Can I detect miss by feeling injector line?

[rabbid79]

I think I have a very slight miss in my engine, which I can really only feel (and maybe hear) at idle.  I gently pinched each injector line with my fingers, and #3 definitely has a more noticable "pulse" to it.  When I pinch the others, it just feels like regular vibrations and I can't "make out a pulse".

I have a new pump, engine, injectors, and injector lines.  Of the four, the injectors seem like the most likely culprit.  I didn't pop-test them before installing, and I'm wondering if one of them had a different popping pressure (maybe higher?) than the others, if there would be more sensation in that line?  Anybody ever tried this?  Thanks.

[fatmobile]

I took a mechanic's stethescope to the injectors once.
 One injector sounded a little different.
 Maybe some day I'll be able to translate that to mean something. 

[92EcoDiesel Jetta]

If you can come up with these parts, try clamping an acoustic guitar contact mic or a crystal phono cartridge from an old record player to the injector line and feed it into your Walkman mic input and listen with headphones. If you can't discern the difference by ear, feed it into an oscilloscope to measure the amplitude/ frequency.

[VW Smokr]

Hat's off to you, Superman, for being able to pinch the injector lines with your bare hands ("fingers").   Seriously, I haven't really had any success finding bad injectors by squeezing the fuel return hoses. You might try loosening up the injector lines from the injector tops, one at a time, to see which one doesn't slow down the idle speed. That will be the one that's missing. It's a quick but messy job, requiring rags to soak up the leaked-out fuel.

J.R.
SoCal

[rabbid79]

Hey guys, thanks for the ideas.  Smokr, it's the hard lines that I can feel a distinct pulse in, not the rubber return lines.  I'm familiar with the technique of cracking the lines, but I don't think it's a bad enough miss that it will be obvious which cylinder it is by cracking the lines.  I think I'll order a single reman'd injector and try replacing #3 just to see what happens.  Fortunately it's the easiest injector to get to.

[R.O.R-2.0]

i find that the pulses change when the brake pressure of the injector changes..

basically, if the tip is damaged, and you have a pi$$ing injector, the pulses from that line will be weak, if detectable at all..

so, i think that the only thing you are detecting by injector line vibrations, is if the injector is braking at around the same pressure as the rest..

if 3 have identical vibrations, and one has almost none, then its not building much pressure before it brakes, and shoots its load..

i doubt you could detect a misfire at idle if your problem was from low compression, and not an injector issues..

[rabbid79]

if 3 have identical vibrations, and one has almost none, then its not building much pressure before it brakes, and shoots its load..

See, and I'm wondering if I have just the opposite problem, where maybe one is building a lot more pressure than the others.  It might not be a bad injector from the leaking or spray pattern standpoint, but just a higher breaking pressure than the others.  If that's the case, then the timing would be retarded for that cylinder, and would essentially cause the "miss" that I think I'm having.

For testing purposes, I guess a cheaper option than replacing the one injector I think might be bad, is to swap it with another injector, such as #2, and see if I can feel the pulse of the injector lines move to that cylinder.  It will only cost me two heat shields and about 15 minutes to try it out.  Maybe that's what I'll do tomorrow when everyone else is watching Madonna.

[ORCoaster]

http://imageshack.us/photo/my-images/709/meteredreshapeofshim.jpg/ 

Save yer money and use this tried and tested Mark Method for reforming those heat shields.   

Been doing this for a year now myself so I know it works.  Just a little squeeze is all it takes to deform it back 1mm.