LPG Discussion Forum

Hi all,

I'm running a Bigas system on my 2.0T Z20LET-engined Astra, with the Bigas double reducer and black injector rail. I have also fitted the OMVL XXI-N ECU.

Recently I have been suffering from a random misfire, usually when the engine is hot and under extra load (air con or rad fan coming on). I have replaced the coil pack with a genuine GM one and new spark plugs, and the car runs perfectly on petrol so I know that's not the issue.

I have tried to re-calibrate the system and it keeps telling me the injector nozzles are too small, despite not having any giglers fitted and them being the correct size for my engine.

Most of the map is full of 255 values so I guess it can't provide any more gas and even with the adaptivity working and enabled, the misfire is still present. If switched over to petrol for a minute, the car will usually run on gas again.

I recently installed the injector repair kit to rule that out as a potential issue.

Does anyone happen to have any idea as to why the misfire is occurring and why the LPG ECU thinks my injectors are too small? I've not made any changes to the system and everything else checks out as being fine.

Thanks

What is the gas pressure on idle and what is the gas pressure set to in the software? The 255's in the map is the max value

There's no option to change the gas pressure but at idle is 1.2bar

I guess raising the pressure would be a good place to start - can you recommend the sort of value it should be?

steviewonder wrote:There's no option to change the gas pressure but at idle is 1.2bar

I guess raising the pressure would be a good place to start - can you recommend the sort of value it should be?

There may be the option to change the LPG ECU's reference pressure if you use later software for the laptop. Old Bigas software / firmware will either assume pressure to be around 1.2bar (always use 1.2bar as reference pressure) or will set reference pressure close to actual pressure the first time you run autocal after an LPG ECU reset.

As Dai implies, if you raise the actual pressure without changing the reference pressure the LPG ECU may simply account for actual pressure being higher than reference pressure by pulsing the LPG injectors for less duration. E.g. If car idled on petrol with 3ms petrol injector duration and you had 150 in the map, the LPG ECU would make LPG injectors pulse for maybe 4.5ms IF reference pressure and actual pressure were the same. But if you have actual pressure twice as high as reference pressure the LPG ECU might only pulse LPG injectors for 2.25ms...

Not to worry much about the injectors too small message on a turbo setup, again as Dai implies the 255's in the map are the concern.

Simon