The great big Electronic Fuel Injection thread!


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Rather than take BraneDeadX's very cool project log off track with general EFI discussion or resurrect other old threads, I decided we could have a dedicated thread right here. Many people seem to be interested in fuel injection, but it is not generally a simple task. It requires some knowledge of electronics, computers, and internal combustion engine operation and theory.

This can be the new place to ask questions about all that. Anyone with answers to those questions is free to jump in and share so that we all might benefit.

So.....any questions?
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I love all the EFI talk, I just wish I had the mechanical skills to fabricate all the stuff to play with one. I write powertrain software for an automotive supplier and it would be interesting to see what some things they do on cars/trucks would do on a small engine.

P.S. MargayKart needs to post more because his setup was probably one of the best I've seen! :D


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Oh yeah? What programming language(s) do you use most often? I have been pecking away very slowly at upgrading my MegaSquirt MAP sensor with a 700kpa part(highest the supported upgrades go is 400kpa), but it requires code changes to both the firmware and Megatune software and I'm not a programmer by any means. Kinda wingin' it. :blink:

Yeah, MargayKart79 has an awesome cool setup on his kart....turbocharged and injected for those unfamiliar.
We use C most of the time, but for the eTPU on the Freescale MPC55XX family we sometimes need to use assembler or what they call microinstruction set. The compilers that are out for it are complete trash.

Currently we are mostly doing projects for GM, Ford and Chrysler, not much import business. You name it we do it, direct and multiport injection, with solenoid and piezo injectors.

I specifically work on low level hardware drivers, not the application part that contains the actually algorithms, but I have been know to have a look here and there :)

I actually wanted to do an EFI briggs engine back in college 6 or so years back, but no one else was interested and it would be impossible for me to write all the software and fabricate anything in that amount of time.

I'd really just like to see where people are getting parts, scavenging from cars/motorcycles and what they are fabricating.


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That sounds pretty cool. I have some limited (and now very very rusty) experience with C and Java. Don't ask me anything about them because I'll have to dig out the textbooks. :doah:

Scavenging parts isn't that hard IMO, but finding fuel injectors small enough for sub-10hp engines can be difficult. I don't have any injectors smaller than 14lb/hr, which are very conservatively capable of ~17-18bhp on gas. One way to get around that is to use a fuel with a numerically lower stoich AFR so the "excess" flow capacity can be used.
Here is a current profile, for an amplified common rail fuel injection system. This is only the main injection pulse, there is also a post injection. Each injection actually has 3 "micro" injections and it also features negative current to open and close the spool faster. Purple is open coil, Green is close coil.


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Cool! Our own great big pile of stinkin' tech info! Gotta love it ;).

Here is the FFV sensor you're looking for. They're pricey, though. They were also only on a few years of FFVs. You'd have to wire it, supply the power, and plumb the fuel lines from an external source. I could see larger generators benefitting from that, but a minibike just makes it too complicated to fit. That sensor is about a pound or two with its own internal logic.

I have some C and assembler experience as far as bit level languages go. I got really into Japanese ECUS from Denso and Unisia. I was trying to hack my RS forever but it has a funky chip set that doesn't take well to reflashing.

I think we would be able to whip up something very basic that uses a low level of current draw. Take a look at this water injection setup. It has a 10ma draw and can handle pressures from 3-30psi. I think it could be fun and simple enough. If you guys aren't up on the analog dial idea, then maybe we can get a small digital controller with 3D mapping.

I thought about this more last night. (BTW, thanks for the ignition replies. We can deal with that separately.) Finding the right sized fuel injector is indeed a problem. For the TB, I think we can find one that is the right size that is triggered off of the TPS. If we just concentrate on fuel delivery, then that'll minimize our technical requirements and electric current needs.

If ignition curves and timing are easily changed, then I wouldn't want to mess with that separate system or make it more complicated than necessary.
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I should have clarified that I wouldn't use the FFV sensor on a vehicle; I would just use it to determine the ethanol content of the fuel for tuning/mixing purposes. For a high power/high risk E85 setup, I would probably tune for the "worst case scenario" E70 and cut the warm weather E85 blend with premium gas to get it.

I was going to post up some handy formulae, but the vBulletin formatting doesn't want to play. :thumbdown: Oh well, RC Fuel Injection has them on their site under "Technical Notes / Sizing."


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It depends on what kind of trigger wheel is needed. I used a "bare minimum" 4-1(four minus one) made from a Briggs pullstart clutch and three steel screws, but a 12-1 (up to a standard 36-1) would have been a lot better. IIRC, MargayKart79 mounted a 36-1 on the flywheel end of the crank.


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With so many variations in engine design, it's really up to your imagination. The wheel itself has to be made out of ferrous steel and will have a relatively small diameter, so it should be able to handle anything the engine can.
Ive always liked the idea of EFI small engines,

what do you guys think about an efi unit from an ATV, I know there for 500CC engines, But Im sure theres a way to water it down a little, and run a 250, or GX390


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what do you guys think about an efi unit from an ATV, I know there for 500CC engines, But Im sure theres a way to water it down a little, and run a 250, or GX390
If there is a way to program it, then it can probably be used. The '09 Honda CRF450 has a batteryless EFI system that can be programmed with the HRC(Honda Racing Components) programmer. I don't know how flexible it is regarding injector size or anything else; just throwing it out there. Dynojet also has a Power Commander for it as well as the TRX700XX.

Is there a 22mm TB unit available, or something close?
If there is, it would be from one of the smaller European/Asian bikes or scooters. That stuff is usually more difficult to get here stateside. The Honda CBR125 also has EFI, but there again, it's only available everywhere but here.