Cannot fix Single cylinder misfire under load.

I’m also wondering if I need to look at secondary now? How do I know what’s going on inside?
I guess I could also pull the coil and look for tracking? But I wouldn’t think that would be the case since I’ve already swapped plugs and coils? 
 

You may want to look at the clip signal which is the base for misfire detection.

juergen.scholl wrote:

You may want to look at the clip signal which is the base for misfire detection.

 

I’ll be honest. I don’t know what that is, but I will try to google it. 

No, I don't think it would shut them down. It would throw a code related to ignition confirmation. It knows from the crankshaft speed that the cylinder is firing.

I don't know why you're not getting an IGF signal, but I don't think that's your problem, though it may be related in some way.

Juergen, what is a clip signal? I don't know either.

I don't think your problem is secondary ignition due to swapping coils and plugs, but you could wrap a wire around the coil and hook that up to your scope while driving.

I think your problem is the #3 direct injector. Perhaps can't open properly under high cylinder pressures.

Are you only getting a misfire code P0303? No other codes?

I am going to load the freeze frame data from one of the misfires last night. It’s generic but that’s the only scan tool I have access to. Maybe you guys will see something I’m not since you’re more experienced. 

The last few

I ran two tests that Josh asked for to the best of my ability. The first if on the positive side of the #3 direct injector with a trigger on #3 coil. The second is the same test but on the negative lead to #3 direct injector. With the first test the misfire happened earlier up the hill than usual and at a slightly lower rpm. The second was pretty typical at around 3500 rpm going up the hill. with the second one though, the signal comes back after the backfire as I'm getting off the road to restart the engine. I am not sure why.

 

 
 

 

I was able to get the IGF to show up on the scope this evening. I think i had a bad ground? 

  

Either way, the coil told my ecm that there was a spark throughout the misfire event, so that leads me to believe that I have a no fuel issue (Josh pointed out that the fuel trims would most likely be higher if this were the case and that seems to reflect most of what I find online as well), it's a compression issue (I have already done a leak down and it showed only a percentage or two difference across bank 1 and I'm only having an issue with 3 (I cannot rule that out just yet though as it could be a compression issue that only shows at speed vs a static leak down)) or there's a possibility that I am getting a spark outside of cylinder or perhaps a weak spark? 

I am wondering if I would get any new information from the secondary ignition waveform? I have been watching videos on that but I'd have to order the probes to do this kind of test since its a COP ignition system. I am also limited because of the 2 channel scope. 

JoshuaK wrote:

Juergen, what is a clip signal? I don't know either.



Clip signal is the butchered version of ckp  signal, executed by autocorrection.
 

OMG, Look what happened with the quote function....

Again, clip is the butchered you CMP signal, inspired by autocorrection.

JoshuaK wrote:

Juergen, what is a clip signal? I don't know either.

I don't think your problem is secondary ignition due to swapping coils and plugs, but you could wrap a wire around the coil and hook that up to your scope while driving.

I think your problem is the #3 direct injector. Perhaps can't open properly under high cylinder pressures.

Are you only getting a misfire code P0303? No other codes?
 

Apologies! I never saw this reply. I think you’re probably correct, I just wish I could prove it before swapping that injector out. Like I said before I’ll need to get new gaskets and seals to do that and the direct injectors require a tool as well to change out the seal. I have a lot of money in this already so you’d think I wouldn’t be pinching pennies now, but my wife is definitely not pleased seeing our bank account when I buy a new tool here or there. 
I did a test earlier with the positive and negative feeds for that injector so maybe that will help? I’ll go ahead and order gaskets to seap that injector. I’ll be pissed if it was that simple but also relieved to find an actual issue. 

juergen.scholl wrote:

OMG, Look what happened with the quote function....

Again, clip is the butchered you CMP signal, inspired by autocorrection.
 

Ok, I’ll try to get them tonight. I have 4 on the motor, so I’m not sure if I can get them all today since I have to do one at a time in order to have another channel for a trigger. 

Have you done a cranking compression test? (Listen audibly and also a scan tool function that compares relative compression). Be sure to have the accelerator pedal all the way down.

You said it backfired... is that correct, or did you mean misfire? Backfiring indicates low fuel.

I think your #3 injector is firing but allowing insufficient fuel through under load (high cylinder pressure). This would account for the lower positive fuel trims you're seeing because some of the oxygen is being consumed in combustion, but not all of it.

Would you say the injector waveforms look identical when you compare #3 to another cylinder, or when you compare the misfire event to when it's not misfiring? I'm not able to tell at what point on your waveforms the engine is running fine vs misfiring. I can only tell when intentional shutdown occurs, of course.

JoshuaK wrote:

Have you done a cranking compression test? (Listen audibly and also a scan tool function that compares relative compression). Be sure to have the accelerator pedal all the way down.

You said it backfired... is that correct, or did you mean misfire? Backfiring indicates low fuel.

I think your #3 injector is firing but allowing insufficient fuel through under load (high cylinder pressure). This would account for the lower positive fuel trims you're seeing because some of the oxygen is being consumed in combustion, but not all of it.

Would you say the injector waveforms look identical when you compare #3 to another cylinder, or when you compare the misfire event to when it's not misfiring? I'm not able to tell at what point on your waveforms the engine is running fine vs misfiring. I can only tell when intentional shutdown occurs, of course.

I have not ran a relative compression test yet. I don't have a large enough amp clamp. I did see a video yesterday about how to do it using the battery and setting the scope on 1v AC and watching the waveform, so I may try that. 

If I wrote backfired, that would have been a typo or an autocorrect if I was using my phone to post. I dont believe I have ever heard this truck backfire.

I think you may be on to something about that GDI, so I guess I will need to swap it to be sure? 

I honestly haven't been able to see any noticeable differences between the GDI num 3 vs any of the others. The waveforms look the same to me. The hardest part about this whole thing has been not knowing when which injectors are supposed to be on.


Here is my report on the cam sensors. This may not be exactly what you were wanting, but maybe it will be good enough to deduce something if there is anything there to see. After the fact, I thought it may have been better to do each sensor with the crank sensor as a reference point, so I may have to do this again if necessary.

I personally don't see anything that sticks out but I am not trained in what to look for. The only thing that didn't seem to match was the correlation between the intake and exhaust cams varied between banks. If you look at bank one, the waves almost match, large, medium and small as if you could lay them on top of one another. But with bank 2 there seems to be about a 10-12 milisecond delay between the large signals as they start? Now this could just be how the motor was built? I couldn't find any "known good" waveforms for this motor online anywhere.

This screenshot is of both intake cams during the event.
 

This is both exhaust cams during the event.
 

This is bank one only with intake cam being channel 1.


This in bank two only with intake cam being channel 1.
 

 

I was able to find a set of cam sensor waveforms online from the same model truck as mine and it matches my capture. I was curious if maybe I installed the cams a tooth off, but I guess that's not the case.

You may want to replace the injector instead of swap because if that's the problem, then you're done, instead of having to take it apart again to replace the bad one. But swapping is a more sure diagnostic because it eliminates the possibility of the new one being bad.

I thought the direct injectors fired around TDC, or maybe a little before. So under load, they should be after the spark, because the spark is advanced by 30-40 degrees, right? So you could trigger on #3 coil control, and know that it's the injector that fires right after that.

JoshuaK wrote:

You may want to replace the injector instead of swap because if that's the problem, then you're done, instead of having to take it apart again to replace the bad one. But swapping is a more sure diagnostic because it eliminates the possibility of the new one being bad.

I thought the direct injectors fired around TDC, or maybe a little before. So under load, they should be after the spark, because the spark is advanced by 30-40 degrees, right? So you could trigger on #3 coil control, and know that it's the injector that fires right after that.

I agree that would probably be the easiest, but I bet the parts store will make me return the set since I bought them as a set. 

I believe you are correct about the injector timing as well, so I will trigger off the num 3 coil. 

Just because I want to see it, I ordered an extension plug wire and lead to test secondary ignition. I’ve never messed with this before, so it will be a fun experiment. 

Coming into this late and honestly haven't read most of the posts, but I see that you are about to go after the injectors, so thought I'd offer two tests that may help you. Hopefully I'm not repeating something from early on here...

If you clear the dtcs and monitor the rear o2, a lean misfire from a poor spraying injector may show a drop in voltage after you feel a misfire event. It's quick and easy, and may just help you feel better about going in that direction.

Another method I've heard other people have luck with is AC coupling the scope at the rail pressure sensor, where you may be able to compare injector contributions and spot one being a jerk.

I did the secondary test last night. I'm no expert on what to look for, but from the videos I've watched, it defintely appears to be very lean. I'll show all the frame from a throttle blip, so there will be around 10 or so. half in this post and the rest in a following post.

This one from idle.

 

And here is the blip.









 

And the rest.