Can an LPG-fuelled engine run lean?

**p38arover** · 16th February 2015, 08:43 PM

I've been playing around with my LPG system because the engine kept switching back to petrol, usually on deceleration.

I think I've fixed that because it isn't doing it anymore but I may have screwed up the LPG maps. The length of time the LPG injectors are open is about 1mS less than previously but that's at idle. I haven't checked on the road because I don't know how long they stayed open previously.

The car isn't idling well but seems to be running OK. It surges at idle with the RPM dropping down to about 350.

I've recovered copies of my car's old fuel maps from the installer's dead laptop and will try to load those this week but I'd like to know if the engine will run reasonably well if lean.

**Blknight.aus** · 16th February 2015, 09:29 PM

yes it can and it will idle like a dog,

fumigation systems will be the worst for it espeically if the diapragm has gone stiff.

If your doing lpg gas injection and your control solenoid is sticking or contaminated you can get the symptoms your describing as the gas will be converting from gs to liquid at the shut off solenoid and not at the vaporising orifice which will provide low pressure at the injectors.

Id guess the same deal for liquid injection but I havent played with that yet.

**p38arover** · 16th February 2015, 09:41 PM

Thanks Dave.

The gas pressure was 0.74 bar when it was shutting off. I increased that to .82 bar and the switching back to petrol on deceleration (foot off throttle) stopped. Further discussion on the LPG forum saw me increase that to 1 bar.

However, a couple of days later, the system was reading .74 bar again. I readjusted it to 1 bar and it seems to be staying there.

I was wondering if the converter diaphragm may have been on the way out and whether I should replace it.

The system I'm running is a KME Akme Diego system. The gas pressure/MAP sensor failed some time back and I replaced it with the latest type but the software doesn't know know that model, just the very early two models (no longer available) so I don't know just how accurate the gas pressure measurement in the software really is.

I guess the consequent questions are: will the engine be damaged by running lean on LPG? How can one tell if it is lean?

Ron

**bee utey** · 16th February 2015, 09:54 PM

A couple of days ago I had a 100 series cruiser with vapour injection come in and one of the symptoms was dropping out on decel. Plugged the software in and found a listed fault for his relatively new looking MAP sensor. I had a spare daggy looking used one and replaced it with that. Interestingly the pressure reading on screen went down with the replacement sensor to where it should have been, so I'm suspecting that some of those newer MAP sensors are just cheap and dodgy.

As for the lean running, can you read the oxygen sensors? Adding a bit of fuel should happen automatically unless you've hit the limit of your fuel trims in the petrol ECU. If not, adjust that area of the fuel map.

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Can an LPG-fuelled engine run lean?

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