Mpguino: Injector Level Fuel Montoring

[dcb] posted about his work on the mpgduino mpguino. The project uses an arduino with a LCD display to monitor fuel consumption based on vehicle speed and the pulses of the fuel injectors being fired. It’s definitely an interesting project given current fuel costs and the passive nature of the project. You can easily tap the wires needed for the monitor and remove it without voiding your warranty (not that we really care).

28 thoughts on “Mpguino: Injector Level Fuel Montoring

  1. I would think that any fuel monitoring system of a modern EFI engine would be done at the injector level, Where else would you monitor the fuel? I suppose you could run some fancy calculation taking into consideration the engine capacity and air fuel ratio, but it’d be easier just to monitor the duty cycle of the injectors directly.

  2. A better method of monitoring fuel use would be to use the OBD-II connector found in all cars since the mid 90s.

    It’s a serial connection to the engine computer, with a somewhat standard interface. You can monitor things like fuel flow rate, RPM, speed, emissions and all sorts of interesting stuff.

  3. 1) It’s “mpguino”. :)

    2) The purpose of developing the mpguino was to give people with PRE-OBDII (1995 and earlier) vehicles a way to monitor fuel consumption. It will work on any vehicle with fuel injection and a Vehicle Speed Sensor.

    3) OBDII doesn’t provide injector level fuel flow data. (At least it’s not a standard across all vehicles.) Tools like the OBDII ScanGauge infer fuel consumption from air flow rates.

  4. Not only would using the ODBII port be better (which I have used to do this same thing) he is missing one key element. You need to know manifold pressure to accurately calculate injector flow rates. Fuel pressure – manifold pressure will give you the pressure differential used to calculate injector flow for a given injector. This will through off any car, but will render this project COMPLETELY useless on forced induction car.

  5. This is something you could stick in a nice weather proof container and put on your motorcycle, as far as I know motorcycles don’t have the obd2 stuff on them, mine doesn’t at least.

  6. “1. i would think that any fuel monitoring system of a modern efi engine would be done at the injector level,”

    The MPGuino DOES monitor at the injector level. It compares the ON time of the injectors to the amount of distance the vehicle has traveled (deduced by knowing the vehicle speed).

  7. Not to dismiss the project, but it seems to be catering to a rather small audience. We are talking about vehicles older than 1995, but with EFI and speed sensors. I know that EFI was available for quite some time before the 90’s, but it was reserved for the high end cars to my knowledge. Most cars that old would be carburated. I know that some early EFI vehicles (I know GM did in the 80’s) used throttle bodies rather than individual injectors, does the system compensate for that?

    Technical matters aside, any car older than 1995 is likely to be terribly efficient at this point anyway. Even if it started it’s life as a relatively efficient vehicle, the years will have taken it’s toll by now. The engine certainly won’t be running as cleanly as it did over a decade ago.

    1. lol, well im using it on my 82 geo metro xfi which is terribly inefficient, being an old car, i am struggling to get 60 mpg and when loaded with 3 passengers in the mountians Im dropping to 47.5 mpg at highway speeds, so inefficient this old dinosaur pre odbii car

  8. Tom,

    As someone who’s about to buy an 80’s Jeep CJ-7 to play with (custom gauges/electronics), I’m a part of that small audience, and I certainly appreciate this article. Old vehicles are fun to play with, and you don’t have the guilt associated with damaging a brand new car when you screw up ;)

  9. Jack/Mike: The 80’s CJ is most likely carbureted or possibly TBI if it’s from the later 80’s. Holley does make an EFI multi-point system that can be installed on your 4.2L though.

  10. I’m well familiar with OBDII… actually ever car I own is 1995 or older to AVOID the OBDII system (for those who are performance minded OBDII closes a whole lot of doors). I would also like to point out that OBDII is USA only.

    oh and my 1995 240sx gets 28MPG… there’s something to be said for proper tuning and maintenance.

  11. obdii limits modification due to the fact that it does make large strides towards total engine management. you have to remember that obdii came about because of emissions control. A lot of hardcore wrenchheads will downgrade to obdi to get around a lot of the lockdowns that obdii imposes.

    the mpguino does fill a niche market, but then again so does the scanguage for obdii cars. That being said, mpguino is opensource and is going to be cheaper than the comparable supermid. (the dollars fall against the yen, and rumor is the guy making the supermid is just too busy to do them anymore.

    That small market more like than not is also not as small as you think. A lot of people are either ditching their new rides or at least acquiring an older vehicle simply because we’ve got suvs and trucks that just aren’t worth it anymore (myself included) a couple of thousand or less for 30+ mpg is well worth it when you do the math.

  12. i don’t think it is a small market. the tinkerers that would actually install this thing would be likely to drive older cars. i drive an older honda so that i can modify it without having to worry about the resale value.

  13. Wow! Lots of closed minds here. I’ve got a lot to say…

    1. As mentioned before, OBDII can only _calculate_ fuel flow rate, which leaves you with inaccurate information at times. For example, during DFCO (Deceleration Fuel Cut Off).

    2. OBDII is embraced by modern performance-minded individuals and most OBDII vehicles can be tuned a lot easier than non-OBDII, though at times more expensively. The total result can be better.

    3. Fuel injector duty cycle is the most accurate way to measure fuel flow rate. If you’re looking to publish specifications, you’ll need to know your manifold pressure; but if you’re just looking to get relative numbers to understand your engine, this is a great way to measure.

    4. This will work fine on OBDII cars, and gives you data you can’t get, so it’s NOT LIMITED TO PRE-1996 CARS!

    5. Early 90s cars, when decently maintained, are some of the most efficient cars on the road. They were a lot lighter than newer cars (now we have huge amounts of additional safety weight, generally bigger vehicles, and more gadgets weighing us down), often had smaller engines, ALWAYS had far less power, and were tuned for efficiency.

    6. I can’t load mpguino’s page right now, but it sounds like a FI duty cycle measurement combined with VSS (Vehicle Speed Sensor) measurement to give you MPG. That’s great and if it’s made from cheap parts I might make one. However…

    7. For $33, you can get a digital multimeter with dwell reading from Harbor Freight. Tap the injector wire -> positive lead on DMM, ground the negative lead, set to 4 cylinder dwell regardless of how many cylinders your engine is. Total investment: $33 and ten minutes work (plus the time to got to Harbor Freight or the money for them to ship it mail order). The scale is 0 to 90 instead of 0 to 100 so you’ll need to mentally adjust it a bit.

    I’ve been using the $33 DMM that way for a week or two now. I’ve been hypermiling for a couple months and have now improved my 2008 VW by 2mpg just from FI duty cycle monitoring alone. I learned that it uses more fuel at 90% open throttle than at 100% WOT, and that DFCO is very aggressive above 40mph but won’t start under 35. I also learned that my ECU doesn’t go to open loop no matter how I drive, it only uses it for 30 seconds after the car starts and (of course) when in DFCO. (Thanks to monroe74 on for telling me about this hack.)

  14. RE: #6,#18 brian
    Many injected engines have a fuel pressure regulator which compensates for the difference between MAP and fuel pressure, therefore negating most of that error. The MPGuino is adaptable to carburated and diesel engines also. 1900 to 1996 is a fair sized audience.
    Hint: Save your old cam position and crank position sensors.

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