1.8T 20v wont run on LPG

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Noo Noo
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1.8T 20v wont run on LPG

#1 Post by Noo Noo » Mon Nov 06, 2017 9:49 am

Hi All

Got a Prins LPG system running on a VW 1.8 20v turbo.

It had developed an intermittent fault where at certain engine revs / load it would switch back to petrol. For some mysterious reason this cleared. Then all of a sudden it wont run on LPG at all. It seems to switch over fine but it doesn't appear to be fueling. I have an AFR gauge fitted and air fuel ratio basically crashes and then the system switches back to petrol or will stall if engine revs are too low.

Looking for a little guidance on any obvious things to check. My gut tells me it could electrical but I wouldn't rule out anything at this stage.

Any ideas anyone?

LPGC
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Re: 1.8T 20v wont run on LPG

#2 Post by LPGC » Mon Nov 06, 2017 11:20 am

On the front face of the reducer (where there's an allen key pressure adjusting socket in the middle) is there a narrow pipe fitted (or fitting for such pipe)? If so, then if such pipe has come off at either end it could cause cutting back to petrol under high-ish engine load.

Other than that, simple stuff to check are the gas solenoids (one on the reducer one on the tank), Prins reducer solenoids seem to get gunked up easily, such problem could restrict flow of gas from the tank the reducer. Also check the ignition system.. worn plugs / failing coil pack symptoms show up first on LPG, symptoms are often misfires at low rpm high load. Misfires usually result in lean air fuel ratios being read, the Prins system can be configured to switch back to petrol if mixture is read as lean for a length of time.

Simon
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Noo Noo
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Re: 1.8T 20v wont run on LPG

#3 Post by Noo Noo » Mon Nov 06, 2017 12:23 pm

LPGC wrote:On the front face of the reducer (where there's an allen key pressure adjusting socket in the middle) is there a narrow pipe fitted (or fitting for such pipe)? If so, then if such pipe has come off at either end it could cause cutting back to petrol under high-ish engine load.

Other than that, simple stuff to check are the gas solenoids (one on the reducer one on the tank), Prins reducer solenoids seem to get gunked up easily, such problem could restrict flow of gas from the tank the reducer. Also check the ignition system.. worn plugs / failing coil pack symptoms show up first on LPG, symptoms are often misfires at low rpm high load. Misfires usually result in lean air fuel ratios being read, the Prins system can be configured to switch back to petrol if mixture is read as lean for a length of time.

Simon
Cheers Simon

I suspect that its not getting any gas at all or very little anyway as it simply switches over as soon as the ECU switches fueling to LPG (or I do it manually).

I'll check the solenoids. I dont think its coil packs or plugs although the plugs are certainly due changing so no harm in doing that.

LPGC
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Re: 1.8T 20v wont run on LPG

#4 Post by LPGC » Mon Nov 06, 2017 5:30 pm

If it won't run at all on gas now, then yes the solenoids are where to start looking.

Cheers, Simon
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240

Noo Noo
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Joined: Sat Mar 05, 2011 11:15 am

Re: 1.8T 20v wont run on LPG

#5 Post by Noo Noo » Fri Nov 17, 2017 4:39 pm

Just an update on this.

I dismantled and cleaned the solenoid / filter on the vaporiser. It looked pretty clean inside to be fair but cleaned it all the same. No difference sadly. Next is to find a moment to see if there's one at the tank end.

Brian_H
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Re: 1.8T 20v wont run on LPG

#6 Post by Brian_H » Fri Nov 17, 2017 8:18 pm

There will be one at the tank end, if there wasn't you'd have had lpg coming out as you took the front one off

Be aware that if its a single hole tank you can disassemble the solenoid post when the tank is full provided that you have a working shutoff tap and shut it off first!

If its a 4 hole tank you will lose the contents of the tank if you remove the post as theres nothing there to hole the contents inside. If you decide thats your only option then you need to do it somewhere outside away from any ignition sources or open drains/pits etc.

If you want to confirm your getting nothing out of the tank the best bet is to check immediately after trying to switch over - there should be pressure in the pipe that leads between the injectors and vapouriser if both solenoids are working, if the front one isn't working then you should still have pressure in the line from the tank to vapouriser (be careful undoing these as the lpg in that pipe will be liquid and will burn you if it gets on you - undo the pipe slowly, wear gloves if your not sure whats going to happen!)

Best thing to check first is to pull the wires off the solenoid coil and check resistance of each of them. Should be approx 18 Ohms, open circuit would obviously be a problem!

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