Petrol injector tester

[Henrik]

I've been working away on a computer controlled fuel injector tester lately.

I'm using an old Subaru fuel rail, with a petrol pump from a mazda MX-5, and a Fuelab pressure regulator.

The pump and injectors are controlled by an Arduino board. The injectors have a little driver circuit board, with a logic level (5v) MOSFET transistor controlling the higher voltage for the injectors.

Some in progress pics (its still work in progress)

This version is much easier to use than the one I built previously, where I used compressed air to pressurise the fuel tank, as it's much faster to change the injectors out.

One annoyance is that any fuel spills don't drain back into a tank. I think for version 3, I will have a tank underneath the machine, and let fuel drain into it,rather than a separate tank.


The user interface is also much nicer now (version one would just start 5 seconds after power up, and pulse for 10 seconds, then stop until the next power cycle).
I'm using a cheap LCD shield with buttons (3.50 GBP), which works surprisingly well. The buttons are all connected to an analog pin, with different voltage ranges signifying different buttons. A bit shonky, but at least saves digital input pins.

Some videos of the thing in action (very basic tests):

I've used it so far to test 9 injectors (two well known ones, and 7 Subaru STI injectors). I previously cleaned 4 of the STI ones, and it's nice to see that they all seem to flow equally well now. The left column in the pic below is the injector number (just my internal number I make up), the middle column is a simulation of 1000 rpm at 50% duty, and right is 6000rpm@50%. The actual value is cc flowed in 10 seconds.

1-4 are the cleaned injectors, and 5-7 are dirty ones off eBay.


If you want to build something similar, I've uploaded the source code for the microcontroller here: https://github.com/hbilar/arduino-injector-tester

I'll try to remember / find time to upload some pics of the injector driver as well.

 

[armalites]

That's cool, did you use the Arduino to pulse the injectors in an ultrasonic cleaner too?

 

[Henrik]

That's cool, did you use the Arduino to pulse the injectors in an ultrasonic cleaner too?

No, not yet.

I've only sprayed carb cleaner down the injectors so far, whilst pulsing them (and back flowed them using the same method). Worked remarkably well on the 4 I did so far, but I am considering investing in an ultrasonic cleaner for other bits and bobs, and it would come in handy for this too!

I'd need to modify the code slightly to provide a fifth mode where the injector pulses at varying intervals for the ultrasonic clean, but that's easy enough

 

[truckdoctor]

Impressive electronics build. It is important to look at the spray pattern from the injector which you won't see with it spraying into a tube, maybe use a larger vessel for collection ?. What liquid are you using?

 

[Henrik]

Impressive electronics build. It is important to look at the spray pattern from the injector which you won't see with it spraying into a tube, maybe use a larger vessel for collection ?. What liquid are you using?

You're right, the cylinder is too narrow at the moment. I'm thinking of getting a pair of wider ones, but that loses accuracy, so might keep the narrow one and use a jam-jar type vessel to see spray pattern.

Re the liquid, I've been trying to figure out what the professionals use, and it seems a lot of them actually use white spirit (except they call it some American trade name, which I can't remember at the moment). Hence, I'm using white spirit too at the moment.

The viscosity is slightly worse than e.g. petrol, so the injectors flow less, however I'm hoping that I can come up with a correction factor as I know how much a standard injector SHOULD flow, Vs what it does in my setup.

I used brake cleaner in my old setup and calculated a correction factor, which worked out exactly between the three types of injectors I have.

For example, I know that a standard Subaru WRX injector should flow 380cc/min, and if all my standard injectors flow say 250cc instead, the correction factor is 380/250. I then tested the other two sets of injectors, and using the same correction factor, I ended up very close to the advertised flow of them.

I'm mostly interested in finding out the relative flow, however, and making sure they all flow the same, but everyone else thinks in petrol cc/min

I also want to be able to measure the latencies (open and close) of the injectors using an oscilloscope, because I want to see if that matches the dead time in my PWM mode, to see if PWM can be used to estimate the dead time or not, but that's a project for after MOT.

 

[truckdoctor]

Yes use a jug to inspect spray pattern and transfer into a vile. I have used white spirit but it is flammable and an irritant, so best to aware ( obviously),also the viscosity is an important factor to keep an eye on the temperature. The duty cycle can run up to 90% under full load and is interesting to watch if you have access to a scope. Small changes in fuel pressure seems to have a dramatic effect on stoichiometric ratio. Good luck with your project, you have achieved greatness already please keep us informed with your progress.

 

[8ob]

I bought an injector tester off the bay of thieves , not used it yet but was hoping to make up a rig as in post#1 pic 3 . Where do those calibration tubes come from?

Bob

 

[Henrik]

Ooh, nice what kind of increments do the ms increase/decrease?

This is what I ordered: Rocwing - Boro 3.3 Glass Measuring Cylinder Laboratory Glassware (100ml) https://www.amazon.co.uk/dp/B06W53CWKM/ref=cm_sw_r_cp_apap_84ZWspkDZAiVX

 

[SparkUK]

That looks like a superbly done piece of kit, as has been said already, being able to view the spray pattern is crucial. Having balanced sets of injectors is probably more important than the actual numbers as most times the systems will be individually tuned with that set or will be running a closed loop system.

 

[Indra Nurcahyo]

Wow. Good.