OMVL Dream switches to petrol on deceleration

[LRCounty]

Hi all,

Well the good news is my 110 County is running perfectly on gas without issue. The VX SS commodore however....

- OMVL Dream XXI vapour injection system

Switches from LPG to petrol while beeping and flashing lights on the LPG switch. I have to turn the car off then restart it again to run on LPG.

This occurs only on deceleration..especially when changing down gears.
It has never happened while accelerating.

To prevent it from happening when slowing down, I can press the clutch and use the brakes.

I've searched elsewhere for solutions...my LPG guru goto guy in Perth has shut shop.
Any ideas?

Cheers
Andre

[bee utey]

The difference between idling and over-run (closed throttle) conditions is that the injectors don't open on over-run above say 1600 rpm. I'd think that your LPG regulator is faulty and overpressurising the rail while no fuel is being used, therefore causing a fault alarm to shut down the system. You really need someone with software to look at the system, or buy it yourself online from ebay.

e.g. here

new regulator here.

I've replaced an OMVL reg recently that failed, they're not that long lived. Not the best system I've met.

[LRCounty]

Thanks bee utey,

I'll see what the software tells me when it arrives.

What vapour injection system would you recommend from your experience?

Cheers
Andre

[bee utey]

Thanks bee utey,

I'll see what the software tells me when it arrives.

What vapour injection system would you recommend from your experience?

Cheers
Andre

My experience has been quite good with the Zavoli Alisei system. Although it's probably just another Italian injection system, the regulators seem to be very good quality. The electronic architecture closely resembles that of the OMVL system as both ECUs are made by the MED company.

In the case I mentioned earlier, a 5.7 VT equivalent Statesman came in with intractable problems with poor and intermittent performance. I purchased some software to get into it but I couldn't gbet it to stay consistent. After it blew up a couple of changeover switches ($50 a pop) I asked my wholesaler for his opinion. He promptly sold me a Zavoli ECU of a later version which I installed and programmed and the performance was vastly improved.

Now down the track a bit it failed again, so I looked at the system, decided that one of the two OMVL regs fitted had died and replumbed it to run off just one. Why on earth the original fitter has installed two is beyond me. Now finally the vehicle is tons more toey at all rev ranges and hasn't put a cylinder wrong for ages.

Now in your case I'd think a reg change to another OMVL reg would be easiest, as changing brands always means changing the plumbing on the liquid side somewhere. This is of course illegal for DIY and the place where most handymen come to grief with leaks or poor design. But if you really wanted a better converter, new Zavoli converters are of course cheaper from overseas, see here.

There's even a used one available from a LR wrecker in the UK, see here.

Not sure about the used one, I can't get a good answer as to its condition from the seller and it does look quite corroded.

[ozscott]

Could it be as simple as a vacum hose leak? No vac so lpg computer thinks engine is shut down and switches off with result that petrol is then back on?

Cheers

[bee utey]

Could it be as simple as a vacum hose leak? No vac so lpg computer thinks engine is shut down and switches off with result that petrol is then back on?

Cheers

Very unlikely. Vacuum signal is used by the LPG system to regulate injection pressure (similar to an EFI pressure regulator), it isn't a requirement for running. What stops operating on over-run is the injectors, that would be a better indicator of the problem, otherwise it would shut down at idle too. Manifold vacuum is generally only read for diagnostic purposes. Too high or too low a LPG pressure is much more likely to trigger a fault alarm as written in the OP. A cheap way of diagnostic would be to fit a simple pressure gauge to the injection line, and see if it shoots up during overrun. Mind you the software isn't all that dear and that will read the actual faults as they occur.

[LRCounty]

Vacuum leaks is the first thing I checked for

I have ordered the cable and software, so will be able to see what is going on soon enough.

Thanks for the suggestions regarding injection systems. I'll just do it the easiest way and fix the Dream I reckon. It has run perfectly until now. The system is 7 years old, so I guess that's not too bad for vaporiser longevity.

I definitely prefer the simplicity of the LPG system on the County. R90e, Blos LPG carb, and I bought a wideband O2 sensor and gauge to get the mixtures right.

Cheers
Andre

[LRCounty]

Bee Utey,

Thanks for your advice with this. I received the cable and software. The program freezes a lot, but ran long enough each time for me to see what was going on.

Your diagnosis was accurate. I have already locally purchased and installed a new converter (couldn't be bothered waiting for shipping to save $60)

All is well again, and in fact better than it has ever been during my ownership.

Cheers
Andre

[ozscott]

Nice result. Cheers