I have a 1998 2.2L Chevy Cavalier. One day it was running fine, the next day it had severe misfires and set code PO300 (Random/Multiple Cylinder Misfire). I changed the plugs and wires. Slightly better but still severe misfires. I did a cylinder drop test (pulled wire from each plug - one a time with car idling). Car sputtered as expected when pulled plug on cylinders 2 & 3. There was no change when I pulled plugs for cylinders 1 & 4 - No spark whatsoever. I changed the coil that corresponds to cylinders 1&4.
Car ran great right after that. I let it sit and the next day car began misfiring again - no spark in cylinders 1&4 again.
Next I put my original "suspected bad" coil in the position of the coil for cylinder 2&3 and had spark from it - so the coil that I thought was bad appears to actually be still good.
So, plugs are good, wires are good, and coils are good.
Could it be ignition control module or something else?
Ignition mod. grounds,pcm or timing belt could all be it but, I would have to look at timing first.
SOURCE: 03 chevy express 6.0 misfire
P0300 Diagnostic Code - Random Misfire
Technical description:--
Random/Multiple Cylinder Misfire Detected:---
Exactly what does this code means:--
Basically this means that the the car's computer has detected that
not all of the engine's cylinders are firing properly.
A P0300 diagnostic 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:--
the engine may be harder to start.the
engine may stumble / stumble, and/or hesitate.
other symptoms may
also be present…There may be rough idle,
sputters and stalls and jerks.
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 for this error problem:--
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 vehicle, 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 un-metered air getting past the airflow sensor,
or an EGR valve that is stuck open.
Thanks. Keep updated for any more query. You can rate this
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SOURCE: po300 random mulitple misfire detected p1399
If only one of your cylinders was misfiring, you probably would be getting a more specific code than P1399.
Also check the distributor rotor along with the cap and coils and wires (as mrgreenz suggests); the EGR valve to make sure it doesn't leak; your fuel pressure which can cause random misfires if the pressure is too low; and injectors if they are really dirty. If you have really high mileage, I probably would first just change out the plug wires with a new set, then reset the DTC and see if the code comes back.
Hope this is helpful as well.
Testimonial: "I changed the plugs and put an additive to clean the fuel injectors and changed the egr valve. Still running rough when at idle"
SOURCE: Random misfire on all cyliner a po300 code pops up...
It sounds like the coil is breaking down or the cam sensor may be at fault for the misfiring. Use an inline tester and connect from the coil tower to the spark plug wire to check for a good steady fire. Do this on all coil wires to spark plugs. The best time to do this is at night so you can see it fire. You may want to remove the spark plugs and inspect them for a fouling condition. If all is well then look at the cam sensor for the problem. Hope this will help you.
SOURCE: GMC SAFARI 2001 4WD. RANDOM MISFIRE DETECTED
2 things come to mind, confirm you have proper fuel pressure, and if you've got a MAF (mass air flow sensor)
in the intake hose to throttle body, remove it, and spray it clean with Tuner spray cleaner, or electrical spray cleaner from radio shack or similar store, and then try it. Not uncommon for the MAF sensor to dirty and cause what your experiencing. If that doesn't cure it, start checking EGR and EVAP system.
SOURCE: Cylinder Misfires
It could be your spark plugs or a coil. To see if it's a coil move the coil from #5 to #6 the miss will change to that cylinder with code p0306 and change #1 to #3 and see if it changes to p0303. If it does replace all the coils. You change all coil because if one or two go you know the rest are not far behind
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