Went out and bought me a OSDII Code Reader. I'm getting a Random Misfire Detected code P0300. The misfire is intermittant. Idles real rough, then other times it idles smooth. Seems to be worse after car is warm and at an idle. What's my next step?
Random/Multiple Cylinder Misfire Detected
What does that mean?
Basically this means that the the car's computer has detected that not all of the engine's cylinders are firing properly.
A P0300 OBD code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.
Symptoms
Symptoms may include:
the engine may be harder to start
the engine may stumble / stumble, and/or hesitate
other symptoms may also be present
Causes
A code P0300 may mean that one or more of the following has happened:
Faulty spark plugs or wires
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector(s)
Burned exhaust valve
Faulty catalytic converter(s)
Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective computer
Possible Solutions
If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.
Yes, I have. It was a failed crankcase vent valve. Pull the breather hose off your valve cover and cork it. If the car runs fine, then it's your crankcase valve.
No a timing chain tensioner wont cause misfires. Its electrical related, IE plugs or coils..Try the simple things first like plugs, if it still occurs then you might have an air leak causing a lean run condition and the engine detects this throwing a random misfire code due to improper fuel ratio..If it where a mas air meter or O2 sensor you would get a fault code specific for that..
I had very similar issue. Getting a random miss, usually at startup and usually when increased RPM it cleared up. Only on two occasions did it not clear up and stumbled through the entire RPM band. Both times it threw a CEL. The last time, a couple days ago, I pulled the code and got cylinder misfire on the #1 cyl.
The odd thing is, I've learned that simply turning the car off, letting it sit for 30 seconds and restarting cleared it competely up. The CEL stayed on but the miss was gone.
Any idea what that could point to? Sensor malfunction? O2?
Chris
When you let the engine sit, it might be leaking out pressure. This might be due to exessive pressure being builtup in the motor. Check my posts above and try pulling the breather hose off the valve cover and corking it. You have a different motor than mine so it might not be that. If it's only #1 cylinder you should check the spark plug for fouling or breakage or oil soakage.
Thanks for the tip, I'll try the hose.
I forgot to mention I pulled the plugs earlier and they are spotless. Not even any oil in any of the wells at all.
Thanks for the tip, I'll try the hose.
I forgot to mention I pulled the plugs earlier and they are spotless. Not even any oil in any of the wells at all.
Maybe it's a cracked plug wire. Try switching wires and see if you get the misfire on a different cylinder. Also, try replacing the plug. Just because it looks good doesn't mean it is.
Im getting the same code on my e39, but my car has never ran better. I do have a bank 1 sensor 1 code, bank 2 sensor 1 as well. I used some techron and my cel came on immediately after pouring it in the tank..
I wish there was a definitife answer to this P0300/ P1351 problem. My 2.5L '01 Z3 sometimes idles really rough, turn it off, then on and all normal. I also had codes for the secondary air injection and found a bad hose right at the exhaust valve associated with the sec air inj system. Also the small vacuum connection at the sec air gizmo had deteriorated. Cleared the codes but P1351 (#5cyl fuel cutoff) persists. anyone know how much vacuum should be there on startup while air pump is on, and when air pump stops? that would help me . All this started last fall when putting the car away. Ill try the coil thing but not convinced it is electrical because at times it runs beautifully.
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