Find a bad injector with a stethoscope?

I've heard you can diagnose a bad fuel injector with a mechanic's stethoscope. How does one do this exactly? My 22RE in the 4Runner has been missing, and I think I've narrowed it down to gunked up injectors. What exactly am I listening for?

Consistent clicking. Tick, tick, tick, tick,......

If it is intermittently getting stuck, that will work. If its clogged or flow restricted or has a poor spray pattern the best way to check is flow check them. Fuel rail/injectors into beer bottles and cranking with someone watching will give you a decent indication of health. Don't set yourself on fire.

On my 300ZX you could take a screwdriver and stick it up against the injector tops and then stick your ear to the handle and hear the ticking, no need for a fancy stethoscope.

Yeah, only if it's not working at all. But if the spray pattern is off, or something similar you'll have no idea. But lay some eyes on the plugs and you'll know.

no need for a fancy stethoscope.

I think my stethoscope was like $4 from harbor freight. Works great. Definitely NOT fancy.

I dont want to say you can find a bad injector with a stethoscope, because in my experience it would be rare for the sound to be your smoking gun unless the thing just isnt clicking at all (in which case it's still not your smoking gun until you put a noid light on it). But i will say you can get good info that, corroborating with enough other info, will make you confident in diagnosing a bad injector. It's pretty easy to tell the difference in sound between all the injectors on the same car and when the one that sounds weaker happens to be on the cylinder you're getting a misfire code on and you already checked the ignition side, then yeah, it just makes you feel better about it.

BUT!!!!!!!!!! It is EXTREMELY EASY to hear different sounds from every injector if you arent contacting them in the same place with the same force every time! If you put the stethoscope on different spots with different force on every injector they will all sound different! So you have to be very aware of how you are getting your 'reading'. Most of the time you cant get to EVERY injector easily with a stethoscope without some kind of interference/angle issue so you just have to pay attention to circumstances and judge what the info is really worth. It's a very subjective process.

Vigo wrote:

no need for a fancy stethoscope.

I think my stethoscope was like $4 from harbor freight. Works great. Definitely NOT fancy. I dont want to say you can find a bad injector with a stethoscope, because in my experience it would be rare for the sound to be your smoking gun unless the thing just isnt clicking at all (in which case it's still not your smoking gun until you put a noid light on it). But i will say you can get good info that, corroborating with enough other info, will make you confident in diagnosing a bad injector. It's pretty easy to tell the difference in sound between all the injectors on the same car and when the one that sounds weaker happens to be on the cylinder you're getting a misfire code on and you already checked the ignition side, then yeah, it just makes you feel better about it. BUT!!!!!!!!!! It is EXTREMELY EASY to hear different sounds from every injector if you arent contacting them in the same place with the same force every time! If you put the stethoscope on different spots with different force on every injector they will all sound different! So you have to be very aware of how you are getting your 'reading'. Most of the time you cant get to EVERY injector easily with a stethoscope without some kind of interference/angle issue so you just have to pay attention to circumstances and judge what the info is really worth. It's a very subjective process.

Yeah, I've used my stethoscope for many, many things but not to diag an injector. Besides looking at plugs, use a pyrometer on each header tube. It'll tell you more than a stethoscope will.