Prins system - stalls when switching to LPG

[GraemeT]

Hi
I have a Prins system fitted to a 6 cylinder Mercedes engine that has just started cutting out when switching to gas.

The vehicle is an automatic but, even so, if we are moving at 30mph or so then there seems to be enough torque getting back through to the engine to keep it turning enough to 'suck' the LPG in - once running on LPG it's fine.

I've changed the filters and looked around for any loose wiring - this has made no difference although my assumption was a blocked filter or similar. I can hear the tank solenoid click in and also the one under the bonnet.

Any clues/pointers as to where I should look next?

(I'm thinking of purchasing a software/link kit as they do not seem so expensive these days - can anybody suggest a suitable make/brand?)

Graeme

[classicswede]

Sounds like gummed solenoid or injectors to me.

[GraemeT]

Sounds like gummed solenoid or injectors to me.

Hi - I've had another look/poke around:

removed under bonnet solenoid - no gunge in there, tested with 12V across the terminals and it's working.
Removed one bank of injectors - again they are clean and operate if 12V applied to them

There is gas in the system as far as the injectors as pressure is bled off when the pipes are slackened. I also found a leak around the sealing bands on the in line filter (LPG kicked in, engine died and left a quiet hissss in my ear).

Replaced the band so that's now gas tight but I'm wondering if there is now excess pressure in the system that forced the band.

OK so I have not checked the tank solenoid or the other bank of injectors yet but is it possible that the injectors are not kicking in?

Graeme

[rossko]

If you are confident there is no longer a leak - as a depressurised rail can cause a hiccup at changeover time.
Overpressure is indeed a possibility, only cause will be gummed or aged vaporiser. Gummed vaporiser can also cause the opposite effect, i.e. slow to start up. It's not uncommon and there are clues visible in the diagnostic monitor.
If the vaporiser hasn't been touched for many years, its probably worth a re-rubbering rebuild anyway. But again you'd need the diagnostic to set up pressure afterwards. You would need Prins specific software and lead.

Tank solenoid or wiring to it remains a possibility.

The injectors will not be at fault. Don't drive them for long at 12V or you will fry them.

[GraemeT]

Hi Rossko

Thanks for the input - I'd originally dated the install as about 2005 so it's not likely had much of an overhaul since then.

Do you recommend a particular Prins diagnosis system?

[rossko]

I'm not sure how you think it works ; you would need the software produced and licensed by Prins for their own VSI system, running on any laptop of your choice (an elderly one with a serial port is actually better in this game). And a serial or USB connection lead by Prins themselves, or by any copy-clone maker but specified for Prins VSI.

It's made harder because Prins themselves only supply this kind of thing to authorised dealers. Have a search around this forum to see how other DIYers have dealt with it.
This sort of thing
http://www.lpgshop.co.uk/ccy-usb-lpg-in ... prins-vsi/
isn't much use unless it comes with the software? or you can find a source?

[Charlie Renard]

A customer of mine bought a version from Tinley Tech - don't know much about it but he said it works.

[GraemeT]

I'm not sure how you think it works ; you would need the software produced and licensed by Prins for their own VSI system, running on any laptop of your choice (an elderly one with a serial port is actually better in this game). And a serial or USB connection lead by Prins themselves, or by any copy-clone maker but specified for Prins VSI.

It's made harder because Prins themselves only supply this kind of thing to authorised dealers. Have a search around this forum to see how other DIYers have dealt with it.
This sort of thing
http://www.lpgshop.co.uk/ccy-usb-lpg-in ... prins-vsi/
isn't much use unless it comes with the software? or you can find a source?

Hi

There's a set of drivers available from that website for the kit but no actual software.
There is also an Ebay seller doing a serial port device with software - up to v 2.5.1 would appear to run 'as is' but later stuff would need Prins to OK use

At the moment I'm playing 'guess the reducer' game - there's no ID or barcode on mine other than the serial number 2302759 and the type approval code - it's failr old so would I be safe assuming that a Type B,C,D & E kit would be the one to go for?

Graeme

[rossko]

That'll be a type "A" reducer, produced before there were different types to require marking. Over a decade old now. "Early types up to E" will do fine. Body securing screws may prove impossible to remove, if there is any evidence of water seepage.

[GraemeT]

Hi all

Looks like I have some sort of over pressure problem - here's where I'm at....

I've overhauled the reducer with a new kit - there was some gunk in there but not a huge amount. The sliding pin in the centre was quite sticky though. Prior to removing & reinstalling I run the software and it gave me two error codes 'Fault 321: Psys voltage to high or shorted to Voltage' on startup and then, when LPG tried to cut in : 'Fault 322: presssure >= 3.5 Bar'

The two securing screws nearest the water inlets were pretty solid - thanks for the heads up.

After overhaul same two errors.

With system disconnected and the filter housing open to atmosphere the Psys is being reported as 0.98 bar which makes me think that the sensor there is OK.

Connect it all back up and it's reading 0.98 until the LPG cuts in and then it climbs quickly to 3.72 bar and the system cuts out due to the overpressure.

Fault 321 - Googling finds 'check the power at the filter sensor' and 'check engine coolnat temperature' - my way of looking at that is that the sensor is working therefore power present and the engine is quite hot with the sensor saying 86 degrees.

My question is then - Fault 321 - voltage - any ideas what is causing that and is that, in turn leading to the 322 error or is the 322 error valid and we do have an over pressure?

Given that the same errors are present before and after overhauling the reducer I'm guessing we can rule that out as a contributary factor so what else may it be?

I've taken the reducer apart again to double check that all the bits were put back in the correct places and it's fine (I was wondering if I had left the new pin out!

p.s. Google translating some Polish and German forums on the 321 error suggests that coolant problem may cause this error - the reducer is quite warm all over but any chance that could be the reason?

[Gilbertd]

Engine quite hot at 86 degrees, reducer quite warm. That may well be your problem, the reducer should also be at 86 degrees, too hot to touch.

[GraemeT]

Engine quite hot at 86 degrees, reducer quite warm. That may well be your problem, the reducer should also be at 86 degrees, too hot to touch.

Hi - sorry - my bad (lack of explanation) 86 degrees is the temperature shown for the Prins reducer on the PC - engine is approx the same (thermostat is 88 degrees) . Reducer is too hot to handle (as they say).

Graeme

[rossko]

Pattern repair kits often contain only the gaskets; this isn't always enough.
The pukka repair kit contains replacement pin, bush, and piston with bonded-in seal. The piston seals can fail. The pistons bore needs to be carefully cleaned. The bush should be fitted with threadlock, its seating needs to be carefully cleaned for a good seal. All debris from the old threadlock must be cleared away.

Perhaps you've lost the light spring behind the piston, there isn't much else you can do wrong. The support plate in the middle of the diaphragm needs to nipped tight enough to seal of course.

[GraemeT]

Hi

The kit was a genuine kit with new brass bits, piston and so on - however you mentioned that little spring and I got to thinking.... looked back at my original sketch of how things were when I'd opened the unit up ....
... reopened the unit and I'd not put the little spring in the correct way - between the red gasket and the brass thrust washer - I'd put it under the washer so 100% pressure from inlet side was going through to the outlet side (good job the ECU is programmed to cut the feed when the pressure gets over 3.4 bar - what a numpty!)

Once I'd stuck that back in the correct way around then it was just a matter of adjusting the idle pressure and now the engine is purring on LPG and switching LPG -> petrol -> LPG on command.

The voltage error is still there so red herring in this instance.

The original problem was, I think, down to the original brass fitting and sliding piston which are pretty well gummed up with gunk - the piston is impossible to withdraw from the brass fitting and only slides with difficulty.

Thank you all for your help with this - couldn't have fixed it without you.

Graeme