Calling electronics gurus

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mzplcg
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Re: Calling electronics gurus

Post by mzplcg » Fri Jul 07, 2017 8:10 am

Cheers Dom. So the thing is being used to provide a RPM signal to an autogas (LPG) system. This is on a Dodge Ram 1500 which my mate's customer converted recently.

The thing is, on the modern ones (this is a 2015 with a 5.7 Hemi) the dashboard tach signal comes from the powertrain control module over a data bus, mixed in with plenty of other signals as well, so it's near on impossible to extract the bit required. The only other places which give an engine speed related signal are the crankshaft position sensor and the camshaft position sensor. The crank one was giving a very small signal which the gas ECU couldn't read and the engine has variable valve timing making the camshaft unsuitable as a source. So this wee amplifier took the crank signal and made it big enough to read.

I did try using the coil packs as a source of the pulse and this would work OK until the engine was unloaded. It has an ECO system on the engine which cuts 4 cylinders when just pottering around and it cuts all the cylinders when on the over-run. I was a bit surprised that even the coil signal was cut (both coil and injector) 'cos that would have saved my ass from soldering and thinking and burning fingers etc.

I have to say I am impressed with these modern LPG systems though. No longer does it crowbar out all the original ECU and leave the EML glowing all the time. This thing is so clever that if one gas injector fails it will run that one cylinder on petrol and the others stay on LPG. Even during the change over between fuels (which used to be quite brutal) it isn't noticeable. It changes over one cylinder at a time with adjustable fuel overlaps and it is programmed to run all cylinders on petrol for at least 2% of the time to keep the petrol stuff working well. It can even be programmed to use both fuels on direct injection engines, sort of 80% LPG and 20% petrol which keeps the injector tips cooled with the petrol running through them.

Oh, and the best bit of all, I came across this last night :lol: :lol: :lol: :lol:

http://www.canm8.com/car-products/canm8-rpm.html" onclick="window.open(this.href);return false;

I'm only positing this as it would well be of use to You, me, Bodsy etc. This company do CAN interfaces for most purposes, all a bit clever.


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Re: Calling electronics gurus

Post by PillowSmuggler » Fri Jul 07, 2017 12:52 pm

Thanks Dom, great write up. That's a very interesting project, and it's good to hear LPG is now a viable black box solution rather than needing an Engineering degree to work it :lol:
Typical that you find such an elegant solution last though; isn't that always the way? In fairness I'd still prefer your solution over any can-bus one though, less to go wrong :thumbright:


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Re: Calling electronics gurus

Post by anglefire » Sat Jul 08, 2017 8:29 pm

Joe fitted a LPG system to his Aveo a few years ago - paid for itself in about 9months I think.

That was pretty much fit it, run the setup program where it tunes itself and carry on. Only thing he found was that some filter or other should be changed every 10000 miles - and he didn't realise until it packed up and had to run on petrol - after 50000. :whistle:


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Re: Calling electronics gurus

Post by Metro1000 » Mon Jul 10, 2017 9:36 pm

Yes, indeed, I forgot to change the liquid phase filter as it was well hidden inside the reducer. I eventually got one from Latvia for a few quid. The real problem was "heavy ends" (oil remnants in the gas) building up inside the injectors, a half hour strip down and some petrol fixes that.
System was fitted at 20k, and is now at 78k, a little over 2 years later. It does all the tricks described above, sequential switchovers, mixed LPG/petrol burning, forced start on gas if required, alteration of the gas map whenever you feel like it, etc etc....and that's from a cheap system.


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