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emohawk11
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Joined: 01 Aug 2018
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PostPosted: Wed Aug 01, 2018 12:16 pm    Post subject: Porsche 991 - engine cut out - intermittent issue Reply with quote

All of these happened on hot summer days, when the car fluids were up to temperature.

The first engine cutout happened on the motorway at approx 70mph.

The second engine cutout was at 15mph after the car had been sat idling for about 20 minutes (I was eating lunch with the air con on)

The third cutout was at a set of lights while attempting to pull away.

The third cutout was again after the car had been sat idling for about 20 minutes. This time the car engine fault light illuminated twice, the PSM warning came on at the same time to say PSM no longer active, and a message said onward travel is possible. However the car engine was shaking, and would barely move. I nursed the car around the corner and let it cool down then restarted and I was away again.

The car is not showing any errors within its ECU logs, and Porsche were unable to find a problem with the car after having it for a week. Has anyone any thoughts on what I can do next ? I'm not really sure what direction to take or what the cause might be as there are very few clues.
 
  
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deMort
Long Beach


Joined: 21 Mar 2015
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Location: Brighton


PostPosted: Wed Aug 01, 2018 6:52 pm    Post subject: Reply with quote

Very difficult to answer im afraid ..

i Really would have thought there would have been a fault code , eml light on and there should have been something so thats a little strange .

Cut out at 70 .. that was foot OFF the acc pedal i take it ?

If it was on and accelerating then thats a massive safety issue .. if on over run then its seems to be a similar fault to the other times .

Car is under warrenty i take it .. perhaps another OPC or a call to customer services saying the car is not safe .

I can give you some total guess items ..

Fuel pump , crank angle sensor .. neither of these are likley to generate a fault code .

Limping the car .. that does sound like a low fuel pressure fault to me .. again there should be a code for the high pressure pump but maybe not if it was the low side .. not sure there to be honest .

Then moveing on a DME fault .. i would say a possible wiring fault .. poor earth etc but i feel it would happen a lot more so im kinda discounting that .

Not something ive come accross so far at work .. sorry.

The fault happens when the car to put it bluntly is stinking hot .. need to push that point accross to the OPC along with its not safe to drive .. not fit for purpose etc etc .
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emohawk11
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PostPosted: Wed Aug 01, 2018 7:19 pm    Post subject: Reply with quote

Thanks for taking the time to reply - I’m grateful for your suggestions.

The cutout at 70 was either with cruise control on or foot gently on the accelerator peddle to maintain speed.

The EML has never lit up or stayed on. I’d hoped when the engine fault light warning text appeared on the display that would have logged something but no such luck, though I did only use an ODB 2 scanner myself to check (the fault light illuminated after OPC handed the car back to me). Would the OPC be able to check more thoroughly for a fault code ?

The Porsche warranty expired 6 months ago. Though the OPC did not charge for their time as they couldn’t find anything wrong.
 
  
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deMort
Long Beach


Joined: 21 Mar 2015
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Location: Brighton


PostPosted: Thu Aug 02, 2018 6:18 pm    Post subject: Reply with quote

well .. first thing we normally check is fault codes as that always leads us in a direction .. without a code then it becomes a lot more difficult .

I would have expected the OPC did exactly that and nothing was listed ..

They probably would have driven it a bit and rechecked .

If not in warrenty then you are also limited as to what you can do ..

My concern is foot off the gass and a stall / cutout is one thing but if actually accelerateing and it dies then thats a potential safety issue .

This IS a heat issue but as to what is over heating is going to be difficult ..

My feeling is its fuel related and the low pressure side rather than the high pressure as you always get codes for a high pressure fault .

It could also be a crank angle sensor .. not the normal symptoms but its possible.
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emohawk11
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PostPosted: Thu Aug 02, 2018 9:48 pm    Post subject: Reply with quote

The weather was cooler today, 22deg instead of 30, with some rain. I Drove the car for about 2hrs and it was fine.

You’re the second person to say the cause may be a low pressure fuel issue. It’s too bad Porsche have not suggested this yet. My understanding is there are two fuel pumps, and two fuel tanks on the 991.1

I’ll continue to monitor the car and use it to see if there are anymore patterns. I’ll need to as you say be careful of any safety issues
 
  
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Magic919
Suzuka


Joined: 05 Jun 2013
Posts: 1011
Location: Berkshire


PostPosted: Fri Aug 03, 2018 6:24 am    Post subject: Reply with quote

If it’s a PDK car it would be worth defeating the coasting feature whilst you have the problem.
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emohawk11
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PostPosted: Fri Aug 03, 2018 3:10 pm    Post subject: Reply with quote

Yes it’s PDK, not sure what you mean about defeating the coasting option though? Did you mean to use the word defeat ?
 
  
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Magic919
Suzuka


Joined: 05 Jun 2013
Posts: 1011
Location: Berkshire


PostPosted: Fri Aug 03, 2018 4:36 pm    Post subject: Reply with quote

Yes, I meant defeat. They are designed to coast under certain conditions - https://www.youtube.com/watch?v=juDfN1pA1ZY

I'm suggesting you might be better off without that at the moment, in case it's just another opportunity for the engine to cut. Just a theory...

I know Sport modes will stop it doing that. Turning off start/stop might from what I recall.
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deMort
Long Beach


Joined: 21 Mar 2015
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Location: Brighton


PostPosted: Fri Aug 03, 2018 6:13 pm    Post subject: Reply with quote

emohawk11 wrote:
The weather was cooler today, 22deg instead of 30, with some rain. I Drove the car for about 2hrs and it was fine.

You’re the second person to say the cause may be a low pressure fuel issue. It’s too bad Porsche have not suggested this yet. My understanding is there are two fuel pumps, and two fuel tanks on the 991.1

I’ll continue to monitor the car and use it to see if there are anymore patterns. I’ll need to as you say be careful of any safety issues


1 fuel tank but x2 pumps ..

The first pump is the low pressure one with the second one being what generates the high pressure ..

The first pump is not just on / off but a controlled pressure depending on need with the second haveing its own inbuilt control valve to regulate pressure .

Ive never seen a high pressure fuel pump fail with out a code and im pretty sure its not possible .. safety issue etc but the low side could in theory cause issues and not generate a code .
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emohawk11
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PostPosted: Sat Aug 04, 2018 12:26 pm    Post subject: Reply with quote

The engine has not cutout while coasting. you’re right about the sport mode preventing coasting.

The info on the fuel pumps is really helpful thank you. I will keep driving the car and see if the pattern regarding the outside temperature plays a factor. Is it possible the low pressure fuel pump might be affected if the outside temperature is significantly warmer I.e 30deg instead of around 20deg or less ?
 
  
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deMort
Long Beach


Joined: 21 Mar 2015
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PostPosted: Sat Aug 04, 2018 3:46 pm    Post subject: Reply with quote

Logically no but control units or basically anything electric can suffer if it gets hot.

I think you have proved this is a hot issue .. its just what item is actually breaking down.

For me i just look for the most obvious things so fuel and Crank sensor are the most obvious as they can cause issues but without a fault code .

To prove what is actually breaking down though is going to be a nightmare ..

Basically if the car starts and runs then theres not a fault there to trace .. it can only be found when the car wont start or is running badly .

It would actually be better if the car cut out and didnt restart im afraid .


If you wanted to throw some money away on a total guess then i would actually start with a crank angle sensor .. its only a hunch though.
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emohawk11
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PostPosted: Sat Aug 04, 2018 8:34 pm    Post subject: Reply with quote

I’m pretty certain Porsche checked the crank angle sensor when the car was with them for 10 days and they told me it was ok. I can phone them back though and speak to them to confirm
 
  
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Magic919
Suzuka


Joined: 05 Jun 2013
Posts: 1011
Location: Berkshire


PostPosted: Sun Aug 05, 2018 6:25 am    Post subject: Reply with quote

I’d follow DeMort’s advice and get the sensor replaced. It’ll be fine most of the time by the sounds of the fault.
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deMort
Long Beach


Joined: 21 Mar 2015
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PostPosted: Sun Aug 05, 2018 2:52 pm    Post subject: Reply with quote

The trouble is unless the fault is actually there then testing a component wont help .. if it starts and runs then everything will test ok .

Crank sensor is a pure guess on my part , its the only thing i can think of to actually replace that fits the symptoms .. the fuel side does but there is no one component i could say to replace that might fix it .

But its a guess so unless your happy probably throwing money away on a part then dont .
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emohawk11
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PostPosted: Sun Aug 12, 2018 7:26 am    Post subject: Reply with quote

Porsche emailed asking how the car has been yesterday. Ive asked if they checked the crank sensor, however as you say, might be intermittent fault with the sensor.

I’ve not used the car in the last week as I’ve been away on holiday. Outside temperatures have dropped to below 20 in Scotland, so will see if there are any issues over the next couple of weeks.

I’d prefer not to take a hunch on a repair as we’ve got a 6 month old and a recently purchased Victorian house that needs some work here and there.

Very grateful for the posts responding, thank you again. I’ll continue to provide updates
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8140
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Sun Aug 12, 2018 11:24 am    Post subject: Reply with quote

Just picking up on something from the first post about the PSM light coming on, on older 996/997's this can be caused by a faulty or dirty MAF?
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emohawk11
Newbie


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PostPosted: Mon Aug 13, 2018 4:23 pm    Post subject: Reply with quote

Response from Porsche today is they can confirm the crank shaft position sensor was inspected for the spacer and all was ok. Not really sure what that means so if someone would like to explain I’d be grateful.

Thank you for the suggestion of the MAF - would the issue not be more frequent ?
 
  
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deMort
Long Beach


Joined: 21 Mar 2015
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Location: Brighton


PostPosted: Mon Aug 13, 2018 6:28 pm    Post subject: Reply with quote

Basically Porsche are saying they couldn,t find anything wrong with the CPS ( crank sensor ) .. the trouble is unless the car was running badly when they checked then theres no way of saying its ok .

I expect they tryed every way you described to get the car to run rough but it didnt hence they wouldn,t be able to find a faulty component .

Spacer refers to the correct gap between the sensor and the flywheel .. its about the magnetic strength generated by the flywheel teeth and the sensor .. too big a gap and you get a weak signal .

Its also a fix for a 996 turbo rev flair problem .. you fit a spacer .. didnt really work on that problem though but i digress Embarassed

If the car runs fine then there is no problem to find and it doesnt matter what you test it will all test as ok.

Trust me faults like this are every mechanics nightmare .. ive had many over the years and have had to be honest with customers and just say drive it and see how it goes .. if it returns or becomes a constant problem then we can find it .

This is were fault codes help .. even if the fault isnt there it still gives us an indication of where to look and then make an educated guess .

MAF sensor .. always possible but i feel the PSM light / Maf load signal was corrupt due to just how bad it was running at that point ..

Mafs tend to be contaminated .. basically they give a false reading .. this will give an incorrect fueling but not Imho the type of fault the Op has .

Its more a constant thing with mafs .. granted the signal could drop out at the temps the fault occurs but a fault code would be generated and so far we have no codes to work on .

The PSM doesn,t care how bad the engine is running it just wants a signal which in this case would have been all over the place.

Its given up and said sod this im off down the beach untill you can give me something i can work with .. hence its shut down and taken the day off!

991 tend to be very good at generateing a code for even the smallest of deviations so a lack of codes means everything that can be tested by the car at that point is with in specs ... although it might be out of range at a given parameter.

Hence all my answers have been based on what i think could fail at high temps but not generate a fault code .
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emohawk11
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PostPosted: Tue Sep 04, 2018 5:50 pm    Post subject: Reply with quote

I forgot to thank you for your explanation before.

Not been using the car more than once per week for a 40min run each way to work, so I’ve not had much to provide an update.

Today the problem happened again. Engine fault light saying possible to drive on, plus PSM loss message, and start stop engine deactivated. Lots of engine shaking in 1st and second gear, then accelerate past it and the car appears to recover.

It was only high teens outside temperature wise, so that rules out the 30 degree heat as a factor
 
  
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emohawk11
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PostPosted: Thu Oct 04, 2018 10:55 pm    Post subject: Reply with quote

Further update, car reliably misfires after a 45 minute journey. One time I restarted the engine half a dozen times and it wouldn’t idle for more than a couple of seconds and then stalled.

Leaving the car for 10 minute or longer and it fires back up and is ok albeit for a limited time. Also notice significant loss of power during misfire.

Given this new info, does this help provide any further clue as to where the fault may lie ? I’m going to take the car to the PC (i’ll Break down on the way as it’s over and he drive) and see about demonstrating the issue I guess now it’s repeatable
 
  
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