Misfires
Thread Starter
Drifting
Joined: Mar 2010
Posts: 1,628
Likes: 15
From: Seattle WA
Misfires
Evenin' gents.
My car has been running great recently. I installed Torque on my new Android head unit, and was adding some sensors to the screens, when I saw that the misfire counters were crazy high.
The 'history' counters ranged from a low of 62 to a high of 850. The 'current' counters would have some values when I started the car, and then they would all go to 0 as I drove, except cylinder 6. Cylinder 6 is always showing at least 2 'current' misfires. It's also the one with the highest historical misfires.
There is no CEL, the car doesn't seem to miss, as I said it runs great and has lots of power.
I checked Torque on my Trailblazer, all 6 cylinders have 0 historical or current misfires, which is what I would expect to see on a healthy engine.
Any ideas on whether I should even try fixing this or what I would do to do so?
My car has been running great recently. I installed Torque on my new Android head unit, and was adding some sensors to the screens, when I saw that the misfire counters were crazy high.
The 'history' counters ranged from a low of 62 to a high of 850. The 'current' counters would have some values when I started the car, and then they would all go to 0 as I drove, except cylinder 6. Cylinder 6 is always showing at least 2 'current' misfires. It's also the one with the highest historical misfires.
There is no CEL, the car doesn't seem to miss, as I said it runs great and has lots of power.
I checked Torque on my Trailblazer, all 6 cylinders have 0 historical or current misfires, which is what I would expect to see on a healthy engine.
Any ideas on whether I should even try fixing this or what I would do to do so?
Tech Contributor
Joined: Dec 1999
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
LMAO.. That made my day!!
When was the last time you changed the plugs. If the plug gap is excessive, it can raise the misfire count and still seem to run fine. Plugs degrade over a long period of time
If you change plugs, most of the time you damage the OEM wires. My recommendation would be to obtain a set of GM Performance Red Wires from Gene Culley at CULTRAG Performance.
They are excellent wires and the fit quality and performance is second to none. They don't cost much either!
When was the last time you changed the plugs. If the plug gap is excessive, it can raise the misfire count and still seem to run fine. Plugs degrade over a long period of time
If you change plugs, most of the time you damage the OEM wires. My recommendation would be to obtain a set of GM Performance Red Wires from Gene Culley at CULTRAG Performance.
They are excellent wires and the fit quality and performance is second to none. They don't cost much either!
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
ALSO SEE THIS POST for additional troubleshooting assistance:
https://www.corvetteforum.com/forums...miles-wth.html
https://www.corvetteforum.com/forums...miles-wth.html
Thread Starter
Drifting
Joined: Mar 2010
Posts: 1,628
Likes: 15
From: Seattle WA
I replaced the plugs about 30k ago, but I did not replace the wires. I'll do them both again (relatively inexpensive as far things on this car go) and see how it goes.
Thanks guys.
Thanks guys.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
What GAP did you run them at?
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Thread Starter
Drifting
Joined: Mar 2010
Posts: 1,628
Likes: 15
From: Seattle WA
I have 136k on the car (76k mine), the wires may be original or they at least have 76k on them.
I'll replace the wires and pull #6 plug (since it's got the highest misfire counts) and see what it looks like.
Thread Starter
Drifting
Joined: Mar 2010
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From: Seattle WA
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From: Anthony TX
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St. Jude Donor '08
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From: New Market AL
Trios - do you have the stock camshaft in your engine? Is the PCM re-tuned from stock?
A longer duration camshaft lope will register to the PCM as "misfire". When re-tuning for the new cam the misfire table values can be increased to desensitize what the PCM considers a misfire. Many tuners simply turn OFF the misfire Check Engine Light, but then the operator doesn't get any notification when there is an actual problem. Hopefully the new plug wires make cylinder #6 happy again.
A longer duration camshaft lope will register to the PCM as "misfire". When re-tuning for the new cam the misfire table values can be increased to desensitize what the PCM considers a misfire. Many tuners simply turn OFF the misfire Check Engine Light, but then the operator doesn't get any notification when there is an actual problem. Hopefully the new plug wires make cylinder #6 happy again.
Thread Starter
Drifting
Joined: Mar 2010
Posts: 1,628
Likes: 15
From: Seattle WA
Trios - do you have the stock camshaft in your engine? Is the PCM re-tuned from stock?
A longer duration camshaft lope will register to the PCM as "misfire". When re-tuning for the new cam the misfire table values can be increased to desensitize what the PCM considers a misfire. Many tuners simply turn OFF the misfire Check Engine Light, but then the operator doesn't get any notification when there is an actual problem. Hopefully the new plug wires make cylinder #6 happy again.
A longer duration camshaft lope will register to the PCM as "misfire". When re-tuning for the new cam the misfire table values can be increased to desensitize what the PCM considers a misfire. Many tuners simply turn OFF the misfire Check Engine Light, but then the operator doesn't get any notification when there is an actual problem. Hopefully the new plug wires make cylinder #6 happy again.
I know I've gotten a CEL for P0300 (random misfire) before, but it's happened very rarely on startup on extremely cold days, and went away immediately, so I never thought much of it.
How many misfires does it take to set the CEL?
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Joined: Sep 2005
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From: New Market AL
There are 7 misfire tables that list "maximum time between events to declare a misfire". The tables are split between "Event Mode" and "Revolution Mode". The "Y" axis is RPM and the "X" axis is 17 columns of some value from 0 to 100. These tables are further divided into idle, medium, and high RPM.
So there isn't a simple answer to your question. But I can say that a longer duration cam with noticeable idle lope will eventually set off a misfire code unless the tables are increased in the idle areas.
If you are showing one cylinder with particularly higher misfire, then try swapping the plug wire; plug; coil (in that order) to see if the misfire moves to another cylinder. Then replace the component that was causing the misfire. I've accurately diagnosed several cracked plugs and bad wires by scanning individual cylinder misfires.
On a couple other occasions I had to pull the valve cover to discover a broken spring or broken rocker arm. But you can feel that there is a dead cylinder when that happens.
So there isn't a simple answer to your question. But I can say that a longer duration cam with noticeable idle lope will eventually set off a misfire code unless the tables are increased in the idle areas.
If you are showing one cylinder with particularly higher misfire, then try swapping the plug wire; plug; coil (in that order) to see if the misfire moves to another cylinder. Then replace the component that was causing the misfire. I've accurately diagnosed several cracked plugs and bad wires by scanning individual cylinder misfires.
On a couple other occasions I had to pull the valve cover to discover a broken spring or broken rocker arm. But you can feel that there is a dead cylinder when that happens.
Last edited by chevy406; May 21, 2015 at 02:45 PM.
Drifting
Joined: Sep 2007
Posts: 1,649
Likes: 50
From: Goldsboro NC
There are 7 misfire tables that list "maximum time between events to declare a misfire". The tables are split between "Event Mode" and "Revolution Mode". The "Y" axis is RPM and the "X" axis is 17 columns of some value from 0 to 100. These tables are further divided into idle, medium, and high RPM.
So there isn't a simple answer to your question. But I can say that a longer duration cam with noticeable idle lope will eventually set off a misfire code unless the tables are increased in the idle areas.
If you are showing one cylinder with particularly higher misfire, then try swapping the plug wire; plug; coil (in that order) to see if the misfire moves to another cylinder. Then replace the component that was causing the misfire. I've accurately diagnosed several cracked plugs and bad wires by scanning individual cylinder misfires.
On a couple other occasions I had to pull the valve cover to discover a broken spring or broken rocker arm. But you can feel that there is a dead cylinder when that happens.
So there isn't a simple answer to your question. But I can say that a longer duration cam with noticeable idle lope will eventually set off a misfire code unless the tables are increased in the idle areas.
If you are showing one cylinder with particularly higher misfire, then try swapping the plug wire; plug; coil (in that order) to see if the misfire moves to another cylinder. Then replace the component that was causing the misfire. I've accurately diagnosed several cracked plugs and bad wires by scanning individual cylinder misfires.
On a couple other occasions I had to pull the valve cover to discover a broken spring or broken rocker arm. But you can feel that there is a dead cylinder when that happens.
(not doing this as of yet). What kind of scanner are u using??
Last edited by ZZ06; May 21, 2015 at 03:34 PM.
Thread Starter
Drifting
Joined: Mar 2010
Posts: 1,628
Likes: 15
From: Seattle WA
Do you have an Android smart phone or tablet? If so, you can pick up a cheap Bluetooth OBDII adapter and run Torque. It can scan all generic and most GM-specific PIDs (with the ability to add custom PIDs), perform logging, clear codes (not that we need that for the 'Vettes, but it's useful on my Trailblazer), etc. Pretty damn handy app.
Drifting
Joined: Sep 2007
Posts: 1,649
Likes: 50
From: Goldsboro NC
Do you have an Android smart phone or tablet? If so, you can pick up a cheap Bluetooth OBDII adapter and run Torque. It can scan all generic and most GM-specific PIDs (with the ability to add custom PIDs), perform logging, clear codes (not that we need that for the 'Vettes, but it's useful on my Trailblazer), etc. Pretty damn handy app.
Thread Starter
Drifting
Joined: Mar 2010
Posts: 1,628
Likes: 15
From: Seattle WA
First you purchase
.
Then you purchase and install Torque Pro
Then you connect to the Bluetooth adapter and start playing around
Then you purchase and install Torque Pro
Then you connect to the Bluetooth adapter and start playing around