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I think looking at the ignition and injector current patterns during your fault condition is the next step. If those both look good, then it must be a compression problem. Have you swapped or replaced the #3 direct injector? Another thought is you could unplug all the direct injectors - perhaps the car will run on the port injectors as a back-up, and if you don't have a problem, then that tells you it's injector #3 or the control to it (unlikely).
I think looking at the ignition and injector current patterns during your fault condition is the next step. If those both look good, then it must be a compression problem. Have you swapped or replaced the #3 direct injector? Another thought is you could unplug all the direct injectors - perhaps the car will run on the port injectors as a back-up, and if you don't have a problem, then that tells you it's injector #3 or the control to it (unlikely).
Ok. I got the amp clamp today. I gotta make a loop for it since i didn’t want to spend $20 on a piece of wire and then I should be able to test the current on the injector circuits as well as the coils. I am assuming I’m looking for cylinder 3 to mot match the other 5?
As far as compression is concerned, I did a compression test and got 150 psi. To confirm good compression, I also did a leak down on all three of bank one cylinders and they were all the same with a leak percentage of about 3-4 percent.
Correct, during your fault condition, you're looking for the current ramp pattern to to match the other 5 injectors.
Testing compression isn't useful because this problem only happens under load / i.e. high cylinder pressure. My guess is the problem is not compression. If you can't find the problem with spark or fuel, perhaps then you'll be replacing rocker arms, valves, and valve springs.
Correct, during your fault condition, you're looking for the current ramp pattern to to match the other 5 injectors.
Testing compression isn't useful because this problem only happens under load / i.e. high cylinder pressure. My guess is the problem is not compression. If you can't find the problem with spark or fuel, perhaps then you'll be replacing rocker arms, valves, and valve springs.
Last edit: 8 months 3 weeks ago by type3sqr. Reason: changes to the way the forum replies
I was able to mess with it a little yesterday, but not enough for all the tests needed mostly because I got unexpected results from the first one. I still need to take it on an actual ride with the scope hooked up. I hooked up the current clamp to the power feed for all coil and then triggered off of cylinder 3 injector. What I see is consistent looking waveforms on all cylinders except cylinder 1 which has the same curves, but is a lower amperage. Cylinders 2-6 all show an average of 11.3 amps but cylinder 1 is at 9.1 amps.
This threw me off because I was expecting to see an issue on 3, so I kept retracing wiring to make sure my trigger was on the right injector.
I will to to do the other idling tests today to make sure I have it all hooked up correctly and then I will drive it and get it to do it’s thing.
Your sample rate seems to hover around 6ks/sec which would be very low......
You may have to account for that the injection event does not take place anywhere near TDC compression, especially on port injection but often time also on GDI, depending on the operation mode. So make sure your sync event really happens when it it should in order to get the cylinders identified corecctly.
Eventually you may want to sync on a specific coil using the trigger signal or a secondary wand/probe, just to avoid possible confusion.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
I did this same test again and you are correct. I triggered off of number 3 coil and it lines up with the one with one that is lower in amperage than the rest. Now my question is, why?
I was able to drive the truck with the scope hooked up last night and made the misfire happen. On the picoscope, I'm seeing that the red channel, which is spark, simply turns off and stays off until I'm able to get to side of the road and turn the engine off and restart it. I don't see anything leading up to that though. The amperage draw is still lower than all the others, but it doesn't change throughout the event.
After restarting, I drove home just a few miles away. When I pulled into the drive, I could feel the miss at idle. I watched the scope and could see there was no spark on 3. I blipped the throttle and the spark came back. Why would it do this?
I haven't done the tests on the injectors, but will try to do that today.
Or there is a problem = voltage drop or on the positive or ground side leg of these specific #1 coil circuits or it's the coil itself that got higher primary resistance than the other coils thus limiting current flow. Voltage drop testing will be your friend....
I didn't follow this thread from the beginning so I have a couple of questions:
Is the #1 coil same brand as the others?
When swapping coils will this #1 coil while put in another cylinder draw less current as well?
Will another coil put into #1 cylinder now draw less current than it did in the cylinder where it came from?
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
To get caught up quickly, you should read the first post. I have been at this for a while now. I am just now getting to the point of using a scope though.
The coil in question is a denso coil. I have replaced the coil on 5 and that is the only one that is aftermarket. I have swapped coils and plugs previously and the problam has always stayed on 3.
I was wondering the same, but this is my first time using a scope. I am using the pink wire after the fuse for the current and the light green wire out of the ecm for the coil.
If you zoom in and look at your primary coil dwell time, is it exactly the same amount of time for all coils, or is #3 a shorter time? If so, that would be the PCM/ECM.
Otherwise, swap coils and see if the lower current changes to another cylinder. If not, then do the voltage drop testing at coil #3. If all checks out, replace the ECM/PCM. However, without checking the direct injector waveform patterns, there is a chance that this lower current on #3 coil is not THE problem, and that the problem lies elsewhere such as the injector.
I will try the tests you recommended. I have already replaced the ecm and it still does the same thing it did with the old one.
a quick question on hooking up the scope of you don’t mind.
when hooking it up to test the port injectors where they all have constant 12v and are grounded through the ecm, do I hook the main lead to the trigger and the grounding lead to positive?
same question with the coil. Do I hook the main lead to the trigger wire and the grounding lead to negative?
im asking because I did this previously when testing injectors and the injectors for 4 and 6 shut down. I had to restart engine and clear codes to get it to run again.
Compare another cylinder's IGT signal to its current ramp, just to make sure it looks similar or not.
I understand the misfire occurs when putting the car under load. This may go along with a shift from gdi to port injector during this load increase.
You may want to hook the two channels of your scope to both injectors of a non misfiring cylinder and make the engine misfire. Then look for a possible shift between injectors. Then repeat the same on the misfiring cylinder #3. and compare.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
You hook the channel's signal lead to the control side of the injector. This is the wire that runs to the ecm. It is NOT the common power feed for all injectors. It is the other one! You will need an attenuator other wise your scope may get damaged!
The ground lead of your channel goes to battery negative or a good chassis ground.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
Has somebody done some new wiring and made a parallel circuit?
The total current in a series circuit is the same as the current through any resistance of the circuit. This total circuit current would remain the same through all the individual circuit resistors. Before any current flows through a resistance, a potential difference, or voltage, must be available.
Did you test the trigger wire at the computer? I should disconnect the connector at the computer and do a loaded test at the trigger wire with a test lamp.
I was able to mess with it a little yesterday, but not enough for all the tests needed mostly because I got unexpected results from the first one. I still need to take it on an actual ride with the scope hooked up. I hooked up the current clamp to the power feed for all coil and then triggered off of cylinder 3 injector. What I see is consistent looking waveforms on all cylinders except cylinder 1 which has the same curves, but is a lower amperage. Cylinders 2-6 all show an average of 11.3 amps but cylinder 1 is at 9.1 amps. 
I was able to drive the truck with the scope hooked up last night and made the misfire happen. On the picoscope, I'm seeing that the red channel, which is spark, simply turns off and stays off until I'm able to get to side of the road and turn the engine off and restart it. I don't see anything leading up to that though. The amperage draw is still lower than all the others, but it doesn't change throughout the event. 
