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Discussion Starter #1
So, I'm persistently getting misfires on cylinder 6 which is #5 being 6th in the firing order. I've already ruled out the plug, plug wire and coil by way of swapping the coil and replacing all of the plugs and wires with brand new. I checked compression and compared with neighboring cylinders. 110 PSI on #1, 135 on #3 and 125 on #5. I've never done a compression check before so I asked an experienced DIY mechanic buddy and he said that those were good numbers. Finally, I bought a 2-pack of those plug testers and put one on #5 and #1.

#1 has a strong and consistent pulse. #5 not so much. That one will occasionally only flicker or skip altogether. These occurrences seem completely random and sometimes come in tightly grouped waves of random combinations lasting about 5 seconds. Time between individual occurrences or waves is anywhere from 15 seconds to over a minute.

I suppose the next target is the coil connector and it's wires. My DIY buddy has been doing research for me and found stuff about bad crank shaft sensors potentially being the cause. I'm running out of ideas so any thoughts or suggestions would be greatly appreciated.

Thanks for reading.
 

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Ok so it says cylinder 6 misfire but you’re checking cylinder 5 because of the firing order? It sounds to me like you’re on the wrong cylinder if that’s what you’re doing. If the ECM says cylinder 6 then that’s the cylinder you need to be checking and doing your coil swap etc on.
 

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Discussion Starter #3

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Your confusing me for sure ! That second article you posted, looks/reads in error to me also. Assuming that the fault code you are getting is P0306 you best be T/S that 3rd cylinder back on the passenger side (rather than the 3rd cylinder back on the drivers side). If *that's* what you have been doing.
 

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Your confusing me for sure ! That second article you posted, looks/reads in error to me also. Assuming that the fault code you are getting is P0306 you best be T/S that 3rd cylinder back on the passenger side (rather than the 3rd cylinder back on the drivers side). If *that's* what you have been doing.
Yes, I agree that this is all very confusing, which is why I'm reaching out to the G8 community.

My code is P0306. I started this saga focusing on cylinder 6 (third from the front on the right) since that is what the code indicates. Then a friend found that article I posted which states P0306 refers to firing order and not cylinder location. Based on that info, and the fact that I couldn't find anything wrong with 6, I switched to cylinder 5 (third from the front on the left) because G8Board member HSV-GTS-300 posted that cylinder 5 was sixth in the firing order. Since then, I have found a condition on 5 that would cause misfires.

Though I haven't used that spark plug tool on cylinder 6, I did use it on 5 and it definitely has the issue that I described in my earlier post. So, unless I'm having misfires on both 5 and 6, and the computer is missing one, what the article is saying seems to support my findings so far. But, I know from reading your posts in the past that you're a very knowledgeable mechanic and if you say the article is wrong, I believe you and would greatly appreciate your explanation.
 

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Learning this cars systems has been through reading an re-reading thru the huge factory service manual that I bought for this car, as well as the knowledge I learned through the many years as an Airline mechanic. The hall effect crankshaft sensor sends a pulse back to the ECM each time a segment from the encoder ring passes by it. I want to say that it has 58 segments including a blank space for 2 segments for timing (or something like that). If for any reason the time lag from one pulse to the next pulse varies (slows down) from an expected time period, the ECM treats this as a misfire condition (if it happens often enough). Based on the dedicated blank space on the encoder ring, the ECM can tell which cylinder firing caused the crankshaft slowdown problem, an would fault that particular cylinder. But for sure, a failing fuel injector that cannot spray enough fuel when it is its turn to do so. will be treated as a misfire condition. If you feel that the ignition circuit is OK, it wouldn't hurt to check the resistance of the fuel injector on the suspected cylinder. It pretty much *has* to read 12.5 ohms plus or minus 2. Anything above or below that range is, indicates a failing injector (at least in my opinion).

I had a P0301 misfire fault, an it turned out to be a failed fuel injector If what I posted is confusing, I'll try again after (yep) another reading of the service manual.


It doesn't sound like a faulty crankshaft sensor. But being electrical, weird stuff happens.
 

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Discussion Starter #7
Learning this cars systems has been through reading an re-reading thru the huge factory service manual that I bought for this car, as well as the knowledge I learned through the many years as an Airline mechanic.....

I had a P0301 misfire fault, an it turned out to be a failed fuel injector If what I posted is confusing, I'll try again after (yep) another reading of the service manual.

It doesn't sound like a faulty crankshaft sensor. But being electrical, weird stuff happens.

This is what I love about your posts. You don't just spew out a bunch of technical jargon and specs without actually explaining it. You take the time to educate and enlighten. As a novice DIY, I really appreciate that.

I've been a sort of "mechanic" in the aircraft field myself for nearly 20 years. Not with engines but from the avionics and cabin equipment side. As for cars, I've been doing basic maintenance like oil, brakes and belts etc for even longer. Only in the last 10 years or so have I been getting more adventurous. Mainly for the sake of saving money and due to a few experiences with some very shady shop mechanics. Now, everything is a learning experience. I don't know much but I know enough to recognize when a job is beyond my capacity.

As for this issue, I think I understand your explanation pretty well. Same friend that found that article also found information that suggested a faulty crankshaft sensor could cause this problem. If by "circuit" you mean the electrical pathway to the plug, then no, cylinder 5 is not ok. Using the in-line spark plug tool, I can see that there is a definite intermittent disruption of electrical power getting to the plug.

What I've done so far is replace all of the plugs and wires with new. I've swapped coils on both 5 and 6 with other cylinders. No change. Even though it only popped up once, I've replaced the B2/S2 oxygen sensor because I got code P0157 when this whole thing started. I used a mechanic's stethoscope to listen to the fuel injectors and they all sounded the same to me.

I have not checked compression or electrical power going on cylinder 6 yet. I can and will try to do that next. I only say "try" because as we all know, the passenger side of the engine is a real pain in the ass and I can't promise that I'll be able to get the compression tool in there. I will also do the resistance check on the fuel injectors on 5 and 6.

For cylinder 5, I'm eventually going to have to start looking for the cause of that intermittent disruption. Can you recommend the best method for doing that? Obviously I'll start by examining the harness connector and wires for the coil. Is it safe to put a multimeter on those contacts and if so, what kind of readings should I be getting?

Thanks again for your help.
 

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Learning this cars systems has been through reading an re-reading thru the huge factory service manual that I bought for this car, as well as the knowledge I learned through the many years as an Airline mechanic.....

I had a P0301 misfire fault, an it turned out to be a failed fuel injector If what I posted is confusing, I'll try again after (yep) another reading of the service manual.

It doesn't sound like a faulty crankshaft sensor. But being electrical, weird stuff happens.

This is what I love about your posts. You don't just spew out a bunch of technical jargon and specs without actually explaining it. You take the time to educate and enlighten. As a novice DIY, I really appreciate that.

I've been a sort of "mechanic" in the aircraft field myself for nearly 20 years. Not with engines but from the avionics and cabin equipment side. As for cars, I've been doing basic maintenance like oil, brakes and belts etc for even longer. Only in the last 10 years or so have I been getting more adventurous. Mainly for the sake of saving money and due to a few experiences with some very shady shop mechanics. Now, everything is a learning experience. I don't know much but I know enough to recognize when a job is beyond my capacity.

As for this issue, I think I understand your explanation pretty well. Same friend that found that article also found information that suggested a faulty crankshaft sensor could cause this problem. If by "circuit" you mean the electrical pathway to the plug, then no, cylinder 5 is not ok. Using the in-line spark plug tool, I can see that there is a definite intermittent disruption of electrical power getting to the plug.

What I've done so far is replace all of the plugs and wires with new. I've swapped coils on both 5 and 6 with other cylinders. No change. Even though it only popped up once, I've replaced the B2/S2 oxygen sensor because I got code P0157 when this whole thing started. I used a mechanic's stethoscope to listen to the fuel injectors and they all sounded the same to me.

I have not checked compression or electrical power going on cylinder 6 yet. I can and will try to do that next. I only say "try" because as we all know, the passenger side of the engine is a real pain in the ass and I can't promise that I'll be able to get the compression tool in there. I will also do the resistance check on the fuel injectors on 5 and 6.

For cylinder 5, I'm eventually going to have to start looking for the cause of that intermittent disruption. Can you recommend the best method for doing that? Obviously I'll start by examining the harness connector and wires for the coil. Is it safe to put a multimeter on those contacts and if so, what kind of readings should I be getting?

Thanks again for your help.
As GOPHERIT already stated, a failing injector or even low compression on a particular cylinder can register a misfire. The computer isn’t sophisticated enough to completely diagnose the problem on that cylinder unless it’s a complete electrical failure on that circuit ( injector circuit or coil circuit fault codes would usually present with the misfire). I would definitely check cylinder 6 for injector pulse as well as compression if nothing is found on the electrical side. You could also swap injectors around if they check out electrically and see if it moves cylinders.
 

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Discussion Starter #9
Okay, what's the trick? I can't get the connector off the fuel injectors. I've been able to lift the locking mechanism by squeezing on the sides but once I get that far, it won't move.
 

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... If you feel that the ignition circuit is OK, it wouldn't hurt to check the resistance of the fuel injector on the suspected cylinder. It pretty much *has* to read 12.5 ohms plus or minus 2. Anything above or below that range is, indicates a failing injector (at least in my opinion).
I would definitely check cylinder 6 for injector pulse as well as compression

Ok. I got the fuel injector connectors off. Cylinder 5 rang out at 12.8 ohms and cylinder 6 at 12.7 ohms.

I also did the compression and inline spark plug tests on cylinder 6. I got 130 PSI and the spark looked strong and consistent.
 

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Discussion Starter #11
I was reading a thread here where the guy had similar symptoms and it turned out to be a bad lifter.

Could this be a bad lifter? The ticking noise just started when this misfire issue began.

https://youtu.be/mJPBTEf1aLM
 

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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).
 

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Discussion Starter #13
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).
Yeah, I can see your point.

What do you think about the ticking sound? A colleague told me that sounds like that would be expected if the engine is running short a cylinder. Could a mechanical issue like a bad lifter affect ignition spark like what I'm seeing on cylinder 5?

I haven't swapped any of the fuel injectors yet but they did test okay electrically. I suppose one could be clogged but I doubt it. I always use Shell gasoline and last year I did a seafoam treatment followed up later with a bottle of Techron.

But, I'll give the swap a try. After that, I've been looking into replacing the camshaft and crankshaft sensors. Do you know if the system has to be recalibrated or relearned either of those are replaced?
 

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As per the re-programming list which states *which* items need that function performed, the cam an crank sensors are *not* included. Those particular 2 items are just plug an play type devices.

*To me*, spark cycling as well as strength of the spark for any cylinder, should be just as intense an constant as all the other cylinders. So if the compression is OK, any cylinder not producing its fair share of power, sounds like a problem of it not getting its fair share of fuel/air to produce a matching power explosion on the compression stroke to match what the other cylinders can produce. If the spark is less than ideal on one cylinder (as compared to any other), I personally think that circuit need further T/S to figure out what the heck is going on there. Which of course is not the easiest thing to do, being that its happening in that always mystifying electrical world.
 

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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.
 

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Discussion Starter #16
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.
Yeah, all new plugs and wires. It was in the process of troubleshooting this issue that I discovered that the plugs I installed last year appear to have been fakes. That's a whole other thread.

https://www.g8board.com/forums/19-g8-gt-talk-v8/284139-bad-plugs-new-post.html


I started that thread because I was focused solely on the plugs and assumed that changing them would solve the misfire issue. When it didn't, I started this thread because at that point, the plugs didn't appear to be the cause.

P0306 has been the only persistent code. I did get a P0157 low volt O2 sensor code on the first day but it never came back after I cleared it. I replaced that O2 sensor because it was suggested that it could cause the engine to run rich, wet fouling the plugs therefore resulting in the misfire.

Every time I've disconnected and/or cleaned connectors, removed plugs or whatever, I've been plugging in the OBD2, clearing the code, power off and let it sit for a few minutes. The code always clears but the engine light never goes out. I restart and no improvement.
 

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....#1 has a strong and consistent pulse. #5 not so much. That one will occasionally only flicker or skip altogether. These occurrences seem completely random and sometimes come in tightly grouped waves of random combinations lasting about 5 seconds. Time between individual occurrences or waves is anywhere from 15 seconds to over a minute.

I suppose the next target is the coil connector and it's wires. My DIY buddy has been doing research for me and found stuff about bad crank shaft sensors potentially being the cause. I'm running out of ideas so any thoughts or suggestions would be greatly appreciated...
Could be the best insight into the problem since the spark plug needs a good signal from the ignition coil. Could always purchase an ignition coil connector, splice it in and see if the problem goes away. Lowest price for an aftermarket is about $15 from the auto place that rocks. Recommend checking the wires and wiring harness on that particular cylinder.

I was reading a thread here where the guy had similar symptoms and it turned out to be a bad lifter...
Presume this is the thread referenced above... https://www.g8board.com/forums/5-v8-engine-tech-l76-ls3/245794-chasing-misfire.html.
 

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Discussion Starter #18
Could be the best insight into the problem since the spark plug needs a good signal from the ignition coil. Could always purchase an ignition coil connector, splice it in and see if the problem goes away. Lowest price for an aftermarket is about $15 from the auto place that rocks. Recommend checking the wires and wiring harness on that particular cylinder.
Yeah, that's the one. Really scares the hell out of me because my symptoms are nearly identical and I've already done all the same T/S. This is everything I've done on cylinder 6.

1. Replaced the plug
2. Replaced the wire
3. Swapped coil with #4
4. Checked compression (normal)
5. Checked injector resistance (normal)
6. Verified spark with in-line tool (normal)

I've done this on #5 also. That one is the only one where I've seen a problem which is the intermittent spark. I haven't removed and inspected any of the fuel injectors yet but I'll get there eventually.

In the meantime, I'm hoping someone could tell me if it's possible that clogged injector or mechanical problem such as a broken lifter could cause the intermittent spark. Or, is that solely an electrical problem from the power source.
 

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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
 

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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.
 
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