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Jamesx19
Nürburgring


Joined: 10 Jul 2015
Posts: 468
Location: Brighton


PostPosted: Sat Aug 31, 2019 3:37 pm    Post subject: Intermittent misfire Reply with quote

Out for an early morning drive earlier. All was going very nicely and engine well warmed through.

Slowed down for a junction and as I pulled away the engine stuttered almost a full cut. Then accelerated, albeit with a slight (single cylinder?) misfire. Wouldn’t take more than a slight throttle.

I drove slowly for a couple of miles. Tried again. Better, but still a slight misfire on heavier throttle applications.

Idle speed and part throttle light cruising seems ok.

Coil pack(s)??????

I have pulled all the coil packs and spark plugs. Plugs are fine and all identical in appearance. Coil packs all look ok though there maybe a very very slight hairline crack on one or two, but nothing obvious. All the Low tension connectors were secure.

Since doing this I took it for another short drive and all appeared well.
No fault codes are stored via the OBD2.

Before I replace all 6 coil packs on the basis I don’t know what else may be likely (I have a long 2,000 mile trip planned soon) ……….. anyone got any other thoughts?

Many thanks, James
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deMort
Dijon


Joined: 21 Mar 2015
Posts: 7184
Location: Brighton


PostPosted: Sat Aug 31, 2019 7:10 pm    Post subject: Reply with quote

A single coil pack faulty .. obvious on idle but not so obvious when higher revving.

Same with a single spark plug .

Almost cut out doesn't strike me as a single coil pack .. more like a lack of fuel or an air mass sensor .

There should be a fault code for a misfire .. save the planet stuff ... no misfire code again indicates fuel or maf .. the car can't really see these .

maf unplugged and drive to see if its fine is one test .. clear the code after refitting though .

For me .. i would be running the car and looking at the misfire log on a tester with the fault happening... there is also a rough running section i would look at .. depending on the tester to see if the values were high on a single cyl .

A crack on a coil .. this mainly causes issues when wet .. not dry running .

it's possible it is a coil .. but atm its kinda the wrong symptoms .

I'm in tomorrow should you wish to drop by with your tester .. i can have a look but can't promise anything .. i still owe you after the last time young man .. far too generous Smile
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Jamesx19
Nürburgring


Joined: 10 Jul 2015
Posts: 468
Location: Brighton


PostPosted: Sat Aug 31, 2019 7:43 pm    Post subject: Reply with quote

Cheers Demort. I definitely owe you, rather than the other way round!!

Hmmm, saves me splashing out on coil packs, at least in the short term. Sadly I am back to work tomorrow so can't swing past, thanks for the offer though.

Might have to book her in for a proper scan to see what fault codes pop up? I never got to the bottom of the lean AFM on the MOT but the MAF appears ok as the engine almost cuts out when disconnected, then restores to idle.

As it got better as I cooled the car, I was thinking hot running issue? etc...Fuel pump on the way out?
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deMort
Dijon


Joined: 21 Mar 2015
Posts: 7184
Location: Brighton


PostPosted: Sat Aug 31, 2019 7:54 pm    Post subject: Reply with quote

we agree to differ there young man Very Happy

I'm just not convinced its a single coil pack atm from the description .

Hot running .. fuel pump are all possible .. atm its further investigation required .. a comment i often say at work .. sorry .
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She's not going until july 2020 though .



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Now At An Indy.
 
  
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Jamesx19
Nürburgring


Joined: 10 Jul 2015
Posts: 468
Location: Brighton


PostPosted: Sun Sep 01, 2019 3:58 pm    Post subject: Reply with quote

Ha ha, well you don't know until you know.... pm'd
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Jamesx19
Nürburgring


Joined: 10 Jul 2015
Posts: 468
Location: Brighton


PostPosted: Sun Sep 01, 2019 6:06 pm    Post subject: Reply with quote

Demort may have solved it!

MAF was definitely working (engine idle speed affected) before yesterday, now unplugging doesn't affect at all except possibly improving the quality of the idle.

I think I'll just pop a new one in. Possible that the K and N air filter is letting oil onto the MAF? I'll replace with a standard air filter and report back.

Cheers
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cvega
Spa-Francorchamps


Joined: 25 Feb 2013
Posts: 253
Location: Cambridge


PostPosted: Mon Sep 02, 2019 9:21 am    Post subject: Reply with quote

Had this with a single coilpack (exposed one on the left hand side) starting to be sad.
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Teto10
Newbie


Joined: 02 Sep 2019
Posts: 4



PostPosted: Mon Sep 02, 2019 5:03 pm    Post subject: Reply with quote

For me MAF was definitely working very nice , now unplugging doesn't affect at all except possibly improving the quality
 
  
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deMort
Dijon


Joined: 21 Mar 2015
Posts: 7184
Location: Brighton


PostPosted: Mon Sep 02, 2019 7:07 pm    Post subject: Reply with quote

A maf sensor fault is a little tricky to diagnose .. you wont get a fault code unless its totally dead ( open circuit ) .. you should get around 18 kg/hr at idle so that's an indication but does not prove its faulty .

I have graphed a good and bad sensor back to back .. i couldn't see any difference in the scope pattern / voltage .

Thats down to the tester takes a snapshot of the values and is not real time logging.

The usual test is unplug and drive and see if its better .. However i will warn you .. this is not always a faulty maf but the car drops to default values and masks the real fault ..

You find out after buying a new one and it doesn't fix the fault .

On a Boxster .. if it wont rev above 4.5 K but will with maf unplugged then its the maf .. this test is not always conclusive on a 996 though .

K&N filters are oil based and as such its possible to get residue from the filter onto the maf .
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My Daughter's Crowdfunding has hit the target see Here

Thank you all so Very much .

She's not going until july 2020 though .



Mechanic

7pm - 9pm

Now At An Indy.
 
  
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Jamesx19
Nürburgring


Joined: 10 Jul 2015
Posts: 468
Location: Brighton


PostPosted: Mon Sep 02, 2019 7:59 pm    Post subject: Reply with quote

Got the MAF. Waiting for air filter. Don't want to oil up a new one, if that's the possible contributer...
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Jamesx19
Nürburgring


Joined: 10 Jul 2015
Posts: 468
Location: Brighton


PostPosted: Thu Sep 05, 2019 1:28 pm    Post subject: Reply with quote

Conclusion for anyone researching this thread in future.

Demort, as ever, correctly diagnosed a dodgy MAF sensor. Now changed for a new Bosch one plus new standard paper air filter.

All good again, if not a good bit smoother than before the misfire. Better throttle response as well. Sounds just as fruity as before, but slightly more cultured!

The old MAF didn't have any part no. stamps. The new one even had the Porsche code.......

Nice one DeMort Thumb
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