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Discussion Starter #21 (Edited)
With the ticking, take off the rocker covers and see if any rockers have extra clearance with the valve stem. If a cam lobe is going down, that rocker will be very loose
If GT Drew's suggestion doesn't yield the answer, you could even have someone crank the car and watch the rockers with the covers off to see if #6's valves are moving as much as the rest. To cause a misfire at least one of them would probably not have to move much at all. I'd try to find a way to stop the car from starting (pull fuel injector fuse?) but I've never had to do this on my car.... You would not want to crank the car excessively with fuel going it as it will wash the oil off the cylinder walls and start causing wear.... Actual starting could also make a mess with oil. Hell, even cranking could, I'm not sure. I used to do this with my gen1 SBCs years ago.

Is #6 a DOD cylinder? I have no idea how these can fail, but my understanding is that they have special lifters that use oil pressure solenoids to control whether or not they open the valve. Not sure if they can fail such that DOD is permanently on for a valve (and thus not opening). But it sure sounds like you have a mechanical issue. I doubt it's the crank or cam sensors for if they failed it seems unlikely that you would consistently get a misfire code on just one cylinder. Also, I believe if the car has both crank and cam sensors, it may be able to detect a failure in one from the other and set a specific code for it (was that way on my Nissan Maxima). If the fuel injector was the problem you could swap it with another cylinder.
What you guys are talking about doing is a bit outside the scope of my experience and capacity. Not sure I'm comfortable with the idea of taking my engine apart to this degree in the parking lot of my three-bedroom townhouse. That's not to say desperation won't get the better of me and force me to reconsider.

I really do appreciate your suggestions and guidance. One thing you haven't told me is how a possible mechanical issue can manifest as an electrical malfunction in the form of an intermittent disruption of current going to a spark plug. In my experience, moving mechanical assemblies and parts don't effect electrical systems. It's usually the other way around.

If you could please help me understand that, it would go a long way towards helping me diagnose this problem.
 

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Sorry when I read the thread I didn't pay much attention to the results of the actual spark tester because swapping the coil is so much more reliable a test. I have never used one, on occasion I have held a plug to ground and looked at the spark there. *Usually* for me it's been an all-or-nothing experience. How confident are you in this spark tester? Did you get a good ground?

Correct, all the mechanical things I said would not cause a weak or intermittent spark. However, I just can't see how a crank sensor failing would target one cylinder consistently. At this point I can only advise to search for a smart mechanic with a nice scan tool who can maybe plot crank pulses or some such.

If you are not confident in the spark testing and wish to pull a rocker cover it's really not much more difficult than what you've been doing.
 

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Discussion Starter #23
Sorry when I read the thread I didn't pay much attention to the results of the actual spark tester because swapping the coil is so much more reliable a test. I have never used one, on occasion I have held a plug to ground and looked at the spark there. *Usually* for me it's been an all-or-nothing experience. How confident are you in this spark tester? Did you get a good ground?

Correct, all the mechanical things I said would not cause a weak or intermittent spark. However, I just can't see how a crank sensor failing would target one cylinder consistently. At this point I can only advise to search for a smart mechanic with a nice scan tool who can maybe plot crank pulses or some such.

If you are not confident in the spark testing and wish to pull a rocker cover it's really not much more difficult than what you've been doing.
Yeah, my friend said the same thing about taking the covers off. Apparently it's pretty simple and low risk. I've done a few extensive car repairs before but nothing inside the engine. I generally don't mess with anything sealed so when I hear talk about taking covers off, I start thinking about what shop I'm going to take it to.

The in-line spark indicator tool goes between the plug and plug wire. It has a light bulb that illuminates when an electrical pulse is discharged from the coil. It's a very simple device. I got a 2-pk when I decided to buy one. I tried both tools on #5, #3 and #6. Results were consistent. #3 and #6 were strong and steady. #5 had intermittent flickers and skips.

The sensor idea is just a thought. Based on what's been said here and what I've been told by friends about how those sensors work, I agree that it doesn't sound likely that either could cause such a specific error.

I guess part of my thinking was more like what if one of the sensors hasn't flat-out failed but has a defect that is effecting it's accuracy. Perhaps then the ECM wouldn't see a sensor failure, but the sensor could be just faulty enough to put the ignition timing out of sync. Again, just a theory.
 

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Discussion Starter #24
Crap!!! I just discovered that one of the two inline spark indicator tools appears to be defective.

When I used them both simultaneously on 5 and 3 before, I swapped them for posterity and only saw the intermittent spark on 5. I tried it on 5 and 3 again tonight with the intent of capturing it on video. This time I saw it on 3. I swapped the tools and the intermittent spark followed the tool from 3 to 5. So, the tool is crap and 5 is no longer a suspect.

I also tried a new test suggested be yet another GM technical guru. With the accessory power on and engine off, I checked for voltage at each of the 4-pin coil connectors. With the connector clip on top, I got 12.16v on the first pin on the left and less than .02v on the other three. It was the same on all eight connectors so it's starting to look less and less like an electrical issue.

I still have to try swapping fuel injectors and then it's onto valve covers.
 

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Discussion Starter #25
Ok, I did the injector swap, switching 2 and 6. Cleared the DTC, let it sit for a minute and then started it up. No changes and P0306 came back within 30 seconds.

I also checked the voltage going to the injectors on the passenger side. All showing 12v.

Valve cover is next.
 

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Discussion Starter #26 (Edited)
One of my friends helping with this was pretty confident that I have a vacuum leak after listening to the engine via that video I posted. He suggested a couple ways of testing for one. So, I decided to give it go before I start tearing into the engine to get at that valve cover.

I cautiously tried the spray method using intake cleaner as well as two unlit gas torch attempts. I got a slight reaction where the idle dropped while I was using the spray but it was so delayed that I really can't say it wasn't a consistence. It only did it two or three times but it was in the same general area, above the belt tensioner and between the throttle body and coil 2. The unlit torch attempts did nothing at all.

So, I figured with all that I've tried and posted about it in this thread, I should post a summary to bring it all together. This is all of the T/S that I've done so far.

* Swapped coils between 4 and 6
* Swapped coils between 3 and 5
* New B2/S2 oxygen sensor
* All new spark plugs
* All new plug wires
* Verified coil discharge with inline tools on #'s 1, 3, 4, 5 and 6
* Checked cylinder compression on: #6 = 130 psi, #5 = 125 psi, #3 = 130 psi, #1 = 110 psi
* Checked resistance on injector 6 = 12.7 ohms
* Checked resistance on injector 5 = 12.8 ohms
* Checked accessory power voltage on all 4-pin coil connectors = 12.16v
* Checked accessory power voltage on p-side injector connectors = 12.4v
* Swapped fuel injectors 6 and 2
* Cleaned all injector and coil connectors with contact cleaner
* Vacuum leak test with unlit MAPP gas torch (no effect)
* Vacuum leak test with intake/throttle cleaner (inconclusive)
* Swapped coils between 6 and 1
* Vacuum leak test with unlit propane torch (extensively, no effect)
 

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Discussion Starter #27 (Edited)
It's not a lifter

I always thought that any valve (intake or exhaust) that has lost its ability to fully open an close as designed, would equal a loss of power from that cylinder (loss of fuel/air mixture in or preventing all of the exploded gas from exiting the cylinder). That in turn (with these electronically controlled engines) would be sensed as a loss of cranking speed. Which I'm thinking would be picked up as a misfire condition (if this makes sense).
Perchance the new genuine AcDelco spark plugs once installed will have an impact on the mystery misfire. If no change, then the search continues. Have you recently scanned the obdII port for codes? Reason being, it doesn't seem likely replacing the crankshaft and/or camshaft sensor will remedy the problem. However, stranger things have happened.
With the ticking, take off the rocker covers and see if any rockers have extra clearance with the valve stem. If a cam lobe is going down, that rocker will be very loose
If GT Drew's suggestion doesn't yield the answer, you could even have someone crank the car and watch the rockers with the covers off to see if #6's valves are moving as much as the rest.
Well, it doesn't look like it's a lifter. This is my car 20 minutes ago.

I checked for play on the #6 rockers and they were solid like the rest.

 

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Personally being that far in and what you’ve already done, I’d pull the pushrods on that side for ****s and giggles. Just cranking over may not show a slightly bent pushrod to the naked eye but running it could show it’s head. I’d pull each one out and inspect since it’s easy to do at the stage your at. I wish I was closer so I could lend you a hand, I love finding little mystery’s like these.
 

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"RuLEoF2" The computer is showing me that you can send out private messages, but that you are setup to *not* receive private messages. So unable to assist with thoughts at this time. So you either have to make a status change, or I can talk to you on the phone, if you want to try that.
 

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Discussion Starter #30
Personally being that far in and what you’ve already done, I’d pull the pushrods on that side for ****s and giggles. Just cranking over may not show a slightly bent pushrod to the naked eye but running it could show it’s head. I’d pull each one out and inspect since it’s easy to do at the stage your at. I wish I was closer so I could lend you a hand, I love finding little mystery’s like these.
Yeah man. This is by far the most ridiculously elusive problem I've ever seen. All the people that are helping me with this are completely stumped.

The push rods might be doable for me. The valve cover was a lot easier than I thought it would be. I guess I need to have a little more faith in my own skills. I just get really apprehensive about the idea of digging too deep into an engine out of fear that I'll break something or get in over my head.

If you wouldn't mind throwing together a short instruction or link to one I would greatly appreciate it. Thank you.

"RuLEoF2" The computer is showing me that you can send out private messages, but that you are setup to *not* receive private messages. So unable to assist with thoughts at this time. So you either have to make a status change, or I can talk to you on the phone, if you want to try that.
I believe I fixed the setting. Yes, please PM me with your number. I'd love to talk. THANKS!
 

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It’s actually REALLY SIMPLE on LS engines. Here’s a link to some rocker arm installation instructions that spell it out fairly simple for ya.

https://www.jegs.com/installationinstructions/500/555/555-20950to20953.pdf

When you remove the rocker arms, pull each pushrod out but keep them organized by which hole they came from and which side was up/down for when you reinstall. Lay them on a flat surface so you can look visually at them from the side for any bends etc and roll them around slightly looking for any wobble etc. then on installation just put them back where you removed them making sure they seat in the lifter. And just follow this instructions. I’ve never stripped a thread installing them all at the same time going slowly with install but with your luck I’d follow the instructions lol
 

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Discussion Starter #32
Bent push rod!!!

It’s actually REALLY SIMPLE on LS engines. Here’s a link to some rocker arm installation instructions that spell it out fairly simple for ya.

https://www.jegs.com/installationinstructions/500/555/555-20950to20953.pdf

When you remove the rocker arms, pull each pushrod out but keep them organized by which hole they came from and which side was up/down for when you reinstall. Lay them on a flat surface so you can look visually at them from the side for any bends etc and roll them around slightly looking for any wobble etc. then on installation just put them back where you removed them making sure they seat in the lifter. And just follow this instructions. I’ve never stripped a thread installing them all at the same time going slowly with install but with your luck I’d follow the instructions lol

BENT PUSH ROD!!!

I tried it on the kitchen counter and the glass-top stove. The back one has a very obvious curve. I could actually see it as soon as I pulled it out and looked down the length of it. The front one has very minor curve that you con only see when you roll it on the glass. Didn't see it at all on the counter.

 

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Discussion Starter #33
Hopefully, RamAirZ wins the title and the push rod is the ultimate cause, but there is one other thing that came up in a conversation with one of the guys. This could be a topic for a whole other thread but since it came up during this issue, it's kinda relevant.

There are a couple strange anomalies that I saw repeatedly with how my OBD2 reader was handling the P0306 DTC. One, was that the CEL never went out after I cleared the code. The reader would re-sync and report that there were no DTCs but the CEL stayed on. The other quirk was that when the P0306 DTC came back, usually within 30 seconds, if I didn't clear it and came back later or even the next day, the reader would show that there were two DTCs but they were both P0306. The description and everything was identical.

Now, this reader is a 12-year-old Innova 3100a. I contacted them about a firmware update and even their technical support agent called it "old". So, maybe this isn't a big deal and maybe it's just due to the age of the reader, but I was wondering if these glitches are an indicator that there's something hokey going on with the ECM.

Any thoughts?
 

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Discussion Starter #34
It’s actually REALLY SIMPLE on LS engines. Here’s a link to some rocker arm installation instructions that spell it out fairly simple for ya.

https://www.jegs.com/installationinstructions/500/555/555-20950to20953.pdf

When you remove the rocker arms, pull each pushrod out but keep them organized by which hole they came from and which side was up/down for when you reinstall. Lay them on a flat surface so you can look visually at them from the side for any bends etc and roll them around slightly looking for any wobble etc. then on installation just put them back where you removed them making sure they seat in the lifter. And just follow this instructions. I’ve never stripped a thread installing them all at the same time going slowly with install but with your luck I’d follow the instructions lol
BENT PUSH ROD!!!

I tried it on the kitchen counter and the glass-top stove. The back one has a very obvious curve. I could actually see it as soon as I pulled it out and looked down the length of it. The front one has very minor curve that you con only see when you roll it on the glass. Didn't see it at all on the counter.
Well, it's no good. Replacing the push rod didn't get it. Actually, I replaced both on cylinder #6 but the misfire's continue.

The CEL is intermittent now. It has gone out a couple times on it's own. Only when I rev it up does it come back on and immediately starts flashing. The idle did change slightly. Maybe a little lower pitched but not any smoother. I took it for a drive around the neighborhood just to see if it needed to self-adjust a bit. No improvement. After I parked it, I heard a faint rattle that I hadn't noticed before. Sounds almost like something loose inside the exhaust.

That's the first time I've driven it in weeks. Something I noticed right away that I remembered seeing before was that the ESP was disabling itself. I remember now that it did that when this all started. It's been parked for so long that I forgot about it.

This is nuts! I think this car is possessed. How the hell are these two things related???
 

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I read that about a year ago, you decided to replace the spark plugs (I guess due to the total mileage attained at that time). From you posts prior to that event, I guess the car ran correclty, as well as continued running correctly (as in no misfire events or MIL light displayed). About a year later, you started sensing a change in the way things were running. I don't know if the *misfire condition* had started during that 1 year period), but after discussions you replaced the plugs again (using the more correct ACDelco type (vs what appears to have been a knockoff version of same). From that point on (for sure) the misfire condition became very evident. If all of this is fairly correct, it reads as thou the primary cause would have to be the ignition circuit.
Maybe the ESP condition is a side bar affect of the ECM telling you that it *can not* perform the engine power reduction function correctly (until the engine misfire condition is corrected).
 

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Discussion Starter #36
I read that about a year ago, you decided to replace the spark plugs (I guess due to the total mileage attained at that time). From you posts prior to that event, I guess the car ran correclty, as well as continued running correctly (as in no misfire events or MIL light displayed). About a year later, you started sensing a change in the way things were running. I don't know if the *misfire condition* had started during that 1 year period), but after discussions you replaced the plugs again (using the more correct ACDelco type (vs what appears to have been a knockoff version of same). From that point on (for sure) the misfire condition became very evident. If all of this is fairly correct, it reads as thou the primary cause would have to be the ignition circuit.
Maybe the ESP condition is a side bar affect of the ECM telling you that it *can not* perform the engine power reduction function correctly (until the engine misfire condition is corrected).
You're mostly correct. The discovery of the bad plugs was prompted by the misfire condition. It was one of the first things that I checked when I was able to get it home.

I've read in a few places where G8 owners talk about their cars going into "limp mode". I believe one person said that they were dealing with a misfire issue too. They describe it as loss of power, restricted speed and RPM, rough running and disabled ESP. Other than the misfire, it's the same symptoms. I was wondering if mine could be in "limp mode" and that is causing the misfire or vise versa.

Is there a way to check to see if my car is in "limp mode" and is there a way to turn it off?
 

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I doubt there is any way to disable the *limp home mode*. That (to me) is a dedicated engine saving function incorporated into the ECM. I think *engine power reduction* is a function that will reduce engine power. If the yaw rate gyro, lateral accelerometer, an steering wheel angle sensor detect an out of control car, individual brakes will be applied, along with temporarily taking away engine power (if the driver still has his foot in the pedal to metal mode so to speak) to quickly correct the cars out of control condition.

Each coil receives a voltage from an I/C source within the ECM (how much, I don't know) to build up primary winding energy. At the correct time, the ECM shuts off that I/C power to that winding an that primary winding energy collapses, inducing that stored power/energy into the secondary winding. That's the energy that gets thru the spark plug wire an plug to ignite the fuel charge. At ignition turn on each coil has 12 volts applied to pin D. Each coil has a constant ground at pin A. Each coil sees the primary winding voltage at pin C (until it is told to stop for ignition firing). All the coils have a constant return ground on pin B which is found within the ECM. Could it be that #6 coil I/C wire from the ECM an arriving at pin C is damaged to the point that it is unable to supply all the voltage/energy necessary for it to function correctly. Not bad enough to set a fault code for the coil itself, but interpreted as a misfire condition. Or some added resistance on the ground return wire at pin B joining up with the other coils going back to the ECM (that might prevent a good primary coil charge from happening).
 

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Discussion Starter #38
Latest tests...

I did another compression test on #6. This time, I removed all of the plugs and the throttle body. I performed the test three times. Got a solid 150 psi each time.

Just for kicks, I also checked the alternator output. Got 14.6v on idle.
 

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Have you tried having the battery load tested? It's a long shot, but I was having weird misfire issues with mine a while back and it seems to have been a bad battery. It was showing mostly random multiple misfires and triggering crank position sensor codes (or not) and then eventually failed to start after an auto-X. Engineering mode would show 100% charge after a day on a trickle charger and alternator voltage was fine but it would only put out ~300 CCA's on a load tester (~1/3 it's rating). I've put quite a few miles on it in the past few weeks after replacing the battery and it's run flawlessly. My shop did the load test for free but it's usually only $15 or so - may be worth a shot?

https://www.g8board.com/forums/5-v8-engine-tech-l76-ls3/283875-rough-idle-have-searched.html

https://www.g8board.com/forums/5-v8-engine-tech-l76-ls3/284269-battery-dead-after-hard-auto-x-runs.html
 

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Discussion Starter #40
Have you tried having the battery load tested? It's a long shot, but I was having weird misfire issues with mine a while back and it seems to have been a bad battery. It was showing mostly random multiple misfires and triggering crank position sensor codes (or not) and then eventually failed to start after an auto-X. Engineering mode would show 100% charge after a day on a trickle charger and alternator voltage was fine but it would only put out ~300 CCA's on a load tester (~1/3 it's rating). I've put quite a few miles on it in the past few weeks after replacing the battery and it's run flawlessly. My shop did the load test for free but it's usually only $15 or so - may be worth a shot?

https://www.g8board.com/forums/5-v8-engine-tech-l76-ls3/283875-rough-idle-have-searched.html

https://www.g8board.com/forums/5-v8-engine-tech-l76-ls3/284269-battery-dead-after-hard-auto-x-runs.html
True. It's a long shot but it can't hurt.

Thanks.
 
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