Need help: P0300 - multi-cylinder misfire
12-04-2007, 12:24 PM
#1
Melting Slicks
Thread Starter
Need help: P0300 - multi-cylinder misfire
2002 Z06. 61,700 miles. Haltech CAI. ~6000 miles on NGK TR55 spark plugs and AC Delco ignition wires. I am the second owner. The car had ~52,000 miles on it when I purchased it in April 2007.
SYMPTOMS:
This problem just recently became obvious but I suspect that it has existed for several days and has just gotten worse.
Exhaust note sounds a bit flat at idle. Kind of like one cylinder is not firing at all.
Exhaust discharge from the left tail-pipe is notably weaker than the right side tail-pipe.
During normal driving the exhaust note sounds like one cylinder is not firing at all and I can tell that the engine is weaker than normal. Someone not used to the car might not even notice that there is a problem during normal driving.
During hard acceleration, at higher rpms there is a whistle sound but that may be related to the known whistle issue with LS6 intake manifolds!?!
During hard acceleration the engine is obviously down on power and feels even weaker as the engine speed increases. Eventually the check engine light will start to blink.
Check engine light does not set (stay lit).
Check engine light will blink on/off during hard acceleration over ~4000 rpm.
Simple code reader, Actron CP9135, captures a P0300 code when the check engine light starts to blink on/off.
The Actron CP9135 has also captured a P0303, (misfire on cylinder #3), during two separate test drives
The DIC shows the following codes:
58-SDM (1 code)
- U1000H (Serial data communication error/malfunction)
AO-LDCM (4 codes):
- B2282H (Left door control module – voltage out of range)
- B2284H (Left door control module – voltage out of range)
- B2262H (Left door mirror position signal)
- U1064H (BCM serial data circuit malfunction)
A1-RDCM (3 codes):
- B2283H (Right door control module – voltage out of range)
- B2285H (Right door control module – voltage out of range)
- U1064H (BCM serial data circuit malfunction)
DIAGNOSIS performed to date:
Performed engine compression test. All cylinders 170-175 psi. (EDIT to add - Throttle plate closed during compression test. I simply forgot to hold at WOT for maximum air intake/compression values. Either way, the important thing is that all cylinders showed equal values)
I found that spark plug #5 was only finger tight when removing plugs!
The spark plugs all look very good. Very consistent appearance from one spark plug to another. Based on appearance, if you absolutely had to judge rich vs. lean mixture I would have to say “slightly lean.”
Performed Ignition wire resistance test. Each wire less than 370 ohms.
Fuel injectors – Using a stethoscope, I determined that all of the fuel injectors are firing. The sound was very consistent from one injector to the next. However, just because they are firing doesn’t necessarily mean that they are flowing!
I inspected the fuel injector wiring harness where it comes around the fuel rail bracket on the back of the driver’s side head. I found no apparent chaffing of the wires.
Pulled one spark plug wire at a time while engine running. I was unable to positively identify any one cylinder being dead using this method.
I have ensured that each of the clamps were tight on the air bridge between the mass airflow sensor and throttle body.
I have located and cleaned the following ground points: G101, G102, G104, G105, and G108. I will eventually locate and clean the rest of them.
I removed the battery and battery tray to inspect for previous leakage. None noted. It was very clean below the battery tray.
Performed visual inspection for vacuum leak but could have easily missed it if one exists.
I found the O2 sensor wire laying next to the exhaust pipe. The mesh wire protector looks a bit charred but not burned through.
I’ve read a LOT of archived threads here on the forum related to the term “misfire.”
Some forum members found the cause of misfire to be:
- spark plug was slightly loose
- exhaust leak
- bad/burned/loose plug wire
- corroded PCM connectors
- corroded battery cables
- O2 sensors cross connected
- clogged fuel filter
- bent push rods
- broken valve springs
- bent valves
I’m sure that the cause of my misfire is simple but finding it is a pain in the ars. Please help!!!
I will be sure to post the results once I finally get this problem solved. It was frustrating to see so many posts in the archive that were left unresolved.
Thanks,
Mike
SYMPTOMS:
This problem just recently became obvious but I suspect that it has existed for several days and has just gotten worse.
Exhaust note sounds a bit flat at idle. Kind of like one cylinder is not firing at all.
Exhaust discharge from the left tail-pipe is notably weaker than the right side tail-pipe.
During normal driving the exhaust note sounds like one cylinder is not firing at all and I can tell that the engine is weaker than normal. Someone not used to the car might not even notice that there is a problem during normal driving.
During hard acceleration, at higher rpms there is a whistle sound but that may be related to the known whistle issue with LS6 intake manifolds!?!
During hard acceleration the engine is obviously down on power and feels even weaker as the engine speed increases. Eventually the check engine light will start to blink.
Check engine light does not set (stay lit).
Check engine light will blink on/off during hard acceleration over ~4000 rpm.
Simple code reader, Actron CP9135, captures a P0300 code when the check engine light starts to blink on/off.
The Actron CP9135 has also captured a P0303, (misfire on cylinder #3), during two separate test drives
The DIC shows the following codes:
58-SDM (1 code)
- U1000H (Serial data communication error/malfunction)
AO-LDCM (4 codes):
- B2282H (Left door control module – voltage out of range)
- B2284H (Left door control module – voltage out of range)
- B2262H (Left door mirror position signal)
- U1064H (BCM serial data circuit malfunction)
A1-RDCM (3 codes):
- B2283H (Right door control module – voltage out of range)
- B2285H (Right door control module – voltage out of range)
- U1064H (BCM serial data circuit malfunction)
DIAGNOSIS performed to date:
Performed engine compression test. All cylinders 170-175 psi. (EDIT to add - Throttle plate closed during compression test. I simply forgot to hold at WOT for maximum air intake/compression values. Either way, the important thing is that all cylinders showed equal values)
I found that spark plug #5 was only finger tight when removing plugs!
The spark plugs all look very good. Very consistent appearance from one spark plug to another. Based on appearance, if you absolutely had to judge rich vs. lean mixture I would have to say “slightly lean.”
Performed Ignition wire resistance test. Each wire less than 370 ohms.
Fuel injectors – Using a stethoscope, I determined that all of the fuel injectors are firing. The sound was very consistent from one injector to the next. However, just because they are firing doesn’t necessarily mean that they are flowing!
I inspected the fuel injector wiring harness where it comes around the fuel rail bracket on the back of the driver’s side head. I found no apparent chaffing of the wires.
Pulled one spark plug wire at a time while engine running. I was unable to positively identify any one cylinder being dead using this method.
I have ensured that each of the clamps were tight on the air bridge between the mass airflow sensor and throttle body.
I have located and cleaned the following ground points: G101, G102, G104, G105, and G108. I will eventually locate and clean the rest of them.
I removed the battery and battery tray to inspect for previous leakage. None noted. It was very clean below the battery tray.
Performed visual inspection for vacuum leak but could have easily missed it if one exists.
I found the O2 sensor wire laying next to the exhaust pipe. The mesh wire protector looks a bit charred but not burned through.
I’ve read a LOT of archived threads here on the forum related to the term “misfire.”
Some forum members found the cause of misfire to be:
- spark plug was slightly loose
- exhaust leak
- bad/burned/loose plug wire
- corroded PCM connectors
- corroded battery cables
- O2 sensors cross connected
- clogged fuel filter
- bent push rods
- broken valve springs
- bent valves
I’m sure that the cause of my misfire is simple but finding it is a pain in the ars. Please help!!!
I will be sure to post the results once I finally get this problem solved. It was frustrating to see so many posts in the archive that were left unresolved.
Thanks,
Mike
Last edited by MIKER; 12-05-2007 at 10:14 PM. Reason: clarify compression test results
12-04-2007, 12:27 PM
#2
Drifting
why dont you change the plugs and put some new NGK's TR55. I would also get the misfire on my C5 and would pull the plugs and they looked good put them back in and started to look at other things, ended up coming back to the plugs and putting a new set and it fixed the problem.
12-04-2007, 02:10 PM
#4
But a vacuum gauge on it and report back. My guess is a clogged fuel injector or weak coil. If your always getting the P0303, swap one component at a time with a different cylinder (wire/coil/injector) and see if the problem occurs in a different cylinder. Just pick up some injector O-rings and go for it.
12-04-2007, 02:51 PM
#5
Former Vendor
Member Since: Feb 2004
Location: Las Vegas NV
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St. Jude Donor '06 & '12
Couple things you can do.
If you are having an injector problem, you will be getting a P0200 code. Which is "Injector Control Module"
Here are the tests you can do.
1) Use a Noid light on each injector harness. Basically, it plugs into the harness, you will see the LED pulse. This will tell you if it is getting the correct on/off pulse.
2) With your spark plug connected to the wire, put it in a spark tester. set the gap of the tester to the gap of your plug, and start your car. This will tell you if your getting ENOUGH of a hot spark.
3) Take an infared temp gun and and test each exhaust port. Verify that they are in an acceptable range.
4) Take a multimeter and test for proper ower at each coil. Every coil should be hot with the ignition key in the on position.
5) Check for an OPEN ground at each goil. This is usually the case on alot of cars.
Finally,
6) On the passenger side, at the back of the motor, in the top corner of the head, there is a wiring harness that comes right around the head. In ALOT of cases, the wireloom rubs right on the sharp edge of the head. If it rubs through the loom, it will cause one of the coil controller wires to ground out against the head. This will cause the problem you are having. If it is rubbing, even if its not cutting through, take some electrical tape and run it around the harness. Then take a clamp and put it on the harness that rubs the head. This way the head will rub against the clamp and not the harness.
If you are having an injector problem, you will be getting a P0200 code. Which is "Injector Control Module"
Here are the tests you can do.
1) Use a Noid light on each injector harness. Basically, it plugs into the harness, you will see the LED pulse. This will tell you if it is getting the correct on/off pulse.
2) With your spark plug connected to the wire, put it in a spark tester. set the gap of the tester to the gap of your plug, and start your car. This will tell you if your getting ENOUGH of a hot spark.
3) Take an infared temp gun and and test each exhaust port. Verify that they are in an acceptable range.
4) Take a multimeter and test for proper ower at each coil. Every coil should be hot with the ignition key in the on position.
5) Check for an OPEN ground at each goil. This is usually the case on alot of cars.
Finally,
6) On the passenger side, at the back of the motor, in the top corner of the head, there is a wiring harness that comes right around the head. In ALOT of cases, the wireloom rubs right on the sharp edge of the head. If it rubs through the loom, it will cause one of the coil controller wires to ground out against the head. This will cause the problem you are having. If it is rubbing, even if its not cutting through, take some electrical tape and run it around the harness. Then take a clamp and put it on the harness that rubs the head. This way the head will rub against the clamp and not the harness.
12-04-2007, 04:34 PM
#7
Melting Slicks
Thread Starter
why dont you change the plugs and put some new NGK's TR55. I would also get the misfire on my C5 and would pull the plugs and they looked good put them back in and started to look at other things, ended up coming back to the plugs and putting a new set and it fixed the problem.
I'm not against installing new plugs but these only have ~6000 miles on them. However, I've certainly heard of defective spark plugs before!
I've read about the LS6 whistling sound many times here on the forum but is sure does make you suspect a vacuum leak. I cannot rule that one out yet.
But a vacuum gauge on it and report back. My guess is a clogged fuel injector or weak coil. If your always getting the P0303, swap one component at a time with a different cylinder (wire/coil/injector) and see if the problem occurs in a different cylinder. Just pick up some injector O-rings and go for it.
I performed another extensive inspection for vacuum leaks. I was able to easily snug down each of the intake manifold bolts ¾ of a turn. That’s probably not unusual though.
I wish that I could get a steady P0303 code. That would make diagnosis easier. It now seems to have settled on P0300.
Couple things you can do.
If you are having an injector problem, you will be getting a P0200 code. Which is "Injector Control Module"
Here are the tests you can do.
1) Use a Noid light on each injector harness. Basically, it plugs into the harness, you will see the LED pulse. This will tell you if it is getting the correct on/off pulse.
If you are having an injector problem, you will be getting a P0200 code. Which is "Injector Control Module"
Here are the tests you can do.
1) Use a Noid light on each injector harness. Basically, it plugs into the harness, you will see the LED pulse. This will tell you if it is getting the correct on/off pulse.
When I pulled each of the plug wires, one at a time, from the coil it certainly appeared to have PLENTY of spark.
I've got a minor suspicion that the left side catalytic converter could be failing/stopped up. The IR temp gun would be useful for many many things. . ... Santa.... did you hear me?
Finally,
6) On the passenger side, at the back of the motor, in the top corner of the head, there is a wiring harness that comes right around the head. In ALOT of cases, the wireloom rubs right on the sharp edge of the head. If it rubs through the loom, it will cause one of the coil controller wires to ground out against the head. This will cause the problem you are having. If it is rubbing, even if its not cutting through, take some electrical tape and run it around the harness. Then take a clamp and put it on the harness that rubs the head. This way the head will rub against the clamp and not the harness.
6) On the passenger side, at the back of the motor, in the top corner of the head, there is a wiring harness that comes right around the head. In ALOT of cases, the wireloom rubs right on the sharp edge of the head. If it rubs through the loom, it will cause one of the coil controller wires to ground out against the head. This will cause the problem you are having. If it is rubbing, even if its not cutting through, take some electrical tape and run it around the harness. Then take a clamp and put it on the harness that rubs the head. This way the head will rub against the clamp and not the harness.
I've read many times about the harnes in the top corner of the driver side head rubbing on the fuel rail support. I checked that too. No contact between harness and fuel rail support.
12-04-2007, 04:40 PM
#8
Melting Slicks
Thread Starter
I don't doubt it one bit. I believe that the quality of gasoline we are buying is going down hill. I've also read that the modern injectors are more susceptible clogging due to smaller holes for better atomization.
12-04-2007, 04:44 PM
#9
Steady vacuum is what your looking for, 17" of vacuum should be fine as long as the needle is STEADY. It's hard do track down clogged injectors without tools. I put a fuel pressure gauge on the fuel rail and have an injector pulser that allows me to pulse the injector 1 or 3 times with the same pulse width. Turn the key on to pressurize the fuel rail (record the initial pressure) then pulse it and record the final pressure. This is kind of like a compression test where you want to see that they are all very close together.
The other way is to raise all the injectors and fuel rail off the intake and do the same thing but catch the fuel in a glass cup. This way you can see the fuel spray (should look like a nice cone). If you is drippling and spurting it a candidate for hydrosonic cleaning.
You could try a pressurized fuel injection cleaning but I send them out to be flow tested, cleaned and rescreened.
The other way is to raise all the injectors and fuel rail off the intake and do the same thing but catch the fuel in a glass cup. This way you can see the fuel spray (should look like a nice cone). If you is drippling and spurting it a candidate for hydrosonic cleaning.
You could try a pressurized fuel injection cleaning but I send them out to be flow tested, cleaned and rescreened.
12-04-2007, 05:00 PM
#10
Melting Slicks
Thread Starter
While checking for voltage at the injectors I noticed that the battery voltage was only 11.7 volts.
My battery charger is capable of checking the "Battery %", "Alternator %", and voltage.
I connected it to the battery and it showed that the battery was only at 20%. This could be the smoking gun. I've read more than once here on the forum that a weak battery can give you all sorts of problems.
I charged the battery for only a few minutes and it came up to 96% but once disconnected it is quickly dropping off. (down to 45% within 15 minutes)
Oddly enough, this battery still spins the heck out of the starter. I disabled the ignition just to test the starter speed.
How is it that the battery can be getting so weak yet still strong enough to spin the starter like a fresh battery?
It is typical to see your headlights momentarily dim when you apply the brakes or when the cooling fan kicks in, etc. but I have noticed it a lot more lately.
If you cant tell.... I'm really hoping that the battery is causing the problem. I've spent too much time on this already but I'm really trying to focus on proper diagnosis vs. simply throwing dollar$ and parts at it until it runs right.
Maybe I'll just trade batteries with another vehicle for testing purposes before purchasing a new one.
My battery charger is capable of checking the "Battery %", "Alternator %", and voltage.
I connected it to the battery and it showed that the battery was only at 20%. This could be the smoking gun. I've read more than once here on the forum that a weak battery can give you all sorts of problems.
I charged the battery for only a few minutes and it came up to 96% but once disconnected it is quickly dropping off. (down to 45% within 15 minutes)
Oddly enough, this battery still spins the heck out of the starter. I disabled the ignition just to test the starter speed.
How is it that the battery can be getting so weak yet still strong enough to spin the starter like a fresh battery?
It is typical to see your headlights momentarily dim when you apply the brakes or when the cooling fan kicks in, etc. but I have noticed it a lot more lately.
If you cant tell.... I'm really hoping that the battery is causing the problem. I've spent too much time on this already but I'm really trying to focus on proper diagnosis vs. simply throwing dollar$ and parts at it until it runs right.
Maybe I'll just trade batteries with another vehicle for testing purposes before purchasing a new one.
12-04-2007, 05:06 PM
#11
Melting Slicks
Thread Starter
It's hard do track down clogged injectors without tools. I put a fuel pressure gauge on the fuel rail and have an injector pulser that allows me to pulse the injector 1 or 3 times with the same pulse width. Turn the key on to pressurize the fuel rail (record the initial pressure) then pulse it and record the final pressure. This is kind of like a compression test where you want to see that they are all very close together.
The other way is to raise all the injectors and fuel rail off the intake and do the same thing but catch the fuel in a glass cup. This way you can see the fuel spray (should look like a nice cone). If you is drippling and spurting it a candidate for hydrosonic cleaning.
You could try a pressurized fuel injection cleaning but I send them out to be flow tested, cleaned and rescreened.
The other way is to raise all the injectors and fuel rail off the intake and do the same thing but catch the fuel in a glass cup. This way you can see the fuel spray (should look like a nice cone). If you is drippling and spurting it a candidate for hydrosonic cleaning.
You could try a pressurized fuel injection cleaning but I send them out to be flow tested, cleaned and rescreened.
As a side note, I did verify that my fuel pressure was up to spec.
12-04-2007, 05:36 PM
#13
Melting Slicks
Thread Starter
It's not the battery. 
I swapped batteries with another vehicle, went for a test drive, and got the same code.... P0300.
It really craps out at around 5000 rpm. Clatters a bit at higher rpms like it's running low octane fuel.
I have also verified that the O2 sensor wires were not damaged where they had touched the exhaust as mentioned earlier in the post.
Keep the ideas coming guys.
I swapped batteries with another vehicle, went for a test drive, and got the same code.... P0300.
It really craps out at around 5000 rpm. Clatters a bit at higher rpms like it's running low octane fuel.
I have also verified that the O2 sensor wires were not damaged where they had touched the exhaust as mentioned earlier in the post.
Keep the ideas coming guys.
12-04-2007, 07:20 PM
#15
12-05-2007, 12:08 PM
#16
Melting Slicks
Thread Starter
I just returned from a test drive following the installation of all new spark plugs. (NGK TR55 gapped @ .050)
The bad news is that it did not fix the problem. However, it did narrow it back down to the P0303 (cylinder 3 misfire). That is going to be easier to diagnose than the P0300 (multi cylinder misfire).
Cylinder 3 has good spark and good compression so I'm going for the fuel injector next.
The bad news is that it did not fix the problem. However, it did narrow it back down to the P0303 (cylinder 3 misfire). That is going to be easier to diagnose than the P0300 (multi cylinder misfire).
Cylinder 3 has good spark and good compression so I'm going for the fuel injector next.
12-05-2007, 05:28 PM
#17
Melting Slicks
Thread Starter
The problem still exists.
I swapped out the #3 fuel injector with a spare that I had.
Following installation of the #3 injector the first code was a P0300 (multi cylinder misfire) during hard acceleration. I cleared the P0300 and the next two times it set a P0303 code.
To top it all off I ran it nearly out of fuel and filled up with a fresh batch of 93 octane. No change.
Next I will swap the #3 coil with the #5 coil.
Thinking ahead, is it possible to have good cranking compression with a cracked/broken valve spring? Im just wondering if it is possible for a broken spring to control the valve during the low rpm produced by the starter yet unable to seat the valve during high rpm such as when the engine is running?
Another question. Is it possible to have a clogged up catalytic converter without the computer setting a code?
I swapped out the #3 fuel injector with a spare that I had.
Following installation of the #3 injector the first code was a P0300 (multi cylinder misfire) during hard acceleration. I cleared the P0300 and the next two times it set a P0303 code.
To top it all off I ran it nearly out of fuel and filled up with a fresh batch of 93 octane. No change.
Next I will swap the #3 coil with the #5 coil.
Thinking ahead, is it possible to have good cranking compression with a cracked/broken valve spring? Im just wondering if it is possible for a broken spring to control the valve during the low rpm produced by the starter yet unable to seat the valve during high rpm such as when the engine is running?
Another question. Is it possible to have a clogged up catalytic converter without the computer setting a code?
12-05-2007, 05:55 PM
#18
Melting Slicks
Thread Starter
I swapped coil #3 with coil #5. I made it set a P0300 code 4 times.
I'm running out of ideas.
I've searched the wiring harness for damage of any sorts (several times) but have not found any.
My fuel pressure is 55 psi with key on, engine off. It reads 60 psi with engine running. Could the fuel pump show good pressure at idle yet fail to deliver during high demand?
I wish my fuel pressure test gauge had a longer hose on it so I could monitor it during hard acceleration.
I might have to bite the bullet and have it hooked up to the mother ship to aquire more data.
I'm running out of ideas.
I've searched the wiring harness for damage of any sorts (several times) but have not found any.
My fuel pressure is 55 psi with key on, engine off. It reads 60 psi with engine running. Could the fuel pump show good pressure at idle yet fail to deliver during high demand?
I wish my fuel pressure test gauge had a longer hose on it so I could monitor it during hard acceleration.
I might have to bite the bullet and have it hooked up to the mother ship to aquire more data.
Last edited by MIKER; 12-05-2007 at 05:59 PM.
12-05-2007, 06:40 PM
#19
I swapped coil #3 with coil #5. I made it set a P0300 code 4 times.
I'm running out of ideas.
I've searched the wiring harness for damage of any sorts (several times) but have not found any.
My fuel pressure is 55 psi with key on, engine off. It reads 60 psi with engine running. Could the fuel pump show good pressure at idle yet fail to deliver during high demand?
I wish my fuel pressure test gauge had a longer hose on it so I could monitor it during hard acceleration.
I might have to bite the bullet and have it hooked up to the mother ship to aquire more data.
I'm running out of ideas.
I've searched the wiring harness for damage of any sorts (several times) but have not found any.
My fuel pressure is 55 psi with key on, engine off. It reads 60 psi with engine running. Could the fuel pump show good pressure at idle yet fail to deliver during high demand?
I wish my fuel pressure test gauge had a longer hose on it so I could monitor it during hard acceleration.
I might have to bite the bullet and have it hooked up to the mother ship to aquire more data.
I'm still voting for clogged injectors.
12-05-2007, 08:39 PM
#20
Melting Slicks
Thread Starter
You may be right. In time we will know.
I can understand injectors becoming clogged over time but how could it have happened within a few days?
Doesn't the filter capture debris smaller than the injector orifices?
Since my last post, I've even washed the car.... and...It's still misfiring. 
I'm grasping now... I let the car sit long enough for the exhaust to cool down. Started the engine and grabbed onto both exhaust pipes directly behind the catalytic converters to see if one side heated up sooner than the other.
They both heated up at the same rate. I wonder if that is a worthy test when checking for a clogged catalytic converter?!?
I can understand injectors becoming clogged over time but how could it have happened within a few days?
Doesn't the filter capture debris smaller than the injector orifices?
Since my last post, I've even washed the car.... and...It's still misfiring.
I'm grasping now... I let the car sit long enough for the exhaust to cool down. Started the engine and grabbed onto both exhaust pipes directly behind the catalytic converters to see if one side heated up sooner than the other.
They both heated up at the same rate. I wonder if that is a worthy test when checking for a clogged catalytic converter?!?