Fuel Economy Issue

[dom14]

Hey Guys,

I seem to be getting only 4km/L on LPG on my RB30 Patrol.
The way I clocked it by putting 22 litres on the seemingly empty tank(couldn't start or drive on LPG) and drive and see
how many km's I can get. So, I'm not sure that's the correct way to do it.
I just assumed 22 liters I put into the tanks(There are two tanks connected via the hydro T valve) would basically get used until the tanks run empty. I got around 80kms out of those 22 liters, which roughly translates to 4km/L.
I used to get 6km/L not that long ago, so this is a considerable fall in fuel economy.

I'm not sure putting just fixed small amount of liters of LPG and run it until tanks empty(seemingly) is the way to go about clocking it, 'cos I don't know whether some gas get trapped in one of the tanks just behind the hydrostatic T valve, but in the past it was NOT an issue.
I used to put certain amount of liters in the tanks(30 liters) and get at least 150kms on normal errands and more if it's highway/freeway driving. Tanks are connected as per below diagram.

http://www.amrgas.com/hydrostatic-tee-valves#prettyPhoto[123]/0/

I checked for LPG leaks near the LPG converter on connections using soap water.

I don't think it's running rich due to LPG converter issue or mixer issue, 'cos there's no soot build up on the plugs
when I run on LPG.

Ignition timing appear to be ok, but I need to confirm that tomorrow, but I think it's 15-20 BTDC range.
I can reduce it to 10 BTDC but it kinda sluggish when cold with that timing.

I can't confirm LPG leaks between the tanks & LPG converter, but I don't think there are any leaks there.

Any ideas, thoughts, tips?

Thanx

[Clunk]

Yeah rip it out and just run petrol ;)

[dom14]

Yeah rip it out and just run petrol ;)

That ain't gonna happen. I'm dirt poor atm. :)

[Clunk]

Pedal power Flintstone style, costs nowt

[GeeYou8]

I think you would get more accurate results doing your run from a full tank to a full tank, filled at the same outlet/bowser, not easy if you are dirt poor. LPG usually want a bit more advance on ignition than petrol.
A mate a work swears that some LPG outlets are ripping him off as he has been charged for more than his tanks capacity when he has filled, if that is true your consumption figures would be affected.
LPG seems to be on death row with many servos pulling it out & the price difference making it less attractive, CNG with a home compressor would be good if it was allowed.
Graham

[threedogs]

could you do your fuel figures like most do and thats Litres per 100Ks
Doubt you'll get soot build up using Gas

[dom14]

could you do your fuel figures like most do and thats Litres per 100Ks
Doubt you'll get soot build up using Gas

Well.......ideally if I put 20 litres, I should get at least 100kms(which I used to without any issues and kept going to 120km or so. So, I'm basically doing it for 100k's, but without having a full tank of gas. I can try doing the clocking with a full tank(two tanks) of LPG, but unless the hydrostatic T valve is causing some gas to be trapped behind it in both tank or one tank, the result would be the same I reckon. I guess, the only way to find out to fill it full tank.
If it's running rich for any reason, soot should build up, shouldn't it, even on LPG?!!

[threedogs]

Gas is very dry cant see how soot would build up

[4bye4]

If it's running rich for any reason, soot should build up, shouldn't it, even on LPG?!! No - nothing in gas to make soot. If you have soot on the plugs its oil in the cylinder.

[dom14]

No - nothing in gas to make soot. If you have soot on the plugs its oil in the cylinder.

Ok, cool.
In that case, I should make sure LPG is not running rich by doing an AFR check, then get into the clocking thing back again, if the LPG AFR turns out to be in stoichiometric range.

[Turtle_au]

Has there been a noticeable change in consumption when running on petrol?
What is condition of air filter?

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[dom14]

Has there been a noticeable change in consumption when running on petrol?
What is condition of air filter?

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I haven't actually tested petrol consumption economy recently.
I've been tuning the carby as it was running rich on petrol, and it appears to be closer to stoichiometric from recent mixture adjustments.
(I used Gunson Colortune spark plug to adjust the carby fuel mixture).

The LPG mixture is set by the LPG Mixer(Impco 300A mixer).

Carby mixture setting obviously has not effect on LPG, but if the auto choke's not working properly then I guess it(LPG) also can run bit too rich.
But, the auto choke's working good. I will check it again today, but I'm pretty sure it's good.

[Turtle_au]

Was thinking if petrol consumption had gone up then it maybe another cause.

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[GQtdauto]

Beware as has already been said about some pumps putting in less than you pay for , I know the maverick tank was 65 Litres but could get 75 litres supposedly in it at one particular service station , for almost the same amount of ks per tank .
You really need to fill it completely , fill to fill to be sure .

[dom14]

Was thinking if petrol consumption had gone up then it maybe another cause.

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Yeah, I would have to find if the petrol consumption is also affected equally.
ATM, I'm affected by poor LPG economy, hence the reason for focus, but I do get your point.

[dom14]

Beware as has already been said about some pumps putting in less than you pay for , I know the maverick tank was 65 Litres but could get 75 litres supposedly in it at one particular service station , for almost the same amount of ks per tank .
You really need to fill it completely , fill to fill to be sure .

Yes, I'm taking you seriously on that, that I may have not be getting what I'm paying for past few months.

I think I start by filling up from a different servo(I've the habit of filling up from the same pump, same servo for years), and clocking it.

[dom14]

I set the timing to 15 BTDC & it was fair bit higher than that when I checked today, which may or may not have contributed to poor LPG economy. I'm yet to find out by doing a relatively long drive.

[Turtle_au]

Just saw this thread
http://www.nissanpatrol.com.au/forums/showthread.php?t=39501
Maybe the advance is playing up? That could explain timing changing.

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[dom14]

Just saw this thread
http://www.nissanpatrol.com.au/forums/showthread.php?t=39501
Maybe the advance is playing up? That could explain timing changing.


I've got two dizzies. The diaphragm is ruptured in one of them.
The one on the car is the good one. I tested it today to make sure the diaphragm is good.

Carburetor has an issue of running rich, which I haven't sorted yet(on petrol).
But, I don't think it would affect the LPG the same way, 'cos the only thing used for LPG from the carby is the throttle valves(primary & secondary) & the choke, which appear to be working fine.
The secondary throttle of the RB30 & TB42 Nikki carby is activated by vacuum on higher revs, so I don't think it has any negative effect on LPG economy.

I still need to do the most basic thing on the posts above pointed out to me.
That is to rule out that I'm getting number of litres of LPG that I pay for from the servo.
I'm onto it.

[threedogs]

If it blows a little blue smoke on startup it may be your valve stem seals are shot.
Question do you run an upper cyclinder lubricatant or Valve seat saver.
You could have valve recession, typically a head would only last about 200k before
requiring a head relacement with SS valves

[dom14]

If it blows a little blue smoke on startup it may be your valve stem seals are shot.
Question do you run an upper cyclinder lubricatant or Valve seat saver.
You could have valve recession, typically a head would only last about 200k before
requiring a head relacement with SS valves

I've been told these engine's built in late 80's onward don't need the upper lubricant protector or valve seat saver, 'cos the valve seats are already made to overcome the issue of excessive wear from unleaded or LPG or high octane petrol.

The head was done few years back by me(a partial rebuild) and I did the valve seats manually using grinding paste.
I took it to a head rebuilder to get the cracks welded and have it machined, the rest was done by me.
I focused mostly on exhaust valves and seats. I should've done the valve stem seals at the same time, but for some reason forgot about it or didn't have enough time or new seals ready. I did a partial rebuild 'cos I was bit paranoid about bottom end failing due extra compression from any new valve seats, valves & head machining.
I reckon valve stem seals are still ok though. No blue smoke per say, but just condensation on cold start, which used to take ages to go away, but since I installed the brand new thermostat, the condensation appeared to have disappeared for the most part.

[threedogs]

never heard that about petrol patrol heads, will ask around not that Im doubting you
Its a dying art hand lapping in valves a skil almost lost Me thinks lol

[dom14]

never heard that about petrol patrol heads, will ask around not that Im doubting you
Its a dying art hand lapping in valves a skil almost lost Me thinks lol

It wasn't that hard. I just used valve grinding paste and kept rolling the valve stem with my palms, back and forward.
Then I checked how go it is by filing up the valve seat with bit of water and see for leaks or blow bit of air from air gun to see if it bubbles up, while holding the valve. It's mostly the exhaust valves that tend to burn a bit(that if it happens). Mine wasn't that bad, but I did the valve seat grinding anyway. If I knew better, i would've used a rubber hose attached to the valve stem and other end of the rubber hose attached to a drill.
It was a good exercise.

Yes, definitely the cylinder heads from 90's onward were LPG ready.
I think the reasons for some of the LPG engine valve seat recession was due to bad tuning and cheap LPG installations. You still could've or can go for stainless steel sort of valves to lengthen the life of the valve seat, but the seats themselves were already LPG ready from what I've heard so far. I don't know if that's the case for all LPG converted engines, but I think it is for most engines. Most LPG issues were/are from bad installations and bad fine tuning of the ignition system, I think.

[mudnut]

Was talking to the dyno guy on Monday when I got the Falcon's gas system tuned. He said: "No matter how much work you put into the head and valves, LPG will cause valve recession because it is dry."

I asked him if I should fit a lube system, and he said: "That stuff does bugger all really as it sticks to everything and gums it up. It does however, work when running on petrol as it gets dissolved and flows to the valves where it should be."

[dom14]

Was talking to the dyno guy on Monday when I got the Falcon's gas system tuned. He said: "No matter how much work you put into the head and valves, LPG will cause valve recession because it is dry."

I asked him if I should fit a lube system, and he said: "That stuff does bugger all really as it sticks to everything and gums it up. It does however, work when running on petrol as it gets dissolved and flows to the valves where it should be."

To tell you the truth, mine didn't have much(or any) valve recession that I could easily detect.
I think it changes from engine to engine. The "dryness" of LPG is something I'm yet to understand in detail.
When compression stroke happens, ideally the valve seats should not be affected. Intake and exhaust strokes cause LPG gas & exhaust fumes to go pass the valves. If he is right about that, then the passing exhaust of LPG must have some properties the valve seats does not like.
Other explanation might be that since the timing needs bit of advancing the valves aren't properly seated when combustion starts?!
I prefer the first hypothesis, 'cos it's generally the exhaust valve seats that are more affected, but that's the case with other fuels too.

I believe(meaning along the lines of a hypothesis), not fine tuning the LPG ignition curve is the real reason.
Since LPG burns differently to petrol, the ignition curve adjustment need to be fine tuned with modifications to the ignition system, for example something like "dual curve ignition unit" that advances the timing a bit initially and retards is a bit later with warmed up or higher revs.
I'm sure that's the case with petrol as well, but the curve is different, which means the ignition fine tuning system has to be different to suit LPG.
For example, typical vacuum advance system in RB30 Patrols, etc are not designed for LPG, but for petrol combustion.

[mudnut]

Have a quick search for Valve recession online. I have found a few forums with threads that explain it.

Here's an Ad but it does explain it. https://www.youtube.com/watch?v=9VR_FE65zpo

[dom14]

Have a quick search for Valve recession online. I have found a few forums with threads that explain it.

Here's an Ad but it does explain it. https://www.youtube.com/watch?v=9VR_FE65zpo

It's actually marketing ad for their upper cylinder lubricant.

For example it doesn't explain why LPG is more "abrasive" as oppose to petrol, where the petrol get it's lubricant properties.
Petrol enters the combustion chamber as a fine mist of petrol fume, so I'm not sure. It may have some lubricant properties for a microsecond prior to combustion, but I'm not sure how that affect valve seats.

I still don't understand that "dryness" concept.

Petrol as a liquid in room temperature might have some lubricant properties by picturing pouring a bit of petrol on to a fine piece of metal and sliding another fine piece of metal on it. If LPG actually does cause excessive valve recession on average non LPG engines, then it's not yet fully explained. Having said that, I haven't googled the subject heavily yet.

I still believe LPG is a good choice of fuel for properly moded engine for LPG, and the engine can last longer than most other fuels.
I think we haven't quite fine tuned the LPG engine to make it commercially successful as a good choice for traditional petrol engines.
As for the LPG price wise at the bowser, it hasn't been worth a great deal for a quite a while now. I keep it going in mine, 'cos it runs better than
petrol(well, except the LPG guzzling atm :) ).

[Turtle_au]

never heard that about petrol patrol heads, will ask around not that Im doubting you
Its a dying art hand lapping in valves a skil almost lost Me thinks lol
I used to lap the valves on my mini's but I didn't think you could lap the modern engines due to the harder or coated seats and valves.

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[Turtle_au]

It wasn't that hard. I just used valve grinding paste and kept rolling the valve stem with my palms, back and forward.
Then I checked how go it is by filing up the valve seat with bit of water and see for leaks or blow bit of air from air gun to see if it bubbles up, while holding the valve. It's mostly the exhaust valves that tend to burn a bit(that if it happens). Mine wasn't that bad, but I did the valve seat grinding anyway. If I knew better, i would've used a rubber hose attached to the valve stem and other end of the rubber hose attached to a drill.
It was a good exercise.

Yes, definitely the cylinder heads from 90's onward were LPG ready.
I think the reasons for some of the LPG engine valve seat recession was due to bad tuning and cheap LPG installations. You still could've or can go for stainless steel sort of valves to lengthen the life of the valve seat, but the seats themselves were already LPG ready from what I've heard so far. I don't know if that's the case for all LPG converted engines, but I think it is for most engines. Most LPG issues were/are from bad installations and bad fine tuning of the ignition system, I think.
I roll between palms for about 10-15 sec ( you feel the valve drag) lift and rotate about 90 degrees and repeat.
Every 4th or 5th time I hold the valve up and squirt a drop of oil on the valve stem.
NEVER use a drill. It only rotates one way and it will kill your valve guides. Valve guides are designed for up/down motion not high rotational motion.
It's one of those jobs that you can't rush if you want a good result.

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[dom14]

I roll between palms for about 10-15 sec ( you feel the valve drag) lift and rotate about 90 degrees and repeat.
Every 4th or 5th time I hold the valve up and squirt a drop of oil on the valve stem.
NEVER use a drill. It only rotates one way and it will kill your valve guides. Valve guides are designed for up/down motion not high rotational motion.
It's one of those jobs that you can't rush if you want a good result.


I don't think there's huge difference between using a drill and manual tapping in this case.
It's not that different from using a hand drill and an electric one.

A drill can rotate both ways, so that shouldn't be a problem. You can momentarily switch the direction of rotation.
You don't need to use a high speed drill, just a power drill/driver unit can do the job without using high speed.

Manual hand tapping can be good, but time consuming when you have twelve valves in a six cylinder engine.
With proper care and handing of the power drill/driver, it should come as good.

Squirting a bit of oil into the valve stem is a good tip, 'cos the rotating motion is not good for valve guides as you explained.

But, in hindsight, I should have replaced the valve stem seals, 'cos rotating motion is not good for them either, be it using hand or power drill. Besides valve stem seals only cost few peanuts, or they always come with the gasket kit.

[Turtle_au]

I don't think there's huge difference between using a drill and manual tapping in this case.
It's not that different from using a hand drill and an electric one.

A drill can rotate both ways, so that shouldn't be a problem. You can momentarily switch the direction of rotation.
You don't need to use a high speed drill, just a power drill/driver unit can do the job without using high speed.

Manual hand tapping can be good, but time consuming when you have twelve valves in a six cylinder engine.
With proper care and handing of the power drill/driver, it should come as good.

Squirting a bit of oil into the valve stem is a good tip, 'cos the rotating motion is not good for valve guides as you explained.

But, in hindsight, I should have replaced the valve stem seals, 'cos rotating motion is not good for them either, be it using hand or power drill. Besides valve stem seals only cost few peanuts, or they always come with the gasket kit.
When you said drill, I assumed you meant power drill.
I always stripped the head completely before cleaning, including valve seals, and fitted seals with valve in guide as I was putting springs back on, less chance of damage to seal lip.
What I did do once when I had a broken wrist was make a bow to rotate the stick. Similar to the method used to start a fire.

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[dom14]

When you said drill, I assumed you meant power drill.
I always stripped the head completely before cleaning, including valve seals, and fitted seals with valve in guide as I was putting springs back on, less chance of damage to seal lip.
What I did do once when I had a broken wrist was make a bow to rotate the stick. Similar to the method used to start a fire.

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Thanx. Bow technique is pretty good way of doing it, regardless of having a wrist injury, it is an improvement.

BTW, I couldn't help being curious, how did you break your wrist? :)

[Turtle_au]

Thanx. Bow technique is pretty good way of doing it, regardless of having a wrist injury, it is an improvement.

BTW, I couldn't help being curious, how did you break your wrist? :)
It was over 30 years ago ( in my mid 20's )
I high-sided a billy cart. Put hand out to stop myself.

That was about a year after I broke 3 toes on a skateboard.

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[dom14]

It was over 30 years ago ( in my mid 20's )
I high-sided a billy cart. Put hand out to stop myself.

That was about a year after I broke 3 toes on a skateboard.

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Have you broken anything recently? :)

[Turtle_au]

No, I think I finally learnt that I'm not 18 anymore.

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[dom14]

No, I think I finally learnt that I'm not 18 anymore.

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:D
I'm happy you've reached that level of wisdom, and unfortunately for me, I'm still on the learning process to realize I ain't superman anymore. :)
Testosterone does kinda weird things to our heads, kinda mess with our sense of reality. :D

[threedogs]

It was over 30 years ago ( in my mid 20's )
I high-sided a billy cart. Put hand out to stop myself.

That was about a year after I broke 3 toes on a skateboard.

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You should have been on Chuck Norris's "THRILL SEEKERS" lol