Mechanics

RANDOM MISFIRE ON ALL CYLINDERS

1999 Honda Civic

Engine Mechanical problem
1999 Honda Civic 4 cyl Front Wheel Drive Manual 91000 miles

Ok, my car is throwing codes p0300-p0304 and p1399, they are cylinder misfire 1-4 and random cylinder misfire. I've changed my distributor, spark plugs and wires, pcv valve, fuel filter, o2 sensor, ground wires, valves adjusted, valve cover gasket, compression test came out good, and injectors are firing. But I still keep getting these codes. Any ideas?
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Lopylobster
September 17, 2008.



Random misfire code can be set on newer vehicles with OBD II onboard diagnostics when multiple misfires occur randomly in multiple cylinders. The cause is typically a vacuum leak in the intake manifold, throttle body or vacuum plumbing, a defective Exhaust Gas Recirculation (EGR) valve that is leaking exhaust into the intake manifold, or even bad gasoline. Less common causes include bad spark plug wires, worn or fouled spark plugs, a weak ignition coil, dirty fuel injectors, low fuel pressure, or weak valve springs. If a misfire is occurring in only one or two cylinders, you will usually find a misfire code for that specific cylinder rather than a random misfire code.

Rasmataz
Sep 17, 2008.
The Car has no EGR because it's a SI model, and it's all the cylinders misfiring. Not sure where to go from here.

Tiny
Lopylobster
Sep 19, 2008.
Normally a P300 Random Misfires are caused by vacuum leak and bad fuel-Start by checking fuel pressure and follow up with the rest above.

Rasmataz
Sep 19, 2008.
Alrighty, couldnt find a vacuum leak, but im going to check the fuel pressure and get back to you. Thanks

Tiny
Lopylobster
Sep 20, 2008.
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 SolutionsIf 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.

Rasmataz
Sep 20, 2008.