random misfire/codes P300, P301 and P305

[jjanari]

**An update**

I was finally able to check the coil packs on cylinder's 1 and 5. I'm fairly certain that the connector to the coil pack on #5 apparently wiggled itself loose as the connector came off too easily. In other words, I don't think it was "clicked" in properly when I changed the plugs our around 200 or 300 miles ago. As for #1, I"m not so sure, but I unplugged and replugged it in, making sure I felt/heard the audible click. So far, I've driven about about 8 miles w/o any misfiring or CELs. However, I'm not so sure if the car is pulling as hard (accelerating) as it was before (I didn't disconnect the battery). Nevertheless, the engine is idling smoothly. I'll update with any changes.

2002 Boxster 2.7; 90k miles

I was nearly 20 miles away from completing a 180 mile trip when i started feeling hesitation while cruising at around 75 mph on the highway. I then began feeling a distinct engine vibration, suggesting misfire. Soon after, I got a flashing CEL for a few seconds, followed by a hard CEL. I pulled off the next exit. By the time I pulled off, it felt that I could barely accelerate and the car didn't want to go over 3k rpm; however the CEL was no longer on. I had it flatbedded to my house. I've only got an actron scanner, which pulled the following codes:

P300 (random misfire)

P301 (misfire cylinder 1)

P305 (misfire cylinder 5)

When I re-started the car after letting it cool down, the idle surged to around 3k or so, but then dropped down. however, the engine was running rough (though no CEL, but of course did not have it on for very long, just enough to limp it into my garage). after shutting the car off, there was a very distinct smell of gas fumes.

Recent work done to the car (w/in the past 300 miles): changed plugs to OEM Berus, cleaned throttle body and MAF (the latter two to fix a hunting idle, which worked).

My questions:

1) for diagnosis, I should begin by checking the conditions of coil packs 1 and 5 for noticeable cracks, correct?

2) is there a way to test the coil packs if there are no visible cracks to the coils? would it be of any benefit to switch the coil packs to see if the misfires follow the other cylinders?

3) any other suggested diagnostics? I'm thinking if the coil packs don't solve it, I should just have it towed to my local indy, which has better diagnostic tools than I have..

thanks in advance!

-jimmy

Edited May 19, 2009 by jjanari

[bmohr]

to chime in here i would say with those codes and symptoms its a clear sign of cracked coils, but as you said they were recently replaced maybe just the coil leads/connection wires popped off or shorting out. Ensure all connections to coil paks "click" into place first. Then other routes can be looked into.

[Loren]

...or the electrical connectors on the coils are not all the way on.

[jjanari]

thanks guys.

Loren,

you posted the cylinder location for a 996, iirc, in another thread. Is the cylinder location the same on the 2.7 boxster? I would imagine so. thanks.

[Loren]

thanks guys.

Loren,

you posted the cylinder location for a 996, iirc, in another thread. Is the cylinder location the same on the 2.7 boxster? I would imagine so. thanks.

Yes, but the Boxster engine sits in car turned 180 degrees.