Injector failure or dod? - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 12 (permalink) Old 10-30-2018, 08:11 PM Thread Starter
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Injector failure or dod?

I had posted under another section regarding this but I am not having much feedback, so let me try here.

I had a weird knocking ticking sound last week and this past Saturday my car took a dump. I passed a semi truck and it started misfiring. So long story short i have taken off the intake only to find fuel sitting on top of intake valve #6 (cylinder 6) so I swapped injector, coil, plug, and wire to other cylinders and cylinder 6 keeps having fuel on top of the valve....GET THIS...i have pulled the valve covers and BOTH intake and exhaust valves move on cylinder 6...so WTF! I ALSO checked resitance on all wiring plugs to that cylinder and they all check out. So I am stumped...i really need some help here before i lose my mind. Valvetrain seems to work and everything electrical is working...could this be a pcm issue?

I dont want to pull the heads off if the problem isnt mechanical...

2009 G8 GT SRM, OBX Catless Long tube headers, DOD Delete, LS3 stock cam, tuned by Top Gun Tunning, 380 RWHP on a mustang dyno.
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post #2 of 12 (permalink) Old 10-31-2018, 01:08 PM
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Are you sure it's not a bad head gasket and are you more than positive it's getting good spark?

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post #3 of 12 (permalink) Old 10-31-2018, 02:22 PM
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Have you drained your oil to look for metal? Have you done a compression test?
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post #4 of 12 (permalink) Old 10-31-2018, 04:05 PM Thread Starter
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Idk of its a headgasket, oil is clean and so is the coolant. So there is no cross contamination. Swapped out every item on cylinder 6 to another cylinder and misfire is still there. Also checked the voltage on them and it checks out with the rest.

I have not done a comoression test. I also read on here that compression sometime checks out but the lifter is still bad.

Havent drained the oil but dip stick shows no metal shavings

2009 G8 GT SRM, OBX Catless Long tube headers, DOD Delete, LS3 stock cam, tuned by Top Gun Tunning, 380 RWHP on a mustang dyno.
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post #5 of 12 (permalink) Old 10-31-2018, 05:40 PM
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I'm thinking (but don't know for a fact) that you could have both valves open an close (which might look to be normal to the eyes), but actually never make it to it/their required open dimensions. That might allow for an acceptable compression reading (if the valves close an seal correctly), but fall way short of allowing that cylinder to receive an explode the correct cylinder charge. To me, that would be sensed as a misfire in my mind. But seeing all that gas hanging around (where it shouldn't be), has me lost. Will need input from those that are way more into this type of problem.
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post #6 of 12 (permalink) Old 10-31-2018, 09:33 PM Thread Starter
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Originally Posted by GOPHERIT View Post
I'm thinking (but don't know for a fact) that you could have both valves open an close (which might look to be normal to the eyes), but actually never make it to it/their required open dimensions. That might allow for an acceptable compression reading (if the valves close an seal correctly), but fall way short of allowing that cylinder to receive an explode the correct cylinder charge. To me, that would be sensed as a misfire in my mind. But seeing all that gas hanging around (where it shouldn't be), has me lost. Will need input from those that are way more into this type of problem.
I did think of that when I was checking the way they open and close. But here is another curve ball. I tested the compression of cylinder 6 and it checks out to 190 give or take...so I put everything back together, checked coils, plug, plug wire, and injector...everything is working as it should. All volts are checking out, coil sparks when i removed the wire from the coil. All I have left is to check the injectors witha noid light...but since the volts on there check out with the rest, I dont even know what to think anymore.
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2009 G8 GT SRM, OBX Catless Long tube headers, DOD Delete, LS3 stock cam, tuned by Top Gun Tunning, 380 RWHP on a mustang dyno.
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post #7 of 12 (permalink) Old 11-01-2018, 12:39 PM
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Your motor is stock, right???

Knocking/ticking is always hard to lock down. We always tend to think lifter, but sometimes it's not. Still, it IS a textbook prerequisite to a lifter failure, which is why it is so highly anticipated. Plus, your misfires started after this prerequisite, which points more to mechanical failure. You'd need to physically rule this out, and it may mean a 2nd opinion locally.

Before that 2nd Op, if it is still making the noise now, get yourself a stethoscope if you don't have one and find the location of the ticking noise.

There are a few ticks that could result in poor mixture or erroneous mixture calculation.

1. Exhaust Manifold Leaks (tick tick tick) result in a false lean, which causes the computer to dump fuel into the motor thinking it needs more. That causes excessive fuel and causes the misfire if the false lean is bad enough. Would be interested to see what LTFT and STFT says. Those MLS manifold gaskets would make such a sound if exhaust is allowed to pass through.
2. Injectors can tick as well if overly clogged, but that usually means less fuel. Still, a leaky injector with a poor spray pattern wouldn't allow for a proper combustion event, and it too would cause a misfire and could also show up with excessive fuel after the valve is already closed.
3. Excessive vacuum leak (may not qualify as a "tick tick tick" ). That would let air into #6 if it was an intake manifold gasket, though it doesn't mean another air leak can't be the cause. It may just be biased on #6 if it isn't mechanical.
4.Finally, there's the lifter tick. If this is confirmed, you already know what you'd need to do.... At idle the lifter tick is usually most perceptible, and it would be around 5 times per second on average if your motor is stock. (Counting 600RPM / 2 Rotations = 300 / 60sec = 5 events per second)

These are suggestions, but I've no idea how accurate. I figured I'd throw a bunch of darts up for you to consider. It sounds like it is mechanical, but I can't really intelligently draw that conclusion from here with confidence. I hope I've given you some angles to consider.

'09 PSM G8 GT - OPG Intake, DOD-Delete w/ Stage 1C 218/229 .600 Lift 117.5LSA, Kooks 1 7/8 Mids, Solo Axle-Back w/ X-Pipe, SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
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post #8 of 12 (permalink) Old 11-01-2018, 02:43 PM Thread Starter
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Quote:
Originally Posted by Jova007200 View Post
Your motor is stock, right???

Knocking/ticking is always hard to lock down. We always tend to think lifter, but sometimes it's not. Still, it IS a textbook prerequisite to a lifter failure, which is why it is so highly anticipated. Plus, your misfires started after this prerequisite, which points more to mechanical failure. You'd need to physically rule this out, and it may mean a 2nd opinion locally.

Before that 2nd Op, if it is still making the noise now, get yourself a stethoscope if you don't have one and find the location of the ticking noise.

There are a few ticks that could result in poor mixture or erroneous mixture calculation.

1. Exhaust Manifold Leaks (tick tick tick) result in a false lean, which causes the computer to dump fuel into the motor thinking it needs more. That causes excessive fuel and causes the misfire if the false lean is bad enough. Would be interested to see what LTFT and STFT says. Those MLS manifold gaskets would make such a sound if exhaust is allowed to pass through.
2. Injectors can tick as well if overly clogged, but that usually means less fuel. Still, a leaky injector with a poor spray pattern wouldn't allow for a proper combustion event, and it too would cause a misfire and could also show up with excessive fuel after the valve is already closed.
3. Excessive vacuum leak (may not qualify as a "tick tick tick" [IMG class=inlineimg]/forums/images/smilies/biggrin.gif[/IMG] ). That would let air into #6 if it was an intake manifold gasket, though it doesn't mean another air leak can't be the cause. It may just be biased on #6 if it isn't mechanical.
4.Finally, there's the lifter tick. If this is confirmed, you already know what you'd need to do.... At idle the lifter tick is usually most perceptible, and it would be around 5 times per second on average if your motor is stock. (Counting 600RPM / 2 Rotations = 300 / 60sec = 5 events per second)

These are suggestions, but I've no idea how accurate. I figured I'd throw a bunch of darts up for you to consider. It sounds like it is mechanical, but I can't really intelligently draw that conclusion from here with confidence. [IMG class=inlineimg]/forums/images/smilies/smile.gif[/IMG] I hope I've given you some angles to consider.
I appreciate you chiming in! i have sprayed carb cleaner along the edges of the intake to rule out an intake vacuum leak and there are no rpm changes. I did install headers a month ago, but the exchaust gaskets are ok, they are not leaking anywhere that could possibly cause a tick sound, BUT I will unbolt the header and check the gasket you never know what i cpupd find. Finally, the noise or tick comes from the bottom right side of the motor and I can hear it between the headers and the oil pan.

Also, wouldn't the compression be good even if the lifter is bad? I though compression tests are in case you have a bad piston ring or valves that aren't closing properly. (Like a broken valve spring)

2009 G8 GT SRM, OBX Catless Long tube headers, DOD Delete, LS3 stock cam, tuned by Top Gun Tunning, 380 RWHP on a mustang dyno.
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post #9 of 12 (permalink) Old 11-01-2018, 03:45 PM
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I seem to remember, a member had either a noise or power issue a while back. I can't find his thread about it to refresh my memory. But the thought of a possible broken valve spring might be part of the problem. At first, he could not confirm that. Then after a further tear-down, he in fact found a broken valve spring (assigned to the cylinder with the problem). But his overall problem was very bad. He had to get the engine rebuilt due to all the internal damage incurred on his engine. This makes me think, you could have a broken spring, an not be able to tell, until it has been released from its normal compressed height on the valve itself. Of course, a bad lifter and/or a ground down cam lobe would prevent the valve from working as it should, an probably make that dreaded (I'm all messed up) noise.
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post #10 of 12 (permalink) Old 11-01-2018, 04:47 PM
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Just get a mechanic's stethoscope. It'll tell you where the tick is situated. You're hearing it from lower in the motor than I'd want to attribute "lifter tick" to. If you confirm that it is bottom end, then I'd take a gander at the dip stick to see if it is well situated. You never know....

I've never considered a broken spring as something that would ever appear to be intact, but that's an interesting thought. Easy to check. You do have a lever style spring compressor, right? I consider "The Claw" to be a crime for installing or reinstalling springs.

Do you have a data logger like an OBDLink or similar?

'09 PSM G8 GT - OPG Intake, DOD-Delete w/ Stage 1C 218/229 .600 Lift 117.5LSA, Kooks 1 7/8 Mids, Solo Axle-Back w/ X-Pipe, SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
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post #11 of 12 (permalink) Old 11-01-2018, 05:19 PM
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I can see that the injectors are all powered up at ignition turn on, an you say that the power looks good to them. Each injector has its own dedicated return ground wire back to the ECM. The ECM makes each of those ground return wires actually become a ground source at the correct time to make the injector pulse. If something has/had gone wrong with that #6 ground wire (as in broken/open condition), any injector installed in that position will fail to operate. Or if that ground wire found a way to become a intermittent or solid ground, any injector at that location could/would remain open all the time. You may have already verified that the #6 return ground wire is OK back to the ECM. But how to eliminate the ECM's triggering action stumps me (other than what the GM scan tool can/does verify). for a price. But the noise is a noise that would supersede the above.
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post #12 of 12 (permalink) Old 11-02-2018, 09:20 AM Thread Starter
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Gopherit and Jova, I hope that is not my case with a completely damaged engine. Although mine made some knocking/ticking sounds, it never sounded like the usual videos I've seen with G8s and DOD failure, that is a reason as to why I was puzzled with the thought that I had a collapsed or sticking lifter. Guess if my engine is too screwed up that I would have to invest over 2k, I would just look into dropping a 6.2 in there.
I did not get a stethoscope as I was going to check the injector pulse on the car with some noid lights. Turns out that I have good pulse from the injectors, they all check out, even injector 6 harness. So seeing that I have good injector pulse, I don't think that the PCM is the problem. I have a properly working coil, and the plugs and wires are new. On top of all of this, I have moved every singe items to other cylinders and the misfire remains on cylinder 6. Even though compression looked good, I am thinking I have an internal problem (about 95% sure, unless anyone else has an idea of what could be wrong). I think its safe to take the next step and remove the passenger side head to check the lifters.

this brings me to my next debate.

I purchased an LS3 cam, springs, and timing chain from a Camaro5 member for 50 bucks. Parts were on the car for 2k miles so it should be fairly new. I know that this cam is not too popular but I just need the G8 to be reliable since my wife uses it. I'm not really after power on this one. CAN L76 push rods be used with the LS3 cam? I know the right thing to do is measure, but I read that both these cams have the same base circle and I have read a member on here installed his LS3 stock cam with the same push rods on his otherwise stock L76 and he did not have problems. My L76 is also stock aside from headers. The link to what i was referring to is below, post#68

https://www.g8board.com/forums/5-v8-...estions-4.html

any input is greatly appreciated guys!

Last edited by Joepeinado; 11-02-2018 at 10:03 AM.
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