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LPG tuning and repair help needed (pics and videos) 

 

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 Post subject: LPG tuning and repair help needed (pics and videos)
Posted: Wed May 10, 2006 10:24 pm 
Getting Side Ways
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OK I need help.

My EL 6 cyl is guzzling LPG but is perfect on petrol getting around 10-11 litres/100km on petrol but around 18 litres/100km on LPG. It used to do around 12-13 litres/100km on LPG (450-500km to 60 litres in both city & country driving).

I initially stuck the multimeter on the oxy sensor and found it was stuck on 1 volt, indicating rich. I suspected the oxy sensor faulty, I had a spare sitting around so I exchanged it and there was no difference. Still stuck on 1 volt and not moving.

I put it back to petrol and it started swinging zero to one volt around once per second at 2000rpm. Heres a vid of it on a CRO
http://www.altedperformance.com/bozz/petrol.avi (0.5mb)
That shows the oxy sensor, factory computer and general engine is working perfectly.

Here is a vid of it on LPG, the bottom trace is the oxy sensor, you see it stuck on high right until the end where I give it a rev and snap the throttle shut, it backs off a little from rich then goes right back to being completely rich. The top trace is the LPG mixture control valve that goes between the converter and mixer. It is an active ground, so when its high, the valve is inactive and when its low the valve is active (has 12 on it).
http://www.altedperformance.com/bozz/lpg.avi (1.5mb)
At idle, its extremely rich, so rich you can smell raw LPG out of the exhaust. When I rev it, the oxy sensor does not respond at all indicating its still extremely rich. Only when I rev it to around 4000rpm then snap the throttle shut at the end of the vid the oxy sensor shows a reading.... When revving the motor you can see the LPG computer trying to alter the mixtures by opening and shutting the mixture control valve but its achieving nothing...

Now, can anybody help with what is going on with this LPG system:
Image

Image

I've tried adjusting the screw on the side which is appears to be idle mixture and it doesn't affect the idle at all.

I'm suspecting I've got a dodgy mixer but I hope someone here may know more than I do about LPG (which is bugger all) and offer some advice how to repair the fault...

Cheers!
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Posted: Thu May 11, 2006 5:14 pm 
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the Impco's are extremely sensitive to dirty air filters, that can cause them to run very rich. There are two adjustments on your setup, idle mixture and power enrichment, maybe you are adjusting the wrong one.
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Posted: Thu May 11, 2006 7:30 pm 
Getting Side Ways
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I'm fairly sure its idle mixture that I'm adjusting because I think the WOT adjustment is next to the gas supply hose and you can only turn it 45 degrees or so. The (I think) idle screw is just visible in the bottom picture right above the uppermost housing screw that holds the mixer together. Its spring loaded and can turn about 3 turns either way.

I did a search for Impco FB200-2-2 mixer which is what that appears to be and the exploded views show there are only about 10 parts or so, I'm going to pull it apart and see if there's anything obviously wrong with it.

The air filter is quite OK, only done about 20,000km and has very little dirt and contamination on it - should be good for another 30-50,000km...

Cheers
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Posted: Thu May 11, 2006 7:47 pm 
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sorry a bit of topic, but i didnt want to start another thread, we got the same problemn on our el, but on the tickford gas system. How can i make it run leaner?
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Posted: Thu May 11, 2006 10:04 pm 
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Did a bit of playing around tonight. On the converter (Its some strange LP Motor Gas brand, with big writing 'AUSSIE' on it), when you suck on that small hose between the valve and mixer, it leans out the mixture and when you blow on it, it richens it.

I pulled the mixer apart and it was horribly simple. It seems the LPG pressure pushes the diaphram out, the more vacuum the engine has, the more LPG the mixer allows through. The diaphram is held back with a spring on the rear, I weakened the spring which should let more air through and lean out the mixture. Well, it worked straight away. It went far too lean and I could barely richen it up. I pulled it out and stretched it near to what it used to be and put it back together. It now works well but I'm concerned I've cured the symptom but not found the problem - the spring shouldn't get "stronger" overnight, rather there will be something in the converter giving more gas pressure maybe?

Tomorrow I'll rig up an LED to the oxy sensor to see the duty cycle while driving and under load to see if the mixtures are similar and correct when under load, like they are when free revving.

Its also amazing to see the closed loop in action - you can see the duty cycle increase and decrease based on oxy sensor feedback.
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Posted: Fri May 12, 2006 9:43 pm 
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You probably already know this, but the mixture screw works in reverse to what a normal carby mixture screw does.

The screw controls the air that can bypass the diaghram, and not the LPG.
Therefore, by screwing it out a bit, you are increasing the air, and leaning out the mixture.

 

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Posted: Fri May 12, 2006 10:02 pm 
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If you leave the balance line disconnected from the mixer and converter, does it run ok when its stationary?

Check for a leaky converter diaghram - you'll be able to smell gas coming from the balance line on the converter if its buggered. Also, depending on the converter model, theres one or two seats which regulate how much vapor is allowed into the mixer. If the seat is worn and letting too much gas through, this could be your problem. Might pay to put a kit through your converter, but a new one might not be that expensive if this is your problem.

 

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Posted: Fri May 12, 2006 11:22 pm 
Getting Side Ways
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EBGimzo, yeah I saw that when I had the mixer apart.

I might have a go at pulling apart hte converter in a week or two when i get a chance and seeing if anything is obviously fudged in it.
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Posted: Fri May 12, 2006 11:35 pm 
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gt-p simple answer is you cant, they have a stepper motor on the converter (vialle) which is controlled by the ecu.... sometimes they do stuff up and to get a new one costs (sit down when I say this) nearly $300, the other simple solution is to put in a manual power valve in the line so you can manually tune it

 

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Posted: Sat May 13, 2006 12:23 am 
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if someone can let me know how to host images ill get some pictures of the setup in my ef,
BODGY!

lol. how old is your converter man? mines 11 years old now.

 

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Posted: Sat May 13, 2006 10:25 am 
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Its 2 years old.

Email me the pictures i'll host them
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Posted: Sat May 13, 2006 2:37 pm 
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300 bucks that a rip off, but may be worth while looking in to it, i do about 50,000ks a year, thanks for that jim3964
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Posted: Sat May 13, 2006 8:03 pm 
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try cleaning the converter by removing the screw a cleaning off all the greasy residue thats left behind from the LPG (prob. not the solution but cant hurt)
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Posted: Tue May 16, 2006 12:38 am 
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Well it seems to have markedly better economy. The first LED on the LPG level gauge used to go out at 70-80km, now I'm up to 100km and it still hasn't extinguished. I'll know more tomorrow after another 100km or so how its going.

ex-cabi - I might try that when it goes bad again. I still haven't rigged up the LEDs to monitor what the oxy sensor and mixture control valve are doing because I couldn't find a FET to use as an input from the oxy sensor. I'll buy one next weekend from Jaycar so I have visual feedback from the car's systems.

Cheers, it seems the problem is cured for now because of the weakened spring in the mixer.
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Posted: Tue May 16, 2006 1:33 am 
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So what do you think finaly fixed your problem.
As i have the same if not very similer problem, aka very rich and very low economy, on gas.

 

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