Misfiring issue - help needed

[dvenman]

All:

My 2003 2.7 Boxster, 40k miles, developed a misfire the other week. I was driving, got lumpy firing from the engine, and a CEL. No abnormal noises (I know what a collapsed lifter sounds like...) so took it at the first opportunity to my local specialist.

He said there were codes for misfire on cylinders 1,2 and 6. The coil packs had previously been flagged as cracked and needing replacement (but not urgently) so I did those last night. No signs of oil in the tubes so that's good. I'm still getting what I think is misfiring.

Relevant history:
Oil filler tube replaced about 10k miles ago.
Spark plugs replaced about 10k miles ago.
Left bank (as you look from the rear of the car) lifters, camshaft, tappet ladder and oil pump replaced about 5k miles ago
No oil on startup
I can take the oil filler cap off when the car's running


Any suggestions ? The misfiring manifests itself as a shake from the back of the car and it's unsettling and ruins the smoothness of the drive...

 

[Motorhead]

Dave,

If you've not already done it, it might be worth confirming that the misfires have been cleared on cylinders 1,2 and 6. If they have, I'd be inclined to replace the other three coil packs and all the plugs; and if not, you need to look more closely at connectors and wiring.

As a long shot, it might just be worth checking and, if necessary, cleaning or replacing the MAF too.

Incidentally, I'd be more concerned if I was unable to take off the oil filler cap when the engine's running due to high vacuum levels in the crankase possibly caused by air-oil separator failure.

Jeff

 

[dvenman]

Jeff:

Thanks for that. I replaced all six coils - thankfully a mate of mine close by has a 2 post lift so it made it easier - so all 6 coils packs are new.

I had done research into the AOS issues hence the info about being able to get the filler cap off, as it eliminates that.

If the MAF is dirty or faulty, would that affect only some, or all cylinders?

Also, I forgot to say I run it on unleaded 95 with a (very) occasional treat. This misfire is only in the last 1000 miles - it's done 10k or so in 6 months quite happily...

 

[Motorhead]

Dave,

I would have thought that a dirty MAF sensor could affect any of the cylinders and could be intermittent. You could try disconnecting it to see if the the problem still persists - the engine will still run with a default setting.

If you think it's misfiring, it would be worth running the diagnostics again to see if something else shows up (faulty lambda sensor, dirty injector?).

If it's run happily on 95-octane (the knock sensors will have adjusted the engine tuning to suit) I wouldn't have thought that would be the cause.

Really just trying to think of simple things that you can do - changing the plugs, cleaning the MAF and lambda sensors are about it I'm afraid.

Hope that helps and that you find a solution.

Jeff

 

[dvenman]

Latest update - the car's still misfiring but only on cylinder 3 now.

I swapped the packs from 3 and 5, and the fault was still on 3 - so at least the packs are ok.

Next step, after a decent run, is to swap injectors and see if the fault moves...

 

[CLIFFWILKINS]

Have you tried changing the plug in cylinder 3

 

[dvenman]

Cliff:

No, not yet. Given that 1,2 and 6 were the first to throw off codes, then 3 was misfiring after the coil packs were changed. Plugs are a cheap check for sure, but I'm not convinced.

Would incipient fuel pump failure cause misfires ? Dunno - clutching at straws, I want my purring porker back, not the "bub bub bub" one I have now. The car feels like it's trembling...

 

[CLIFFWILKINS]

As said plugs are cheap worth a try if you just change cylinder 3 for a plug change.
Then thats another off the list.

 

[Chris_in_the_UK]

Has it been stood for a while with unleaded in the system?

If so, this might be contributing - I once had a motorcycle that did the same and it was a combination of the fuel going sour and a spark plug issue.

 

[dvenman]

It gets driven most days, longest it's been stood before the misfiring is a few days.

 

[Motorhead]

Dave,

You say that the plugs have done about 10k miles so, as Cliff and I have suggested, it would be worth changing them if only to eliminate them as the source of your problem. Like you I'm not convinced, but you never know.

If that doesn't cure the problem then unfortunately I think you're going to have to bite the bullet and get a PIWIS or Durametric diagnostic check to see what error codes are showing up. A local Indy should be able to help if you're not keen to use a Porsche Centre.

Where are you located? There could be someone on the forum local to you who has the latest Durametric kit.

Jeff

 

[Richard_Hamilton]

I'm in Maidenhead, and could plug in my PIWIS if you like.

 

[dvenman]

My local specialist checked it about 2 weeks ago and the codes were for misfires on 1,2 and 6. New coil packs all round - and still a misfire on 3.

Swapped packs on 3 and 5, still misfiring on 3, so it's a plug or an injector, or something subtle...

I plan to swap plugs on Saturday morning (the car's currently parked at an airport until I get back from a business trip) and see how it goes. If the plug is definitely bad then I'll get a new one in straight away, but if the fault moves or stays it will aid it.

If this step doesn't identify the problem then it's off to an independent specialist...having forked out almost £3k after my camshaft issues I'm loath to have a garage keep replacing bits until the problem goes away especially at Porsche part prices.

 

[dvenman]

I've been researching misfires, and the issues range from coil packs (sorted by replacing them), to plugs (possible, let's see what mine looks like when I remove it), to injectors (dirty), to MAF (removed, cleaned, replaced), to fuel pump problems (low pressure, odd effects) to air leaks.

As part of all that, some people have tried fuel additives (Redline SR-1, Techron) and even sometimes water in the air intake as a means of cleaning both injectors and those hard-to-reach places.

Does anyone have experience / advice on a fuel additive as an easy and cheap attempt to fix this ? I'm checking the plugs this afternoon but if that ain't the problem then hopefully it's fuel pump or injector problems.

 

[Motorhead]

Dave,

I've not myself used a fuel additive but it would be worth a try. Or you could fill up with a premium fuel like Shell V-Power which contains additives designed to clean up the fuel system, the injectors included.

While you're working on the car, I'd be inclined to disconnect the MAF sensor temporarily to see if the problem still persists.

Jeff

 

[dvenman]

I might be getting somewhere with this, I hope...

No fault codes on the engine - so it looks like replacing all 6 coil packs fixed a misfire on 1/2/6. Even if they didn't need replacing, they're good for a while and I got my hands dirty under my car. And the cylinder 3 misfire may have been a loose connection, even though I double checked everything after I replaced the plugs, and when a renowned specialist says "single cylinder misfire ? Broken valve spring?" you have thoughts of another £3k bill or breaking for parts...

The trembling persists. Googling and reading various forums (fora ?) leads me to believe I may have a front engine mount on the way out - no clunking noises (not yet) but a whole-car vibration which is apparent when decelerating through 3000 RPM and other stuff which matches. But I'll ask a nice specialist to check for me.

Good news ? Replacing the front mount is doable if you have access to axle stands and a trolley jack, and the new part (987 375 023 05) is £95 or so including VAT. Better news ? Lemfoerder make the bushing which they sell to Porsche for inclusion in the carrier, and it's available from them (Google 987-375-023-05-M69 or Lemförder's part number 34705 01) at about £40. And I know someone who has a hydraulic press...

 

[Motorhead]

If you're getting a lot of powertrain-induced body vibration when driving the car, a dodgy front engine mount (or any of the three mounts for that matter) certainly is a strong possibility Dave, and certainly worth checking out.

Good luck and keep us posted.

Jeff