wicks

Setting my mixture recently, I placed an AFR meter sensor approx 12 inches into the right exhaust, and after a warm-up drive, set the AFR to 14.5. I did not do any air hose/vacuum/o2 sensor or other changes.

Reviewing the K-Jetronic manual, noted the page on the procedure has additional steps. Wondering if I should have also taken any of these other steps:

• Plug secondary air pump check valve
• Plug vacuum limiter hose connecting to T above throttle plate
• Install CO sensor (in this case I'm using IM AFR meter) ahead of catalytic converter instead of tailpipe

911 2

be careful adjusting the afr incorrectly will cause some serious damage to your engine including melted pistons
Is the afr 14:5 at idle as at wide open throttle on a turbo im sure it should be lower ie richer

Metal Guru

Do not confuse idle mixture with enrichment.
Enrichment is handled by the WUR and is determined by control pressures and engine load. Idle mixture has no effect on enrichment.
The adjustment screw on the fuel distributor sets idle mixture by establishing the initial opening of the metering plate when the engine is at idle.
In reality, idle mixture only needs to be rich enough for the car to start and run but the factory spec is stoich (14.7/1).
The air injection needs to be disabled to set the idle mixture.
The wide band O2 sensor goes behind the cat. The narrow band O2 sensor is in front of the cat.

wicks

Thanks - yes this is just idle. I think I need to raise my control pressure a bit but that's another thing.
I had thought the mixture screw doesn't move the plate, but rather the plunger's base (idle) position. This is good to know.
With air injection pump belt not installed, that should be enough to eliminate the flow of air into the exhaust from it yes?
So with the LM-2 in the exhaust pipe I can't get a legit setting for idle? Do I need to use something else, or remove the cat, or...unplug the O2 sensor, or...
Also, will do a driving/under load/WOT AFR test soon and post results.

heliolps2

Hey Mr Wicks

You need to do all of the above, Air pump disconnected which you have already done, next is disconnect the 02 sensor and remove the cat and use a cat bypass to get the best reading, I feel raising the system pressure could help, I also plan on raising mine to 6.8/7.0 bar .

Metal Guru

My experience with raising system pressure was to lose the ability to move the control pressure to a point where I could achieve 11-11.5/1 AFR at WOT. I was too rich and no amount of control pressure manipulation would lean it out.
System pressure and control pressure oppose each other in the fuel distributor to act as a damping mechanism (control pressure acts on one end of the metering piston and system pressure on the other). Otherwise, the metering plate would bounce all over the place.
I would recommend setting system pressure somewhere between spec minimum (that's where I'm at and it works just fine) and nominal.

wicks

I think I will just try to raise control pressure a bit before changing system pressure...but only after I get a full running test of AFRs logged via the LM-2 and it seems like the right next step.

wicks

I've run the AFR running test with the LM-2, here's what I am getting: this is with the cat and everything stock on the car. And the LM-2 clamp installed in the primary exhaust. M64 3.6 Turbo no mods.

Without O2 connected:
Idle: ~14.0
WOT: ~10.1, but saw 9.8 once

With O2 connected:
Idle: ~15.2
WOT: ~11.3 on full boost.

Thoughts?

Metal Guru

10.1 at what rpm? Is that at boost onset?
Usually you will be rich at low engine speeds and leaner near the redline.
In any event, 10.1 is too rich. You leave torque on the table but more importantly, you risk washing the oil off the cylinder bores and accelerating wear and thinning the oil.
If your engine is stock, use the factory values for system pressure and control pressure. If you do this the afr should be near 11.5 at boost onset and 12.5 near redline. You don't want to vary much from this or it could be expensive.

wicks

That reading was with the engine’s O2 sensor unplugged. With the engine’s O2 sensor reconnected I got 11.3 at full boost onset, more air coming in towards your 12.5 number as revs increased...

Metal Guru

Or add a bung ahead of the cat (between the turbo and cat), using Innovate's special bung that spares the O2 sensor from extreme heat.
I forget how to do these steps as I removed the air injection, narrow band O2 and cat a while ago.

Metal Guru

That upper end number is really important. Lean out much more and you can break piston rings, pound holes in the piston tops, drop a valve (which will lunch your entire engine; one of the local guys did that to his Turbo 3.6 by being stupid) or blow a hole between the cylinder and head.
I'm trying to understand how having the Lambda system operating would affect a WOT run. The Lambda computer/narrow band O2 sensor only manipulates control pressure during constant engine speeds/normally aspirated operations. Once you stab the throttle, it shuts off and your enrichment is controlled by the boost control pressure.
Let me read the setting proceedure to verify.

wicks

I am going through the manuals and can't seem to find this setting procedure - maybe it's in a separate TB or something? The difference with engine's O2 connected and not is very noticeable on the readings (as above).

My air injection is de-belted but not removed, so I imagine some air still moves through it when running. Is that an issue? Perhaps it needs to be plugged to stop any air from being added to exhaust?

wicks

In the Service Teknik book we've got the procedures for setting idle mix, duty factor and fuel pressure and such, but I am not finding anything about AFR reading or the influence of the O2 sensor circuit on running mixture, etc.

Metal Guru

If it's de-belted then it isn't pushing air into the cat.