Flashing CEL
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Legend
Joined: Jul 2007
Posts: 7,843
Likes: 13
From: DFW, Texas
Hank's already given me a wealth of help on this. He suggested a while ago that I might have a valve seal going, and It looks like I'm narrowing it down to that unfortunate possibility.
Hall Of Fame
Joined: Jul 2006
Posts: 12,204
Likes: 10
From: Gainesville, Ga.
i don't see how seats or seals either one would contribute to pinging.
if a seal is bad, then its leaking oil down on the valve stem. if its the exhaust, then its getting flushed out the exhaust port, with possibly a teeny weeny tiny bit getting down to the cylinder. if its the intake, then its oozing down the stem and getting sprayed with fuel and sucked into the cyl. assuming its not a huge amount it will just burn up and maybe smoke a tad. also assuming its not fouling the plug (which would be visible), then i don't see that it hurts anything. it certainly doesn't make it leaner, or hotter, and i don't how it would cause ping.
if a seat is bad, then your going to lose compression, and blow compression and unburned fuel either out the exhaust (hp loss and extra emissions) or back into the intake (?). i don't see that causing ping.
ping = predetonation, related to high temp, lean mix, high compression, low octane, and/or timing too far advanced (although i've never understood that one)
if a seal is bad, then its leaking oil down on the valve stem. if its the exhaust, then its getting flushed out the exhaust port, with possibly a teeny weeny tiny bit getting down to the cylinder. if its the intake, then its oozing down the stem and getting sprayed with fuel and sucked into the cyl. assuming its not a huge amount it will just burn up and maybe smoke a tad. also assuming its not fouling the plug (which would be visible), then i don't see that it hurts anything. it certainly doesn't make it leaner, or hotter, and i don't how it would cause ping.
if a seat is bad, then your going to lose compression, and blow compression and unburned fuel either out the exhaust (hp loss and extra emissions) or back into the intake (?). i don't see that causing ping.
ping = predetonation, related to high temp, lean mix, high compression, low octane, and/or timing too far advanced (although i've never understood that one)
Hall Of Fame
Joined: Jul 2006
Posts: 12,204
Likes: 10
From: Gainesville, Ga.
ok. being a carb guy i didn't think of injectors. what about this....
(from another forum, in another universe....)
Usually when it flashes, it means you have a misfire in progress.
Checked the resistance on my fuel injectors and found injector at cyl 1 at 74 ohms which is way out of specs. Checked the other fuel injectors and found it at 14-18 ohms which is normal. Thus it was a bad fuel injector which is one of the probable causes of misfires. The OBD2 scanner works great!!!
(from another forum, in another universe....)
Usually when it flashes, it means you have a misfire in progress.
Checked the resistance on my fuel injectors and found injector at cyl 1 at 74 ohms which is way out of specs. Checked the other fuel injectors and found it at 14-18 ohms which is normal. Thus it was a bad fuel injector which is one of the probable causes of misfires. The OBD2 scanner works great!!!
Legend
Joined: May 2005
Posts: 8,663
Likes: 8
From: Central Oklahoma
ok. being a carb guy i didn't think of injectors. what about this....
(from another forum, in another universe....)
Usually when it flashes, it means you have a misfire in progress.
Checked the resistance on my fuel injectors and found injector at cyl 1 at 74 ohms which is way out of specs. Checked the other fuel injectors and found it at 14-18 ohms which is normal. Thus it was a bad fuel injector which is one of the probable causes of misfires. The OBD2 scanner works great!!!
(from another forum, in another universe....)
Usually when it flashes, it means you have a misfire in progress.
Checked the resistance on my fuel injectors and found injector at cyl 1 at 74 ohms which is way out of specs. Checked the other fuel injectors and found it at 14-18 ohms which is normal. Thus it was a bad fuel injector which is one of the probable causes of misfires. The OBD2 scanner works great!!!
Hall Of Fame
Joined: Jul 2006
Posts: 12,204
Likes: 10
From: Gainesville, Ga.
ok, i pulled together several discussions of what causes flashing CEL (misfire in progress), as well as how the misfire is detected (i never knew and always wondered). a misfire is pretty much equivalent to the old fashioned term - "its skipping", as in one or more cylinders is not contributing power, as measured by rpm drop at its firing cycle. as always, it can misfire (skip), for any of a thousand reasons including fuel, or spark, or timing, or compression.
Usually when it flashes, it means you have a misfire in progress.
Checked the resistance on my fuel injectors and found injector at cyl 1 at 74 ohms which is way out of specs. Checked the other fuel injectors and found it at 14-18 ohms which is normal. Thus it was a bad fuel injector which is one of the probable causes of misfires. The OBD2 scanner works great!!!
The computer monitors RPMs and O2 sensor readings to determine a misfire. If a cylinder misfires, it isn't contributing to engine power. The computer knows when it ordered the plug to fire and watches for a dip in RPMs that would signify that cylinder isn't pulling its weight. A corresponding change in O2 readings then confirms the misfire.
The engine detects a misfire by watching the timing of the crank sensor pulses. It senses which cylinder is misfiring by watching the cam sensor position at the time of misfire. Just because that is the only misfire code does not necessarily mean it is your only misfire. Start with the basics, if your ignition wires are original, replace them. G.M. wires dont hold up well past 100k. You say that you have power to the injector, but it also needs a ground pulse from the computer just like an ignition coil does to turn it on and off. Injectors can go bad but not that often. 95% of all misfires are usually due to bad plugs , wires, corrosion on your coil towers, intake leaks(this will occur at idle) or coolant getting into the cylinder. Do not change your O2 sensor. An oxygen sensor is in no way reactive enough to detect a misfire. It can cause multiple misfires by delivering the wrong info to the computer for fuel trim mapping but that will cause multiple misfires and other obvious running problems. An oxygen sensor will switch your fuel trim from rich to lean an average of 20 to 50 times per second. These are called cross counts The oxygen sensor is also used to check E.G.R, operation on many cars. It cannot tell if a cylinder is misfiring.
how does the pcm know when a cylinder misfires and which cylinder it is ??
Misfire is detected by analyzing crankshaft speed fluctuations. The crank sensor detects engine speed, and an rpm value is established for each cylinder for comparison. When a sufficient difference in rpm occurs among cylinders, a misfire count is recorded. The rpm varies slightly because of different input variables.
Two types of misfires can be detected. A two-trip misfire, which occurs about 2% of the time, will result in an emissions increase. A one-trip misfire, also called a catalyst-damaging misfire, occurs in about 10% to 20% of the events.
To detect a misfire, the PCM must first learn the spacing of the crank target windows. This is done when the engine is in the Deceleration Fuel Shutoff mode. To learn the crank target spacing, three closed-throttle decelerations from 55 mph to rest must be performed. The misfire monitor will not be enabled until this spacing is learned.
The PCM also checks the machining tolerances within each group of slots on the flywheel. The PCM calculates the variation among each group of slots. This calculation is called rpm error. The variation in rpm readings between cylinder pairs must be less than 5% in order to run the misfire monitor.
Once the PCM has detected a misfire for two consecutive trips, the MIL will be continuously illuminated and a permanent DTC will store. If the PCM detects a catalyst-damaging misfire, the MIL will flash. If the active misfire ends, the MIL will change to continuous illumination. The MIL will remain on for more than one trip, but will go out if the conditions that set the DTC are not found on subsequent trips.
The Misfire Detection Monitor is an on-board strategy designed to monitor
engine misfire and identify the specific cylinder in which the misfire has
occurred. Misfire is defined as lack of combustion in a cylinder due to
absence of spark, poor fuel metering, poor compression, or any other cause.
The Misfire Detection Monitor will be enabled only when certain base engine
conditions are first satisfied. Input from the ECT, MC-VAF or MAF, CKP
sensors, and Misfire Detection sensor on distributor ignition applications
is required to enable the monitor. The Misfire Detection Monitor is also
performed during on demand self-test.
1.. The PCM synchronized ignition spark is based on information received
from the CKP sensor. The CKP signal generated is also the main input used in
determining cylinder misfire.
2.. The input signal generated by the CKP sensor is derived by sensing the
passage of teeth from the crankshaft position wheel mounted on the end of
the crankshaft.
3.. The input signal to the PCM is then used to calculate the time between
CKP edges and also crankshaft rotational velocity and acceleration. By
comparing the accelerations of each cylinder event, the power loss of each
cylinder is determined. When the power loss of a particular cylinder is
sufficiently less than a calibrated value and other criteria is met, then
the suspect cylinder is determined to have misfired.
4.. Misfire type A:
Upon detection of a Misfire type A (200 revolutions) which would cause
catalyst damage, the MIL will blink once per second during the actual
misfire, and a DTC will be stored.
Misfire type B:
Upon detection of a Misfire type B (1000 revolutions) which will exceed
the emissions threshold or cause a vehicle to fail an inspection and
maintenance tailpipe emissions test, the MIL will illuminate and a DTC will
be stored.
The DTC associated with multiple cylinder misfire for a Type A or Type B
misfire is DTC P0300.
The DTCs associated with an individual cylinder misfire for a Type A or
Type B misfire are DTCs P0301, P0302, P0303, P0304, P0305, P0306, P0307,
P0308, P0309 and P0310.
Usually when it flashes, it means you have a misfire in progress.
Checked the resistance on my fuel injectors and found injector at cyl 1 at 74 ohms which is way out of specs. Checked the other fuel injectors and found it at 14-18 ohms which is normal. Thus it was a bad fuel injector which is one of the probable causes of misfires. The OBD2 scanner works great!!!
The computer monitors RPMs and O2 sensor readings to determine a misfire. If a cylinder misfires, it isn't contributing to engine power. The computer knows when it ordered the plug to fire and watches for a dip in RPMs that would signify that cylinder isn't pulling its weight. A corresponding change in O2 readings then confirms the misfire.
The engine detects a misfire by watching the timing of the crank sensor pulses. It senses which cylinder is misfiring by watching the cam sensor position at the time of misfire. Just because that is the only misfire code does not necessarily mean it is your only misfire. Start with the basics, if your ignition wires are original, replace them. G.M. wires dont hold up well past 100k. You say that you have power to the injector, but it also needs a ground pulse from the computer just like an ignition coil does to turn it on and off. Injectors can go bad but not that often. 95% of all misfires are usually due to bad plugs , wires, corrosion on your coil towers, intake leaks(this will occur at idle) or coolant getting into the cylinder. Do not change your O2 sensor. An oxygen sensor is in no way reactive enough to detect a misfire. It can cause multiple misfires by delivering the wrong info to the computer for fuel trim mapping but that will cause multiple misfires and other obvious running problems. An oxygen sensor will switch your fuel trim from rich to lean an average of 20 to 50 times per second. These are called cross counts The oxygen sensor is also used to check E.G.R, operation on many cars. It cannot tell if a cylinder is misfiring.
how does the pcm know when a cylinder misfires and which cylinder it is ??
Misfire is detected by analyzing crankshaft speed fluctuations. The crank sensor detects engine speed, and an rpm value is established for each cylinder for comparison. When a sufficient difference in rpm occurs among cylinders, a misfire count is recorded. The rpm varies slightly because of different input variables.
Two types of misfires can be detected. A two-trip misfire, which occurs about 2% of the time, will result in an emissions increase. A one-trip misfire, also called a catalyst-damaging misfire, occurs in about 10% to 20% of the events.
To detect a misfire, the PCM must first learn the spacing of the crank target windows. This is done when the engine is in the Deceleration Fuel Shutoff mode. To learn the crank target spacing, three closed-throttle decelerations from 55 mph to rest must be performed. The misfire monitor will not be enabled until this spacing is learned.
The PCM also checks the machining tolerances within each group of slots on the flywheel. The PCM calculates the variation among each group of slots. This calculation is called rpm error. The variation in rpm readings between cylinder pairs must be less than 5% in order to run the misfire monitor.
Once the PCM has detected a misfire for two consecutive trips, the MIL will be continuously illuminated and a permanent DTC will store. If the PCM detects a catalyst-damaging misfire, the MIL will flash. If the active misfire ends, the MIL will change to continuous illumination. The MIL will remain on for more than one trip, but will go out if the conditions that set the DTC are not found on subsequent trips.
The Misfire Detection Monitor is an on-board strategy designed to monitor
engine misfire and identify the specific cylinder in which the misfire has
occurred. Misfire is defined as lack of combustion in a cylinder due to
absence of spark, poor fuel metering, poor compression, or any other cause.
The Misfire Detection Monitor will be enabled only when certain base engine
conditions are first satisfied. Input from the ECT, MC-VAF or MAF, CKP
sensors, and Misfire Detection sensor on distributor ignition applications
is required to enable the monitor. The Misfire Detection Monitor is also
performed during on demand self-test.
1.. The PCM synchronized ignition spark is based on information received
from the CKP sensor. The CKP signal generated is also the main input used in
determining cylinder misfire.
2.. The input signal generated by the CKP sensor is derived by sensing the
passage of teeth from the crankshaft position wheel mounted on the end of
the crankshaft.
3.. The input signal to the PCM is then used to calculate the time between
CKP edges and also crankshaft rotational velocity and acceleration. By
comparing the accelerations of each cylinder event, the power loss of each
cylinder is determined. When the power loss of a particular cylinder is
sufficiently less than a calibrated value and other criteria is met, then
the suspect cylinder is determined to have misfired.
4.. Misfire type A:
Upon detection of a Misfire type A (200 revolutions) which would cause
catalyst damage, the MIL will blink once per second during the actual
misfire, and a DTC will be stored.
Misfire type B:
Upon detection of a Misfire type B (1000 revolutions) which will exceed
the emissions threshold or cause a vehicle to fail an inspection and
maintenance tailpipe emissions test, the MIL will illuminate and a DTC will
be stored.
The DTC associated with multiple cylinder misfire for a Type A or Type B
misfire is DTC P0300.
The DTCs associated with an individual cylinder misfire for a Type A or
Type B misfire are DTCs P0301, P0302, P0303, P0304, P0305, P0306, P0307,
P0308, P0309 and P0310.