fuel injector voltage probe location

[persistent]

having recently repaired a failed set of piston rings on 1 cylinder, i'm trying to improve my diagnostic skills and evaluate a hypothesis from @Pressureangle about the corresponding fuel injector having a problem, e.g. opening for too long relative to the other cylinders. i've got a picoscope and have started to read current and voltage waveforms from the engine, but in order to get a clear picture of both the opening and the closing of each injector, i need both the current and voltage waveforms for the injectors.

i should be able to acquire the current waveform by using a fuse buddy / fuse loop device at the fuse box for each injector bank with a current clamp, which will show when each injector opens. i will check the current data in the next few days. in order to see when each injector closes, i need to acquire the voltage waveform on the control side, which is between the injector and ground, which is much harder to get at with gm's engine design.

since the injector banks and wiring are located underneath the intake manifold, this makes it difficult to access the ground side of the injector wiring, particularly while the engine is running. is there a trick i'm missing to access the ground side of the injector wiring while the engine is running, or am i stuck only being able to acquire the current waveform for the injectors on this engine?

 

[Fless]

You may be able to find the waveforms on Ivan's site or he might tell you where you can find them; check on https://www.pinehollowdiagnostics.com/. His YouTubes mention places that he gets waveforms.

A simple injector balance test would show the differences between the injectors, without the scope.

 

[persistent]

i was looking to get the live waveforms from this vehicle in particular, but it's not a huge deal if i can't access the injector ground wiring.

appreciate the pointer to do an injector balance test because that accomplishes what i was after with less work. it looks like most decent bidirectional scan tools can do the balance test. i'll try it out on my launch i have here.

 

[persistent]

i finally got around to doing an injector balance test with mdi2+gds2 and i got some surprising results. bank 2 pressures show as being a flat 50% higher than bank 1.
the results for all injectors (in kPa) are: 1 - 173, 2 - 299, 3 - 194, 4 - 292, 5 - 202, 6 - 310, 7 - 176, 8 - 299

i have read in a few places that injector balance test data is inaccurate, but i wouldn't expect one bank to be 50% higher than the other. i have an injector test stand, so assuming i can extract the injectors without damaging them, i can test them individually.

any thoughts on how this could have occurred and if the data is correct? the engine idle has a lot of vibration, and this problem has been present since at least 60k mi, and it's currently at about 90k.

 

[persistent]

ah, this is actually expected behavior per this video from phillip bailey. the top comment claims that these pressures are supposed to be compared within each bank, not across all 8 cylinders, which makes sense. however, the gm service manual does say to compare the pressures across all 8 cylinders, not for each bank separately.

 

[Fless]

ah, this is actually expected behavior per this video from phillip bailey. the top comment claims that these pressures are supposed to be compared within each bank, not across all 8 cylinders, which makes sense. however, the gm service manual does say to compare the pressures across all 8 cylinders, not for each bank separately.

Not seeing a video at that link, just some apparent data files or some such.

 

[persistent]

Not seeing a video at that link, just some apparent data files or some such.

sorry about that, i've updated the link.

pardon the cut-and-paste error.