Menu toggle

2004 986 Boxster S Misfiring, Again....

M

MrKieranHale

New member
Hi there,

I bought a 2004 986 Boxster S a couple of years ago, which has just ticked over 88,000 miles and it's beginning to misfire.

Just to give a bit of history on the car, I had the car serviced by a Porsche specialist local to me in June before I was going to take the car to do the NC500 towards the start of August. The work carried out was a minor service, using 5w50 Mobil A40 oil (if the invoice is correct), and replacement of the manual gearbox fluid.

After this, I began to notice the car was misfiring and the dreaded white smoke. I began trying to diagnose the car and notice that one of the coil packs was ever so slightly unplugged and that there was a pretty heavy build-up of oil in the plenum coming from the air oil separator. Thus, a new air oil separator was ordered from Design 911 (and new Iridium spark plugs and Beru ignition coils for good measure as I didn't have the history for when these and last been replaced.) The issue seemed to go away.

Design 911 part numbers for these if anyone is interested,

Air Oil, 99610702602
Spark Plugs, 9991700IK20
Ignition Coil, 99760210404/1

Come to yesterday the misfiring issue has reared its lovely head again.
It has been misfiring enough to flag a check engine light, firstly P0305 (generic cylinder 5 misfire).
Then after a little more driving on the motorway P0300 (random/multiple misfire), P0305 (cylinder 5 again), P0304 (cylinder 4) and finally P0303 (cylinder 3) - the exact same codes it was flagging before I replaced the AOS a couple of months ago.

My troubleshooting steps so far have been to disconnect the hose from the AOS to the plenum and noticed quite a bit of oil building up in the pipe (after the car has been sat for 12 hours), as well as a slight bit of oil on the opposite side of the throttle body. Though a bit more worryingly there was a slight in the plastic which lead to it snapping as I was trying to manoeuvre the hose out of the way. I haven't gone through the steps of looking at the coil packs as I'm not in a position where I can get the car jacked up to get a proper look at
them.

I did see a video from La Rose Porsche when they had a 986 in with AOS failure and they tested it by trying to take the oil filler cap off while the car was running it was impossible, though after the AOS has been replaced it comes off as though the engine isn't running. Trying it on my car yesterday, it was impossible to get off.

Has anybody had experience with an AOS failing again after 4 months of it being replaced or a split hose causing enough of an issue to create the same symptoms as a failed AOS?
Also, has anybody had any experience running a lighter oil with the AOS?
Any other insight would be welcome as I'm really clutching at straws at this point hoping it's nothing majorly wrong with the car.

Look forward to any insight anyone might be able to bring,
Thanks, Kieran.
 
Seems odd it started misfiring after a service. To ask a really basic question, where is the oil level on the dipstick (I seem to remember 986s had those!) when you check it at the correct temp as per the manual? Some service techs seem to struggle to put the right amount of oil in.

 
I agree with Brian very odd to misfire after a service i would be looking at a coil pack if the plugs were changed its been know they can crack disturbing them.

Might need diagnosis at a Porsche Indy might be the fastest and less expensive route in the end.

Good luck with your fix.

 
Hi Kieran,

So you’ve replaced the plugs, coil-packs and the AOS? Unless you’ve been very unlucky I doubt that the random misfires are plug or coil-pack related, and you’ve started to get oil in the intake system so it sounds as though the problem most likely is down to a failed AOS again. Also the fact that you’re unable to remove the oil filler cap indicates a problem with the AOS circuit.

Something else to look at re the misfires is a malfunctioning Variocam solenoid, but as Cliff has said it would be worthwhile running some Porsche-specific diagnostics to see if any error codes are flagged-up.

Jeff

 
I think your ordinal misfire was probably coil pack and unrelated to aos - the two don’t usually go hand In hand

don’t know about oil filler vacuum with a broken pipe. I guess that’s possible. when things are normal then there is a slight vacuum on the filler cap but

not enough to stop you being able to remove it. If you have a broken pipe now then that needs to be addressed

misfire on cyl 3 4 5 is across both banks. so my thinking is what’s common ?

Aside from the broken vacuum pipe.

i would suggest looking at the maf - if you unplug it then the car will run a default map and if the misfire goes then you have your culprit.

Failing that. I think the coil packs all share a common ground - so multi cyl misfires could be that but I don’t remember reading that anyone has ever actually found an issue there.

as others have said some Porsche specific diags might give you some more “circumstantial“ info

 
Misfire on one bank can be a faulty Variocam solenoid. My 997 had this and Opc replaced it and been ok since.

 
Cylinder 3 is bank 1

Cylinders 4 and 5 are bank 2

agree on variocam if it was all bank 1 or all bank 2 but this appears to be across both banks.

 
Hi everyone,

Apologies for the radio silence since the original post, things have been manic with going back to work - thanks everyone for the replies.

Since the original post, I've bit the bullet and bought an iCarsoft V2.0 to replace my Amazon basics OBD reader and it's highlighted some codes I haven't seen before - perks of having the right tool, I guess.

Along with the original codes, I'm now looking at,

P1101, Below limit value. Input variables, charge measurement.

P0205, No signal. Injector circuit, cylinder 5.

I still haven't managed to start the car as I'm waiting for a replacement vent line from the air-oil separator.

My plan of attack for the moment is to get the air filter cleaned and reoiled, previous owner put a silly cone filter on (sounds lovely but it's been a pain since day one).

Hopefully check the wiring to the cylinder 5s injector and see if there's anything obvious, same with the mass air flow sensor - I've been advised to check the resistance is between 2.5 – 3.1 Ω.

The cars had new coil packs, spark plugs and an air oil separator since the service I mentioned when it started misfiring in the past, the coil pack to the rearmost cylinder on the passenger side (believe that's cylinder 5).

Thanks to everyone for their opinions, I'll share an update when I manage to get my teeth into the car again this weekend.

 
Hi

Glad you got a couple of codes to work with, for me I would be looking at cleaning the MAF or if that fails replace it. That's the problem with after market oiled air filters they can play the Maf up.

 
Hi everyone,

A 'minor' update for the fun and games with the Boxster, I decided to look into the injector fault code for cylinder 5 (P0205).

I started by sticking my hand down the passenger side fuel bank and felt something fall past my hand, turns out it was the injector plug for cylinder 5...

A quick blast of contact cleaner later and ensuring it has seated correctly in the injector - not sure how it's come undone but it doesn't bear thinking about.

I've done about 50 miles now, with a mixture of motorway miles and typical street driving, touch wood the car is behaving correctly.

My friend's garage offered to do an inspection on the car for me and haven't found any faults or anything noteworthy.

Minus one of the boots for the handbrake cables has split so there's that to look into now - Boxster, the gift that just keeps giving.

Thanks to everyone for their help along this journey, hopefully, there aren't any more updates to have.

 
Seems to me that these and all modern cars are full of these things, small and big surprises.

Good you have found it, nice and simple, also good your garage has checked the car, fresh eyes always Good.

 
You must log in or register to reply here.

Posts made and opinions expressed are those of the individual forum members

Use of the Forum is subject to the Terms and Conditions

Disclaimer

The opinions expressed on this site are not necessarily those of the Club, who shall have no liability in respect of them or the accuracy of the content. The Club assumes no responsibility for any effects arising from errors or omissions.

Porsche Club Great Britain gives no warranties, guarantees or assurances and makes no representations or recommendations regarding any goods or services advertised on this site. It is the responsibility of visitors to satisfy themselves that goods and/or services supplied by any advertiser are bona fide and in no instance can the Porsche Club Great Britain be held responsible.

When responding to advertisements please ensure that you satisfy yourself of any applicable call charges on numbers not prefixed by usual "landline" STD Codes. Information can be obtained from the operator or the white pages. Before giving out ANY information regarding cars, or any other items for sale, please satisfy yourself that any potential purchaser is bona fide.

Directors of the Board of Porsche Club GB, Club Office Staff, Register Secretaries and Regional Organisers are often requested by Club members to provide information on matters connected with their cars and other matters referred to in the Club Rules. Such information, advice and assistance provided by such persons is given in good faith and is based on the personal experience and knowledge of the individual concerned.

Neither Porsche Club GB, nor any of the aforementioned, shall be under any liability in respect of any such information, advice or assistance given to members. Members are advised to consult qualified specialists for information, advice and assistance on matters connected with their cars at all times.

Porsche
Lockton
Pirelli
Officially approved
Oracle Finance
WEX Esso
Collecting Cars
Archant Dialogue
Back
Top