View Full Version : Questions about injector test rigs

07-21-2009, 06:07 PM
Ive built a single injector testing machine

with a separate 555 chip for pulse width and pulses per second

plus an injector driver chip

no pump ...this is air over hydraulic

I'm getting good consistent results for each injector tested

example... simulated tick over for 50mins....will produce about 150ccs in the measuring cylinder and the next test on that same injector will only vary by 2-3 cc

BTW I'm bleeding the device before each test ..so no air ..(hopefully)

..having not seen one of these work before...and not been able to hear properly the examples on you-tube
the question is this

during tests ..the pulses are not all the same ..
I sort of get 50 pulses perfect ...pop pop pop etc

then i get 6- 7 phuts in a line ..before it returns to the pop pop pop

through-out the tests, this happens randomly, no matter which injector out of the four I'm testing is fitted

is this a basic characteristic of injectors ..or do i have to do some more work to do..

Ive emailed this to a guy that uses the pro machines

he says briefly that it is normal.........nothing else added in his reply as explanation ..

so... if it is normal........why?

all the best.markj

07-21-2009, 07:39 PM
Slight pressure variations maybe?
Back wen I did a lot more automotive paying work, I would always see that.

Never could get a clear explanation, so pressure variation is guesswork on my part.


Ya could post a schematic....

07-21-2009, 08:04 PM
I've never seen it , but I would guess the same.

Remember in another thread, I said something about pressure waves in the fuel from the injector opening and closing. You might be in the range of some harmonic of those pressure waves.

07-21-2009, 08:34 PM
it's so random i was thinking radio interference or something.

come to think of it ...ive never heard any car tick over for more than a min, without some sort of offbeat exhaust note for a couple of secs, that also happens randomly.

all the best.markj