The V8 Owners Forum -

Hi guys, little question for you. I have a stepper motor in the gas line between vapouriser & mixer ring & all was well after recent head gasket replacement (6 weeks ago) until last weekend when it would shut on switchover. If removed & replaced with 1/2" nipple & it runs fine. Now with stepper motor still plugged into wiring loom, when it switches over it shuts but opens as engine idles. When throttle is applied it shuts instantly but steadily opens again just after engine drops to idle. I've unplugged connection from throttle position sensor & stepper motor does not react when throttle applied. Could it be tps failing or electrics with lpg system? Any ideas?
Cheers....terry

Sounds like the LPG stepper motor input from the TPS is missing, so the motor is behaving correctly for a "closed throttle" condition. Do you have any kit to look at the TPS signal into the engine ECU? That would eliminate or highlight whether the TPS or LPG circuit was dodgy.