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Scott, Master Mechanic
Category: Australia Car
Satisfied Customers: 251
Experience:  30 yrs experience with Aussie, Japanese & British cars
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I have recently bought a vx commodore auto with dual fuel

Customer Question

Hi I have recently bought a vx commodore auto with dual fuel but apparently the petrol sensors have been switched over to gas sensing. Anyway the problem is the motor intermittently stalls when either not accelerating or when pull up at an intersection where normally car would normally idle. When motor is restarted it sits there idling perfectly. Any suggestions or test procedures that you recommend? Please advise. Regards David
Submitted: 1 year ago.
Category: Australia Car
Expert:  Scott replied 1 year ago.

Hi there,
It sounds like the tachometric relay is faulty, or the wiring between it & the ignition system. It's there to cut gas supply if the engine stalls. It's probably wired in as a 'stand alone' separate from the relay box. Usually there's an LED indicator to tell when it's powered up. If the LED is intermittent or dropping out, it's a sure sign of an issue..
I hope this helps!

Customer: replied 1 year ago.
Thanks for that. Can you tell me where the tachometric relay may be located on vx commodore? I have read in some Holden forums that the same symptoms may be caused by faulty crank angle sensor. How would I check if it was that? Please advise on these 2 questions. Thanks. Regards David
Expert:  Scott replied 1 year ago.

Hi again,
I can't really be specific regarding the relay location - they vary depending on where the LPG installer has ta***** *****berty to install it. It should be around the relay box area though. Turn the ignition on & look for a relay with an LED lit up.
The usual test for ignition problems in dual fuel vehicles running on LPG is to switch to petrol & run it on that & see if the fault remains. If it's pretty much identical that points to the ignition system, & your advice is right - first port of call is the crank angle sensor. That is tested in the case of intermittent faults by a swap out, as the fault is unlikely to be apparent when you test it..
I would be visiting an LPG specialist first up - he will be able to eliminate any LPG running faults as a possibility, or confirm..
Best of luck!

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