LPG Discussion Forum

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Author:  Motorvating [ Thu Jul 28, 2016 5:48 pm ]
Post subject:  Fault

a few months ago the LPG intermittently switched off, mostly when revs dropped when coming to a halt in traffic. During its service the garage said the pressure of the Prins system was to low and pressured it to the correct level. Now the LPG is switching off again. It is an intermittent problem with a pattern.

When cold everything is OK. When the engine has done a run and is hot, the LPG will switch off when I gas it, or the revs drop when coming to a halt. If the weather is particularly hot it seems to be worse.

When it is working OK there are no symptoms at all, and like today it didn't happen at all, but tomorrow it may happen again. When it does happen I can switch the gas back on, it might switch off once or twice but eventually it will switch back on.

Called the LPG garage to book it in. they said it will be the vaporizer and will cost me £300 for part and fit without even looking at the car, which concerns me because I could end up paying for an expensive repair that doesn't resolve the issue.

For the LPG experts on here, does this sound like a vaporizer?

Do the vaporizer repair kits work?

Author:  LairdScooby [ Fri Jul 29, 2016 5:30 am ]
Post subject:  Re: Fault

From your description it sounds very temperature and/or pressure related. Does it happen more on an empty-ish or a full-ish tank or is there no difference?

Also are all the hoses secure and in good condition, particularly the one that feeds the pressure sensor assuming your system has one?

What condition is the air filter in? I've heard of clogged air filters causing similar problems as it throws the mixture on LPG out and causes the engine to stall from running too rich.

I'm not an expert, just an enthusiastic amateur but those are the bits i would look at first. That said, regardless of whether it's an alternative fuel system or a Fuzzy-Logic controlled concrete batching system or plastics thermo-forming machine, you have to start somewhere and work methodically. The evidence is always there to point the way to the fault but often can't be seen until the end of the diagnosis.

Author:  LPGC [ Fri Jul 29, 2016 12:24 pm ]
Post subject:  Re: Fault

The installer turned up pressure, so we can assume this is a pulsed LPG injection system (VSI etc), not a Prins mixer system...

In which case problems are very unlikely air filter related.

Points to check: pressure, LPG rpm reading, reducer temp sensor (also covering coolant flow problems through the reducer), solenoids, ECU working properly, ECU settings, LPG Injector driver unit, vehicle lambda probes, ignition system, other electrical problems. Given the nature of the problem, a diagnosis should involve a test drive with laptop connected to the Prins system and OBD scanner plugged in.

Prins reducers are seldom vacuum referenced (output pressure isn't relative to manifold pressure), so reducer absolute output pressure doesn't change much as engine load changes. Seems the installer found pressure was too low - Implying he will have looked at the working and minimum pressure settings in software and found actual reducer pressure to be lower under some conditions than one of these software settings to the point where the ECU generates a low pressure error or believes you have run out of gas, either situation will cause a switch back to petrol. This is a common thing to see on older Prins installs (the spring which controls the pressure goes soft over time) but is usually easily sorted by turning up reducer pressure (increasing pressure on the spring). Some installers cheat, don't even go into software but just guestimate the problem and turn up the pressure a bit.

As an aside, I see many Prins systems setup to expect a certain pressure (software settings) when they would have been better setup to use a different pressure and software configuration - Possible that a check/adjustment of calibration could cure all your problems and leave you with a better calibrated/setup system for just the price of a diagnostic/simple tune up, i.e. maybe calibration should be changed rather than pressure, or both should be changed. At least this should be checked.

Reducers can also fail in a way where pressure increases when no gas is being used, the ECU then interprets an over-pressure fault condition, more likely to occur on engine over-run (when no gas is being used) and with much the same result i.e. causing a switch back to petrol.

Don't know who the installer was, I probably wouldn't comment on an individual firm unless they were well known in the industry as rip-off merchants (there are a couple in this area), but as a general comment I don't have much faith in the abilities or intentions of a lot of Prins specialists while at the same time many other installers don't have much knowledge on Prins but some would still take your money.


Author:  Motorvating [ Fri Jul 29, 2016 6:17 pm ]
Post subject:  Re: Fault

Thanks for the replies.

The installer installed th system three years ago and did a cracking job. He did the first annual service and worked fine until the following year. Couldn't use the installer as he had gone out of business so used a business in Coventry who did the next service, which was OK for several months, then developed the problems I have now. Took it to another business in Coventry as I just had a bad feeling about him. the second business in Coventry increased the pressure, but it has never worked properly since.

Does anybody know of an installer in the East or West Midlands they would refer?

Author:  LairdScooby [ Fri Jul 29, 2016 10:34 pm ]
Post subject:  Re: Fault

Mid Yorkshire ^^^^^ isn't that much further than the west or east midlands taken as an entire area. At least Simon has given several possibilities and pointed out investigation would be advisable to get a proper diagnosis rather than simply changing the reducer and although the extra fuel to get there might make it seem dearer to start, you could try several other places locally who might cure it short-term but then the problem returns.

Author:  Brian_H [ Sat Jul 30, 2016 9:50 pm ]
Post subject:  Re: Fault

I have trusted Simon with calibration and he's done a spot on job from what I've seen. He may be slightly further away than you'd like but it's worth the trip

Author:  Motorvating [ Mon Aug 01, 2016 7:05 am ]
Post subject:  Re: Fault

Where in Yorkshire is Simon based?

Author:  Brian_H [ Mon Aug 01, 2016 12:06 pm ]
Post subject:  Re: Fault

South Elmsall - his website is in his signature above, full address is on there.

Its reasonably close to the Barnsdale Bar Shell service station on the A1 that does autogas if that helps?

Author:  rich r [ Mon Aug 01, 2016 12:44 pm ]
Post subject:  Re: Fault

Yep - straight up the A1, off at Barnsdale Bar (Jcn 38), then follow the road to South Elmsall. Over the roundabout, left at the traffic lights then it's on the right near the pub/club. Dead easy to get to. :) Probably just over an hour (guessing you're sort of Leicester area if you're asking about West/East Midlands).

Author:  Motorvating [ Tue Nov 15, 2016 7:55 pm ]
Post subject:  Re: Fault

Due to problems life throws at you I didn't get up to Yorkshire to see Simon, however a gut feeling followed through resolved the issue. I was suspect of the coolant thermostat for a while, in hot weather of town traffic it would creep up to around 95*, so I changed the thermostat which has resolved it, however it has shown the radiator fan temp sensor to be faulty as well, so that will be changed this weekend.

Author:  LPGC [ Wed Nov 16, 2016 2:29 pm ]
Post subject:  Re: Fault

Glad it's sorted.

Still wouldn't expect the system to complain about the reducer being too hot - but did the reducer stay hot during the overheat conditions? It would be possible for such hot conditions to cause a water/vapour lock in the reducer which might lead to the reducer to get cold under those conditions but then we might expect the engine to be boiling over at the same time, something you'd notice. On the other hand the system may have switched back to petrol because the ECU was interpreting signal from the reducer temp sender as in-feasibly hot thus interpreted this as a problem with the temp sender - which could actually be the case, because unless the engine was boiling over (steam might be quite a bit above 100c) we wouldn't expect the temp to be so far above 100c that the ECU would interpret the measurement as a problematic sender. Even with a good thermostat the coolant temp may get up to around 100c with stationary vehicle before the fan kicks in - so the figures bartering around 100c wouldn't leave Prins systems with much margin (regards temp readings) if they were to interpret temps just a bit higher than 100c as an error condition.


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