Cold start Stepper position 14cux

[Belle427]

Could anyone tell me the steppers approx position when starting from cold?
I’m trying to iron out my cold starts on a Megasquirt conversion and not having much luck.
Megasquirt runs from 0 to 200 steps, 0 being closed.
I’ve confirmed it’s moving as it should but I’m struggling to get my head around why I can’t elevate my rpm above 900 at cold idle.

[ric355]

I'm not on Megasquirt but I am using a stepper in open loop mode. On mine I have the idle position varied according to coolant temp, so it depends on the weather as to where it is for cold idle. The step range on mine is 189 steps. I don't have access to my map right now but I'd estimate that with the coolant at say 10 degrees I probably have the stepper at around 100 steps from closed.

Remember that the stepper position is only one factor that can affect idle rpm. You've also got ignition timing and fuelling. In particular, if you're putting a lot of fuel in because the engine is cold this can make it run lumpy until it warms through at least a little bit so its worth checking you haven't gone too far with warmup enrichment.

It's also worth making sure your stepper is moving in the correct direction; i.e. when you think it is opening it is definitely opening, and not closing.

[Belle427]

Thanks, I’m happy enough with the timing and warm up enrichment, Tunerstudio for Megasquirt has a handy autotune feature for warm up enrichment and it seems to work well.
I’ve had the stepper out and confirmed it’s moving in the correct direction but can’t seem to lift idle higher than 900 cold no matter where I move the settings.

[ric355]

Belle427 said:

Thanks, I’m happy enough with the timing and warm up enrichment, Tunerstudio for Megasquirt has a handy autotune feature for warm up enrichment and it seems to work well.
I’ve had the stepper out and confirmed it’s moving in the correct direction but can’t seem to lift idle higher than 900 cold no matter where I move the settings.

If you get the stepper wide open, screw it into the manifold but leave the stepper plug disconnected, and then start the engine, will it idle above 900rpm? This will give you the largest air bleed as possible, and guarantee that the ECU is not changing it without you knowing.

If it will not idle above 900 with the stepper forced wide open, then shut off the engine and remove the bypass tube off the end of the throttle body. With the stepper wide open you should be able to easily blow through it. This will verify there is nothing stopping the air bleeding through. You can also repeat this test with the stepper connected (cycle the power to ensure everything is reset). Again, if you can't blow air through then that tells you the stepper pintle isn't where you think it is.

If all of the above check out, then you need to look for other causes. Strong enough spark? It it running smooth at 900 or is it lumpy? What AFR is it running at when cold? How much timing and have you played with it? Is there any idle via ignition advance control and is it turned on or off.

I'm assuming you have your stepper set to open loop operation and not closed loop where there is typically an rpm target rather than a step target?

[Belle427]

Currently set to open loop, I’m just starting to tinker with cold starts so will try as you suggest and open it fully to see what happens.
Engine seems happiest at 13.8 afr cold but again can experiment with this further, be interested to know what afr others are seeing from a cold start.
Thanks

Edited by Belle427 on Saturday 7th December 15:33

[ChimpOnGas]

Belle427 said:

Currently set to open loop, I’m just starting to tinker with cold starts so will try as you suggest and open it fully to see what happens.
Engine seems happiest at 13.8 afr cold but again can experiment with this further, be interested to know what afr others are seeing from a cold start.
Thanks

Edited by Belle427 on Saturday 7th December 15:33

During warm up enrichment I run 13.0:1, when I enter closed loop at 70c I shoot for a 14.3:1 idle.