Too much advance

[David Milne]

To my horror, I have discovered that the ignition timing on my GW (purchased a couple of weeks ago) is 38 degrees BTDC. I'm amazed that it runs at all at this, and put it down to the fact it is running Liquid Petroleum Gas which has an octane rating of 110 to 115. It will scarcely run at all on unleaded 92 octane petrol, and fortunately I haven't really tried to.

The plugs are in a bad state, being the original ones I think, and appear slightly orangey (never seen plugs orangey before, but hey), but no glazing.

Consequently, I'm puzzled as to why its running at all, and why it's not pinking. Also puzzled as to why it's not running really hot. Any thoughts ? I'm definitely timing it on the correct cylinder, and its a good timing light.

A couple of the LPG shops I phoned (before I checked the ignition timing) said that they didnt adjust the ignition to run on LPG. I'm surprised by this as there is a big difference between 92 and 110 octane. If anyone else is running LPG, I'd be interested to know what your setting is.

Do you think I will have suffered engine damage ? I know there is only one way to find out, but I don't have the time to pull the heads at the moment..

[andy d]

if its not pinking then no damage should be occuring. one of the first places you would see damage would be the plugs. Graham Doust, an Australian, runs his wag on propane and gas. he has a cable operated advance on the dist that allows him to manually advance and retard the spark. the high octane fuel should allow for more advance than gas. LPG is cold, maybe that helps keep the operating temp down?

[David Milne]

I'll change the plugs first, and try changing the seeting to 12 degrees BTDC (give an extra 2 degrees for lpg) to see how it runs on that.

[carrotman]

Are you running manifold pressure to the distributer or ported vacuum? Manifold pressure will show advanced timing at idle. Or is the dizzy just rotated for high initial advance? With such high octane, and AMC's liking advance, your FSJ must be running great.

[David Milne]

Good point - the timings were taken with the vaccum pipe connected to the dizzy, but surely not enough to advance it 30 degrees at a fast idle ?

As for the running, it runs ok on gas, but wont do above 50mph on petrol !

[River Beast]

definitely check the dizzy.. should have ported vacuum and not manifold vacuum... 38 is high for sure.... when I got my wife's Chero... base timing was 19 BTDC... I didnt know how it was running either...

[David Milne]

It is ported vacuum ; those readings were with the vaccuum pipe connected. I assume I time with the pipe disconnected and plugged at the carb end.

Unfortunately, its not running now at all (cut out after 5 mins running) . It is around freezing, and the lpg pump has a thick layer of frost on it. I think (well, hope really) the LPG has iced up the carb.

[Rogue]

i always wondered about the guys that wrote the service manuals - with ported vacuum at idle speed you don't need to disconnect it because their ain't nothing there at idle speed with ported vacuum ??? another mystery of life...

anyhow if you were at fast idle and your base timing is off it could very well have read that high

whenever our LPG forklifts would freeze over like what you said we always had to put a rebuild kit to get them to run again, i don't know why - never knew much about the LPG's just knew the boss said "here put this on"

[ February 24, 2004, 06:22 PM: Message edited by: Rogue ]

[David Milne]

Hopefully I haven't damaged the LPG. It fired up straight away on petrol (which it didnt do last night), so that at least is a good sign. I never understood the disconnect at idle idea either, for exactly the reasons you describe !

Will reset the timings once the weather gets warmer at the weekend.

[graham]

Originally posted by David Milne:
It is ported vacuum ; those readings were with the vaccuum pipe connected. I assume I time with the pipe disconnected and plugged at the carb end.Correct. If you are running straight LPG then set inital timing around 7-10* (degrees) more then standard. I run around 18*. LPG has a different timing curve than petrol. 7-10* more intitially, the same at about 1750 rpm and 10* less over 4000 rpm. If you are runing dual fuel then you will have to pick a happy medium between the two. Unlees you have a TAP (Timing Advance Proccessor) of some description. I do it model 'T' style smile.gif
ANZAC IFSJA Site (http://home.off-road.com/~ozifsja/) has some very good Gas info, well worth checking.

Unfortunately, its not running now at all (cut out after 5 mins running) . It is around freezing, and the lpg pump has a thick layer of frost on it. I think (well, hope really) the LPG has iced up the carb.DANGER .... DANGER. When LPG leaks it freezes Make sure you don't have a gas leak :eek:
If its not a leak then I'd say that the convertor is not getting enough heat. What you refer to as the 'Pump' I think is the convertor. This changes the LPG from a liquid to a gas. There may be a regulator tap to control water flow. This may need to be adjusted to suit you're seasonal changes. Too cold and it'll run rich, to hot and it'll be to lean.
I'd get it checked out, that freezing/frost bit scares me :(

[David Milne]

Hi Graham,

I had the same thought re the leak, but I checked LPG only a week back and nothing was visible or smellable. Nevertheless, it was going into the original shop that fitted it for checking anyway (I booked this before the event fortunately).

As for the unit I was incorrectly referring to, it is a circular unit with water pipes going into it, and a few electrical connections. I guess it can't be a pump as the gas is pressurised (doh !). As for not getting enough heat - it certainly didn't as the engine had only been running for a few minutes. The frost was like the hoar frost you see on gas bottles running garage heaters after they have been on for a long time. Temperature was about -4 C, so not *that* cold. There was no frost visible elsewhere, and none inside the air filter pan. I am a bit puzzled...

Tonight it fired up first time on LPG, no smell. I understand LPG naturally has no smell but that some stinky stuff is added. I'll keep my eye on it.

[graham]

Dave the unit is the 'convertor' Water pipes go in to assist with the conversion proccess. If the motor was not at operating temp, then is quiet possible that it's just frozen up. Given the ambient temp -4 :(
May have to start on petrol and switch over once the engine reaches operational temp.
If you are able to cold start then I'd suggest it may be a little rich.

[David Milne]

I assume the converter does the metering and probably knows what the engine temperature is from the water pipes, but is it clever enough to allow extra fuel for cold starting ?

[Rogue]

oh so those things are called convertors eh? that's the things we rebuilt whenever they froze up like that

[David Milne]

I think I have just discovered why someone removed the thermostat - to keep the coolant going past the converter. The converter is mounted at the rear of the engine bay passenger side ; I was told that it is best to keep it low down to aid heating. Is this true ? Where is the best place to mount it ?

[graham]

Originally posted by Rogue:
oh so those things are called convertors eh? that's the things we rebuilt whenever they froze up like thatFor what reason did you rebuild these? Very little that could be damaged by a bit of frost ???

[graham]

Originally posted by David Milne:
I think I have just discovered why someone removed the thermostat - to keep the coolant going past the converter. The converter is mounted at the rear of the engine bay passenger side ; I was told that it is best to keep it low down to aid heating. Is this true ? Where is the best place to mount it ?Dave in you situation low down and to the rear could be better. Heat from the exhaust manifolds may assist with intial heating until water/coolant has reached operating temp.
In my situation, I'm the reverse. I'm tring to keep it cooler although not cold. If it gets to hot then the LPG act like a petrol vapor lock and runs lean. This is when damage can be done to the motor. Burnt valves result unless the motor has been setup for LPG or a 'Upper cylinder lubricant' is being used.
I feel you setup is very close to being right, just needs time for everthing to reach the correct temperature.

[Rogue]

For what reason did you rebuild these? Very little that could be damaged by a bit of frost#1 -
the boss said "here put this on"#2 -
DANGER .... DANGER. When LPG leaks it freezes .
whenever we had a forklift that wouldn't start or run - the convertors would be frozen and the boss would have me rebuild them ( just a new rubber diaphram thing you throw in there ) and then they would run

[ February 28, 2004, 09:55 AM: Message edited by: Rogue ]

[David Milne]

Graham, it isn't actually that low - its mounted on the inner wing. I've retimed it to 18btdc as you suggested, and the lpg performance is unaffected. Petrol is still too rich ; there have been various bits of the emissions system disconnected when the lpg system was put in, and I think the MCU is running in open loop / cold mode...