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dino986
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Joined: 17 Aug 2017
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PostPosted: Thu Aug 17, 2017 7:06 pm    Post subject: 986 2.7 tip cylinder 1 misfire only at high revs issue Reply with quote

Hi everyone. I'm a newbie to the forum. I have owned a boxster 2.7 986 tiptronic for about 3 years with zero issues until now. Recently had overheat due to thermostat/ waterpump issue ( I think) and simultaneously a coil packed up. My tech tells me I was lucky as appears no adverse from overheat. Coils plugs waterpump and thermostat all changed. On way home from garage engine didn't feel right. Radio started crackling then gearbox not changing as before then after a couple of spirited drives noticed a hesitance and finally a cel flashing.
Diagnosis showed injector cylinder 1'but after a swap of coils and plugs and injectors. Cylinder 1 is still reading misfire but seems to only occur above 5000 6000 revs. I'm going to try a maf tomorrow purely to eliminate.

Help help help any ideas !!!!! Tia.
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
Posts: 3247
Location: Sussex


PostPosted: Thu Aug 17, 2017 7:38 pm    Post subject: Reply with quote

A strange one , in theory a maf cant cause problems to a single cylinder .. but i have had a faulty maf show misfires on a single bank and its only on a Boxster .

I assume the box didnt go into limp home mode ?

Maf faulty and it doesnt normally want to rev about 4k .. it goes very flat so you do have some of the symptoms of a maf fault .

More likely if the fuel and spark are ok is the tappets for that cylinder though .
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dino986
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PostPosted: Thu Aug 17, 2017 8:19 pm    Post subject: Reply with quote

Hi demort
Cheers for reply. I think you are right about the maf as seems weird it only appears to affect the same cylinder each time and only noticeable at high revs. tickover and normal driving feels fine. My tech is begining to rule out electrical and started thinking mechanical problem.
I wasn't driving when the overheat issue occurred and orig misfire. It certainly didnt go into any limp mode since the orig repairs. I'm starting to fear worst as tech says it's rare but a valve spring break is a possibility. Which to diagnose is a strip down and ££££££'s.
The only thing I keep coming back to is my stereo crackling. Never did that before the repairs. Coincidentally?????
Tech has also ruled out oxygen sensors as tested which I think rules out cats too.
I have tralled through various forum posts and can't find anything that resembles my symptoms. Love the car but this is making me think is it worth spending anymore and off loading.
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
Posts: 3247
Location: Sussex


PostPosted: Fri Aug 18, 2017 7:17 pm    Post subject: Reply with quote

Lambdas and cats are out .. its a single cylinder fault .

Maf is pretty unlikely .

You have swopped injector , plug and coil i take it so they are fine ..

Do a compression check .. i would look at compression generated on the first stroke and the final compression compaired to the other clinders .

Cylinder leakage test whilst your at it .

My thoughts atm are the spark is breaking down under load so i would be checking the wireing to that cyl injector and the coil for resistance .

I would also suspect the DME as it uses individual transistors to switch each cylinder .. one of these might be breaking down under load / high rpm .

Hmm overheat .. has the coolant lvl dropped at all ? a headgasket is a possible if unlikely cause .. this is something to rule out pretty quick .. coolant in a cylinder isnt good .

Radio crackleing .. im struggleing with this one as it would indicate a general problem with feeds / earths which would effect many systems and not just a single cylinder .

Was the coil that failed also on cylinder 1 ?

Just read through your first post again .. Injector fault clyinder 1 .. the dme is seeing open ciruit or a short cuircuit .. check the wireing for that injector to the dme .
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dino986
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PostPosted: Fri Aug 18, 2017 7:34 pm    Post subject: Reply with quote

Hi again and thank you for your thoughts. My Tech has done a compression test (I asked this morning funny enough) and has confirmed ok but not sure if he's compared to others cylinders etc. Will ask him next week so thanks for that!
Didn't get a chance to pop maf on but tbh not even remotely convinced that is the cause.
As the car actually runs great when driving sensibly. I have a Porsche specialist who is going to do a diagnostic check with a Porsche tool and hoping this will give us a finer point. If at least rule a few other things out. During conversations today it appears a valve spring issue fits the bill. But this is purely speculation.
I can't get out of my head about the interference that has appeared on stereo. Again could be something or just coincidence. The other thing is the interference becomes more noticeable happens on aggressive braking and aggressive acceleration so again my thoughts are electrical instead of mechanical. ??????? Really appreciate the thought again tho.....saga continues.
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
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Location: Sussex


PostPosted: Fri Aug 18, 2017 7:42 pm    Post subject: Reply with quote

Valve spring is certainly possible and i was hopeing it might be picked up on a compression check .. if not its cam cover off to inspect .


Radio .. hmm .. a loose earth wire engine / battery .. multiple faults in different systems .. its more likely to be an antenna fault i would have thought but i also dont like coincidences .

Hard acc or brakeing flexes things which indicate a poor conection to the antenna .

Im even thinking the feeds / earths to the dme but again these will cause multiple faults . in fact everything i can think of will do this in reguard to the radio.

I edited my last post a bit .. check the wires for the injector on cylinder 1 if you didnt see that .
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dino986
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PostPosted: Fri Aug 18, 2017 7:54 pm    Post subject: Reply with quote

You are right seems too much going on to point. Just to throw something out there..... is it poss (purely from the mention of dme and poor connections) is it at all poss that the overheat has caused a wire issue. I'm not fully versed with the route of the important wiring to engine components but could it be feasible that heat could have damaged something.
I wasnt driving the car when overheat occurred so not sure how long and how hot.
Can a dme be tested or the wiring from it to confirm continuity easily enough????
I'm really looking to explore every alternative before making the increasingly inevitable strip down. Question
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
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Location: Sussex


PostPosted: Fri Aug 18, 2017 8:09 pm    Post subject: Reply with quote

The fault code relates to the injector .. ie internal short or a wireing fault .. basically at times the dme cant see it so this from a fault code point of view this is the main part to rule out .

The wireing could in theory have got hot and caused this .. a bit unlikely but either way the wireing needs to be checked ..

It could be as simple as a poor connection to the injector .. had one on a cayenne the other day and as you moved the wireing on the injector it would mis fire or not depending on the possition and that was the connector pins .

Easy enough to check the wireing though .

DME is not so easy , a swop test is the most effective but youll need a dme to swop it with .. there are places that can test a dme though.

Rule of thumb for a control unit fault is check everything .. if its all ok then you are only left with the control unit .


EDIT

Dme is behind the bulkhead panel in the boot .. it can get hot .. wireing runs from it to the injector .
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dino986
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PostPosted: Fri Aug 18, 2017 8:35 pm    Post subject: Reply with quote

Mmm good to hear my theories aren't totally out there. TBH I'm pretty sure my tech has done the wiring checks to the injector (think that was first thing he did) so poss rule out connection. He also did swap over of injectors so the plugs would have been physically handled.
Just going to have to wait till Monday to try a few more options (the ones you mentioned if not already done)
Then a trip to Porsche spec with the Porsche diag tool and go from there.
Seeing as you have a vast knowledge and experience with these engines have you heard of a timing valve actuator (or something like that) cause a misfire. And again would that be local to just a single cylinder. Would have thought would be present at differing cylinders.
Something that's just crossed my mind but in the past I have moved the car in out of the garage a couple of times...on say third startup I would have noises tappet for around 3-4mikes then go silent. This only happened say three or four times in the three years of owning. Is this an indicator of an issue or just a characteristic. Thanks again for your expertise and sharing thoughts.
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
Posts: 3247
Location: Sussex


PostPosted: Fri Aug 18, 2017 8:42 pm    Post subject: Reply with quote

The vario cam side of it would effect all cylinders on that bank and not just one ( valve timeing thing )

Tappet noise is not uncommon on startup .. its a "lazy " tappet .. if it doesnt clear then its a replacement .. its an oil blockage basically .

Normally its fine after a few miles though so doesnt indicate a fault as such but it is one thing i mentioned several posts back as a possibility .

A Porsche specialist is better if your normal mechanic isnt one .. we have a bit better understanding of these cars and how the systems work .. not to doubt your own mechanic but a specialist only deals with Porsche and so has a little advantage which might help with difficult faults .

Btw .. keep me informed as to how it goes please .. im always interested in faults like this and the causes .
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dino986
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PostPosted: Fri Aug 18, 2017 9:43 pm    Post subject: Reply with quote

Will do as it seems a rare set of circumstances and faults.

It hasn't put me off porsche ownership so far. Might think a little different if £££'s start to dry up with no fix tho. I have my eye on upgrading to 987. I know it's mater of opinion on models but is the reliability probs and driving pleasure any better or worse in your opinion. Looking at a 3.2 this time.

To be continued..... Thumb
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
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Location: Sussex


PostPosted: Sat Aug 19, 2017 3:45 pm    Post subject: Reply with quote

Each new gen of Boxsters has been an improvement with the ultimate being the 981 IMHO .. 718 .. hmm .. no , not one i like .

But to be fair each have their own set of problems as does any car .

I would say though that an upgrade to a 987 would certainly be an improvement .. have to be an S though and my preference would be a Tiptronic.



If you do seriously think about going down that route then ill give you a list of things to look out for that can go wrong .
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dino986
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PostPosted: Sat Aug 19, 2017 3:51 pm    Post subject: Reply with quote

Fab thanks again. Got to convince the better half it's a good idea first. Might be a tad difficult due to the situ with the current one !!!
I convinced her the last time it was an investment. WAS an investment. gonna have to pull all the stops out if that's my direction.
 
  
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dino986
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PostPosted: Mon Aug 21, 2017 9:43 am    Post subject: Reply with quote

Well. I can't believe im saying this but my tech has just called me. He popped the pre arranged maf sensor on. Has taken car to point where the misfire occurs three to four times admitting at one point to push it through gears.......NO MISFIRE ????????

My tech and I are flabbergasted. He's obviously not promising but may have just cracked it.
He thinks the maf was at early stages of deterioration so throwing weird symptoms out there.
I'm collecting car today hopefully and will give a good run tonight. Watch this space as they say....,,
Cheers again for your input. Great fully received.
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
Posts: 3247
Location: Sussex


PostPosted: Mon Aug 21, 2017 7:30 pm    Post subject: Reply with quote

Interesting .. i can only assume the other cylinders were at the point of regestering a misfire but hadnt quite reached the limit.

As i said earlier i have seen a single bank with misfires from a faulty maf but never a single cylinder .. one to watch out for i guess Smile

Glad its fixed though Thumb
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dino986
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PostPosted: Mon Aug 21, 2017 8:06 pm    Post subject: Reply with quote

Hi again. took car from garage tonight and drove it through rush hour so no chance to give proper run.... however, I can already feel the difference. Even the tip seems to be behaving itself. So much more responsive. Feels like my old car again.
It's def a new one on him. So suppose it's always worth trying the elimination process first even though logic says different. So glad as was really contemplating an early trade in. Put a smile back on my face....even at rush hour!!!

Needs a good run just to be sure but feeling confident... fingers x'd.

Cheers once again. Hopefully this post will remain on the site for a while so if anyone has a similar set of issues this might just prevent a few sleepless nights. Cracking still on stereo so appeared to be a red herring ????? It's no biggie as was planning a double din conversion and speaker upgrade. might get a suppressor or two fitted just to get rid of the noise.

🤞🤗 Thumb
 
  
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dino986
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PostPosted: Wed Sep 06, 2017 9:42 pm    Post subject: Reply with quote

Well here we are again.
Drove the car tonight pulled away from lights with a bit of vigour and hesitation then a thud from the gearbox when changing up. It appears that the issue is still present.
I have a theory. Would a blocked catalyst give me these symptoms as I'm struggling to work out what's going on.
Also the only other theory is the gearbox itself. Super smooth most of the time but as soon as a sharp acceleration is applied then it clunks into gear once then doesn't do it again.
I think there's a link with the misfire/ hesitation and the clunk into gear.
Local Porsche specialist next me thinks. Dont know
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
Posts: 3247
Location: Sussex


PostPosted: Thu Sep 07, 2017 7:57 pm    Post subject: Reply with quote

I did wonder at the Maf sensor fixing the fault as it didnt make sense to me .

Ok too work ..

You need a fault code check to confirm you still have a high rev misfire on No.1 as if you do then this is a fault that needs correcting before moving onto things like gearbox or blocked cats .

Im still with the wiring or dme for that injector atm , the fault code is specific .. the car is seeing an open circuit ( break in the wire ) or a short circuit .. with the fault you have then i will throw in high resistance in the wiring .. not huge but at high rpm a small resistance could well do this .

Or its just an intermitant break in the wire .. you wiggle it with engine running basically .

A blocked cat .. it will affect every cyl on that bank .. you wont get a single injector fault .. you will get a severe lack of power .. you will have adaption faults and if put on an emissions tester then that bank will be way off .

Gear box wont affect the engine as such .. torqure convertor clutch at certain rpm can but not really at high rpm .. and it doesnt sound like a box fault to me .. sounds like as the car is saying you have a misfire .


Suggestions .. it needs a Porsche indy really and you to tell them what has been done and what the fault is in detail ..

Or a 987 ... Porsche do make some excellent cars and most dont have many problems Thumb
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