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LPG and MegaSquirt


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Hi all.

I'm starting this thread to ask for opinions, ideas and experiences on how to use LPG with Megasquirt, and to hopefully provide a collection-point for this kind of stuff.

I'm in the process of building a megasquirt system to run a GEMS 4.6, and have the plan for the petrol side of things well in hand. On the LPG side, what I'd ideally like is a way of having a second MS map run a bank of LPG injectors, run from the same vaporiser and tank set up that I've used for my carb-fed 4.2, but the things I've been told I'd need have varied wildly. :blink:

So come on, tell me what you're running, and why. What parts do you recommend, and what's the simplest way of getting MS to run them?

Thanks,

Jake.

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You're probably best asking on the Megasquirt forums as there's a far more variation there than on here.

Fpr my 2p worth, as I've looked at this myself and chatted to the Tartarini tech people in the UK (at their distributors)...

There is no real reason why MS cannot run an LPG system direct, the injectors aren't dissimilar from petrol ones and timing of the injection isn't critical. Running a single MS to do both petrol and LPG causes a hardware issue in that you only have two injector channels and, to avoid fuel rail pressure drops, you really need to keep them in two banks of four.

You could, however, use some form of switching circuit that allows you to "direct" the injectors you are firing based on the same input that is switching your maps. This could be as simple as a couple of relays but you may find the changeover a bit lumpy as you won't be able to run an overlap period. (Normally you run both fuels for a fraction of a second, particularly changing from petrol to LPG as the LPG feed to the injectors may be empty of gas.

You'd probably end up pretty reliant on a closed loop setup for LPG because LPG pressure may not be as constant as a petrol system, meaning more variation in injector opening times as the LPG tank pressure drops. The regulator on the vapouriser helps but I get the impression that the variation is far more marked than you would see on a petrol system. Allowing such a wide lambda compensation may cause you problems as the MS code can be a bit lumpy when you allow it too much freedom, wideband may cope better than narrowband as you can switch target AFRs too (I think).

As I say, I have looked at it and pondered it a bit but haven't taken the plunge so it's all conjecture on my part. On the MS forums there will almost certainly be people with real world experience. I've stuck with a single point closed loop system for mine but if you go ahead with it I' be interested to know how you get on as I quite fancy running a Thor 4.0 on MS with LPG.

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Thanks Dave, that's food for thought.

I'm looking at the MS forums as well, but I've posted this to see if anyone here's had any experience with this kind of thing. Nige has pointed me in the direction of Bobtail84, as he might have done something like this, and I've had a few different ideas and questions from different people, so there's definitely a bit of support for this idea.

It seemed like a good idea to collate everyone's experiences of this in one place, even just as a library of links off-site, so if anyone else fancies this taking this path, they have a little guidance.

You said that the Tartarini main distributor is round your way. Who are they? I'd like to give them a ring.

Thanks,

Jake

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Jake,

I've done 3 MegaSquirt and LPG conversions on challenge trucks and used single point purely for simplicity. If the ECU gets drowned or fails for whatever reason you can remove the DB 37 and link the earth to the fuel pump relay. The EDIS 8 will run at 10 btdc and with single point LPG you can get out of the poo or home. In the near future woodyTZ, who runs his own LPG conversion company called gastech and I will be squirting an LPG injected V8 and I will keep you informed. We have gone through the possible problems and cant see any major hurdles but this will be LPG only to start with.

Jeff

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Jeff

Please post on here so we know how you get on with this project. I am in the process of MegaJolting my LPG 3.9. If I could find out enough about full MS and LPG injection I could be tempted to have a go at that :)

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Hi all! same thoughts for my 3.9. I have been trying to find out if Ms can run two maps but haven't yet found an answer. I am also wondering if Ms 1 v2.2 is suitable or is v3 the only way to go? or shuold I pay a little more and go for an Emerald ecu

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Hi all! same thoughts for my 3.9. I have been trying to find out if Ms can run two maps but haven't yet found an answer. I am also wondering if Ms 1 v2.2 is suitable or is v3 the only way to go? or shuold I pay a little more and go for an Emerald ecu

MS 1 V3 you can have 2 x different spark and 2 x different fuelling maps

Definate :)

Nige

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Hi all! same thoughts for my 3.9. I have been trying to find out if Ms can run two maps but haven't yet found an answer. I am also wondering if Ms 1 v2.2 is suitable or is v3 the only way to go? or shuold I pay a little more and go for an Emerald ecu

Do you mean V2.2/V3 circuit board or MS1, MS2 or MS3 firmware?

Most folks round here run V3 boards with MS'n'S-Extra firmware, which gives switchable fuel & spark maps and is more than enough for a Rover.

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Fridge, Nige, just to clarify, which of the little 'squirts will actually run two separate sets of injectors? I mean the injectors themselves, not the maps.

I know that you can operate a relay to switch between the two injector sets, but that leads to a lumpy change over, as the lpg takes a moment to get up to the injectors. I've also seen on the MS forums a guy who uses a daughter-board to achieve this, but I'd be more elegant if that wasn't necessary. There was one chap on't MS forum who says that you can run both sets from MS, but he's not replied after making that proclamation... :(

Any thoughts?

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Hi all! same thoughts for my 3.9. I have been trying to find out if Ms can run two maps but haven't yet found an answer. I am also wondering if Ms 1 v2.2 is suitable or is v3 the only way to go? or should I pay a little more and go for an Emerald ecu

A v2.2 will do the job if you use EDIS for the ignition but a v3 board is the way to go if you don't already have a 2.2 available. The V2.2 board has fewer available connections than v3 board but if you're using EDIS and a PWM idle valve you'll just about get away with a v2.2 board.

You can switch maps quite easily assuming that the LPG fuelling takes care of itself, the best way is to use the 12v from the LPG solenoid circuit to switch fuelling and ignition maps and just set the secondary fuelling map to all 0 so it doesn't fire the petrol injectors when running on LPG. You can set up the ignition map specifically for LPG then and set the changeover delay to give as smooth a transition as possible (I use a 0.7second delay normally). I've just installed a 3.9 petrol/LPG setup using a v2.2 board because I happened to have one kicking around as a spare.

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Fridge, Nige, just to clarify, which of the little 'squirts will actually run two separate sets of injectors? I mean the injectors themselves, not the maps.

I know that you can operate a relay to switch between the two injector sets, but that leads to a lumpy change over, as the lpg takes a moment to get up to the injectors. I've also seen on the MS forums a guy who uses a daughter-board to achieve this, but I'd be more elegant if that wasn't necessary. There was one chap on't MS forum who says that you can run both sets from MS, but he's not replied after making that proclamation... :(

Any thoughts?

Without additional hardware or software modifications it can't be done on either the MS1 or MS2 platform. You could potentially modify the MS-Extra code to run the 2 injector circuits individually. You'd need to look at the current alternating/simultaneous code and modify it based on the state of your fuel map input. You would need to use the simultaneous mode and suppress the firing of one or other of the injector circuits based on the fuel map switching input, it wouldn't be a big modification but would make upgrading more complex as you'd have to rewrite the code every time you upgraded. This will also prevent you using alternating mode which, on petrol at least, can give much smoother running than simultaneous mode because fuel rail pressure is more consistent if only 4 injectors fire at a time.

You MAY be able to persuade one of the mainstream developers to include this as an option but realistically I'd have thought it very unlikely they'd release a new version of MS1-Extra at the moment, even MS2-Extra might be pushing it as they're all busy working on MS3.

It's probably simpler to either duplicate the output circuits and use a logic level gate to switch the inputs between the CPU and the output circuits or use a relay after the existing output circuits. The changeover may be a bit lumpy, especially from petrol to LPG (no changeover delay). Personally I'd either do the logic level switching and duplicate the output circuits as it seems to me it would be less prone to noise and would increase redundancy between the two systems.

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As has been said above - any unit can switch, and all MS's currently available have two injector outputs - A and B, usually wired to bank A and bank B of inejctors but can be set to run two separate sets of injectors, one from A and one from B.

Although this could give less than perfect performance (fluctuations in fuel pressure due to all 8 firing at once) in reality I doubt it would make a big difference on the RV8. You could always fire the injectors twice as many times per rev to compensate.

If someone fancied trying it it's a one-click test to change the setting from alternating to batch (simultaneous) in the injector settings:

constants.png

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My grasp of this isn't as firm as it might be, so tell me if I'm wide of the mark. My thinking on this is as follows...

However I switch it, the LPG injectors can't be building up pressure BEFORE I push the switch (Unless MS3 is so clever it's actually psychic :P ), but is there a way of having it delay the switchover onto LPG for a moment after the button-pushing? I'm guessing that it'd again require a modification of the code, or a quite fancy add-on to allow this. I've probably answered my own question there, but if you don't ask, you don't get told that you're an eyjit.

Could you explain a little more about the logic-level switching? I'm assuming that this is something I'll have to make up, as opposed to be able to get whole. I'm more than capable of making boards up, but I'd need pointing at an appropriate diagram.

Lastly, this is probably a really obvious point that I'm just being blind to, but it'll bug me if I don't ask. When you say "Fire only 4 injectors at one time", what do you mean? I was under the assumption that having sequential injection meant that the injectors fired individually, and I know that this is the case with the LPG setup that I was looking at before I started down this road (Or muddy track :D ). I'm probably missing something simple but crucial here, but as I've said before, I'm new to EFI, as well as MS. I must admit that I'll miss having a fuel system that you can fault-find by sticking yer fingers in :D

Thanks,

Jake

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WELL, from my knowledge of the LPG systems out there, the worse then useless injector emulators had an adjustable time delay after switching the LPG on to before switching off the petrol injectors, so... you could, I think.... do this:

Switch to LPG, and feed the signal from the switch to the LPG system to enable it, then using the switched injector output from the emulator feed that into MS which would switch fuel tables to a blank one.

Can't see why that wouldn't work at all, and would only need one of the 4 channels from an emulator off a scrappy, or you could just make an adjustable timer circuit up yourself to do the above ^^^

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Does the LPG system have a pressure sensor? If so, wire the output of that to the MS switching pin. Just switch over to LPG, and when it's ready it'll tell MS to switch injectors.

(Disclaimer: as per usual I'm talking from the darkest hole in my body here.)

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The delay between switching actually means on a "normal" dual fuel setup that the MS continues to fire the petrol injectors for a period of time after the switchover has occurred. So when switching from petrol to LPG it allows the LPG system to sort it's act out and get the fuel flowing before the petrol injectors finally switch off. Going the other way is less important as the petrol system should be ready to go, assuming you leave the petrol pump running.

The current MS releases, MS1 and MS2 only have two injector outputs and don't support sequential injection. Instead it uses two injector outputs connected to 4 injectors each. You can choose if you want to fire both injector outputs at the same time or alternating where it fires each one at a different part of the cycle (every time it hits TDC, for example. I'm not yet familiar with MS3 but, if it is to support sequential injection on a V8 it will obviously need 8 injector driver circuits.

Logic switching is pretty simple, you take the output from the CPU (for each injector) and route it to one input of an AND gate. You will not get an output from the AND gate unless the second input is also high thus allowing you to switch the output on and off.

This is a possible schematic for an MS1 or MS2 configuration. When the fuel select input is high (+5v) the petrol injector drivers will operate in line with the CPU output and the LPG injectors will stay switched off. When the fuel select input is low (0v) the inverter provides a logic high output switching on the LPG injector drivers.

post-2025-126988910294_thumb.png

If you wanted to implement a changeover delay you could add in a small timer circuit that artificially kept the petrol injector AND gates high for a short period after the input goes low. I'd probably use a simple monostable IC although you could also just use a resistor/capacitor setup.

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As has been said above - any unit can switch, and all MS's currently available have two injector outputs - A and B, usually wired to bank A and bank B of inejctors but can be set to run two separate sets of injectors, one from A and one from B.

Although this could give less than perfect performance (fluctuations in fuel pressure due to all 8 firing at once) in reality I doubt it would make a big difference on the RV8. You could always fire the injectors twice as many times per rev to compensate.

If someone fancied trying it it's a one-click test to change the setting from alternating to batch (simultaneous) in the injector settings:

constants.png

Mmmmm I might just try that. A little more pressure in the fuel rail should sort the fluctuations out. The req fuel and injector characteristics settings might be a problem with the LPG injectors though...

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MegaSquirt FAQ Ref: Sequential injection - the short version is you don't need it.

Ref: Logic level witching and all that, this seems to be spiralling in complexity for what is a fairly simple thing to do.

To add any input/output to the ECU via the spare pins on the processor you need a transistor (usually 2n2222), a resistor (usually 10k), and a diode (1n4001 etc.). If you need a higher powered output to directly switch something (rather than a relay) then a TIP122 will work.

Here you can see what I class as a standard unit, which is what the majority of guys on this forum are running: an MS V3 PCB running MegaSquirt'n'Spark-Extra 029v, modified for EDIS, with a TIP122 in the Q16 slot (top right) to control a PWM idle valve, and two spare outputs wired to SPR3 and SPR4 (although the circuit is basically the same to use one as an input).

V3_Mods_sm.jpg

The circuits and info are in the MS-Extra manual here.

For lots of IO in an easy package you could buy a driver array IC in the style of the ULN2003 etc. etc. which takes care of all the fiddly stuff for you.

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Hi all , Jeff and me have been talking about this for a while now, we have all the parts we need [lpg wise that is]someone asked earlier if they can use the vaporiser from a carb set up.. no you cant you need constant pressure,normally about 1.5 - 2 bar.

The change over from petrol should,nt be a problem,if you power up the solenoids with the ignition,this will have a priming effect,so when you change over the pressure will be there already.

We have the technology and accesss to all the best parts.

Cheers Woody

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Thanks for the reply will go for Ms rather than emerald and get a Ms2 v3 which seems to be best for possible upgrades. Will no doubt be following this topic whith great interest.

Nooooooooo, you don't want an MS2! MS-1 is plenty fine and means you can easily use maps & settings from others on here. MS2 is more complicated than you need.

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Arg! I have a fair few relevant questions, inspired by the comprehensive and knowledgeable replies you lot have posted, but my brain's turning to mush with tiredness. I'll ruminate on all this, and try to make more sense tomorrow. Maybe.

The only one that I have ready-to-go is this... Why have separate injectors, if they all fire at once? Surely the point of them being individual is that then you only squirt the expensive stuff at exactly the right moment, so how would having 8 injectors firing in unison be any better than a single-point closed-loop system? Again, I'm probably severely ove-simplifying things, or missing something essential.

Woody, I like the simplicity of the pre-priming idea, that's nice. I'll be watching your progress with interest.

Being well over on a budget, I'll be assembling a lot of this myself, so if anyone has any recommendations or steer-clears for the vaporiser or injectors, I'll be grateful.

Ta all

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The fuelling for each cylinder can be spread more evenly with multiple injectors, the fuel "charge" is injected into the manifold above the inlet valve, it then stays there (more or less) until the valve opens and the charge is sucked in. For that reason sequential injection isn't really that advantageous on a petrol engine. Depending on the plenum and manifold design, some cylinders can leach fuel charge from others but this is minimised both by plenum/trumpet/manifold design and by using multiple injections per cycle.

Single point LPG doesn't use an injector as such, it's more like a gas hob injecting a constant stream of gas into the airstream, it has more in common with a carb than EFi. All the ECU does (if it has one) is control the flow of gas with a stepper motor as opposed to injecting the gas into the manifold.

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Right, in the light of day that makes a bit more sense, ta. I'd imagine then that if you set your injectors far enough down the manifold that there's relatively little chance of leaching with a V8. Is there an optimum point to have them, or is it a case of "as far down as is practical"?

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