Prins VSi reverting to petrol when engine hot.

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zac0
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Prins VSi reverting to petrol when engine hot.

#1 Post by zac0 » Mon Feb 03, 2020 11:51 pm

My 2005 Mondeo 3.0 V6, bought in 2006, had a Prins VSi conversion done in 2008 with 24K on the clock. She’s now done almost 189K, and still going great (on petrol at least).
It has developed an issue whereby the fuel system will only flip over from petrol to LPG when the engine starts from cold.
Around 70% of the time, once running on LPG, it will remain so until I reach my destination – typically, the 17 mile commute either to, or, from work.
However, once the engine is warm enough to be running on LPG, if I then have to break my journey, which necessitates switching off the engine for more than 20—30 seconds, when the engine is restarted, it will only run on petrol.
Perversely, this includes when I fill up the LPG tank, but have to continue my journey on petrol! It will not run on LPG again until the engine is restarted from cold.
On the other 30% of occasions, it will suddenly revert to petrol when I am part way through my journey.
This usually occurs after about 8-12 miles, but, very seldom prior, unless, I have been sat in traffic before reaching this distance.
It is presumed that the trigger, is when the engine has had time to reach, or, the driving conditions allow it to reach, a particular temperature?
So, it would appear to be a temperature related issue, but, I am not convinced that the fault lies with the Prins VSi system, but rather, the car’s cooling system?
Once the engine is up to normal running temperature, the temperature gauge on the dash stays rock steady, even if sat in a queue of traffic for an extended period.
I can confirm that the radiator cooling fan cuts in periodically as expected.
There is no evidence of coolant loss, but, I do notice quite often, that when I reach my destination, the engine smells distinctively hot!
I bought a complete, used, Prins VSi system (bar the tank) from a written off BMW X5 where the Prins VSi system was fully operational prior to the accident.
From it, I exchanged the vaporizer, installing a new temperature sensor in the process, but, no change in behaviour.
I changed the Bosch sensor by the gas filter near the injectors, which also has a temperature function, but that had no impact either.
Could it be that the car’s cooling system thermostat is intermittently sticking, or perhaps, given the age of the car (15 years old) and/or mileage, that the cooling system…, most probably the radiator, is partially blocked, allowing the cooling system to get abnormally hot? Maybe the excessive heat is causing a hose to become overly pliable, and collapsing, thereby restricting coolant flow (to, or, from, the vaporizer)?
Is there is an upper temperature limit set in the Prins ECU that would instruct it to revert back to petrol if this threshold is reached?
If so, why would it not flip back to LPG when the engine temperature has clearly dropped, albeit, not cold?
I live in South Cumbria, and frustratingly, this area seems to be particularly devoid of LPG specialists I could approach.
I bought a serial interface, and what I assume is a copy of BexPrins software.
I am hoping that this may help pinpoint the likely source of the problem?
Where and what should I be looking for?
Any tips\pointers would be most welcome.
Many thanks
Zac

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Re: Prins VSi reverting to petrol when engine hot.

#2 Post by LPGC » Tue Feb 04, 2020 12:15 pm

Using the interface and software watch the temperatures and pressures that the Prins ECU is reading. If temperatures seem OK it won't be temperature readings that are preventing it running on gas (but could still be temperature related as described below).
If pressure falls when you switch to gas when the engine is warm it may be that you have a sticking reducer solenoid or faulty solenoid coil (presuming you didn't change this solenoid when you changed the reducer) or sticking tank solenoid/faulty tank solenoid coil. A faulty coil can go open circuit when heat soaked but seem to work OK under warm-up and normal running conditions... under normal running conditions the coil won't get as hot as it does during heat soak because it gets quite a bit of cooling from flow of cool gas from the tank. A faulty reducer solenoid would be more likely to suffer problems after heat soak than a faulty tank solenoid because the tank isn't in the hot engine bay. Even if coils are OK a solenoid may still stick at a certain temperature (just gunge etc preventing the solenoid plunger from opening). Solenoids posts can be removed, posts and plungers can be cleaned up.
Other electronics can go wrong on Prins systems and some electronics problems can be temperature related.
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Re: Prins VSi reverting to petrol when engine hot.

#3 Post by Fox vehicles » Tue Feb 04, 2020 10:03 pm

It could be the ecu itself that is overheating :?: If you can get your software & lead working you could try the spare ecu. Would probably try swoping the solenoids first though as already suggested. Good luck let know how you get on :D

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Re: Prins VSi reverting to petrol when engine hot.

#4 Post by LPGC » Tue Feb 04, 2020 10:45 pm

Don't think VSI features an ECU temp sensor, some of the later (and far better) systems we fit feature an ECU temp sensor and even a switch temp sensor! This weather some of the self adhesive double sided switch stickers won't work at first but once switch LED's have been lit (on bright level) for a while and the switch has heated to around 30C due to the LEDs they usually still stick very well. Never known a VSI ECU go wrong because it got too hot but then again never known an installer fit an ECU in a crazy enough position to get so hot as to not to work, especially not in a relatively sparse/easy engine bay like on a Mondeo V6 - who'd stick a Prins ECU near the exhaust on a V6 Mondeo! But there's always the potential for temperature to make the difference between function and dysfunction with PCBs, seems more true of ancillary Prins components such as injector switching/emulation boxes than ECUs though I'd say.
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Re: Prins VSi reverting to petrol when engine hot.

#5 Post by zac0 » Sat Feb 08, 2020 12:37 am

Many thanks for the info and suggestions guys. I hope to conduct some checks this weekend. Some further info; The issue with refusing to flip to gas when starting from warm, has existed for about 7 years now and I have just endured it. It was never really an issue as I seldom broke my journey, or, if I nipped in to pay for fuel etc. for a few mins, and had a passenger, I would leave the engine running. The cutting out mid journey lark only started about 18 months ago. Lately, it has been doing it less often, and ironically, on all ten legs of my five trips to and from work this week, it flipped to LPG when it should, and stayed on the whole journey! It still won't switch to gas if I turn the engine off for a minute though!
The system did suddenly stop working altogether about 2.5 years ago. Starting small, I bought a complete new solenoid assembly, temperature sensor and both liquid and gas filters. I had assumed that as my car produces 150Kw (204bhp), it had been fitted with the 255Kw vaporizer which I believe differs from the 135Kw model by having an 8mm feed rather than 6mm? Having bought a solenoid with 8mm inlet, I was surprised and dismayed to discover that I had the 135Kw version with 6mm pipework. The supplier was happy to exchange, but, the 6mm solenoid was out of stock. I couldn't get one anywhere, so looked for a second hand vaporizer with a 6mm solenoid, and ended up with the whole system for £160.
The vaporizer is mounted to the inside of the chassis rail beneath the gearbox and is nigh on inaccessible without a ramp. I was unable to get a spanner onto the vaporizer mounting bolt to remove or rotate it, so, tried to swap just the coil to see if that solved the fault? When I attempted to undo the small nut that secures it, it just sheared off along with the thread within it. I couldn't even swap the coil and hold it place with a zip tie, as I found there was insufficient clearance to slide the coil off the solenoid! When my car was next in for a service, even though they were not LPG specialists, I asked them to swap out the vaporizer. I had fitted the replacement with a new coil, temp sensor and wet filter beforehand. Gleefully, with no set up or calibration etc, the system was resurrected, and remarkably, it ran, and continues to run just fine! Regrettably, it didn't solve the longstanding, 'won't run on LPG when starting warm issue', which is why I am prepared to rule out the vaporizer\solenoid assembly being responsible?
With the engine running, up to temp, and operating on gas, I can press the fuel change over switch repeatedly; 10, 20 or more times, and it flips back and forth between gas and petrol without hesitation, with the tank solenoid audibly clicking away when selecting gas. If I turn the engine off, as long as I restart it within 30 seconds ish, it will flip to gas immediately, but, if left much longer, there's no chance until several hours later when the engine is cold. It can't even be luke warm, tepid or whatever.
Whilst I have your attention, my gas level indicator on the fuel changeover switch shows full (4 green LEDS lit) no matter how much gas exists in the tank. It's a Stako donut tank. How does it work? Is it internal to the tank? Would I need a new tank, or can the fuel level mech be replaced?
Finally, as an aside, I was browsing through some posts on here, and observed one from a chap with a Mondeo ST220. There was reference to the Mondeo V6 engine needing flash lube \ valve saver. My 3.0 Ghia X's engine is the same block\head etc. as the ST220, just not tuned, but mine doesn't have a flash lube system fitted. The installer; F1 Automotive in Bolton, said it was unnecessary. There appears to be some validity in that, as even after doing 165K miles since conversion, she still appears to go as well as she did when I bought her in 2006, no tapping or other odd noises from the engine and blows no smoke. Maybe she is now producing less power and I just haven't noticed a gradual change?

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Re: Prins VSi reverting to petrol when engine hot.

#6 Post by Gilbertd » Sat Feb 08, 2020 9:59 am

Afraid I can't help with the changeover when hot problem but I may be able to give some info on the level gauge. There should be a gauge on the tank itself, does this read correctly? When you fill up does the pump shut off with a healthy clunk or does it gradually slow down before stopping? There's a float inside the tank that operates the shut off valve and drives the gauge through a magnet. The gauge then feeds a signal to the ECU to display an approximate fuel level on the switch. If the float has stuck, the shut off valve won't close so the pump won't shut off with a clunk but will gradually slow down as the pressure in the tank reaches the same pressure as the pump is supplying. The gauge can be checked easily enough by removing it (there's no physical connection between the gauge and the inside of the tank so nothing will leak out) and waving a magnet on the back of it which should cause the needle to move. If the float is working and the gauge is working then either the wiring to the ECU is wrong or damaged or the wrong type of gauge has been selected in the Prins software setup.

As for Flashlube, some engines need it, others don't, it depends on how hard the valve seats are. Ford engines tend to have soft valve seats so will need it but if you have done 165k on LPG and the valve seats haven't worn away and the valve clearances closed up to the point the valves aren't fully closing, then you probably have a different version of the engine with harder seats.
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Re: Prins VSi reverting to petrol when engine hot.

#7 Post by LPGC » Sat Feb 08, 2020 6:37 pm

Refusing to switch to LPG when the engine is warm could be due to ECU settings. Some systems like BRC and Prins can be set to switch to gas after a minimum of X seconds if started when the engine temp reading is below T temperature and a minimum of Y seconds if the engine was started when the engine temp reading was above T temperature - You can imagine the effect if Y is set to a silly figure like 5000 seconds... Or could be the ECU ignition live signal is connected to an engine component that doesn't get 12v when started when hot, or a component (such as e.g. gas pressure sensor, injector emulator/switching unit, RPM filter box) not working properly when heat soaked (not working when heat soaked because the part is broken), or the reducer pressure needs increasing (can be due to the spring going soft over time) so actual pressure is now set to a lower pressure than the pressure at which the system thinks the gas tank is empty, or the ECU may have become partially corrupted (sometimes fixed by clicking on 'initialise the ECU' in software).

The Ford V6 should have a lube fitted, if it's lasted 165k on LPG without noticeable symptoms/issues it's probably because it's a fairly big engine and hasn't been worked as hard as the usual 4 cylinder engines in Mondeos. Still if the engine was stripped I'd expect to see more VSR than on the same engine in a Mondeo that had done the same mileage running on petrol. It's the same engine as in V6 Jags etc and I have seen V6 Jag engines with symptoms of VSR when they haven't had a lube system fitted.

The small Prins reducer should be OK for the V6 Mondeo. I'd have had both types of reducer plus solenoids and ECU etc on shelf ;-)
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Re: Prins VSi reverting to petrol when engine hot.

#8 Post by zac0 » Mon Feb 10, 2020 12:42 pm

Some valid suggestions that are worthy of investigation\trial... particularly since I have a spare of each main component. Just need the weather to improve!
A component breakdown, or, a missing input under heat related conditions, does seem more likely than an ECU setting, and, would be the more likely explanation for the sudden reversion to petrol mid journey that happens occasionally.
Incidentally, when this occurs, it's not accompanied by any 'out of fuel' warning beep, it's as though I have selected to run on petrol via the switch, although it doesn't happen in a controlled fashion.
It is typically accompanied by the engine lurching as it is momentarily starved of fuel; the engine management system realizes there's no gas, and reactively moves to petrol rather than the hand over being 'managed'.
Also, if it were an ECU setting, using the 'Y' parameter of '5000 secs' as an example, then once the engine temp was above the threshold where the 'Y' parameter applies, it presumably wouldn't come back to gas for 5000 seconds at 'any time' the engine was switched off, yet it does, and without hesitation, as long as it is not left too long.
Presumably, the 5000 second wait would also apply if momentarily reverting to petrol via the switch?
It also doesn't explain why, with the engine significantly cooler, say after an hour or two wait, and quite likely now, below the 'T' threshold, it still won't run on gas when the engine is started.
I typically have to wait until 'ALL' residual heat has fully dissipated.
LPGC, in the absence of anybody locally, I would be quite prepared to take a day off work (unless you're available weekends?), and drive over to Ponterfact for you to conduct some investigative work, perhaps servicing the LPG system at the same time.. paying for your services of course. I wouldn't be able to leave the car with you, so, would be hanging around for the duration, but, with your blessing, I would be keen to observe?

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Re: Prins VSi reverting to petrol when engine hot.

#9 Post by Gilbertd » Mon Feb 10, 2020 1:07 pm

As long as you can operate a kettle, he wouldn't object to someone cluttering up his place.
96 Saab 900XS, AEB Leo, sold
93 Range Rover 4.2LSE, Lovato LovEco, sold
97 Range Rover 4.0SE, multipoint, sold
98 Ex-Police Range Rover 4.0, AEB Leo, daily motor
96 Range Rover 4.6HSE Ascot, AEB Leo, my spare


Proud member of the YCHJCYA2PDTHFH club.

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