2000 Pontiace Bonneville 3.8 non supercharged throwing P0300 code and sometimes a P0305. Running very rough. Kind of like a miss but different than when I pull one spark plug almost like it'* not firing correctly maybe out of time almost. Here is what I have done:

New MAF
New 02 sensor
New fuel filter
New wires and plugs
have checked fuel pressure and injectors
checked coils and plug wires
Replaced the gas and put good fuel in

I'm at a loss here. Doesn't seem to be the fuel pump or any of the above that I have replaced and looking for some guidance. Hoping someone else has had this problem. I have read all of the posts I could about this and I'm stumped.

When you drive the car down the road it barely has any power and the SES light will flash. Even when you rev it up while parked it just sounds like it'* missing and not firing on all cylinders.

Could this be related to a crankshaft or camshaft postiion sensor? Ignition control module? Each of these is slowly draining me so want to know what I should try next.

Thanks in advance as this forum has been a big help to me so far.

Take a look at this. https://www.gmforum.com/showthread.p...40#post1390843

You didn't mention checking the ICM. Clean it and look for any corrosion. Also post up the numbers you have when testing the coils. Check your cat, it could be plugged up.

All of the coils were around 6.5 and .7. I did also pull the ICM plug and cleaned up the connectors, also added some dielectric before I re-attached. Yesterady I also dropped the cat to see if it would change anything and while it was much louder you could still feel the hesitation.

I would have to double check, but I don't think those coil numbers are the best. about 5.7 and .5 is what you want. Those numbers are in but high. Is there any chance you can get another set to try? Also, what plugs are you running and what do you have them gapped at?

i think i would run a cvompression test to verify the mechanical end of it.

I am curious about some things here:

How did the old plugs look when you pulled them out?
How long has this been going on?
Did the problem gradually come on, or all of a sudden?
Has anything changed affected the issue at all?
Was it running exactly the same with and without the exhaust connected? Or was it a little better, but still not perfect?

Document ID# 432115
2000 Pontiac Bonneville
DTC P0300 Engine Misfire Detected

<A href="http://127.0.0.1:9001/servlets/BlobShtml?ShtmlFile=432115&evc=sm&pubid=195&cellId =24979&mspsdsubkey=949#ss1-432115">Circuit Description

The powertrain control module (PCM) has the ability to detect a misfire by monitoring the 3X reference and camshaft position input signals from the ignition control module. The PCM monitors crankshaft speed variations (reference period differences) to determine if a misfire is occurring. If 2 percent or more of all cylinder firing events are misfires, emission levels may exceed mandated standards. The PCM determines misfire level based on the number of misfire events monitored during a 200 engine revolution test sample. The PCM continuously tracks 16 consecutive 200 revolution test samples. If 11 or more misfires are detected during any 10 of the 16 samples, DTC P0300 will set. If the misfire is large enough to cause possible 3-way catalytic converter damage, DTC P0300 may set during the first 200 revolution sample in which the misfire was detected. In the case of a catalyst damaging misfire, the MIL will flash to alert the vehicle operator of the potential of catalyst damage.
<A name=ss3-432115><A href="http://127.0.0.1:9001/servlets/BlobShtml?ShtmlFile=432115&evc=sm&pubid=195&cellId =24979&mspsdsubkey=949#ss3-432115">Conditions for Setting the DTC

The PCM is detecting a crankshaft RPM variation indicating a misfire sufficient to cause 3-way catalytic converter damage or emissions levels to exceed mandated standards.
<A href="http://127.0.0.1:9001/servlets/BlobShtml?ShtmlFile=432115&evc=sm&pubid=195&cellId =24979&mspsdsubkey=949#ss4-432115">Action Taken When the DTC Sets

• The PCM will illuminate the MIL during the second consecutive trip in which the diagnostic has been run and failed unless three way converter damage is possible in which case the light will illuminate after the first failure.
• If equipped with traction control, the PCM will command the EBTCM via the serial data circuit to turn OFF traction control, and the EBTCM will illuminate the TRACTION OFF lamp.
• The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

<A href="http://127.0.0.1:9001/servlets/BlobShtml?ShtmlFile=432115&evc=sm&pubid=195&cellId =24979&mspsdsubkey=949#ss1-311985">Conditions for Clearing the MIL/DTC

• The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.
• The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
• The DTC can be cleared by using a scan tool.

<A href="http://127.0.0.1:9001/servlets/BlobShtml?ShtmlFile=432115&evc=sm&pubid=195&cellId =24979&mspsdsubkey=949#ss5-432115">Diagnostic Aids

The scan tool provides information that can be useful in identifying the misfiring cylinder. If the DTC P0300 is currently stored as DTC status Failed Since Code Clear, the misfire history counters (Misfire History Cyl #1-#6) will still contain a value that represents the level of misfire detected on each cylinder. The scan tool displayed misfire counter values (Misfire History Cyl. #1 through #6) can be useful in determining whether the misfire affects a single cylinder, a cylinder pair (cylinders that share an ignition coil - 1/4, 2/5, 3/6), or is random. If the largest amount of activity is isolated to a cylinder pair, check for the following conditions:
A misfire DTC may set if components that affect the crankshaft position sensor have been recently replaced, and the CKP System Variation Learn Procedure has not been performed. If the diagnostic table does not identify a problem then perform the CKP System Variation Learn Procedure .
If the misfire is random, check for the following conditions:

• Crankshaft Position System Variation Refer to CKP System Variation Learn Procedure . The crankshaft position system variation compensating values are stored in the PCM non-volatile memory after a learn procedure has been performed. If the actual crankshaft position variation does not match the crankshaft position system variation compensating values stored in the PCM, DTC P0300 may set. The crankshaft position system variation learn procedure is required when any of the following service procedures have been performed:
  • The PCM has been replaced.
  • DTC P1336 has set.
  • The engine has been replaced.
  • The crankshaft has been replaced.
  • The harmonic balancer has been replaced.
  • The crankshaft position sensor has been replaced.
  • Any engine repairs which disturb the crankshaft/harmonic balancer to crankshaft position sensor relationship.
• Check the secondary wires associated with the affected cylinder pair for disconnected ignition wires or for excessive resistance. If any spark plug wire resistance is more than the specified value, replace the affected spark plug wires. VIN 1 Spark Plug Wires Resistance 3280-4921 ohms per meter (1000-1500 ohms per foot)
  VIN K Spark Plug Wires Resistance 3280-4921 ohms per meter (1000-1500 ohms per foot)
• A damaged or malfunctioning ignition coil. Check for cracks, carbon tracking, or other damage. Also check the coil secondary resistance. The secondary resistance should be within the specified range. Ignition Coils Secondary Resistance 5000-8000 ohms.
• Switch ignition coils and retest. If the misfire follows the coil, replace the ignition coil.
• Check the system grounds. Ensure all the connections are clean and properly tightened.
• A mass air flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition. Try operating the vehicle within the Failure Records conditions. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the MAF sensor.
• If the PCM stops receiving data from the EBCM/EBTCM, DTC P0300 can set due to a loss of rough road data. Check for stored ABS/TCS DTCs, especially DTCs related to a serial data malfunction. Refer to Diagnostic System Check - ABS in Antilock Brake System .
• Vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Check for disconnected or damaged vacuum hoses, an incorrectly installed or malfunctioning crankcase ventilation valve, or for vacuum leaks at the throttle body, the EGR valve, and the intake manifold mounting surfaces.
• Perform a fuel system pressure test. A malfunctioning fuel pump, plugged fuel filter, or malfunctioning fuel system pressure regulator will contribute to a lean condition. Refer to Fuel System Pressure Test (VIN K) or to Fuel System Pressure Test (VIN 1)
• Check the fuel injectors. Refer to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Between 10-35 Degrees C (50-95 Degrees F) or to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Outside 10-35 Degrees C (50-95 Degrees F)
• Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
• Check the EGR system for a leaking valve, adapter, or feed pipes which will contribute to a lean condition or excessive EGR flow.
• Excessive open loop operation caused by extended idling or short trip driving may leave deposits on the heated oxygen sensors. The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to be set, review the freeze frame and fail records data for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC P0300 to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures less than 80°C (176°F), the condition described above is very likely the cause of the DTC P0300 being set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows above 15 gm/*.

Important:

If the level of misfire was sufficient to cause possible catalyst damage (if the MIL was flashing), ensure that the DTC P0420 test is completed and passed after verifying the misfire repair.

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.