It is missing even while cold. And the spark test would have shown if it was failing to fire the spark plug, or was weak. However, that is exactly what I'm worried about with the injector firing. A noid light shows a signal, but does not put any load on the circuit. That is why I am planning on pulling the injectors and checking the spray when actuating them through the computer. Otherwise I could pull the connections and load test the circuit, but that wouldn't test the pcm's output at all.

I figured the valves would be more likely to not open fully when hot, so I drove it before I pulled the valve cover to check. Didn't matter. Misses the same cold and hot. However before replacing injectors, it would idle smoother when warm than cold.

 

Ran the engine to temp before testing just to be sure, but it was clearly missing right after startup anyway.

Vacuum test was a pain. There aren't any normal vacuum lines, one plastic line for evap and one rubber for the brake booster. So I spent 20 minutes finding enough fittings to get the 1/2" booster line down to fit my gauge. Vacuum set with a little shake between 19-20inhg. Exhaust didn't have any pull, but a little pulse out, no doubt from the miss not producing.

I repeated the compression test. All cylinders at 100psi on the first stroke. All max out about 180psi.
Swapped coils, plugs, wires when putting it back together on both sides. No change. Only thing to note was the #7 plug was slightly cleaner than the rest, with NO wetness at all even though I just ran the truck. So it is firing, just not steady enough or producing the power it should.

Pulled fuel rail and lined below the injectors with clean napkins. Pulsed injectors one at a time running the fuel pump a few seconds between each. Efilive labels injectors A-H, and are not in numerical order, might be firing order I wasn't paying attention, just watching the spray on each. All significantly wet the napkins with a 2 second shot. 7 isn't any less wet than any other, almost looked more wet.

Swapped all injectors when going back together. No change.

Repeated the spark test to compare cylinders. The spark from all 4 LH coils look the same.

I can pull the RH valve cover, but at this point I don't suspect I'd find anything.

I could pull the LH Valve cover again and measure rocker movement, but I may not find anything there either, as many people have stated they had good valve movement when hand cranking and not when running, so that might be a waste of time.

At this point I'm out of ideas. Only thing that keeps coming back to mind is cam/lifters, but everything looks good. Because the plug isn't wet on 7, I wouldn't suspect it is running rich due to a lack of airflow. I could pull the intake again, pull the valley cover off and take the lifters out of #7 and physically inspect them. Also look down to try and see the lobes on the cam.

RANT-
Problem is that I don't do anything half way. If I had extra money to burn, I'd just pull the heads, but then I'd send them to be rebuilt, and replace the cam/lifters with a non afm cam. That would cost me nearly $2k in parts If I stopped there. I bought a 2012 acadia with timing chain problems a few years ago. Ended up rebuilding the engine and replacing damn near every wear part on the car, costing about $9k in parts. So my wife decides to buy a newer traverse instead and we sold the acadia. Last winter I had a head gasket go out on my wife's 2005 duramax, found the cylinder walls scored (big surprise with 280,000 miles on it). So I rebuilt that engine and replaced a bunch of stuff so it would be good for years to come, but that cost about $18,000 in parts. The list goes on. We're out of money to throw at vehicles. Yes it still cost us less to fix than to buy a new vehicle, but I'm sick of fixing everything. My towing truck, for camping, boating, moving equipment, etc is a 2006 duramax. Which runs almost perfect. Almost because it has had a steady decline in MPG over the last 6 years, and no other symptoms. I believe the injectors were damaged when I got several gallons of water in a tank a fuel, but can't verify it. But it sucks to get 10mpg pulling a car trailer with a pickup on it now, where before I averaged 15mpg pulling almost the same truck 280 miles. Empty I use to get 19-19.99mpg on every tank for highway driving, and about 17mpg for normal trips to town. Now I'm lucky to get 16mpg highway. Before I got 12mpg puling out big camper and the last trip I got 8. So I'm getting almost gas engine mileage and paying diesel prices. With the price of diesel I can't afford to drive it. But a new set of injectors would come to close to $4,000. Which can buy a lot of fuel. I've come to the conclusion that I have too much stuff to afford to maintain it all.

If I pull this thing apart, I know I'm going to have the heads rebuilt, with nearly 200,000 miles, it would not be worth slapping them back on. Ding $2,000 gone min. If I see any problems in a cylinder, I'll pull the block out. That would be a minimum of $1,000 more in parts if it doesn't need to be bored and the crank is good.

 

viewing the live misfire monitors....the only cylinder accumulating is cylinder #7?

 

Yes. Cylinder 7 is the only one with consistent misfires. Cylinder 8 and 2 have 2-10 for every 1000 on #7. Which is close enough to be reading an echo.

I don't think 7 is a complete dead cylinder, judging by the length of time it takes for the misfires to climb (they climb steadily but not fast enough to be every firing cycle), the clean spark plug, and how smooth it seems to run up around 2000 rpm (though that could be just hiding the misfire at a higher rpm). That is just a feeling though. I could confirm by matching the count to rpm and time, but now I have it apart and need a valley cover gasket. Also need to figure out how to get the new gasket under the afm solenoids.

I got pissed. Pulled the intake back off. Pulled the valley cover. Looked at the cam. Need to be fully on top of the engine to do so, but I can view the lobes of 1, 2, 7, and 8. All are good. No significant wear or damage. Used a magnet down the rod holes, 7s lifters move very freely, definitely not stuck. Also looked down at the intake valves. Rotated the engine, watched all intake valves move. 7 looks identical to every other valve. Push rods were straight, rockers move freely. Engine is still warm, but not hot. If it only misfired hot, then that wouldn't mean much, but because it does it cold, I think I can rule out the cam/lifters. But now what?

 

post a close up pic of the rocker arms and the ends of the push rods for cyl 7. needs to see where the push rod seats on the rocker.

 

I can't see anything wrong, and can't get a great pucture either. Here is what I got.

 

pic are to blurry. if it did it all the time i'd say take a shot and replace the dod lifters. the ok hot is a mystery. I"ll ask my old coworker...he is a gm tech.

 

Sorry, I couldn't get it to focus on the right spot. I don't know if I miswrote, or just wasn't clear. It is missing all the time. Cold and hot. Lifters are my best guess at the moment. But I'd be really unhappy if I rebuilt another engine, only to have the problem still be present. I've decided to throw a couple more parts at it. I ordered a non-afm valley cover, to guarantee the lifters aren't being actuated unintentionally. I also ordered a pair of valve springs. Figured they'd be fairly easy to replace at this point, they were cheap, and there is a possibility that they aren't closing the valves fast enough, or broken and I can't see it. I also ordered a new ECM. I took the ecm out to check the part number, and it has paint pen writing on it, likely from a junk yard. It is $200 extra, but would be the last possible thing besides a mechanical problem I can think of.

Parts should be here Tuesday. Hopefully I can program the ECM myself with efilive instead of taking it to a dealer. I've programmed an ecm from a junk vehicle to another and had it work, but never a new one. Then I can shut off the AFM at the same time. Like I said, I wouldn't be able to just replace the lifters. If taking off the heads I would want to have them rebuilt. If going that far I would want to delete the AFM with a new cam. That's going to be around $2,000 or more (a lot more if I see anything wrong in a cylinder). I'd rather try the ECM, valley cover, and springs for about $400 even if just to rule them out for sure. Which I won't feel bad about spending if I end up doing major engine work anyway. And will be really glad I did if it does fix the problem.

 

with no electrical dtc that lead to ecm...its doubtful. make sure to do a crankshaft variation relearn after pcm replacement or false misfire dtc will set at high rpm.

 

For the last several years I've rebuilt one engine a year. Looks like this won't be any different, but I can hope. I know the chance is small that the ECM is at fault. But I have ruled out everything else besides ECM and hard parts. The valley cover will prevent the ecm from actuating the dod. Valve springs will rule out the replaceable parts I can get to without removing the head. I've seen some very peculiar ECM failures in the past, and despite it not being likely to be the problem. There is still a chance. And in the end I'll have a new ECM to go with my rebuilt engine. Only thing I am not sure of that worries me, is if the afm lifters will still function properly with a non afm valley cover. I could be making things worse, but can't find specific information about that. I'll find out in a few days.

Recent Rebuilds;
2017 Johnson 140hp Outboard
2018 Kawasaki 18hp Lawn Tractor Eng
2019-2020 2008 Acadia 3.6L
2021 1997 Cat 3126 7.2L
2022 2005 Duramax 6.6L
2023 Cat 3044 (Head replacement only)