error 45 "LOW AIR" 1989 350 tbi

[Drunkcanuk]

I think what @Pinger was trying to ask you was this.
When does the 45 code come on?
When using gasoline?
When using propane?
Or it comes on with either fuel?

Maybe clear the code and then run one fuel for a while then switch and see if it comes in.

Not a lot of us here have propane experience other than BBQ's.

 

[Pinger]

My lpg is totally indipendent from the factory computer and line

Not if it is multi-point. The LPG system has its own ECU but that ECU is taking signals directed to the gasoline injectors from the GM ECU and massaging them to suit LPG characteristics. I have no direct experience of multi-point systems but I am aware that what can happen is that on account of the GM ECU still being active in determining injector durations, mixture weakness or richness when running on LPG can manifest as changes to 'fuel trim' - which will then affect running on gasoline (until fuel trims re-adjust to gasoline again). It becomes a rinse, repeat process.

 

[giaguaro]

Not if it is multi-point. The LPG system has its own ECU but that ECU is taking signals directed to the gasoline injectors from the GM ECU and massaging them to suit LPG characteristics. I have no direct experience of multi-point systems but I am aware that what can happen is that on account of the GM ECU still being active in determining injector durations, mixture weakness or richness when running on LPG can manifest as changes to 'fuel trim' - which will then affect running on gasoline (until fuel trims re-adjust to gasoline again). It becomes a rinse, repeat process.

It has sense! When I did the check in OBD with the clip method I did reset the check engine light.
I did drive only on gasoline and no error.
I switched to lpg again and error again.

 

[Pinger]

It has sense! When I did the check in OBD with the clip method I did reset the check engine light.
I did drive only on gasoline and no error.
I switched to lpg again and error again.

Looks like the LPG system is running rich and throwing the GM ECU when it tries to run on gasoline again. There are adjustments to the LPG system that can be made with a lap-top. You'll need the appropriate connecter lead and software (sold together). Maybe you have that. If not, have a look here >> https://lpgautosupplies.co.uk/product-category/lpg-parts/software-and-leads/ for the kind of thing required.

 

[giaguaro]

i did get in touch with the LPG expert, let's see what he find. Next week!