Fuel flow meter for cars .. ?

They're not any use with injection as the fuel runs in a loop sending unused back to the tank. And at high pressure. The normal way these days is to count injection pulses and duration.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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**Here is an article published in and Australian magazine which describes a car computer:

None of the local suppliers supports the kit any longer. However, as I recall, the kit was designed by a contractor to the magazine. As a consequence, that person probably can assist with stuff like sensors, PCBs, programmed microcontrollers, et al. You will probably need to purchase the article to ascertain the details. Or perhaps a polite email to the publisher may elicit the contact details of the author.

Good luck. I almost built one, but found a (second hand) commercial device at a very good price first. I do recall that the design was most impressive.

Trevor Wilson

I suppose you could employ two (2) in-line sensors -- one on the supply side, and one on the return side and subtract the return flow from the supply flow in the u-processor. (I'm assuming the project used a MicroChip [or similar uP) thingy.)

Jonesy

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I must admit to being surprised. Both my cars are injection and both use the pulse measuring system to calculate MPG and both are very accurate. Years ago I did have an aftermarket one that measure fuel flow and it wasn't.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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Hi,

Fuel flow is porportional to the Duty Cycle of the injector signal. A volt meter across across an injector will give you uncalibrated fuel flow, Assuming the time delay to open is = to the closing delay and the waveform is square. Web search indicates typical wave form is sq. with a 70v inductive kick. Current rise time ~1.5ms so I guess the on time is long resulting in a positive offset. Anyone know how = the times are? The injectors take >.6A so I'd start with a 470 ohm R and a zener or LM431 to filter battery changes. For relative calibration: connect across battery =

100%. Good enough for my needs: check effect of tire change, syn oil, wax job, etc..

Check

for injector flow rates and discussion of on/off delay..

Chuck

Look up Megasquirt, it's a DIY fuel injection system and related sites have all the information you could want about injector pulsewidths.

**As I understand it (please note, I am not speaking from any real authority here) no injector is perfect. Some are clogged a little. Some are clogged a lot. Some are not clogged at all. Pumps are subject to wear. As a consequence, the BEST way to measure actual fuel consumption, is to measure the amount of fuel used, rather than inferring how much fuel SHOULD be going into the cylinders.

Having said all that: My present car probably uses pulse measurement techniques and the computer appears to be respectably accurate (though I've never actually checked it).

Trevor Wilson

i used to just coast down hills to gain MPG advantage ;-))

Anyone can do that. OTOH, if you can do it while going uphill... ;-)

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Michael A. Terrell
Central Florida

All injectors should be within 5% of rated flow, or engine performance and fuel economy will suffer. When new, they're within a percent or so, and usually hold up pretty well. Measuring the pulsewidth should in most cases be at least as accurate as typical flow sensors.

Yehbut EFI systems are closed loop and if the injectors are slightly out of spec, the ECU will compensate. If they're wildly out an inaccurate OBC will be the least of your worries...

That assumes you can make the perfect flow meter which will maintain its performance.

I have to log all fuel bought for tax purposes so I can do a pretty accurate check of the overall MPG - and when I have, the OBC has been as near as dammit spot on.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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**OK, here's where my ignorance begins to show. EFI systems are sort of closed loop. However, under certain conditions, that may not be the case. At startup, for instance. Under very heavy acceleration, for another. There are probably other conditions where the system is not closed loop. So-called 'limp-home mode' would be another. I'm not well versed in automotive issues to comment with great authority. I do understand a little, however. **Indeed.

**As has mine.

Trevor Wilson

Yes - but a 'dribble' from an injector or injectors would have far more of a percentage effect at cruise or low throttle conditions. Remember the combination of depression and fuel pressure acting on the injector is a constant. If you think of a dripping tap (faucet?) the drip is irrelevant when the tap is fully on.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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What's an injector? Some of us don't have 'em and still want a diy fuel metering system.

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**Then you need a fuel flow sensor.

Trevor Wilson

Then I'd ask why. Wanting fuel metering suggests you're concerned with MPG. Converting to injection will improve this.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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LOL, of course a modern EFI vehicle uses less fuel if you coast with it in the highest gear and the throttle closed. Drop it out of gear or use the clutch and it uses fuel to keep the engine spinning.

--
Clint Sharp

The farthest I've ever coasted downhill was about seven and a half miles, after I ran out of gas at four in the morning.

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Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Well that obviously was not here in Florida, but sounds like an adventure.

Mike