When my scope failed me !!!! (no pintle movement)

Let me start this off by saying I am a pretty Adiv scope user and do use my scope as needed for testing components ,systems, and networks while admittingly the scope is often not my first grab but I will use it when I know it would be more beneficial.

2008 Honda pilot with 3.5L engine with a dead hole P0302 ,car belongs to a buddy and he ask me if I could diag it and he will do the work (work in shop in the past but overall very inclined and does most his own work).

I scan it with my Autel scanner and get a P0302 at idle it's a dead mis (mis fire PIDs racking up for cyl 2)so I'm already thinking coil or injector related I tell him to swap coil 2 with what ever is adjacent to it and lets see if the misfire moves . So he googles cyl IDs and swaps coil 2 ,, so he thought ...

Apparently the imagine he got from google wasn't the correct one (he jumped the gun and went off the first one that came up) and he swapped 4 with 5 thinking it was 2 with 4 , fired back up and cyl 2 still racking them up like a good light on the slot machine floor !!! so lets verify coil power , Gnd , and control . Back probe each wire with my scope and get a good 12V feed , a good 0.2V gnd while firing and a good input command (coil function was apparent slight allowable voltage drops while saturating ) so the 3 legs of the triangle are in place...

Now what ???? well obviously lets attck the fuel injector , soI gain access to the ECM and find the control wire for injector 2 (B-8 red wire) and back probe it and grab about 20 captures of injector voltage before the computer shuts it down . I zoom in and all the main components are there `12V pulled within 200mV of gnd , released and approx. 65V spike except 1 thing is missing ........pintle hump !!! well looks like we cracked the case but to be sure I grab a current ramp waveform and it shows no opening of the pintle so bam ... it needs the cyl 2 injector... So I thought

Gets injector and swaps it with "cyl 2 " (really 4 ) buttons it all up and ... CEL flashing and cyl 2 still counting WTF!!!

Scope it again and the same no pintle hump ?? something isn't adding up , "Are you sure that's the right cyl layout ??" he looks it back up and what do you know he was wrong .. cyl 2 is the rear bank second one in from front pretty much how Ford IDs their cylinders 123-456.... Ok so he takes it all back apart in record time and swaps the injector(old one ) into the correct place . Fire it back up and still racking them up !!! scope pattern on the new injector still shows no pintle movement !!! wtf its a good injector from what's actually cyl 4 that had no counts !!!

So he swaps coils with what is now the correct cyls .. swaps coil 2 with 1 can fire is up and what do you know cyl 1 is now racking them up the misfire followed the coil so needs a coil ... Put me not seeing a pintle hump caused me to call an injector when it was obviously working I even scoped another injector and the same no pintle hump .... WHY?????

inserted is a capture of a working interjector

Autel maxiscope with AESwave/PDI low amp probe on 20 amp setting (100mV=1amp)

Thanks for sharing this experience. Perfect example of why not to put all your eggs in one basket.
I use a Verus Edge scope, and pintle hump can be difficult to identify. When in doubt, I compare to one that I know is firing and if needed, I will manually energize the injector with an injector timer tool and a fuel pressure gauge to verify that it is moving the same volume of fuel as the others.
The last Triton v10 I had with a bad exhaust valve comes to mind. Another mech put a coil and plug in it to fix a misfire, and when I was asked to help him check the injector, pintle hump (on the control circuit waveform) was virtually non existent on the offending cylinder. A known good cylinder wasn't much more defined, so from there I knew I couldn't hang the diag on pintle hump, or lack there of. An injector timer tool can be found on E-Bay or Amazon for under $50. I think I paid $30 for my All Sun quite a few years ago

Thank you for the reply.

And yes if I had a fuel pressure gauge I would have at least gave it a fast tap to ground through my test light that I modified to flow 800 mA peak and 350mA full time . I'm sure it would have been enough to move the pintle to just look for a slight change in rail pressure .

There are quite a couple of injectors that won't showthe "classic" pintle hump though working fine. Nissan from early 90's to mid 2000's come to mind immediately, especially the D22 2.4l engines among others.

mark.boggess wrote:

my test light that I modified to flow 800 mA peak and 350mA full time . I'm sure it would have been enough to move the pintle to just look for a slight change in rail pressure .

Keep in mind that the testlight put in series will drop the voltage available to the fuel injector significantly. With the given numbers , 350mA and a resulting voltage of 4 to 6 volts the injector may not be able to open.