GQ TB42EFI Dual Fuel will no longer start on LPG when cold or left overnight

[aflman]

Hi all,
I have a mid 90's GQ TB42EFI Patrol on dual fuel that always started fine on gas and petrol. I normally leave the switch on the gas position as it is an Impco system that starts on petrol then switches to gas.
In the last week, first thing in the morning or if I've left it for most of the day parked, it would start on gas but then die a few seconds later. Has never done this before. So, I would put the switch to the bottom petrol position and it starts ok and then when warmed up, I would flick the switch back to gas by raising the revs to around 1500rpm and it then runs fine on gas as it always has and starts on gas no problem again if I am using it during the day.
However, next morning it does the same thing of starting momentarily and then turning off a few seconds later. Today it would not start on gas at all but when I switched to petrol and let it warm up and repeat the above, all is good again.

Anyone know why this is happening thanks?

The lpg installer I had who did this conversion a while back is no longer is around but I noticed they bypassed the solenoid attached to the Converter (as in the pictures attached) and there is only one wire coming from under the dash that goes to a possible second solenoid behind it that the gas hose is attached to (as in pic). The other wiring loom from the back of the dash switch goes to the PEEL CP30 Safety Switch.
I cleaned the terminal connections and earth wires up since the pics but no difference noted.

[mihit]

LPG has lower calories and higher octane (so is harder to ignite)
This indicates to me that it's an issue in the spark system. Plugs obviously the first culprit to check/replace, then work your way back the HT system...

[mihit]

Or... how old is the battery?

[aflman]

Hi mihit, spark plugs were changed not long ago and the HT leads. Battery also a year old. Have a battery tester for CCA and still tests good.
Could it be the CP30 Gas switch?

[mudnut]

It could also be icing up in the cooler weather. My Brother in law used to boil the kettle and take it with him to start his LPG converted F100. He would poor the hot water over the diaphragm casing. It turned out that the installer had incorrectly fitted the water hoses, and it took too long for hot coolant to warm the Impco unit.

Getting gas installed, is like a lucky dip.

If you can't find your fault, try looking at this thread. http://www.nissanpatrol.com.au/forums/showthread.php?37458-LPG-Missfiring-rough-idle-and-rough-running

[aflman]

Thanks mudnut. That happened to me once years back with low coolant so since then I check and renew it and never been an issue.
I can't figure out the install I have but it's been like that for years and never had an issue till now.
You can see the water/coolant hose in the pic and that's all fine also.

[mudnut]

Thanks mudnut. That happened to me once years back with low coolant so since then I check and renew it and never been an issue.
I can't figure out the install I have but it's been like that for years and never had an issue till now.
You can see the water/coolant hose in the pic and that's all fine also.

If all the easy stuff checks out, maybe undo a hose and see that the coolant is actually flowing when the engine is first started. Could be a blockage or thermostat problem.

[aflman]

Still got me baffled. Definitely not the Peel CP30 gas safety switch either...

[mudnut]

Still got me baffled. Definitely not the Peel CP30 gas safety switch either...
Could you give us a rundown on what you have checked so far?

[aflman]

Hi mudnut, have checked all the electricals in engine bay, cleaned/re-grounded earths including the CP30 which I swapped over to another and checked coolant hose to the convertor. I even took bypass cover off and replaced the thermostat with a new one.

Once warmed up from cold start, the car will switch ok to the top gas setting from bottom petrol setting and run fine on gas all day. It also starts fine again on the gas setting as it always had, if I restart it within a few hours.However, the problem always resurfaces when I leave it overnight (it's parked outside) or for long hours off since the morning while at work.
It always starts fine on petrol when cold but not on the gas setting, where it will either start for a few seconds and then engine stops or it will not start at all.

[mudnut]

Hi mudnut, have checked all the electricals in engine bay, cleaned/re-grounded earths including the CP30 which I swapped over to another and checked coolant hose to the convertor. I even took bypass cover off and replaced the thermostat with a new one.

Once warmed up from cold start, the car will switch ok to the top gas setting from bottom petrol setting and run fine on gas all day. It also starts fine again on the gas setting as it always had, if I restart it within a few hours.However, the problem always resurfaces when I leave it overnight (it's parked outside) or for long hours off since the morning while at work.
It always starts fine on petrol when cold but not on the gas setting, where it will either start for a few seconds and then engine stops or it will not start at all.

Hopefully someone with the same set up as you sees your thread an can offer advise. I do know that over a long time the diaphragm goes slack and and the engine needs tuning. A neighbour's vehicle had all kinds of problems with wires that weren't crimped properly. Also spade lugs can feel tight but can get a layer of carbon under the contacts. I had to re-crimp all the conversion wires and use pliers to tighten the spade lugs before his car ran properly.