P38A Prins LPG Problem,, P38a 4.6 HSE

Hi Everyone,,

I have a problem with my LPG system, Last fortnight I was driving my p38 down the m56 and everything was fine, the system was on lpg and was working. I was travelling at 60 mph, the p38 was in sport mode and put my foot down and the speed increased to 80 and then this is when the problems started,, the lpg switched over to petrol and kept beeping to tell me there is a problem, there is 3/4 of a tank of lpg, so I know its not out of fuel. I drove home on petrol, the following morning I put the laptop on the ecu of the LPG system and everything was reading correct, but as soon as the system changed over to LPG the pressure dropped below 1 bar and the p38 stalled.. so changed over the fuel to petrol and started the car and the engine ran, as soon as i switched the system over the car stalled again.. so I thought that the vaporizer was at fault last time as this was the same symptoms and I stripped down the vaporizer and put new seals and diaphragm, and a new LPG solenoid valve and new solenoid on the tank on January 2017, so I know that these are working, I checked all the pipes from the tank inlet to the vaporizer there is gas present, checked from the vaporizer to the duel filter and there is gas present and from the gas injector rails there is gas present, so i know there is fuel, but the system fails to run. All the software tells me is that there is low pressure.. the only parts of the system I've not tested (Because I dont know how to ) are the Injectors them selves and the electronics for the injector rails and the ecu,, I have replaced the system with new fuses.. If anyone could help be very greatful as running this on petrol is hurting my wallet!! LOL

Have you tried the soapy bubble check on the lines and joints. Low pressure or to high pressure could effect the valve on the vaporizer. If no joy still it would be worth making sure the petrol side is perfect then having a LPG service garage check for safety side.

There is a pressure sensor that measures gas rail pressure and inlet manifold pressure. It will be a black box probably on the firewall with vacuum hose going to the inlet manifold somewhere, and the gas rail. There is also an electronic connection to it. I'd check that there are no problems with any of that lot too. A loose connection or broken wire would tell the gas ECU there's no pressure in the system and so it wouldn't run.

I had the same problem. If both relays kick in then temperature, revs, gas pressure must all give the thumbs up for them to open. I did as you, suspect the reducer and put the service kit on. It turned out that the barrier between the water jacket and the business side had gone to pot. There's a page on the software where you can switch between petrol and LPG injectors per pot. As you switch it's the same kind of elimination as unplugging spark plugs only you don't get a clout. Unlikely all 8 are playing up out of the blue. Anyway, you can't do that as your LPG has gone west. Mick at tinleytech is the god of LPG. You're obviously LPG savvy but that's my twopence worth. Nobody takes any notice of me in here, anyway.

Can you hear something?!

Thanks everyone, I will try all you suggestions and I will be checking the connections for the lpg filter which has the temp/pressure sensor, i read up on this and there should be a +5v, a ground and two sensor wires will be checking these with my multimeter tomorrow... will let you all know the outcome

update: I checked the cabling for the bosch pressure sensor and all seems ok no break in the cables so all good! So after doing the elimination of problems, I stripped down the vaporiser and checked the diaphragms, there ok, although the center pin and the brass collet and rubber were heavily soiled with black grease substance, so cleaned these and it's now working freely, so it's looking like it's is the pressure sensor on the filter casing that is at fault, so straight onto the inter-web! and bought a new brc polyester filter and sensor from the good chaps at LPGShop.co.uk. Just waiting now for them to arrive so i can fit them to the P38 and then retune the Vapouriser as it have been restripped and cleaned.

OK the parts arrived and the sensor is fitted and it still over pressurised the system to over 3.5Bar, I am now stumped,, do I buy a new vapouriser kit and solenoid valve, or pay loads of cash to a company to figure out,, the Prins software had fault 321 Psys voltage to high.. solution gave is Check power connection to temp/pressure sensor in the filter, the connector has 4 wires brown which is earthed -5v dc, red at +5v dc, green and grey which cant seem to get a reading from when running because the lpg system cuts out before i get a reading,, I know these are ok in the continuity tests. Any ideas on how to proceed guys???

MrGorsky is away. @Saint.V8 used to play with LPG before he got dirty.

Hi Darkforces
I also have had the exact same thing happen in my falcon xr8 ute while driving on the motorway. Did you get your problem solved as I’m interested to fix mine without the huge expense of training a mechanic.

Hi Darkforces, I know it's been a few years but did you ever get to the bottom of the fault as I seem to have an identical fault, thank you