LPG Mileage

[mandala1111]

Hi all.I have a 94 auto update model with a 97 3.9 in it and am running on dual fuel.I have had the car running now for 8 months with the import engine with 70,000 kms on it and am a little concerned about the gas mileage.I have the triple scuba tanks in the cargo area with a usable 58 to 60 ltrs.I am getting around 210 kms per tank.I live in the country and drive on mostly hilly and windy roads and not much highway.I think the economy should be better than this am am wondering if I have a gas leak.The engine is running really sweet so don't know if a gas tune will help.
Cheers
Shane

[bee utey]

You are most likely burning the gas. a leak of significant size would be easy to spot by the big frosty patch developing around it. Try finding the main mixture adjuster, mark its current setting, then try a leaner setting for a while. Test drive after the adjustment, you can always go back to your marked setting.

For optimum economy you should have an O2 sensor and LPG processor fitted, parts cost is around $300. They usually save between 10 and 20% of your fuel use in a normally tuned engine.

[Gary S11]

Hi, what's your timing set at? I have a 12/96 d1 same setup,since kicking the timing to 10 deg BTDC it helped heaps, my only set back is it now holds a high idle 1500 rpm for a little bit before settling. Down to normal ...Gary

[mandala1111]

Thanks guys,I will have a play with the mixture setting.Regarding the timing,I have the higher compression engine so have set the timing back a little at 6 deg BTDC.What mileage should I be looking at on LPG ?
Cheers
Shane

[bee utey]

Thanks guys,I will have a play with the mixture setting.Regarding the timing,I have the higher compression engine so have set the timing back a little at 6 deg BTDC.What mileage should I be looking at on LPG ?
Cheers
Shane

What compression ratio? Does it "ping" or detonate under load? Your fuel consumption should be around 20-25 l/100km but this really depends on the terrain. If it is burning 100% cleanly you should be able to wipe your finger in the tailpipe and have it come out clean, not sooty. Note: to do this test you must clean the tailpipe, don't run on petrol at all, and do a tank full. There should be no new soot deposits from excessive fuel burning. Your engine can be 25% richer than optimum without losing any power. Best economy will lose a small amount of power unless you have that processor installed.

[mandala1111]

What compression ratio? Does it "ping" or detonate under load? Your fuel consumption should be around 20-25 l/100km but this really depends on the terrain. If it is burning 100% cleanly you should be able to wipe your finger in the tailpipe and have it come out clean, not sooty. Note: to do this test you must clean the tailpipe, don't run on petrol at all, and do a tank full. There should be no new soot deposits from excessive fuel burning. Your engine can be 25% richer than optimum without losing any power. Best economy will lose a small amount of power unless you have that processor installed.
Thanks Bee utey,I have just set timing at 10 deg BTDC and wound in the mixture a bit.Just took it for a drive and I have a little more power.I will see how things go.The gas system is an Impco mixer type so when setting the mixture manually is there a rough guide as to where to set it to.If I wound the mixture screw in all the way then where would be a good starting place to set it to from there ? I have a lot of experience tuning an engine on fuel but I am a bit lost when it comes to LPG so thanks in advance for any guidance.

[bee utey]

Thanks Bee utey,I have just set timing at 10 deg BTDC and wound in the mixture a bit.Just took it for a drive and I have a little more power.I will see how things go.The gas system is an Impco mixer type so when setting the mixture manually is there a rough guide as to where to set it to.If I wound the mixture screw in all the way then where would be a good starting place to set it to from there ? I have a lot of experience tuning an engine on fuel but I am a bit lost when it comes to LPG so thanks in advance for any guidance.


Hehe, on an Impco what you have done is wind in the idle mixture screw (which is an air bypass screw), making it richer. It should even have the word "idle" cast next to it, with an arrow for adjustment direction. The main mixture adjuster is a small cam on the gas inlet to the mixer marked "L" and "R" with some marks in between. Move the cam one mark towards "L" and see how it goes.

Basically your Impco is like major restrictor in the inlet at low speed, you need more hoof to get it going so you lose the vac advance under even light load. Advancing as you have done should help correct that.

[mandala1111]

Hehe, on an Impco what you have done is wind in the idle mixture screw (which is an air bypass screw), making it richer. It should even have the word "idle" cast next to it, with an arrow for adjustment direction. The main mixture adjuster is a small cam on the gas inlet to the mixer marked "L" and "R" with some marks in between. Move the cam one mark towards "L" and see how it goes.

Basically your Impco is like major restrictor in the inlet at low speed, you need more hoof to get it going so you lose the vac advance under even light load. Advancing as you have done should help correct that.
Thanks again bee utey,I have now adjusted the idle screw to where the engine idles nicely and then just out a little tweak more.Also I found the mixture cam and it was sitting dead centre so I have tweaked it 2 marks towards L.I am going away on a nice trip today for a few days and will see how things go.One question though regarding mixture,I spoke to a mechanic friend yesterday and he suggested to make the mixture a little on the rich side,his theory is that with a richer mix you can be a bit lighter on the pedal due to more power so therefore using less gas this way,what do you think about this ? Also my engine has a 9.35 compression ratio and it does not ping,it is running very smooth and quiet.
Cheers
Shane

[bee utey]

Thanks again bee utey,I have now adjusted the idle screw to where the engine idles nicely and then just out a little tweak more.Also I found the mixture cam and it was sitting dead centre so I have tweaked it 2 marks towards L.I am going away on a nice trip today for a few days and will see how things go.One question though regarding mixture,I spoke to a mechanic friend yesterday and he suggested to make the mixture a little on the rich side,his theory is that with a richer mix you can be a bit lighter on the pedal due to more power so therefore using less gas this way,what do you think about this ? Also my engine has a 9.35 compression ratio and it does not ping,it is running very smooth and quiet.
Cheers
Shane

You can adjust your particular system for EITHER best economy, OR best power, not both at the same time. Best economy is at about 20% less mixture than best power. The idea being that if you use 20% less mixture and lose 10% power at full throttle you are still ahead. Without a dyno and quality time spent changing your mixer characteristics you have only one adjustment for economy on the road. Go drive it and see how it feels. Old mechanics' theories aren't all they are cracked up to be. The reason that electronic mixture controllers rule in the modern era is because they can do both power and economy as needed, and you don't have one.

[crossedup]

You are most likely burning the gas. a leak of significant size would be easy to spot by the big frosty patch developing around it. Try finding the main mixture adjuster, mark its current setting, then try a leaner setting for a while. Test drive after the adjustment, you can always go back to your marked setting.

For optimum economy you should have an O2 sensor and LPG processor fitted, parts cost is around $300. They usually save between 10 and 20% of your fuel use in a normally tuned engine.

Hi , can you please give me some more info on the processor and the o2 sensor. I have a 93 disco 3 tanks in the back. I still have a plx device afr set up from an old blown motor set up I can use, if that helps.
Thanks Jason

[bee utey]

Hi , can you please give me some more info on the processor and the o2 sensor. I have a 93 disco 3 tanks in the back. I still have a plx device afr set up from an old blown motor set up I can use, if that helps.
Thanks Jason

Sorry???

What type of gas mixer and converter do you run?

For fixed mixers (not Impco) I use a Gastec FP50-TOW processor and fit a Falcon 3 wire heated O2 sensor to the "Y" junction. If you cut the relevant harness plug off a wrecked Falcon to can easily run a harness up to the engine bay. The sensor then easily unplugs if you need to change it in the future.

http://www.aulro.com/afvb/attachment.php?attachmentid=24293&d=1270604317

Pic of fixed mixer, processor, O2 sensor and used harness plug.

[crossedup]

Hi, I just checked. The mixer is an Impco 200, p/n 200m-2-2, s/n 000317
Converter, Impco L ,part no LB-2, serial no 000121.
Thanks again for your time.

[bee utey]

Hi, I just checked. The mixer is an Impco 200, p/n 200m-2-2, s/n 000317
Converter, Impco L ,part no LB-2, serial no 000121.
Thanks again for your time.

Impco uses a different type of processor, easily available, althought I haven't bought one for ages (I don't fit Impco) I believe the processor was about $300. You should be able to find them second hand as Impco systems fitted to later Falcons and Commodores should all have them.

Edit: found one online for $170 here:

http://lpgshop.cart.net.au/store/gore-research-gastec-imp6-processor-suit-american-converters.html

[mandala1111]

Thanks Beeutey for the link,I will look into getting one I think.I just got back from a trip and am happy to report that I got 50 kms more to the tank after adjusting the mixture to be a bit leaner and setting the timing to 10 deg BTDC.Also I finally got around to fitting a new 88 degrees thermostat,the old one was 82 degrees so that should make it run a little leaner also.
Cheers Shane

[98 LS]

I too would be interested in hearing more about this controller & O2 sensor set up. Some actual numbers would be great, before and after fuse usage data etc..

My 98 V8i runs an IMPCO system too, (Twin tanks under the rear) but has no L & R mixtre adjustment, I think it is done by a plate and spring set up inside the mixer itself, or something of that nature

Currently it runs 14 deg BTDC initial timing, and has awesome off the mark response, with no ping under load on either LPG or Petrol.

Getting around 280 to 320kms (average) per 70lts of 'bang air'

But before the inlet manifold gasket started to leak badly (this weekends job!) I would regularly see 350kms per tank, which is about 20lt per 100kms.


NOTE** Bee Utey, so maybe I can get an Impco controller and the O2 sensor harness of an LPG Falcon at the self serve wreckers yard?? in your experience where would one be fitted?

many thanks~!!!!!

[bee utey]

NOTE** Bee Utey, so maybe I can get an Impco controller and the O2 sensor harness of an LPG Falcon at the self serve wreckers yard?? in your experience where would one be fitted?

many thanks~!!!!!

It will be connected to a small vacuum control valve connected by a 10mm hose to the front cover of the converter. Trace the wires back to wherever the control box is. As there are many brands of controller I refuse to speculate further on location or wiring difficulty!