Spark Plug Issue… Help!
Thread Starter
Intermediate
Joined: Jul 2018
Posts: 40
Likes: 4
Spark Plug Issue… Help!
Been chasing a spark plug issue at cylinder 8…
Car had a misfire. Sent a log to my tuner. There was nothing obvious tune related. Pulled the plugs. #8 plug was a little oily and black. Did a leak down and compression test. All cylinders came back healthy. (Twice) We replaced the coil pack and changed plug wires. No dice! We then replaced the valve seals. No dice! We then sent the heads out for a valve job. I also replaced the intake and exhaust valves and valve springs while there. The oil on the plugs went away. But the plug is still turning black from what looks to be fuel. This is after very minimal driving (maybe 50 miles) and not WOT. We sent the injectors out to be flow tested and checked for leaks. Results came back with no issues on the low or high pressure side and all are flowing as should be. So… Back to the drawing board. Again! Any suggestions or recommendations on where to look next???
Thanks in advance!
Car had a misfire. Sent a log to my tuner. There was nothing obvious tune related. Pulled the plugs. #8 plug was a little oily and black. Did a leak down and compression test. All cylinders came back healthy. (Twice) We replaced the coil pack and changed plug wires. No dice! We then replaced the valve seals. No dice! We then sent the heads out for a valve job. I also replaced the intake and exhaust valves and valve springs while there. The oil on the plugs went away. But the plug is still turning black from what looks to be fuel. This is after very minimal driving (maybe 50 miles) and not WOT. We sent the injectors out to be flow tested and checked for leaks. Results came back with no issues on the low or high pressure side and all are flowing as should be. So… Back to the drawing board. Again! Any suggestions or recommendations on where to look next???
Thanks in advance!
Last edited by JimmyLith; May 20, 2024 at 08:34 PM.
Thread Starter
Intermediate
Joined: Jul 2018
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Le Mans Master
Joined: Oct 2014
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From: Atlanta GA
Any mods done to the car , do u have a blower on it , have you measured the camshaft lift on number 8 both intake and exhaust ?
Dave
Thread Starter
Intermediate
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GDS2 and a GM MDI comunications device is what GM uses for diagnostics, HP tuners is not a diagnostic tool although you could use it as such it's not as good . GDS2 along with any commercial hi grade scanner gives you the ablity to log live events and monitor all the PIDs , if you can replicate the event you will see exactly what's going on at that time . In my opinion, either the plug is not firing or the there is something wrong with injector causing it to send more fuel than needed, seeing all the PIDs especially injector data and spark at once at the time it starts to miss might lead you in the right direction
Any mods done to the car , do u have a blower on it , have you measured the camshaft lift on number 8 both intake and exhaust ?
Dave
Any mods done to the car , do u have a blower on it , have you measured the camshaft lift on number 8 both intake and exhaust ?
Dave
Car is heavily modified. There is a blower on the car. CP Pistons/Rods, XDI 50% over injectors, Landspeed Ported heads with Inconel exhaust valves and titanium intake valves. We did all new seals, retainers, pushrods, springs, trunnion kit, etc. since we were already there. NGK Ltr7ix plugs gapped at .021 and firecore plug wires just to name some of the mods associated around the issues I’m having. Lift was measured when the heads came off to be sent out to porting. The car has been thoroughly inspected. It’s just starting to leave a lot of smart people scratching their heads.
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
Wow ! First off , nice build ! I am jealous 😫
After reading your thread I figured you knew what u were doing but just had to ask. I agree with you that it has to be something electrical but do u have the ablity to monitor what the injectors are doing ? What is the AFM reading when u make a pull , if you have a miss it should be going rich , if it is does the ECM try to pull fuel ?
Have you done a smoke test just to eliminate a leak under boost ?
As far as the spark , I don't think HP Tuners has the ablity to log each cylinder misfire count while making a pull , GDS2 you can but it would take someone watching the screen during the pull to see when the misfire starts ( u will see all cylinders at once )
My brother an I have an old saying , you need air , fuel and spark , You know you have air , you are pretty sure you are ok with fuel so that only leaves spark . Maybe harness, connectors , ECM ?
Dave
After reading your thread I figured you knew what u were doing but just had to ask. I agree with you that it has to be something electrical but do u have the ablity to monitor what the injectors are doing ? What is the AFM reading when u make a pull , if you have a miss it should be going rich , if it is does the ECM try to pull fuel ?
Have you done a smoke test just to eliminate a leak under boost ?
As far as the spark , I don't think HP Tuners has the ablity to log each cylinder misfire count while making a pull , GDS2 you can but it would take someone watching the screen during the pull to see when the misfire starts ( u will see all cylinders at once )
My brother an I have an old saying , you need air , fuel and spark , You know you have air , you are pretty sure you are ok with fuel so that only leaves spark . Maybe harness, connectors , ECM ?
Dave
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Thread Starter
Intermediate
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Burning Brakes
Joined: Jan 2019
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From: Louisiana
Thread Starter
Intermediate
Joined: Jul 2018
Posts: 40
Likes: 4
Wow ! First off , nice build ! I am jealous 😫
After reading your thread I figured you knew what u were doing but just had to ask. I agree with you that it has to be something electrical but do u have the ablity to monitor what the injectors are doing ? What is the AFM reading when u make a pull , if you have a miss it should be going rich , if it is does the ECM try to pull fuel ?
Have you done a smoke test just to eliminate a leak under boost ?
As far as the spark , I don't think HP Tuners has the ablity to log each cylinder misfire count while making a pull , GDS2 you can but it would take someone watching the screen during the pull to see when the misfire starts ( u will see all cylinders at once )
My brother an I have an old saying , you need air , fuel and spark , You know you have air , you are pretty sure you are ok with fuel so that only leaves spark . Maybe harness, connectors , ECM ?
Dave
After reading your thread I figured you knew what u were doing but just had to ask. I agree with you that it has to be something electrical but do u have the ablity to monitor what the injectors are doing ? What is the AFM reading when u make a pull , if you have a miss it should be going rich , if it is does the ECM try to pull fuel ?
Have you done a smoke test just to eliminate a leak under boost ?
As far as the spark , I don't think HP Tuners has the ablity to log each cylinder misfire count while making a pull , GDS2 you can but it would take someone watching the screen during the pull to see when the misfire starts ( u will see all cylinders at once )
My brother an I have an old saying , you need air , fuel and spark , You know you have air , you are pretty sure you are ok with fuel so that only leaves spark . Maybe harness, connectors , ECM ?
Dave
I believe HP Tuners can log misfire’s per cylinder. But HP Tuners and Data Logging is what starts to go beyond my pay grade. lol. So I don’t have accurate answers to a lot of those questions. My tuner has spent a ton of seat time in my car data logging. And nothing obvious is sticking out to him. The car is also boosting hard, making good power and performing very well. Which again makes me think it’s not mechanical. It’s just that 1 black plug that is lingering.
That saying makes perfect sense. I believe the ECM and harness is going to be our next area of attack.
Thread Starter
Intermediate
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Burning Brakes
Joined: Jan 2019
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From: Louisiana
Could you post some pictures of the fouled plug?
Thread Starter
Intermediate
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It could be the victim cylinder. LPSI in DI engines occurs from the reduced atomization of direct injection combined with oil vapors from the crankcase. The fuel mixes with those oil vapors. Port injection has about 2x more degrees of crank rotation to atomize.
Could you post some pictures of the fouled plug?
Could you post some pictures of the fouled plug?
I unfortunately did not take a picture of the plug. I was standing there when we first pulled them and forgot to take a picture. I will get a picture next time if it does it after this next round of diagnostics.
Burning Brakes
Joined: Jan 2019
Posts: 954
Likes: 377
From: Louisiana
I would think if it was the cylinder. The leak down test and/or compression test would have found something. Which have both been done twice now. Just to be sure. And both showed no evidence of cylinder damage. I would also assume if it were LSPI, there would be some kind of knock. Which there isn’t. Could be wrong though, that’s just an educated guess.
I unfortunately did not take a picture of the plug. I was standing there when we first pulled them and forgot to take a picture. I will get a picture next time if it does it after this next round of diagnostics.
I unfortunately did not take a picture of the plug. I was standing there when we first pulled them and forgot to take a picture. I will get a picture next time if it does it after this next round of diagnostics.
Melting Slicks
Joined: Feb 2018
Posts: 2,177
Likes: 1,044
From: North Texas
Scanner or scope time.
Look at the injector and spark waveforms on cylinder 8 and compare them to the others under different engine speed and loads. They should all follow each other within reason.
Might have to go to a in cylinder pressure transducer and scope, once again compare.
But with all your mods its going to be harder to diagonis than a stock C7. Thats why I keep repeating 'compare' because your set up will give different readings compared to a stock C7.
But something should stick its head up.
Look at the injector and spark waveforms on cylinder 8 and compare them to the others under different engine speed and loads. They should all follow each other within reason.
Might have to go to a in cylinder pressure transducer and scope, once again compare.
But with all your mods its going to be harder to diagonis than a stock C7. Thats why I keep repeating 'compare' because your set up will give different readings compared to a stock C7.
But something should stick its head up.
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
Thank You! I haven’t really been able to enjoy it yet. Still working out these bugs with the new set up.
I believe HP Tuners can log misfire’s per cylinder. But HP Tuners and Data Logging is what starts to go beyond my pay grade. lol. So I don’t have accurate answers to a lot of those questions. My tuner has spent a ton of seat time in my car data logging. And nothing obvious is sticking out to him. The car is also boosting hard, making good power and performing very well. Which again makes me think it’s not mechanical. It’s just that 1 black plug that is lingering.
That saying makes perfect sense. I believe the ECM and harness is going to be our next area of attack.
I believe HP Tuners can log misfire’s per cylinder. But HP Tuners and Data Logging is what starts to go beyond my pay grade. lol. So I don’t have accurate answers to a lot of those questions. My tuner has spent a ton of seat time in my car data logging. And nothing obvious is sticking out to him. The car is also boosting hard, making good power and performing very well. Which again makes me think it’s not mechanical. It’s just that 1 black plug that is lingering.
That saying makes perfect sense. I believe the ECM and harness is going to be our next area of attack.
Instructor
Joined: Nov 2021
Posts: 146
Likes: 23
ii ran into a similar problem long ago that a plug was black compression test was good but found the exhaust was not opening all the way causing incomplete combustion cam shaft lobe was worn since the cylinder was sealed the compression test would be good just my experience
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
@96GS#007 What is this log telling us ... is there detail behind in the history ?
Can u see live data on the misfire count ?
With GDS2 i know i can see live stream data on misfire count along with RPM , speed, and all the other PIDS ... i have only used it as a "View" that i had someone watching but I am almost positive i can record it and play it back like a log file from HPT .
I never have dived into the scanning function of HPT because I have GDS2 for diagnostics and programing of modules
Always open to learning something new
Dave
Can u see live data on the misfire count ?
With GDS2 i know i can see live stream data on misfire count along with RPM , speed, and all the other PIDS ... i have only used it as a "View" that i had someone watching but I am almost positive i can record it and play it back like a log file from HPT .
I never have dived into the scanning function of HPT because I have GDS2 for diagnostics and programing of modules
Always open to learning something new
Dave