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Topic: 555 Based Fuel Injector Tester (Read 4835 times) previous topic - next topic

555 Based Fuel Injector Tester

I've posted this one elsewhere but it's a work in progress so I figured I'd share it here.
I spent about four hours today reworking the schematic and the next step is to make a PCB, solder up the components to it and get it in a new larger enclosure. I'll probably do another video of the PCB build because I'll be using the Laser printer technique with a twist of my own involved.

Since I use two 555 timers in this, I plan on entering it in the 555 contest:

I have a video on Youtube which explains a lot of what his project is about:

You can also visit the project page on my website:


Re: 555 Based Fuel Injector Tester

Reply #1
How precise does this test tool need to be for you to accurately pass or fail a fuel injector?  Because the 555 is analog, it seems like you'd have a bit of variance on the exact timings.  A PIC based circuit could be very precise, although it would require programming and might actually be overkill.

One thing I'm thinking is that if you have specifications on how much fuel a healthy injector of a particular make and model will spit out per pulse, then a PIC could literally count an exact number of pulses to produce a calibrated volume of fuel.  Then you could put a measuring cup to catch the fuel, and the amount should precisely line up to your target volume.  The PIC could even have input (simple up/down buttons and a numerical display, or even a full USB interface) that would allow entry of specifications for a given injector so that the pulse count could be calculated to produce the desired fuel volume.  If an injector is not healthy and operating according to specs, you'd end up with too much fuel or too little fuel.  I've never tested a fuel injector, though, so I have no idea whether it would even be useful.

I do know that some cars have instantaneous MPG displays on the dash, and this is calculated using the odometer to measure distance combined the fuel inject control pulses to measure fuel.  That's what gave me the idea of measuring a precise volume of fuel to see if the injector is working properly.

Anyway, good luck on the 555 contest!

Re: 555 Based Fuel Injector Tester

Reply #2
fuel injectors are finicky things, the coils have specific values for resistance, inductance, opening current, and the time they take to open

Re: 555 Based Fuel Injector Tester

Reply #3
[quote author="sqkybeaver"]fuel injectors are finicky things, the coils have specific values for resistance, inductance, opening current, and the time they take to open[/quote]I'm not surprised.  But I suppose, for the purposes of making a fancy embedded solution, it depends upon whether these variables are documented in the manufacturer specifications or not.  Many car makers do not manufacture all of their parts anyway, but rather buy them from OEMs, so it seems possible that more than one car might have a similar injector, and that there might be documentation.

But I admit, it could be too difficult to track down all of these variables for more than one make and model.  Of course, if you just want to make an MPG gauge for your own fuel-injected car, then you might be able to figure out those values by careful measurement.

Re: 555 Based Fuel Injector Tester

Reply #4
if the car increases fuel pressure as load increases simply measuring the puls with will probaly not be that accurate.

Re: 555 Based Fuel Injector Tester

Reply #5
My intent here was to build a device to trigger the injector in the car with a fuel pressure gauge connected and static pressure applied. You then observe the pressure drop and repeat the process on the other injectors. If one has a low or high flow, the difference will be seen in the pressure drop and then you can pull that injector for further investigation. A bit of variance in the analog output won't matter much.

I spent several hours yesterday drawing up a new schematic that has variable output. Now it can be triggered for 1 second, 5 seconds or continuous.