LPG Discussion Forum

It gave up the ghost a few weeks ago. I get no green light on the dashboard LPG switch
Before it gave up, it seemed to switch the gas on and off repeatedly when driving.

I checked what I could find, and I found that a single yellow wire goes back to the tank, from the switch there are 3 wires,
These 4 wires go into and straight through the fusebox into the main wire loom. There is also a red wire and a black wire that connect to 2 fuses in the fuse box, presumably this is the 12V supply for the LPG unit.

In the engine compartment there is a little black box inside of which is a green "Hella" relay, two 10A fuses (not blown) and a diagnostic port.

I checked the relay, it's good,

The following may be irrelevant but it is what I observed,
The relay has a 12V supply on terminal 86 - terminal 85 is the negative side of the coil. With terminals 30 and 87 being the switched circuit, the switched circuit is open until a 12v is applied to +86 accross to -85. With the relay off the car, using a good 12V battery, the relay switches fine with 12V applied.

With the relay removed from the unit and the ignition on, I get 11.3V at the wire feed for terminal 86 (the battery itself gives 12.4V) and 0V at the wire feeding terminal 85
With the relay installed and the ignition on I get 10.3V on both 85 & 86 but the circuit 30-87 does not switch, it stays open circuit.
Starting the engine makes no difference.
With the ignition on if I close the relay switch manually I hear the solenoid in the LPG tank click - I didn't try this with the engine running.

I imagine under normal working conditions this relay would not switch until the engine has started and the engine has become warm enough

The problem probably lies with something else before the relay. That something else is not feeding the green light in the dashboard and is not switching the relay over when the engine is turned on.

Any ideas how to test and how to fix this?

By The Way:
Petrol costs me £1.32 for 10 miles (42.7mpg) --- I get 54mpg on a long motorway journey being extra gentle
LPG cost £1.02 for 10 miles (28.8mpg) --- I think I get about 40mpg on a long motorway journey being extra gentle
So it's not a huge saving,- £30 per 1000miles £300 - £400 saving a year. The car is running fine without the LPG in operation

I can take pictures of things if you want me to, I don't know if it is necam or koltec or whatever.

Rosanbo wrote:The problem probably lies with something else before the relay. That something else is not feeding the green light in the dashboard and is not switching the relay over when the engine is turned on.

That something else is probably an LPG ECU, but this itself might not be getting power due to a blown fuse etc.

When the tank solenoid clicks, the solenoid on the reducer should also click, the two solenoids are usually wired in parallel on factory fitted models. If the reducer solenoid does not click it could be that the reducer solenoid has blown (with lower than correct resistance) thus blowing the LPG system fuse.

Surprised at your economy figures - You should be getting more of a saving on LPG. Your figures suggest you are getting 45mpg on petrol but only 31mpg on LPG... Unless you drive faster on LPG than on petrol because you know it won't affect your wallet so much!

Simon

Forgot to say there is a diode at the back of the switch on some models - check the switch and check the diode.

Simon

No click from the reducer when I close the relay switch but I do get a click from the rear of the car.

My dashboard switch seems too small to have any diode inside it.

I'll have to post some pictures to try to find out what is what on this car, but those will have to wait.

I think I can see the LPG ECU but it is not very accessible it's under the coolant bottle.

It is a koltec reducer and a necam inline fuel filter.

Thanks for the help, I'll come back when I have some pics.

A common failure is the coil on the valve at the reducer, sometimes this valve can gum up. Check for 12V at the solenoid coil when the solenoid should activate.