Had a 2010 Cadillac SRX 2.8 with a misfire. After doing several ignition and compression tests I came to the conclusion that it must be an injector issue. This is one of the few GM non direct injection vehicles that does not have a flow test for the injectors in the scanner functional tests so went to a wave form test for the injectors first. There are 2 pink/black wires in the injector harness to supply power to the injectors and one of the injector control wires is also pink/black. I by mistake had my low amp probe around all three injector wire when I went to check injector 3 which is the one with the pink/black control wire. As you can see in the screen shot below the control wire is grounding the injector but the current ramp is missing. I thought i had found my problem. Before I confirm anything though I have to check things a little further as my misfire code was for cylinder 5 not 3. Sure enough I figured out that when you have your low amp probe around both the current supply and the ground wire of the same circuit the current moving in both directions seems the cancel each other out as far as the low amp probes ability to sense that current. Hmmm. As you can see in the next screen shot when I corrected the low amp probes position to just the 2 supply wires and still back probed the ground wire the current ramp is back on the screen.
So back to the vehicle in question. All injectors looked good in both current and voltage wave forms so I did a manual flow test by ground each injector with a piece of wire and found that the number 5 injector did not flow any fuel when grounded. The resistance on all injectors was also similar. The vehicle had been to a GM dealer ship before it came to me for second opinion. They had done a coil swap and when that did not change the misfire they recommended to the customer that the engine would need repair or replacement !!! Geez guys, put a little effort into your diagnostics.
So back to the vehicle in question. All injectors looked good in both current and voltage wave forms so I did a manual flow test by ground each injector with a piece of wire and found that the number 5 injector did not flow any fuel when grounded. The resistance on all injectors was also similar. The vehicle had been to a GM dealer ship before it came to me for second opinion. They had done a coil swap and when that did not change the misfire they recommended to the customer that the engine would need repair or replacement !!! Geez guys, put a little effort into your diagnostics.
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