alan111

Hi Everyone,

On Tuesday morning last week, I got a solid CEL about 30 seconds after starting the car up in the morning. Later than night, I check the codes and got P0300 P0305 P0306. The car has been driving strong, no shortness or stumbling of power and I figured it may have been from some bad gas, so I just reset the CEL.

I have driven about 300 miles since last week until now.

This morning (a week later) I started my car in the morning and about 30 seconds after starting it, I got the CEL again. I haven't had a moment to check the codes, but I'm guessing it would be the same.

Any ideas? I'm really not concerned because the car is pulling strong and I have not noticed even a slight change in performance.

Anything would help!

It's an '02 C4 Cab with 53k miles.

Thanks

chsu74

You may want to join Renntech. Loren runs a great site for this type of information.

911SLOW

P300 misfires

P305 cylinder 5
P306 cylinder 6

Misfire, cylinder 5 - 6
Diagnosis conditions
• A cycle of 1,000 crankshaft revolutions is evaluated (for misfire
damaging to the TWC, 200 crankshaft revolutions). The misfire
rates are compared with a threshold value. If the misfire rate is
greater than the threshold value, a fault is recorded in the memory.
• The Check Engine Malfunction Indicator Lamp (MIL) is switched
on and stays on when the misfire rate lies above the threshold
value at which the emission limit values are exceeded during two
consecutive driving cycles (in the case of EOBD 3 driving
cycles).
• If the misfire rate may lead to permanent damage to the TWC,
the Check Engine MIL flashes. If the misfire rate is no longer
reached during the first journey, the MIL goes out. If the rate is
reached during the next journey, the MIL flashes. If this misfire
rate is subsequently no longer reached, the MIL changes to a
continuous light.

Notes:
♦ When using a block heater (for heating coolant), start and driving
off difficulties or misfiring can occur if the block heater was connected
for less than 4 hours.
♦ When the fuel tank is driven to empty, misfiring can occur. For
this reason the fuel level in the tank is also stored in the memory
when misfiring occurs. If the tank was nearly empty, there was
probably no fault. Erase fault memory and road test vehicle.
♦ In the event of a short circuit to B+ or ground in the oxygen sensors
ahead of the TWC, the mixture becomes too lean or too
rich. This can cause misfiring. If, in addition, an oxygen sensor
signal fault ahead of the TWC is stored in memory, first correct
this fault and then road test the vehicle.



Possible fault cause
♦ Fault in ignition system
♦ Fault in injection system
♦ Flat-base tappets (valve lift fault)
♦ Mixture too rich
♦ Mixture too lean


Also check:

if VarioCam does not switch over completely

ignition coil(s)
♦ Measure resistance between Pin
1 and Pin 15
0,3 to 0,7 Ω
(at 20 °C)

spark plugs

Check for air leaks in intake air system

Carry out pressure loss test

check fuel pressure

function12

I would bet bad coil packs.
You can swap them to different cylinders to see if the problem follow the coil pack. If it does then you know it is time replace them.

seanmcr6

I too would suspect coil pack....

To John.....whoa whoa whoa....Block Heater? Everyone, including 3 Porsche dealers...said there was no such option for the 911?!

oh and who's the hottie in your avatar?

Macster

She's his block heater!

Sincerely,

Macster.

Macster

Add my vote to the coil pack tally.

Something to keep in mind: There have been a few (very few) cases where misfires and misfires confined to just one bank have been due to a bad MAF, but the majority of persistent misfiring is almost always coil packs.

Porsche owners in some areas of the country (or some countries -- UK comes to mind) seem to go through coil packs like crazy. In other places I talk to the techs and replacing coil packs is very rare. They just don't seem to go bad.

Sincerely,

Macster.

alan111

Well I did not get a chance to check the codes.
I drove about 180 additional miles since this posting. On Thursday, I came home from my 65 mile commute. Went inside and ate dinner. Came back out for a quick grocery run and the CEL was gone and has not returned as of this evening. Could have just been bad gas?

02TX996Cab

Quite possibly, or maybe some crud/water in the tank. Or, since you had just started the car from cold (if I understood your posts correctly), maybe something to do with the secondary air pump system?

The fact the CEL cleared suggests the problem hasn't recurred for some number of driving cycles (10?).

I've had a similar issue with my '02 C2 Cab...replaced plugs and noticed one bad coil pack which I subsequently replaced. No issues now.

Good luck.

jumper5836

Worst case, scored cylinder 6. Have it checked out. New engine time.

gio_73

Alan111,
I have a very similar situation.
What's the latest?

Thanks

Macster

Depending upon how similar there may not be anything wrong.

Earlier this year (Feb time frame) both of my cars upon cold start shortly thereafter turned on the check engine light and the error codes were misfires.

In the case of the Turbo the engine upon cold start and briefly thereafter ran a bit rough, uncharacsteristically rough.

The Turbo had sat out overnight in a pretty heavy rainstorm. I knew the engine, at least part of it, was wet because I could hear the belt squealing a bit upon engine start and for a moment or two (intermittently) afterwards.

I read the codes, wrote them down, cleared them. The car run just fine and has not exhibited any untoward behavior of this or any other kind since.

In the case of the Boxster I ran the engine a very short time -- moving cars about -- and left it parked in a covered parking space for a few days while I was out of town. Upon starting the car the check engine light came on quite soon after, but the engine did not exhibit any odd behavior. I read the codes thinking I'd see the usual P0430 but was surprised to see some misfire codes and a P0420 as well.

I cleared the codes and while the P0430 had reappeared (it was appearing before this misfire/P0420 incident) the P0420 and misfire codes have not reappeared.

The Boxster is on its original coils, now with over 244K miles on them.

The Turbo has its original coils now with over 67K miles.

Now I'm not saying every engine shoudl get this kind of coil life. I elected to clear the codes and see if they returned. Had they returned the Turbo was covered under a CPO warranty and it would have received new coils.

Had the Boxster had misfires again I would have replaced the coils. I certainly have gotten my money's worth out of them.

In your car's case if the engine light is off, remains off, if the engine is running ok, sounding ok, the misfires might have been a transistory event. In this case, the usual procedure is to read the codes, write them down, clear them then resume driving the car.

If the check engine light comes on again, or the engine starts misbehaving the misfires might have been an early warning sign of some trouble (maybe nothing more than one or more bad coils) and you need to have this engine misbehavior investigated.

Sincerely,

Macster.

alan111

The CEL has not reappeared.

alan111

I'd just like to update everyone on here regarding this issue.

I just got my car back from Rich at ROCS Auto in Belleville. He was very professional and knowledgeable. I recommend him to anyone in the tri-state area.

As I'm sure you all guessed it, the problem lied in the coil packs. After inspecting each one, they were all cracked (I saw them myself). All 6 coil packs and spark plugs were changed. The CEL has not returned.

The coil packs are relatively inexpensive. It seems that the coil packs or spark plugs were never changed.

Hope this helps someone.

Thanks again.

dallison28

It's amazing how inexpensive these coil packs are compared to any other car.