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Thread: LPG conversion problem

  1. #1
    Senior Member z80's Avatar
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    Default LPG conversion problem

    I got idle too low, otherwise all is good.

    Any body got a link or ideas on what settings are available with IMPCO open loop system?

    I mean to say is there just a basic idle adjustment or do i need special equipment?

    She stalls when coasting sometimes.

    thanks in advance.



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    what car is it in ?

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    Senior Member global88's Avatar
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    I think z80s car is a volvo.

    z80, can you give me the model of your impco mixer? Its the last part, conected to your intake piping with the largish one inch rubber pipe going into it from your converter.

    If i know the model i can point you in the right direction.
    It should have an idle adjustment screw on it under a cover bolt.

    By the way zzzz is a licenced lpg installer wink wink

    Edit; ever if you take a pic of your setup would help.

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    Senior Member z80's Avatar
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    here's a pic, hope it is good enough

    there's pipes everywhere LOL

    thanks for the offer of help.




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    Senior Member global88's Avatar
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    On your pics their is a yellow label marked r134. To the left of it are 2 hoses held together with 2 white cable ties. Of these 2 tied hoses the one on the right is marked 15mm heaterhose, the one of interest is the one on the left.
    It has a fitting with a spring loaded screw ontop.
    This is your idle air fuel mixture adjustment screw.
    On open loop systems this screw may need regular adjustment to get the idle speed up and smooth by having the idle air fuel ratio adjusted.
    Take note of its position before moving anything just incase so you can put it back where it was if somethings not right.
    Turn it a little in or out (should not need more than 2/3 of a turn max) to find an increase in idle while engine is warmed up and running.
    You want it at the point where you have a high idle but a little more of a turn will drop the idle.
    Edit i said no more than 2/3 of a turn either direction depending on idle sound, it will probably be more like 1/4 of a turn in reality considering its pretty new.

    Its nice to see a clean engine bay.

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    Senior Member z80's Avatar
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    Thanks, I thought it might be that one...but didn't want to attack it without any idea whatsoever...cause the installer said he had put it on a dyno.

    It runs very well apart from the stalling, very ocassionally.

    I also refitted the throttle body retract spring that had been slipped out of its detent position...I think the installer may have adjusted it when this clip was not seated properly and hence made it idle at that.
    He knocked it when installing all the goo around the throttle body i suspect.

    Will report my success/failure as soon as the car is seen again...the kids are revelling in the virtual zero running cost up and down the great ocean road at the moment.

    As for the engine bay..shes 16 years old and has low klms on it....owned by a little old lady.
    Great car for the kids...Volvo 940. $6k with 12 months rego, immaculately serviced.

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    Senior Member global88's Avatar
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    Hmmm return spring was tampered with?
    I wonder if theirs more hidden surprises.

    Just remember the original position of the screw before playing incase you have another problem (like the throttle stops been tampered with, hence the return spring was out).

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    Senior Member z80's Avatar
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    Quote Originally Posted by global88 View Post
    Hmmm return spring was tampered with?
    I wonder if theirs more hidden surprises.

    Just remember the original position of the screw before playing incase you have another problem (like the throttle stops been tampered with, hence the return spring was out).


    Nah...I'll have faith in my fellow man as i can see how he would have done it.
    When tightening the air intake hose clip it's easy to nick the end of the clip with a flat blade screwdriver, it then springs around out of sight.

    The old bloke must have spent considerable time tuning it in vain...LOL

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    Senior Member z80's Avatar
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    Quote Originally Posted by global88 View Post
    Hmmm return spring was tampered with?
    I wonder if theirs more hidden surprises.

    Just remember the original position of the screw before playing incase you have another problem (like the throttle stops been tampered with, hence the return spring was out).



    thanks mate, did as you said, had to turn it a full turn anticlockwise to get it right.

    Got rid of the lambda light by removing the fuel pump fuse for 10 seconds and replacing it as well.

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    Senior Member global88's Avatar
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    Wow, a full turn out?
    Keep a eye on your fuel consumption and how well it starts.
    Could you have got away with a little less of a turn?
    How did removing the fuse for the fuel pump fix your lambda light problem?
    Sorry i cant get my head around that solution, could you explain how that worked?
    Anyway good to see your cruzing again.

    Oh one more thing z80, NICE avatar, when will you get her hands rubbing so i can sit here perving at her all day.
    Last edited by global88; 21-01-08 at 09:38 PM. Reason: added some more

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    Senior Member z80's Avatar
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    it needed a full turn out to not stall when coasting.

    played with it for hours before settling on that setting.

    now it won't idle on petrol properly.

    the fuse resets the ECU from displaying the lambda sensor erroneously the dealer told me.

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    Senior Member global88's Avatar
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    Sounds like yourve got some problem.
    Runs well on gas now but bad on petrol.
    Whats wrong on petrol? Black smoke/rough idle or just idleing too slow.
    Could the problem have been there on petrol after you put the spring back on but you may have missed it?
    Could this problem be why you had to richen the gas mixture?
    No vacuum hoses loose or leaking?
    Some ecu's need to relearn after being reset. Have you given the ecu sometime to readjust.

    Id put the gas mixture screw back, reset the ecu (try disconnecting the battery for an hour) and then test the car on gas and petrol to see if its on both.
    If on both, find and fix the original cause.
    If just on petrol look at your lambda sensor.
    Note the lambda is used to control the mixture under idle, and if the ecu gets a wrong reading from it, your car will run rich (alot of black smoke and rough idle).

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    Senior Member z80's Avatar
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    Quote Originally Posted by global88 View Post

    Sounds like yourve got some problem.
    Runs well on gas now but bad on petrol.
    Whats wrong on petrol? Black smoke/rough idle or just idleing too slow.
    On petrol it's just low idle, no black smoke.

    Quote Originally Posted by global88 View Post
    Could the problem have been there on petrol after you put the spring back on but you may have missed it?
    after I put the spring back on I had to readjust the throttle stop screw because the installer had wound it out, I can tell where it should be due to the dirt on the thread.
    With the spring in the idle was too HIGH.

    Quote Originally Posted by global88 View Post
    Could this problem be why you had to richen the gas mixture?
    The original problem was that it would stall on gas when you let go of accelerator pedal after a high speed run.

    Quote Originally Posted by global88 View Post
    No vacuum hoses loose or leaking?
    None that I can see or hear....

    Quote Originally Posted by global88 View Post
    Some ecu's need to relearn after being reset. Have you given the ecu sometime to readjust.
    yep, that's why i reset it as well, in case it had learned anything silly during the gas conversion.

    Quote Originally Posted by global88 View Post
    Id put the gas mixture screw back, reset the ecu (try disconnecting the battery for an hour) and then test the car on gas and petrol to see if its on both.
    It idles too low and rough on gas if i put it back...tried it.

    Quote Originally Posted by global88 View Post
    If on both, find and fix the original cause.

    I can make it run fantastic on petrol...but then it idles far too high on gas.

    Quote Originally Posted by global88 View Post
    If just on petrol look at your lambda sensor.
    Note the lambda is used to control the mixture under idle, and if the ecu gets a wrong reading from it, your car will run rich (alot of black smoke and rough idle).
    Could the lambda sensor have suffered trauma as a result of the conversion?

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    Senior Member global88's Avatar
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    Hmmm i think you should go back to basics.
    Put your idle stop screw (the one on the throttle body) back to factory original setting with the ecu reset and spring fitted correctly. Does it idle correctly on petrol? No? find the problem, or try adjusting the throttle stop screw.
    Then id turn the gas on and adjust the mixture screw for the idle. There is always a slight difference in idle betwwen the 2 fuels but nothing too severe.
    Remember one thing running both fuels will always be a compomise.
    Lambad sensor should be ok, check its connected, but if your not running rich and idleing lumpy, id say its OK.

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    Senior Member global88's Avatar
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    This is how you adjust the idle speed on a volvo 940

    Put you idle base screw that your mechanic played with back to where you saw the dirt marks, in other words back to factory.
    Point is get it running properly on petrol first. Chances are that if you just put the screw back to its original settings, it will probably run fine on petrol.

    Then turn on the gas and adjust your idle mixture via the screw on the gas hose.

    Hope this explanation is a little better.

    Note plenty of things in that link to check that will get it running right on petrol first.

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    Senior Member global88's Avatar
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    While were talking Volvos

    Read the last post here

    This would be handy to keep for future referance

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    Senior Member z80's Avatar
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    Thanks for hunting that down...I can see that the spring still isn't in its correct position from the diagrams...so will locate that correctly first.

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    IMO,global88 is right,fit throttle return spring in correct position then adjust throttle stop screw for correct idle on petrol.
    switch to gas and lean out gas mixture for correct idle on gas.
    For mixture adjustments I've always used a Colortune device,it's a transparent
    spark plug that lets you see the colour of the burn mixture while running.
    I have seen them on Ebay about $60.
    Dash.

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    Senior Member z80's Avatar
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    Took it back to the installer today.

    I had completely stuffed the mix setting...but it ran well on gas.

    The lambda sensor comes on after 20-30ks running on gas, this then triggers the computer to compensate the injection of petrol.

    Of course it's only when you switch to petrol that the problem is obvious.

    If i pull out fuse #1 with the key in start position, it resets the ECU and it runs fine on petrol.

    Solution is to either run a closed loop LPG system ( more money).

    Or wire the O2 sensor in with a relay to the petrol/lpg switch.

    So when on gas, the O2 sensor disconnected.( and not latching an emission state).

    Apparently this is standard with some dual fuel Ford factory setups.

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    Senior Member global88's Avatar
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    Quote Originally Posted by dashinson View Post
    IMO,global88 is right,fit throttle return spring in correct position then adjust throttle stop screw for correct idle on petrol.
    switch to gas and lean out gas mixture for correct idle on gas.
    For mixture adjustments I've always used a Colortune device,it's a transparent
    spark plug that lets you see the colour of the burn mixture while running.
    I have seen them on Ebay about $60.
    Dash.
    Didnt know they still exist. My father use to tune his VW with one back in the early 70s.

    Good to know your back in order z80. Both fuels running ok now? Did he tell you why your gas went out or what went out of wack in such a short time causing your stalling?
    Yes closed loop is the way to go but i dont think its that much more. Electronic control unit, an idle solinoid, some more wiring plus labour.
    Come to think of it after looking at what id just written, it probably will cost a bit with the price of things today.

    I always reset my ecu on the ford, every service. Car would run great on both fuels but as time goes by the petrol mixture gets richer and richer till it idles like a tractor on petrol. Just disconnect the battery for a while and shes back in buiness again when running on petrol.

    Dont know how a relay connected to the sensor would work. When running on gas the relay would disconect the lambda, so what signal is the ecu receiving, too rich or too lean?
    I think it will drive you petrol mixture either way.
    Could be possible to fit a relay that would cut out the lambda and send the correct voltage signal(replicating the corect air fuel mix)

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