Misfire - P0302, Not Coilpack or Plug, Please HELP.

Hi all, I have a 996 cab 2002 and a few weeks ago we were away on vacation and I got the engine check light come up at idle and in very slow traffic. It flashes at tick over when it's warm and off the "choke" and also when driving very very slowly, at speed it is solid. I took it to my mechanic today and he has sais the errors are P0300 (misfire) and P0302 (cylinder 2) So, coil pack or plugs you would think, but they have both been swapped out twice and no better. The Mechanic has also used his box of tricks to switch off each injector in turn and the engine gets lumpier as each injector is switched of except when switching off cylinder 2 injector. When he switches off injector two it has no effect at all. So we are not thinking it's the injector in cylinder 2. He said this is very unusual so before we go down the road of ordering and fitting a new injector to cylinder 2 can anyone suggest anything else to try? Cheers, Nick

Is it a late 3.4 or 3.6?

Sorry, stupid of me not to say, it's. 3.6 and has done just over 40k miles. Cheers, Nick

Way to new to this to know error numbers (and didn't ask the mechanic duh) but similar to my issue posted yesterday. Had it looked at today. Info under 'Check engine drive to workshop' Mine has also only covered 40K and a 3.6.....

Has your mechanic checked the fuel trim? What tool is he using? Also, ask him to swap the injectors to see if the fault moves to another cylinder

Could it be as simple as a plug lead? I'd also try a bottle of injector cleaner before starting to replace them. Also, did you use an OPC / Indie mechanic, as the codes on 'normal' OBD readers aren't always accurate for Porsches

Thanks for all the info. Yes, he has used the proper diag kit, I can't remember what it was called but he said it was better than his old PS2 system and would do 997 and all the latest Porsche models. As for plug lead and fuel trim I'm not sure. What is fuel trim? I guess it's not a fuel problem as all other cylinders on the rail are working fine. He said it would probably cost me as much in labour to swap injectors over as it would just to buy a new injector and fit it anyway. Cheers, Nick

Would agree with your thoughts on fuel mix and labour charges for swapping injectors, but could be worth trying the injector cleaner - only about £6 a bottle and as simple as chucking it in the fuel tank before filling up. :dont know:

A sticking tappet has also been mentioned, that sounds expensive................ Could it be that with the symptoms I have?

They're all hydraulic tappets and are usually fairly reliable, but a sticking tappet, with it's exhaust / inlet valve stuck in the open positionwould cause a misfire. Not sure if there'd be any other symptoms associated with a sticking tappet :dont know:

The diag tool should allow your techie to freeze the fuel trim readings. If an issue exists the ECU will under or over fuel the injectors(adaptations) and trick the MAF to try and compensate. If it cannot if will reset to it's factory std adaptations. These are typical readings for a 996/Boxster Short Term Fuel Trim - Bank 1 - -7.03 %. Long Term Fuel Trim - Bank 1 - 9.38 %. Short Term Fuel Trim - Bank 2 - -10.94 %. Long Term Fuel Trim - Bank 2 - 8.59 %. A faulty/blocked/worn injector can often cause mixture % to climb well above 12% or well below 5% and run outside the ECU's adapation ranges.....causing misfires and rough running. The fuel trim readings are always a good "tell tale" for possible injector and/or MAF/Lamba issues.

Thanks for the info, I'll pass it on to my techy. Cheers, Nick

It won't tell you what the specific issues is but is will tell you if you have a fuelling/MAF/Lamba issue vs a serious mechanical/valvetrain issue. Another good tip is to do a quick compression test on the affected cylinder

** UPDATE ** Had a compression test this morning and that all came back 100% OK so that is a huge relief. We are still looking at the injector being the issues and will run some more tests on that. Another suggestion is that the one of the two cam sensor may have gone on that side but I would have thought that all cylinders on that side would then have an issues and not just one but apparently this is not always the case. Anymore suggestions would be greatly received and I'll keep you posted on progress, Cheers, Nick

A cam sensor fault would have flashed an error code such as P1531 on any good diag tool If you can rule-out an ignition issues my gut feel is that you have a fuelling issue caused by an injector, MAF or Oxy sensor. The injectors are not that difficult to pull and if the tech has an injector flow meter he can quickly test the injector(s) If it was me I'd swap two injectors and see if the fault follows the specific injector