Ignition timing

[Zebedee]

I've heard a couple of degrees extra ignition timing is beneficial to LPG powered vehicles due to the slower burning nature of the fuel.

The engine i'm planning on converting to gas has an ECU which advances the ignition timing to the point where i assume it senses pre-detonation (using a knock sensor). When using standard unleaded instead of super the ECU retards the ignition timing a couple of degrees due to the lower octane rating.

Is the car's own ECU likely to advance the timing more when running on LPG as it has a higher octane rating and therefore also higher anti knock properties?

[Dualtechuk]

It will advance the timing to the knock as you say, although it may be that it wont advance it as much as it could, this will depend on how the cars ecu is setup. For example, I have been told (by somone in the know!) that a mercedes will not advance at all even though it reads the knock.

[rossko]

Very much depends on what the mystery ECU manufacturer was thinking.
For example, old P38 Range Rovers have knock sensors and will successfully retard ignition for low grade fuels - it's a Land Rover and expected to deal with that. What they won't do is advance any over the standard default settings to take advantage of higher octane fuels - it's not a race car.

[Gilbertd]

I can't think of any ECU which will allow unlimited, or even increased, advance no matter what fuel you run on. If they are designed with super unleaded in mind then the default will be correct for that fuel and it will retard if knock is detected, not the other way round. For the same reason you'll get no benefit running Super Unleaded in an engine intended for normal cooking.....

[mat_fenwick]

I read about a mid 90s Saab (9000?) running on LPG and apparently the turbo would boost until knock was detected. Consequently, when running on LPG the boost pressure was higher. If that's correct or not I don't know, but I read it on the internet so it must be true!

[Zebedee]

Makes sense about it only advancing to the maximum super unleaded would allow. It was just a thought anyway. Electronic control for stuff is all new to me. Most of the cars i've owned have been 30+ years old.