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Discussion Starter #1
I installed CMS Stage 1s in my car and after that I started getting a p0300 - random misfire and p0316 - misfire during first 1000 revolutions code. Car runs really well and doesn’t show any obvious signs of misfiring. The cams were degreed by CMS and I have a tune from tricktuners accounting for the cams.

Anyone have an issue like this?
 

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Have you tried removing/reinstalling the plugs after checking gaps and cleaning threads/etc? I've had problems in the past with a slight misfire/code and that always fixed it. How old are the plugs/coils?
 
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Discussion Starter #4
Have you tried removing/reinstalling the plugs after checking gaps and cleaning threads/etc? I've had problems in the past with a slight misfire/code and that always fixed it. How old are the plugs/coils?
Plugs have about 18k miles on them. I’m going to check them next chance I get. I did some digging through some emails and found that while I was datalogging my bank 2 was 10-20% lean compared to bank 1. The gap narrowed closer to full throttle. Might be related to a vacuum leak, going to check that too.
 

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I had misfires after my cams were installed turn out I had some cop boots that were needing to be replaced
 
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I had misfires after my cams were installed turn out I had some cop boots that were needing to be replaced
Could definitely be the case too, I think it was a dried and torn boot at the root of my problems. Haven't had them since new cops/boots.
 

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Wanted to bump this thread to see if anyone may have any other ideas. Still having the same codes popping up, p0300 and p0316 after cam install. Since last posting I have replaced the spark plugs, installed some new cop boots, ran a compression test (150-160psi across the board), replaced crankshaft bolt holding on the balancer, replaced crankshaft position sensor. This weekend Snorky helped me retime the motor, just to be safe. Bank 2 is still lean compared to bank 1. Not really sure where to go on this.
 

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Discussion Starter #9
Out of those data points I’ve looked at the STFTs. At idle, bank one fluctuates between about 0.85-0.95 and bank two is about 0.75-0.85. Averaged out its close to a 10% difference. Both banks become more similar when I rev the engine and hold it. I’ve also monitored misfires and all eight cylinders are missing.

Are you thinking that a more in-depth tune may be a solution or is there still an underlying problem. I did do a smoke test but the engine was warm, I’m thinking I should try again when its cold.
 

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King Trashmouth
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Thinking out loud, and from what I had seen, is if the injector timing isn't dialed in perfectly it's going to want more fuel than it really needs, as some is going to go out the exhaust due to overlap. It might require a tweak in that direction, depending on what it's set at now. The variation bank to bank definitely indicates there's some difference there, though how I couldn't say. If the exhaust wasn't touched that might rule out sensors or exhaust leaks. It would point more toward something that would affect one bank but not the other, like an intake manifold gasket, or cam timing.

...but even then when my injector timing was way off I didn't pop any misfire codes. So while it may be something to address it may not be the root cause. Have you looked at/inspected your crank trigger wheel? The engine is going to base misfire based on engine speed signal, which boils down to the trigger wheel and sensor. If it's a little loose it could rattle around and give a false random misfire as the wheel bounces around.
 

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Discussion Starter #13
Thinking out loud, and from what I had seen, is if the injector timing isn't dialed in perfectly it's going to want more fuel than it really needs, as some is going to go out the exhaust due to overlap. It might require a tweak in that direction, depending on what it's set at now. The variation bank to bank definitely indicates there's some difference there, though how I couldn't say. If the exhaust wasn't touched that might rule out sensors or exhaust leaks. It would point more toward something that would affect one bank but not the other, like an intake manifold gasket, or cam timing.

...but even then when my injector timing was way off I didn't pop any misfire codes. So while it may be something to address it may not be the root cause. Have you looked at/inspected your crank trigger wheel? The engine is going to base misfire based on engine speed signal, which boils down to the trigger wheel and sensor. If it's a little loose it could rattle around and give a false random misfire as the wheel bounces around.
You might be onto something with the injector timing. Once warmed up the car will start after turning it off but chokes a bit before catching itself, and sometimes it will die. I think some changes in the timing down low as well as in some other areas may help.

My cams were degreed by Jim at CMS. I'm just remembering that I never installed the TFS crank gears that came with the degree service. At the time I thought they were no different to the stock gear, but its been four years since the cams were put in and my memory is a little hazy. However, I did just find a pic of the gears that I took for the for sale ad I made back then.



Unless I am a dumb dumb both of these gears are reading zero degrees advance/retard and if I were to have installed them it wouldn't have been any different than my stock gears. As long as that logic proves correct, that along with retiming the engine this weekend makes me want to rule out a timing issue. I looked at the trigger wheel this weekend and nothing really looked out of the ordinary.
 

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Wickedsnake, When i looked at the trigger wheel nothing noteable stood out to me.
 

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King Trashmouth
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Is signal trace something I can datalog? What would the healthy parameters be for that?
Not really, you'd need an oscilloscope, especially if this misfire is either false or imperceptible to the driver.

When the engine spins it creates a waveform. It should be a series of regular pulses, followed by a gap where there's no teeth on the tone wheel. The engine identifies a misfire by seeing one (or more) of those pulses that are out of phase with the others as the engine briefly slows down on that misfiring cylinder.

You could check out the RPM signal in the datalog and try it with as few other parameters as possible to get the highest sampling rate you can, but a lot of PIDs are heavily filtered and actually have some delay. You would only see it here if it was really, really bad. After all 1000 RPM is 16.67 rev/s, it fires 4 times per rev (8cyl, 4 stroke so 2rev/fire/cylinder), so you would have 66.67 fire/s, and would have to sample at 67Hz or faster. I don't think I've had a log that was better than 10Hz.
 

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Discussion Starter #20
Really great information Wicked, thank you. Do you have any suggestions for data sets that may shed some light? I know the STFTs are good, but I’m not all too familiar with looking at other data. I’ll select the PIDs that refresh at a faster pace.

I’ll fool around with swapping injectors and maybe O2 sensors bank to bank to see if I can influence any changes, although I think the upstream sensors are almost new.
 
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