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V8i 3.9 Gaseous Anomaly


discodave
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Anyone else experienced this with their Lpg'd truck? First thing in the morning the motor starts first time, no problem. Blip throttle and it changes to gas, drive off and still no problem. :) Get about 100yds up the road, stop at the junction and it konks out. :( It then takes a minute or so and some fancy footwork to get it to spark up again. :angry: If I leave it on petrol until after that first junction it's fine. :blink: Gas system has just been serviced by someone who came highly recommended by another mechanic of good repute and it only happens after the first start of the day. Drives sweet the rest of the time. It's only been happening for the last couple of weeks and so I've just been leaving it petrol till after the junction but I forgot this morning and it happened again, so I thought I'd ask the experts. Any ideas? Cheers. DD

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Anyone else experienced this with their Lpg'd truck? First thing in the morning the motor starts first time, no problem. Blip throttle and it changes to gas, drive off and still no problem. :) Get about 100yds up the road, stop at the junction and it konks out. :( It then takes a minute or so and some fancy footwork to get it to spark up again. :angry: If I leave it on petrol until after that first junction it's fine. :blink: Gas system has just been serviced by someone who came highly recommended by another mechanic of good repute and it only happens after the first start of the day. Drives sweet the rest of the time. It's only been happening for the last couple of weeks and so I've just been leaving it petrol till after the junction but I forgot this morning and it happened again, so I thought I'd ask the experts. Any ideas? Cheers. DD

Not experienced the same as my stsrts better on gas than petrol unless its way below freezing and she starts on petrol runs very lumpy until I change her over to gas (manually) and then runs fine and is very economical around 300 miles to 75litres of gas :ph34r: . I think they are all a bit tempremental. :unsure:

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<..>

First thing in the morning the motor starts first time, no problem. Blip throttle and it changes to gas, drive off and still no problem. :) Get about 100yds up the road, stop at the junction and it konks out.

<..>

If I leave it on petrol until after that first junction it's fine.

<..>

Mine does that... Or it would if I tried to run it on gas immediately ;)

I wonder if it's just that the vapouriser can't supply enough gas until it warms up a little? If it's like mine then there is no cold-start enrichment on LPG and so it possibly struggles to ignite a stoichiometric* mix in a stone-cold combustion chamber. On cold mornings I usually leave mine on petrol for a few hundred yards and then (like yours) it's fine after that.

yep, it shouldnt change over to gas till is reached running temp, so what ever he has used as a stat is set wrong

Some older systems (like mine) have no temp sensing in the switchover - mine changes as soon as it sees a closed throttle at more than 2000rpm (or something like that) and it usually switches when I change from 1st to 2nd.

Rog

*Stoichiometric: Who would have thought I would ever use such a word to describe my LPG system? It's such a crude system that I doubt if the designers actually knew what the word meant :lol:

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*Stoichiometric: Who would have thought I would ever use such a word to describe my LPG system? It's such a crude system that I doubt if the designers actually knew what the word meant :lol:

"pertaining to or involving substances that are in the exact proportions required for a given reaction"

I had to look that one up Rog. :P:lol: Yep, mine is an old single point system by Impco I believe. It runs well enough but automatically changes to gas when the revs go over about 1500 - 2000. It was fine down south when I bought it at the end of the summer, but this colder weather in Scotland is obviously having an effect.

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Anyone else experienced this with their Lpg'd truck? First thing in the morning the motor starts first time, no problem. Blip throttle and it changes to gas, drive off and still no problem. :) Get about 100yds up the road, stop at the junction and it konks out. :( It then takes a minute or so and some fancy footwork to get it to spark up again. :angry: If I leave it on petrol until after that first junction it's fine. :blink: Gas system has just been serviced by someone who came highly recommended by another mechanic of good repute and it only happens after the first start of the day. Drives sweet the rest of the time. It's only been happening for the last couple of weeks and so I've just been leaving it petrol till after the junction but I forgot this morning and it happened again, so I thought I'd ask the experts. Any ideas? Cheers. DD

As others have said, it sounds like yours is working as it should for a basic automatic system.

I personally prefer a manual system (as I have on my 130) compared to the Automatic system (as fitted to our RRC).

I find mine always starts better on LPG but if it's very cold and/or damp then I increase the revs to between 1500 & 2000 rpm and switch over to petrol and keep the revs up a bit until it is running smoothly (choke is good for that on Carbs, EFI is a much smoother switch over) then as soon as the Water and Oil (if you've got an Oil Temp Gauge) are just starting to register on the gauge it goes back onto LPG.

It can then stay on LPG for the rest of the day unless it gets very cold or damp again.

Colin.

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Even down to -7C mine started and ran fine on LPG, but it will depend a LOT on the vapouriser fitted as to the problems you get, your symptoms sound like its not warm enough, if it happens again, pop the bonnet and stick yur hand on the vapouriser and see if it is very cold, if so it's definitely the problem.

It could still be your problem however, particularily if it's a sequential system (which I don't think it is, from your description).

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Thanks for all your input. I think your right that it needs to warm up before running on gas, as it only happens when I forget to leave it switched to petrol for the first few minutes in the morning. The only thing I thought was weird was that it was difficult to start again after it konks out, even though I'd switched it back to petrol, as it always sparks up straight away otherwise.

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The problem you describe sounds symptomatic of the vapouriser freezing up. I have found in the past that if I welly it up the road on LPG before the engine is warm enough it will die. Generally this only happens in cold weather and in the first minute or two from startup. The position of the vap. in the engine bay can make a difference (varying cold ram air flow) as to how susceptible it is to this problem.

Also check you don't have an air lock in the cooling system. The vap. relies on coolant to warm it up and prevent a freeze up.

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The problem you describe sounds symptomatic of the vapouriser freezing up. I have found in the past that if I welly it up the road on LPG before the engine is warm enough it will die. Generally this only happens in cold weather and in the first minute or two from startup. The position of the vap. in the engine bay can make a difference (varying cold ram air flow) as to how susceptible it is to this problem.

Also check you don't have an air lock in the cooling system. The vap. relies on coolant to warm it up and prevent a freeze up.

I dont think there is a problem as such. Seems it is just an effect from the cold weather as as you and others have suggested. The missus and me have been in Thailand for 3 months so it's only now that I'm driving it in the cold mornings. The rest of the time it's fine. ;) The bloke who serviced the gas system has a very good reputation and he was pleasently surprised how well she goes. :D

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Anyone else experienced this with their Lpg'd truck? First thing in the morning the motor starts first time, no problem. Blip throttle and it changes to gas, drive off and still no problem. :) Get about 100yds up the road, stop at the junction and it konks out. :( It then takes a minute or so and some fancy footwork to get it to spark up again. :angry: If I leave it on petrol until after that first junction it's fine. :blink: Gas system has just been serviced by someone who came highly recommended by another mechanic of good repute and it only happens after the first start of the day. Drives sweet the rest of the time. It's only been happening for the last couple of weeks and so I've just been leaving it petrol till after the junction but I forgot this morning and it happened again, so I thought I'd ask the experts. Any ideas? Cheers. DD

Hi discodave

When he servised the gas system did he disconect the water pipes off the evaperater? If so they may need bleedding. See if the top and bottom hoses on the evaperater are hot.

Hope this helps ;)

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