Air-Fuel Mixture - plug up Oil Filler hose connection or not?

[DMC1890]

I'm sorry to ask about an issue that seems to have been discussed plenty already. There is a good How-To on 'Set CO Dwell', but after repeated readings, I'm still not clear if the air hose connection to the oil filler (from the air cleaner) should be plugged or not. In some places, it says 'plug'. In others, it says 'no'. The shop manual says to do it with the air cleaner installed and intact. Since the piping for that, which is internal to the air cleaner, is essentially open to the atmosphere, that would tell me if you do not have the air cleaner installed, that you should do the adjustment with the connection unplugged.

I can adjust either way, but then the engine nearly dies if I unplug (or plug) the connection.

Further, with air cleaner and all plumbing installed, doesn't this represent a significant source of unmetered air intake to the system?

Thanks

[mark w]

i dont plug it. the Crankcase needs to be able to vent.

[FABombjoy]

Further, with air cleaner and all plumbing installed, doesn't this represent a significant source of unmetered air intake to the system?

Leave it connected as stock.

If you block the big tube and the oil filler O ring is good, you'll pull a slight vacuum on the crankcase and the flow through the metered portion (connected to the cold start tube) will not be representative of operating conditions.

[Jonathan]

Leave it connected as stock.

If you block the big tube and the oil filler O ring is good, you'll pull a slight vacuum on the crankcase and the flow through the metered portion (connected to the cold start tube) will not be representative of operating conditions.

I agree with this. Keeping the system as close to actual operating conditions while doing testing or adjustments is the best idea. You can reach and adjust the CO mixture screw with everything else on the engine in place. Once you make a TINY adjustment, plug the screw adjustment hole back up and then wait to see how the engine idles after stabilizing to the new setting. Make small adjustments and give it time to take affect before making another.

[FABombjoy]

Oops, I should have said "leave it open to air". You could also set the filter box aside and leave it hooked to that.

And because I *heart* data, here is a log sampled at the dipstick tube.
The large tube to the air filter is blocked, and the vacuum line on the cold start tube remains attached.

First sample: I capped the large line at the oil fill and you can see it drop over the course of 10 seconds (.963 bar).
Second sample: Cap removed, MAP increases as CC pressure equalizes with atmospheric pressure (1.020 bar)

CC_vac.jpg

[opethmike]

Oops, I should have said "leave it open to air". You could also set the filter box aside and leave it hooked to that.

And because I *heart* data, here is a log sampled at the dipstick tube.
The large tube to the air filter is blocked, and the vacuum line on the cold start tube remains attached.

First sample: I capped the large line at the oil fill and you can see it drop over the course of 10 seconds (.963 bar).
Second sample: Cap removed, MAP increases as CC pressure equalizes with atmospheric pressure (1.020 bar)

CC_vac.jpg

nerd seal.jpg

[DMC1890]

What is the role of the cold-start valve in the vacuum circuit? I cannot find it discussed in the FSM. Whatever it is doing, it seems relevant to this discussion. I would guess that it is supposed to connect, or disconnect, the crankcase breather to the carbon canister, but only during the cold-start condition.

[DMC1890]

CC_vac.jpg

I think it's cool.

Is the AFR measurement coming from a separate wide-band sensor? Are we seeing some 'adjustment' between 5:54 and 5:58 due to the increased air? When I uncapped mine, my dwell meter reading shot way up and I quickly recapped it to keep the engine running, which makes me think I've got some additional problem.

[FABombjoy]

What is the role of the cold-start valve in the vacuum circuit?

The cold start tube is tied to all 6 cylinders and provides vacuum for both the vapor recovery and the PCV systems. In the DMCH store photo you can see the "bump" where the cold start tube holding bolt attaches, along with the channels that run to all 6 ports:
http://store.delorean.com/popup.aspx...rge/102260.jpg

In a rare feat of PRV genius design, the spray from the cold-start valve will keep that tube reasonably flushed from PCV oily buildup.

Is the AFR measurement coming from a separate wide-band sensor? Are we seeing some 'adjustment' between 5:54 and 5:58 due to the increased air? When I uncapped mine, my dwell meter reading shot way up and I quickly recapped it to keep the engine running, which makes me think I've got some additional problem.

Before Megasquirt I had an Innovate LC-1 and LMA-3 for data monitoring. They were an invaluable tool for keeping K-jet where it need to be.

Missing is the trace that shows duty cycle on the frequency valve. Attached is a version with it added. The AFR and DC is up and down as I was horsing around with capping and uncapping the large hose port on the fill cap.
CC_vac_with_duty.jpg

Dwell (duty cycle) rising indicates O2 sensor reading lean. That could happen if you were tuned with reduced PCV flow. Lots of variables at play though, so that might not have been the only thing!


PS: Mike - I had shields up so it bounced off me and you actually called yourself a nerd!

[FABombjoy]

To add - the vacuum side should be able to breathe freely through the oil fill cap from both the side and bottom ports.

If the air/oil separator matrix were clogged that could would reduce flow to the vacuum side and cause a mixture shift. That part is sometimes called a "flame arrestor" but it spends most of it's life trying to condense oil vapors so they aren't pulled in to the intake manifold. You should able to quickly bench test the oil fill cap and verify if it can breathe or not.