csertich

Threw a CEL code on a road trip this weekend. Read the codes today:

P0300
P0301
P0304
P0305
P0306

P0300 description from reader:
"Cylinder misfire detected-random cylinders. Probably cause:
-Ignition system fault-spark plug(s), ignition wires, coil, vacuum leak, injector fault, high or low fuel pressure."

Other codes descriptions are the same, except are specific to cylinders (P0301 is cylinder 1, etc.).

CEL has gone lit up once and stayed on for a day, gone off after sitting over night and then came back on during my drive home after starting the car after a gas fill up. And then was off again this morning after sitting overnight.

So, what action(s) should I take? Car runs fine. Looked around for a vacuum leak and found nothing obvious.

Thanks in advance for your ideas....

chuck

cabrio993

How about your belts? Recently changed? What brand? Porsche OEM?

mongrelcat

Sorry Chuck I'm sure more solid replies will come along but my first hunches are;

1) Make sure the gas cap seal is solid (can you possibly swap caps with someone?)

2) Run a can each of lubro-moly ventil-sauber and jectron through the system.

3) How old are the 02 sensors?

csertich

Thanks. Belts replaced about 20k miles ago (30k service done at 26,000 miles-about three years ago). Car has 46,000 miles now. Belts are OEM. I'll take a good look at them. Happen to have a spare set in the trunk.

csertich

Gas cap is about a year old. I usually give it about three clicks when I put it on.
I did run Techron through the system on the trip but will try the other products.
02 sensors are probably original.

Thanks for the tips fellas.

chuck

cabrio993

It's worth a look. If the belt is slipping, it could cause vibrations that are read by the crankshaft sensor as multiple random misfires.

mongrelcat

How many miles? I think Steve@Rennsport has mentioned a 50K or 60K (mile) replacement interval for these in the past.

csertich

46000 miles. Close enough to 50 to give this a try.

Thanks!

pcarhombre

I had virtually the same codes last year. It ended up being my wires. I had fresh plugs put in at the same time. Problem went away, although since both done at the same time, almost impossible to say which was the more likely candidate, but the wires looked funky. GL

flankenspeil

hows your oil consmption?

csertich

"Virtually the same codes..." Might be on to something. Wires are original.


Very good. I use a quart every 2500-3000 miles. Maybe less....

Thanks!

chuck

Davies

I'd investigate wires/caps/rotors/dual dist. belt. It's probably not an O2 sensor, or the gas cap.

Kika

It could even be a bad tank of gas, if it resets itself, then the condition has gone away at the time the ecu checks again. I would keep an eye on it, but run another tank through and see it if continually repeats.
Usual suspects would be wires and connectors, caps/rotors, belts.

csertich

Thanks for all the info guys. I had the caps/rotors changed about 20k miles ago. Replaced distributor drive belt last year simply because it was so old-figured it was a good safety measure.

Belts seem OK. Their appearance shows no fraying, etc. Had my son rev the car while I watched the belts. No slipping in the minute or so I observed them. But that could still be it.

I drove through a very hard rain the night before the light came on. I'm thinking that perhaps the plug wires insulation let some moisture in.

I'll keep running it for awhile, go through another tank of gas or two and see if the CEL comes on again. Good excuse to drive my car more.

Appreciate all the good info.

chuck

Akerlie

The same codes just came up on my car, had a closer look at the wires and it sure looks like they will have to be replaced ( a couple of the lower ones have a very sharp bend hand the rubber is cracked).

I also sprayed the caps and coils with water in the dark and had some blue arching was visible, will start with changing the wires and than see if the CEL still keeps showing up. . .