Can you run sequential LPG on a carb car?

[akku]

Its an auto, its got LPG on it already, just very basic. Other carb cars I own may want LPG in the future too though...

[Clamity]

Dec 29, 2011 11:58:29 GMT pantera2075 said:

Megasquirt has a dual map feature - (well my MS2 v3 does). So you can switch between the 2 maps for petrol/lpg.

However, I find MS generally to be too complicated for its own good. Next time i'm going with VEMS I reckon - especially as it has inbuilt wide band lambda.

Don't know what the difference in cost is between Megasquirt and VEMS but this month's Elektor mag has a four page spread on a DIY controller for the Bosch LSU4.9 wideband sensor. It puts out an analogue signal which I guess Megasquirt would just treat as another sensor.

It's built around Bosch's custom CJ125 chip which would probably be the most expensive/difficult part to source but I reckon the whole thing could be put together for about £40, possibly less.

[tenwierdufos]

I cant see it working on a boogo standard Sequential LPG kit. I think they steal the injection timing and sequence through the injector emulator. Random thought for cheapness, how hard would it be to steal an ecu and a bit of loom going cheap off say, a rangerover classic v8, and stick a crank sensor on the other engine, to steal the timing off...

Might be a no go, just an idea haha

[RobinJI]

As said you can run twin maps with Megasquirt, which could be used to switch between petrol and LPG, you'd just need to switch the live to each set of injectors along with the map.

SOC, I get what you're saying about the timing of the fuel injection, but if you're injecting out of time, then you're removing any advantage of using sequential injection, and might as well just use batch injection. If you're using sequential then it defeats the point to run a set-up that might be injecting against a closed valve for its entire pulse.

I think the answer to the original question, is yes, with a standalone ECU and a few added sensors, but probably not using a normal LPG ECU.


I'm guessing that as it sounds like most of these kits run off the standard engines injector timing/pulse length, then they'll only actually be running sequentially in applications where the original fuel injection was sequential?

[akku]

Interestingly, according to the LPG forum, they don't think I'd see any real benefit in running anything other than the kit thats on it right now. Get it serviced and set up right they say and it will be golden.

We shall see...

[scaryoldcortina]

Dec 29, 2011 20:23:21 GMT RobinJI said:

As said you can run twin maps with Megasquirt, which could be used to switch between petrol and LPG, you'd just need to switch the live to each set of injectors along with the map.

SOC, I get what you're saying about the timing of the fuel injection, but if you're injecting out of time, then you're removing any advantage of using sequential injection, and might as well just use batch injection. If you're using sequential then it defeats the point to run a set-up that might be injecting against a closed valve for its entire pulse.

I think the answer to the original question, is yes, with a standalone ECU and a few added sensors, but probably not using a normal LPG ECU.

I'm guessing that as it sounds like most of these kits run off the standard engines injector timing/pulse length, then they'll only actually be running sequentially in applications where the original fuel injection was sequential?

"true" sequential injection is really, really rare. Batch is more common but mainly because it's cheaper to have several small driver triacs than one big one. The point I was making is that in an indirect system the advantage of precise injector timing is lost by the fact that you can only achieve 25% duty due to inlet valve timing. By the time you have an injector big enough to supply full load fuelling at just 25% duty you have one so big that idling is almost impossible and low load is a nightmare. GDI and extra high pressure overcome some of these problems, but that's not what we are talking about. The injector drivers are cycled by the RPM signal, but not precisely timed by it. The important thing is how long it sprays for rather than exactly when. There would be no point.

[RobinJI]

True, I see what you're saying, but I was assuming that we were talking about true sequential set-ups, because I'm not really experienced with LPG, so I thought that's what we were referring to, so that's what I was saying you'd need the cam position sensor for, as presumably if you're going to the hassle of running sequential over batch, you'll want at least some chance of seeing the advantages.

I would still expect to see some increases in efficiency from a true sequential set-up even with injectors the same size as in a batch application. Like you say, it'd make no difference at 100% duty cycle, but most of your time on the road will surely be spent in the sub 25% region, especially with a big lazy V8.

[dodgerover]

What kit is it running at the moment? I doubt that you would really see a noticable improvement between injection and a well set up correctly spec'd conventional system? Megasquirt is capable of running LPG injectors directly - I asked on the forum and there's an add on box for it.

[jrevillug]

Will Holman (editor of PPC magazine) had electronic LPG injection fitted to his K-Jet (non-electronic) Mercedes, without having to add a standalone ECU like megasquirt - it was all-in.

Mentioned on his website, complete with a phone number for the installer:

www.ppcmag.co.uk/1971-mercedes-280-se/mercedes-280se-imported-lpg-convert.html