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Factory LPG switch + gas 'computer'

Discussion in 'VR - VS Holden Commodore (1993 - 1997)' started by CRCinAU, Dec 7, 2013.

  1. CRCinAU

    CRCinAU New Member

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    Hi all,

    I've found bugger all info on these things - so I'll ask here:

    1) Where can I get a replacement Petrol / LPG switch that goes under the headlight switch on my VR? I've found tons of aftermarket - but not sure on if these will be compatible with the factory impco system. I've managed to find that one of the wires goes to the LPG solonoid, another to pin 20 on the computer - but can't find any other info on how the system is supposed to work.

    2) There is an LPG 'computer' behind the glovebox that is supposed to do something when running on LPG. When I first got the car, there were two LEDs on this box - red and green - and they would flash while the LPG system was on. From what I understand, this controls something with the LPG system and allows the car to switch correctly between petrol / LPG (ie overlaps the fuels). I haven't been able to switch between fuels without stalling at idle for years. I'm trying to find the function of this box and info about it so diagnose what is going on.

    3) There are 2 solenoids that are routed to the front near the air filter box that used to tap while on LPG (kinda like the injectors do for petrol) - however these no longer 'tap'. Does anyone know the function of these and what they are supposed to do? I can't find any info of this at all.

    The car still runs quite well on both petrol and gas - but the changeover is horrible - even if done at non-idle RPMs.

    Thoughts? Ideas? Links? Diagrams?
     
  2. BadDad62

    BadDad62 Member

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    I've got the same here and know as much as you atm, going to get the system rechecked after having the mixer replaced a few weeks ago. I'll ask them and see what I can find out.

    my factory switch has sunken into the dash due to the screws breaking the plastic.

    I,ve looked at swapping either of the other aircon/rear window heater or hazard ones over but just need to find out if they work the same.


    Indash switch/gauge VR-VS Commodore - Blue LPG Shop

    http://forums.justcommodores.com.au...997/152667-vs-factory-lpg-petrol-problem.html
     
    Last edited: Dec 8, 2013
  3. CRCinAU

    CRCinAU New Member

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    My switch looks nothing like the ones in the Blue LPG shop... Mine is just like the hazard switch - but no light.

    The controller and tappy things are exactly the same as the ones in the thread you posted to...
     
  4. kingswood country

    kingswood country Active Member

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    My I laws have the switch problem. I believe if I remember correctly the hazard switch is near identical, the gas switch is now obsolete.

    The also have to pull over when changing from petrol to gas and swap at idle. And from memory, swap it over to petrol just to start.


    Sent from my iPhone using Tapatalk
     
  5. Jxfwsf

    Jxfwsf Well-Known Member

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    The box is just the LPG fuel mixture processor (not really a computer) essentially takes the tps and 02 sensor data and controls the solenoids.
    The red and green leds will indicate rich and lean, they should be alternating at idle, what is it doing now and what led is light etc etc?

    The solenoids adjust between atmosphere pressure and intake vacuum to control the diaphragms in the converter to adjust mixture (not all of them make noise but they do wear out)
    Are they the solenoids with only 2 hoses going to them?
    Hold onto them while it's on LPG and at idle and see if you can feel them working.
    Take them off, can you blow thru them? If you can then they're worn out.
     
  6. CRCinAU

    CRCinAU New Member

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    Well, I pulled the glove box out today and had a look at the 'computer' down there. The green light flickers away - the red lights every now and again when I rev the engine and let it go back to idle again. I presume this is the mixture control happening in real time...

    The valves at the front however seem to do nothing.

    Attached some lovely photos:
    photo 2.JPG photo 1.JPG

    The valves seem to have: FCV 940905 printed on the label. A quick google shows up nothing for this (yay!). I probed the points with a multimeter and got ~2.8vDC on them - however this could easily be an average and the valve is getting a 12 volt pulse (as you'd expect from a valve that goes 'tap tap tap tap tap').

    I tried to blow or suck through the valve (without disconnecting the hose to the LPG evaporator) with no success. I can easily blow through the pushed on hose to the air intake mixer. I'm therefore wondering if the valve is just not working (seems funny that both aren't).

    Any thoughts on how to test these units? Or even where to find info on them (or replacements)?
     
  7. CRCinAU

    CRCinAU New Member

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    Anyone? Bueller?
     
  8. Jxfwsf

    Jxfwsf Well-Known Member

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    disconnect them and put the multimeter across the terminals on them (will see if i can find one to see what it should be) try different setting to see if they are open circuit (burnt out) or have some resistance.

    you are correct that the voltage measured is a pulse so you won't see 12V normally except under whatever circumstance the processor is set to hold them open.
    someone may have played with the mixture screws so the processor may not even be trying to control them.
    o2 sensor could be old and worn out resulting in a similar problem.....

    they may just be gummed up and stuck also, carefully they can be pulled apart with a small flat blade screwdriver unhooking the tabs on the back.

    the flashing leds atleast indicated the processor is getting feedback from sensors and is somewhat working, it could be as simple as the converter and mixer are just gummed up from the years of crap.... mixer is easy, pull it off and spray carby cleaner through it from every hole... converter, bit more in depth and if you're not confident playing with the gas system here i'd say get a professional to look at that part (taking plugs out and/or disconnecting the liquid side if not resealed properly afterwards can cause a gas leak).

    quick look in an impco converter (may not be the same model as yours but they're all pretty close) as can be seen there is alot of crap built up in there, can clog the seals (seals could be worn out) and basically stop it performing as it should, you can't always get these apart as over the years corrosion through the water galleries can leak past gaskets, screws seize and break while trying to get it apart etc etc.
    converter.jpg
     
    Last edited: Dec 11, 2013
  9. CRCinAU

    CRCinAU New Member

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    I think the thing here is that once it is running on LPG, the performance is fine. There is no rough running, no dips in power etc.

    I pulled out the multimeter, measured 20 and 21 ohms across the two coils. I measured ~20ohms between one of the wires and ground (so I assume that's the proper ground) and quite a few Mohm between the other wire and ground (probably the positive).

    I'm just about to wire up an LED to a resistor and put it between the two control wires and see if I get the LED pulsing. If so, then I'd say it's certainly the actual valve / solenoid things that are faulty.
     
  10. CRCinAU

    CRCinAU New Member

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    Ok, so I checked the signal with LED + resistor and the flashing on the LED matches the LED on the controller behind the glove box. Before I look at replacing the solenoid etc - could there be anything on the vacuum or LPG side of things that could stop the valve ticking properly?
     
  11. Jxfwsf

    Jxfwsf Well-Known Member

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    so it sounds like it's working properly, get a gas tune done on it, if the mixture screws have been played with it will have an effect on the operation of the processor.
    not all of them make noise (can go from noisy when new to quiet once used or the opposite), as i said can you feel it while holding onto it when it's operating?

    NEVER ever put the dmm across wires on electronics like the processor! this can damage them, the dmm uses the internal battery to feed voltage down the wires to get the reading, doing so can kill components that are on the other end an not designed to handle that voltage.
     
  12. CRCinAU

    CRCinAU New Member

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    Nah - I can't feel anything going clunk. They both used to both make noise and have a feelable click when they were running up until I had an engine change ~15000km ago (original engine did 440,000km!).

    I used the DMM to try and find the path to ground to make sure it wasn't something stupid like a ground wire not properly connecting. I guess that wouldn't make much difference if the LED was firing anyway...
     
  13. Jxfwsf

    Jxfwsf Well-Known Member

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    And there's the problem, grounding 1 probe and sending power down the other wire to any electronic components, most components are robust but subjecting them to this is enough to fry them.

    Would you start randomly probing your pc, tv, modem or phone without knowing exactly what each point on the pcb does? build a basic logic probe if all you're looking for is a ground point, don't use a multimeter.

    So it seems the coils still have resistance, the fuel processor is doing somethings (leds flash, power to the coils fluctuate....), you can't feel the solenoids doing anything, you can't force air through the solenoids.. it last had a gas tune done well before this problem started... your options are:

    a) clean the mixer with a can of carby cleaner
    b) replace random things like the o2 sensor and hope for the best
    c) shove an afr sniffer up the exhaust and see what's going and if the adjustments actually change anything
    d) spend a couple of dollars on getting someone that works with it to diagnose the problem, will most likely cost less than a + b but then you'll know what to replace if your capable
     
    Last edited: Dec 12, 2013
  14. CRCinAU

    CRCinAU New Member

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    Yeah - I'll have to think about this... The gas system hasn't been serviced in a long time (since a backfire damaged the mixer) - and certainly not since putting in the new(er) motor.

    Problem is, I'm broke as a mofo atm - so I was hoping to do as much as I could myself. The joys of being underemployed....
     

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