Disabling IAC on 7747 for diagnostics??

[Dunksterp]

Hey guys,

I've installed LPG on my Chevy G20, it's a 350 TBI, I'm using an Ostrich 2.0 (with socketbooster) to control the 7747 ECM (mainly the spark tables). I've also installed an Innovate LC1 Wideband and AFR gauge.

I am having an issue where when I start it from cold, the mixture REALLY leans out at idle, which should be the opposite behaviour, as LPG before it's warmed up will stay liquid and run rich. I believe it could be the IAC causing this as I came across another chap with similar issues, but on a carb, turning in his idle control screws resolved the issue.

What would the easiest way of making sure it stayed closed? Or am I barking up the wrong tree?

Also, and this is slightly unrelated, can I use the 2nd analogue output on the Innovate LC1 to connect to the standard O2 sensor connector to get rid of the damn CEL??

[1project2many]

What would the easiest way of making sure it stayed closed?

Easiest way may be creating large vacuum leak at idle so ecm closes IAC to reduce speed. Disconnect IAC when ecm has closed the valve.

Starting and idling cold will require much manual throttle throttle input or will require cranking throttle stop screw to open plates.

Or am I barking up the wrong tree?

Possibly you are barking up the wrong tree. IAC typically closes as the engine gets warm which reduces airflow. Idle control screws on a carburetor are a means to adjust fuel / air ratio, not throttle plate angle. Does the ecm currently control the LPG injection? If not, how is the mixture controlled?

[B52Bombardier1]

If the LP gas stays liquid when cold and then drops out of the aerosol mixture solution to stick on the walls of the intake manifold as droplets, it'll run lean. I see this on cold Honda minibike intake manifolds (from the early 70's) until things warm up - gasoline, not LP, of course.

Rick

[Dunksterp]

Easiest way may be creating large vacuum leak at idle so ecm closes IAC to reduce speed. Disconnect IAC when ecm has closed the valve.

Starting and idling cold will require much manual throttle throttle input or will require cranking throttle stop screw to open plates.


Possibly you are barking up the wrong tree. IAC typically closes as the engine gets warm which reduces airflow. Idle control screws on a carburetor are a means to adjust fuel / air ratio, not throttle plate angle. Does the ecm currently control the LPG injection? If not, how is the mixture controlled?

So the mixture is controlled by two (idle and WOT basically) screws on the LPG mixer, that sits on top of the TBI unit. It works by vacuum as you open the throttle, the vacuum opens the LPG mixer allowing more fuel and air in. This is why I think it could well be effecting my mixture, possibly at all times, as even when driving it opens up.