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MJA911
Sepang


Joined: 10 Dec 2013
Posts: 2752
Location: Berkshire

2012 Porsche 991 Carrera

PostPosted: Sun Nov 18, 2018 3:44 pm    Post subject: Mystery misfiring at cold start Reply with quote

Our 2004 Boxster S 3.4 has on 3 occasions over the past couple of weeks acted up when starting from cold. It’s sluggish to fire up and when it does it runs roughly with the engine shuddering. The CEL comes on and the last time it behaved like this it flashed, so quite alarming Surprised

However, we dared to try again after switching off and it fired up perfectly well, sounds as sweet as ever and subsequently drives as well as ever too. It’s only done this at cold start up and does live outside so it is quite cold and damp.

After it did it again yesterday I took it to my friends workshop. His PIWIS told us it had misfired (on cyclinders 1,4,6) but there were no other faults such as sensors or coils, which along with plugs were all renewed a few months ago at its major service in any case. Thought about dodgy tank of petrol but it did this before and after it was filled it up.

All fault codes were cleared and I filled it up again just in case on the drive home, during which I gave it a spirited burst and it was good as gold. It also started and ran fine for my wife this morning, so we’ll to run and observe.

When it does it again we’ll get it back on the PIWIS and take a closer look, in the meantime if anybody has any ideas and/or has had something similiar it would be great to know Thumb
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ragpicker
Estoril


Joined: 14 Apr 2013
Posts: 3797
Location: North East England


PostPosted: Sun Nov 18, 2018 3:53 pm    Post subject: Reply with quote

Interesting fault MJA911. It might be worth running some injector cleaner through a couple of tanks of fuel in case the injectors are a bit clogged up Dont know

If it clears with the cycling of the ignition I would be suspicious of something electric Question

Demort will surely be along soon to put his finger on the matter..

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MJA911
Sepang


Joined: 10 Dec 2013
Posts: 2752
Location: Berkshire

2012 Porsche 991 Carrera

PostPosted: Sun Nov 18, 2018 4:07 pm    Post subject: Reply with quote

Thanks @ragpicker, any recommendation on the injector cleaner ?
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deMort
Zolder


Joined: 21 Mar 2015
Posts: 5756
Location: Brighton


PostPosted: Sun Nov 18, 2018 4:35 pm    Post subject: Reply with quote

If the fault codes were misfire on the same bank .. so 4,5 and 6 i would say high lift solinoid is messing around but what you have seems to be a bit random.

I think as a check i would still swop the solinoid side to side to rule it out though .

cracked coils would be the most obvious but they are new or have been checked ?

Fuel pump .. hmm .. random fault codes for that so if you get misfires on different cyls each time then i might lean towards that .
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ragpicker
Estoril


Joined: 14 Apr 2013
Posts: 3797
Location: North East England


PostPosted: Sun Nov 18, 2018 4:50 pm    Post subject: Reply with quote

Fuel pump, good shout! Possibly low pressure at start up?

It could also be clogged injectors too when thinking along those lines...?

@MJA911, I've always used Redex. Wait until you've got about 30 miles left in the tank and then pour half of it in. Then run it until nearly empty and fill up with the usual stuff. You don't want to dilute it too much in the fuel otherwise you'll lose what effect it does have.

Can you hear the fuel pump prime when you turn the ignition (before starting the car)?
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MJA911
Sepang


Joined: 10 Dec 2013
Posts: 2752
Location: Berkshire

2012 Porsche 991 Carrera

PostPosted: Sun Nov 18, 2018 4:51 pm    Post subject: Reply with quote

Thanks demort. Yes it had new coils (and plugs) in the summer and has been sweet as a nut until now.

Thanks for the tip on the solenoid and fuel pump, our thinking is to see if the misfires are on the same cylinders next time or if it’s as random as it seems.
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deMort
Zolder


Joined: 21 Mar 2015
Posts: 5756
Location: Brighton


PostPosted: Sun Nov 18, 2018 5:03 pm    Post subject: Reply with quote

It could be injectors but i tend to go with what i see most of the time and by logic ..

You would have to have 3 injectors blocked / damaged or have a feed problem .. always possible though .. some things i come across and i would never have guessed at the fault in a million years .

Nothing wrong with useing fuel cleaner and a good call .

Also you had already mentioned injectors so i didnt need to Very Happy

Fuel pump is possible but i would like to see different cylinder misfires the next time to lean towards that .. also its more common to have a high rev lack of power as the pump never really delivers quite enough pressure .

I doubt you will hear it prime.

I think your car is too new to have a fuel filter but always best to make sure it hasnt .
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