yaknart33

If its possible to connect a vacuum guage to your engine ,then when it misses if the guage fluctuates rapidly you have a engine problem ,if not its electrical.The dealer should have a data recorder that automatically records pre selected data that you can road test for a week or until the concern happens .They will want a deposit on the tester ,but they should be able to read the data to see whats happening when concern happens.The domestic manufacturers have the ability to do this.

Kalashnikov

Med, I would try injector swap...If it doesn't work, leave the car alone. Your car is ahead of 95 percent of 996s on mileage and this is intermittent. It sounds like an electrical issue, something that flooded car would experience. One wire shorting or ECU getting some silly reading will have you chasing **** for a long time.

5CHN3LL

In his case (unless there are other codes present), the blinking MIL is warning about potential damage to the emissions control system due to the presence of unburned fuel. If this was my car, and I was certain (after scanning the codes w/ my phone) that the misfire is the only fault logged, I wouldn't bother with a tow.

I'm sure I'll get torched for suggesting that you might choose to NOT flatbed your car somewhere. The control freak in me has the need to know WHY the light is flashing.

Please consider the context before lighting me up. If my elderly neighbor called me and said her MIL was blinking, I'd tell her to call AAA...but if it was my wife, I'd troubleshoot it first. Sending a car on a tow truck with an undiagnosed issue to a dealership can turn expensive fast.

I agree. I despise leaving issues unresolved, but at some point you have to balance time and money against the irritation caused by an intermittent misfire. My Corvette has a 15-year-old oil leak. I tried to diagnose and failed. I had my indie take a look; he shrugged and told me it leaks less than other C4's, but he'd be happy to dig into it and try to track it down. However, he doesn't really want to spend his time looking for a drip when he could be test-driving the Corvette he was finishing supercharging, and I don't really want to fund a $150/hr fishing expedition.

Cheekybird

Please keep posting in RED it is easier to follow.

m3driver

A good check would be to get one of those infrared thermometers and point it at each exhaust port when it's acting up. Yes it requires you to get under the car when you least expect it, but your misfiring cylinder will be significantly cooler than the others. This could help pin point the problem

fpb111

Interesting that your voltage dips as soon as the cel pops up. I see that the rpm drops also but the car is still running so wouldn't expect that steep of a drop.
Then when you increase rpm the cel goes away as the voltage increases. Alternator/regulator bad or introducing A/C spike?? Alternator connections clean, emphasis the ground?

Have you tried a clamp on ammeter to see if there is a current draw spike concurrent with the cell activation?

Paul Waterloo

Interesting how the voltage is bouncing all over the place. That seems very odd to me, on my 99, the meter never moves.

Macster

Just to recap: P0302 is a misfire at cylinder 2.

Are there any other codes?

Any pending codes?

Any "permanent" codes? (These can only be "erased" by the DME after so many warm up cycles with the error condition no longer present.)

What is the freeze frame error code and the freeze frame data?

Having a hard time envisioning a bad injector causing this behavior.

I don't wish to belabor this point but at idle the low intake valve lift mode is activated and if even one intake lifter fails to switch over the cylinder will misfire. When you raise RPMs low lift is disabled and high lift is enabled. Since at least one lifter is "stuck" in high lift mode its mode agrees with all the other lifters and the misfire goes away.

Just thinking out loud, so to speak (well, type), a tech with the proper Porsche diagnostic computer could monitor when the switch from high lift to low lift and back again takes place.

He could then with the engine ready to generate the misfire monitor misfire counts and the low lift/high lift setting and see if there is any correlation between misfire counts increasing (which if they get high enough triggers a CEL) and the low lift mode being activated and then raising RPMs while continuing to monitor misfire counts and seeing the misfire counts dropping below the CEL trigger threshold concurrent with high lift mode becoming active.

BTW, the slight change in the voltage meter reading is I believe an artifact of the engine RPMs varying due to the cylinder misfiring and the engine losing some RPMs. Additionally any vacuum gage reading while it would change during this time would also be an artifact arising from the engine experiencing some RPMs variability during the misfire event.

fpb111

I would investigate this one in more detail.

Medevack1

ok guys again thank you all for the great job I did go the cheaper rout and pour a can of Techron into the gas tank and follow the steps as someone told me in the forum. the code hasn't come back at all I"m in my second tank of gas and I pour 1/2 of a bottle and the car is running great no hesitation or codes. now I'm definitely confused lol

anyone else have any input on this.

Medevack1

Thank you!!!

808Bill

Macster the magician!

Macster

Too soon to know.

Just continue to drive the car. 'course, if the engine acts up starts to run rough, anything out of the ordinary, shut off the engine ASAP and get the car to a qualified tech for a professional's diagnosis.

But if you continue to drive the car if the Techron can help it will help.

If it does help and the error stays away this suggests the problem is (well, was) with a "dirty" injector, valve (intake valve most likely) or combustion chamber chamber deposits. Less likely but still possible is dirty (with deposits) O2 sensors.

(I don't know if I mentioned this but just a couple of tanks of gasoline after I switch my Boxster over from Shell V-Power to Chevron the engine was running remarkably better. That Techron can work a minor miracle.)

If the misfire comes back well, you have done about all you can without special tools and training.

Here's hoping it stays away.

Imo000

The voltage drops because the engine rpms also drops when the missfire happens (the engine start to run only on 5 cylinder). The alternator needs a certain amount of rpm to produce the required voltage. Too low idle will produce low voltage.

Medevack1

Well Guys so far so good!!!! I have been through 3 full tanks of gas and NO Cel..... I keep a bottle of techron in the car Just incase... I did forget to mention when I was having issues with the car and it will act up and throw a cel of misfire #2, while the car was running I would turn the car off and back on really fast and the car would stop acting and idle perfectly... I know I will catch hell for doing that.... lol