cyl all the time is a mystery to me.

All setting/checking values can be found below:

61685

P.S. Thanks to Dave (Bitsyncmaster) for bumping heads with me!

[82DMC12]

I'm going through these settings now. How does one "apply 1.5V to sensor lead"? Is there some device or multimeter that does this?

Sent from my Pixel 3a using Tapatalk

[Bitsyncmaster]

I'm going through these settings now. How does one "apply 1.5V to sensor lead"? Is there some device or multimeter that does this?

Sent from my Pixel 3a using Tapatalk

You use a flashlight battery. Just tape some leads on it.

[82DMC12]

You use a flashlight battery. Just tape some leads on it.Smart! Thanks!

Sent from my Pixel 3a using Tapatalk

[82DMC12]

You use a flashlight battery. Just tape some leads on it.

Dave, should have asked - do you touch both leads to the terminal on the end of the sensor wire, or do you ground the negative and apply the positive to the wire?

[Bitsyncmaster]

Dave, should have asked - do you touch both leads to the terminal on the end of the sensor wire, or do you ground the negative and apply the positive to the wire?

You ground the flat side and touch the wire to the + (side with bump).

[AugustneverEnds]

I recently had my distributor and warm up regulator rebuilt and need to check the dwell, I have a digital dwell meter (I know analogue is better). My question is, do I use the 8 cylinder setting like its been shown with the analogue meter, the 4 cylinder and double the figures, or the 6 cylinder setting?

[82DMC12]

I recently had my distributor and warm up regulator rebuilt and need to check the dwell, I have a digital dwell meter (I know analogue is better). My question is, do I use the 8 cylinder setting like its been shown with the analogue meter, the 4 cylinder and double the figures, or the 6 cylinder setting?

Without knowing the specifics of your digital meter, I like to use the 8 cyl setting on my analog because it seems like the settings/numbers for 8 cyl are more the vernacular around here.

[AugustneverEnds]

Without knowing the specifics of your digital meter, I like to use the 8 cyl setting on my analog because it seems like the settings/numbers for 8 cyl are more the vernacular around here.

I'll try it on 8 cylinder and 6 cylinder and compare values. If anyone is bored and needs specifications to peruse here is the meter in question: https://www.harborfreight.com/lcd-automotive-multimeter-with-tachometer-kit-95670.html

I had a gift card and store credit to use.

[Ron]

The only difference between using analog or digital is that it is harder to read a pulsing signal with a digital.
Select 8 Cylinder (set it to swing/pulse across 20°).

[IIRC, you will get ~27° degrees using 6 Cyl.]

[MrChocky]

The only difference between using analog or digital is that it is harder to read a pulsing signal with a digital.
Select 8 Cylinder (set it to swing/pulse across 20°).

[IIRC, you will get ~27° degrees using 6 Cyl.]

It's pretty hard to read a signal when the ancient analog meter, which several insisted here was insisted was "better", you get is all corroded inside.

Also here:

https://www.youtube.com/shorts/Cd2o1qrPzec

[Ron]

It's pretty hard to read a signal when the ancient analog meter, which several insisted here was insisted was "better", you get is all corroded inside.

Also here:

https://www.youtube.com/shorts/Cd2o1qrPzec...especially so when you use the wrong values and ground. :smile: