Dies on switchover. CNG
 

Alright, so what happened? I was having issues with the distributor. CNG was leaking in the intake manifold and choking the car, but it otherwise worked.

I went to fill up my car with CNG and CNG was working before this, I started the car, waited for switchover and it died. Works fine on Petrol. But every time I attempt to switch over, it fails to switch and stalls.


Causes?

The Necam system can be a pig to fault-find. Suspect:

1. Diaphragm in reducer
2. Diaphragm in dizzy.
3. Solenoid in dizzy - less likely.

However your description - what-happened-when, is limited thus diagnosis is not easy.

I have more symptoms! Works when cold! Dies and does not work when warm! I managed to drive for a while yeah and then as the car warmed up, it died.
And then I switched to petrol and the car starts again. I attempted to switch to CNG and this time there was a very loud whistling sound.

I have CNG stepper motor type B. I took it out, re-did the solder joints. I removed the piston and plan to use SILICON-FREE WD40, it specially says NO silicon in it and lubricate.

NOW, Spring 105....I cannot get to it, the allen key screw stripped on the bottom, not sure why, they were on there TIGHT...and one went the way of the dodo with a circular hole.. So I cannot stretch the spring anymore. Bummer and CNG is always leaking in the intake manifold choking the car on startup.

Since I cannot edit my previous post, I wish to say after resoldering the stepper it works again. I managed to drive all day long on CNG.

I also managed to get the three allen bolts from the bottom out and stretch spring 105, unfortunately it did not help at all. The membrane looked fine to me, but I guess it's not good enough still as CNG still leaks in the intake manifold and chokes my engine on startup.

All I have left to do is replace the main supply hose from the vaporizer/reducer as it is leaking a lot of CNG, reducing my range.

How did you manage to purge the system from cng before removing the stepper?
Did find here how to do it, but as I have similar issue on cng it just stalls and no way to purge it by running the system. Would it work to just loosen the pressure sensor and let the gas out this way? Filled up just few days before so the tank is full.
Another thought is to solder it on the car after removing the fan assembly and using 12V solder iron.

I did like that, i loosed the pressure sensor little bit and gas leaked. Tank will remain full, at least mine did...

I mean unless you have a failed solenoid to keep the main tanks from leaking cng, just pull the component and bleed it slowly. It's not an infinite amount of cng, just do it outside where the CNG cannot pool around you.