Continually getting P0304 code -- misfire #4 cyl.

[Mark44]

Car is a 2002 911 Carrera with about 88,000 miles on it.

I've had this car for two years now, and have been getting this code periodically since then, and it's also something that the PO tried to deal with.

From the records from previous owners, the coils had been changed not long ago (within about three years), as well as the spark plugs. I didn't see any record of the injectors being changed, so I've done that. Thinking that possibly a coil was faulty, I put in a new one. The plug looked reasonable, so I didn't change it.

The tech (who isn't a Porsche specialist) I've had do most of the work said he didn't think the problem was a faulty ECM, as he used noids to compare the signal to cylinder #4 and #5. Instead he thought that there might be a mechanical problem, like a bad lifter or cam.

My plan is to take it to a local mechanic who specializes in European cars, and who BTW races his own 911. In the meantime, I thought I would post here to see if anyone at this site has run into a similar problem.

Edited to add: There was no oil present in the spark plug tube when I pulled the coil and plug on #4 cylinder.

[Rusty Heap]

swap a coil pack from a known good cylinder to the "bad" one on #4, and see if your fault code follows the coil pack.

[Mark44]

I installed a brand new coil in #4 with no change. I'll give this suggestion a try by swapping the #4 and #5 coils.

[jchapura]

When does it misfire?
Just at idle
Certain RPM range
Only at cold start up
Only under load
Etc.

[Mark44]

Looks like the problem has been solved - fingers crossed. As already mentioned, the cylinder 4 misfire (P0304) has been plaguing me for the two years I've owned the car, and was noted on two invoices for services for the previous owner.
After getting no joy after replacing the injectors and the coils, I took it into a shop that specializes in repairs for German cars. They used a borescope to determine that one of the intake valves wasn't opening all the way, which points to a malfunctioning intake lifter. They replaced both intake lifters on cyl. 4, and so far, the engine is back to running how it should.

The lifters aren't all that expensive, at about $150 for the pair, but the labor involved ran to 13 hours (engine was not removed).

In case you're not aware, the intake lifters on this vehicle are pretty trick, being operated hydraulically and electrically. The lifter is cylindrical, with an inner cylinder inside an outer cylindrical shell. Each intake valve is paired with three cam lobes, an inner lobe and two outer lobes. As I understand it, at low engine speeds, the inner core of the lifter rides on the inner camshaft lobe. Under higher engine loads, the inner lifter retracts into the lifter and is locked in place by a solenoid, and the lifter then rides on the two outer cam lobes, which cause higher valve lift and longer duration. The Bentley manual has pictures of the lifter and cam lobes.

[jchapura]

Thank you for letting us know - it helps the community.

Do you have any pictures of the borescoped area to show what prompted the mechanic to conclude it was the lifter?

[Mark44]

Originally Posted by jchapura

Do you have any pictures of the borescoped area to show what prompted the mechanic to conclude it was the lifter?

Nope, no pictures. The shop, Chris's German Auto Repair, in Redmond, WA, replaced two intake lifters on the #4 cylinder, and the P0304 hasn't come up since, and has run great since then.

[Traveller]

Too many think that a misfire is related to an electrical issue maybe due to the term "misfire". Not all the time.

[yelcab1]

Hard to find that problem. Good tech.