CEL P0303

[Paul Fraser]

Hi. I have got a CEL -- flashing initially -- and a rough running engine, especially noticeable at low revs. My OBD2 gives a P0303 which is a cylinder 3 misfire, damaging to the cat. Any ideas what may be causing this misfire?

48000 mile service around 250 miles ago.

Thanks.

PS I assume P0303 is bank 1 and the left hand side of the engine.

[Loren]

Since it is only one cylinder it is likely the spark plug, ignition coil (on that plug), cable to the plug, or a bad injector.

[Paul Fraser]

Thanks for the diagram above; useful.

This was a much harder job than I thought it would be. The coils and spark plugs are very hard to access and work with. I would have thought that the spark plugs at the back are difficult if not impossible to take out. What do the OPCs do? Drop the engine?

Anyway, the first thing I did wrong was jam a ratchet in the innards of the car trying to take out the rear cover plate retaining bolt. That wasted a lot of time and was eventually extracted the second go I had at sorting the problem. Once this was done I swapped the coils on 3 and 2, and, hey presto, the fault code changed to 0302, but only once I had the wheel on, had packed my bags and set off home. Returned to my father's, got replacement (cost £37, so I got two).

The outer cover was cracked so I assume that the dielectric inside had started breaking down as a result of this. Pic to follow.

What does the coil do? Is is some kind of high voltage capacitor system?

[Loren]

Plugs 1 and 4 are the tough ones since the exhaust is partly in the way. Those two will taken as long to remove as the other four put together.

The right tools are essential to removing the spark plugs. I use a ball-socket hex wrench (or do you say spanner?) for the coils. The plugs will need a small 3/8 inch drive socket wrench, a 4 inch "wobbler" extension and of course a deep spark plug socket. For plugs 1 and 4 you might find it easier to loose the spark plug then remove the wrench and wobbler extension and then use the extension (or a shorter one) to pull the plug and the plug socket out.

Yes, the coils are just that. Did you notice that most modern auto designs no longer have one large ignition coil? The coil packets now do this individually. So, if you have a cracked coil - by all means replace it.

[jcraw]

Since it is only one cylinder it is likely the spark plug, ignition coil (on that plug), cable to the plug, or a bad injector.

Hello, would this diagram be the same Boxster? I'm having the same issue and want to try switching my coils on 2 and 3 cyl.

Thanks!!

[Loren]

Hello, would this diagram be the same Boxster? I'm having the same issue and want to try switching my coils on 2 and 3 cyl.

Thanks!!

As log as you know which way your engine is facing... :D

The pully side faces the front in a Boxster. In a Carrera the pulley side faces the rear.

[Kim]

Loren,

Just so I will be prepared when the time comes (hate to start a project, then have to go shopping for tools);

Can you more fully describe a "ball-socket hex wrench for the coils" I'm a fairly experienced shade tree guy, but the "ball-socket" part doesn't ring a bell.

And:

Can you tell me the required size for the "deep spark plug socket". I have a couple of the common sizes, but haven't investigated far enough to know if one of them will fit my 996 plugs.

Thanks,

Kim

2000 Cab

[Loren]

Loren,

Just so I will be prepared when the time comes (hate to start a project, then have to go shopping for tools);

Can you more fully describe a "ball-socket hex wrench for the coils" I'm a fairly experienced shade tree guy, but the "ball-socket" part doesn't ring a bell.

And:

Can you tell me the required size for the "deep spark plug socket". I have a couple of the common sizes, but haven't investigated far enough to know if one of them will fit my 996 plugs.

Thanks,

Kim

2000 Cab

A Ball socket hex wrench allows you to be offset as much as 30 degrees and still turn the hex bolt. Here is a link to a set I bought a few years ago Ball End Hex Wrenches. Be sure and get the metric ones.

The spark plug socket is pretty standard 5/8" is US. The spark plug socket is common but you will need a wobble extension to get the angle a couple of the plugs.

[Kim]

A Ball socket hex wrench allows you to be offset as much as 30 degrees and still turn the hex bolt.

The spark plug socket is pretty standard 5/8" is US. The spark plug socket is common but you will need a wobble extension to get the angle a couple of the plugs.

Thanks .... I have a set and have long sworn by the ball end allen wrench. I was mentally picturing some sort of box end wrench with a universal incorporated somehow. I guess that's because I associate the English term "spanner" with an plain jane open end wrench.

I also have the 5/8 plug socket. I have found it to be about 50/50 with the 13/16 in American and European cars over the years.

Kim

2000 Cab