Running Lean At Warm Up

[arbita1]

My 83 SC is running lean at warm up. No issues with starting at all. The 15 deg switch works as it should. Idle shoots up to 1,200 rpm on initial start up. Once the switch opens the idle drops down very low. Maybe around 600 rpm. Engine shakes surges and pops through the intake. Seems to be very lean. I have to keep the revs up to keep from stalling. This will improve as the engine warms up. Once fully warm idle is where it should be.

I don’t believe I have any substantial air leaks. And I believe mixture is set okay. I checked it yesterday with a duty cycle meter and I was running between 50-52% fully warm engine.

The last cold control pressure test I did was years ago but it was low. 2 bar at 85 deg F. Should have been 2.5 bar at that temperature.

Thoughts on issues or more tests. Maybe I should check cold control pressure again to see where it’s at.

[timmy2]

Do the pressure tests.
WUR may be off. Low pressure when cold should make It run richer. May be in the transition to warm running.
Decel valve (pancake) failing perhaps. Need to test it if WUR is working in spec.

[boyt911sc]

Matt,

Check the resistance (Ohms) reading of the WUR when the engine is cold. Then measure the cold control fuel pressures until it stabilized to WCP (warm CP). Keep us posted.

Tony

[arbita1]

Originally Posted by boyt911sc

Matt,



Check the resistance (Ohms) reading of the WUR when the engine is cold. Then measure the cold control fuel pressures until it stabilized to WCP (warm CP). Keep us posted.



Tony

Ohms reading was 26. I read it should be around 30 - 40. So I’m guessing the heating element it ok.

Haven’t had a chance to take fuel pressure readings yet. Maybe this weekend.


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[gazzerr]

Your AAR might be closing too quickly too. You can check the resistance of the windings in the internal heating element across the pins on the electrical connector.

[arbita1]

Had a chance to check fuel pressures this morning. Here is what I found:

System Pressure - 5 bar
Cold Control Pressure - 1.2 bar at 14C
Warm Control Pressure - 3.6 bar
It took 2 minutes 40 seconds to reach this pressure.

Based on this it seems system pressure and WCP are within spec. However the CCP is low. According to Bentley it should have been 1.6 - 2 bar at this temperature. Would this cause my warm up idle issues? But this would mean I am too rich at idle and I don’t think that is the case because if I push up on the meter arm (or press the throttle) the idle smooths out.

Thoughts?


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[arbita1]

It’s possible my mixture was set way too lean. I did some tuning today with my duty meter. It was in the 75-80 range. I richened the mixture until it was in the 35-40 range. (I know this is outside the spec but I’m going richer because I have SSI’s). I also found my timing had no advance. So I set that to spec. I also confirmed the lambda was working. When I took off the oil cap to create a lean condition the duty cycle shot up again to the 50-60 range.

We’ll see hat happens on the next cold warm up cycle.