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Scubadiver
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Joined: 03 Jun 2017
Posts: 29
Location: Norfolk, UK


PostPosted: Sat Jun 03, 2017 2:01 pm    Post subject: Broken down on the way home... Reply with quote

Hi everyone, just joined after buying my first (2003 955) Cayenne Turbo yesterday.

Sadly, my first post is in the form of a desperate plea for some knowledge

I went to collect my Cayenne in response to an ad from over 300 miles away, apart from being in need of a new battery, the car seems in great shape with plenty of bills and full service history to show it has been looked after in it's 140,000 miles of use. I bought it and took to a local place to replace the battery and set off home.....

Everything was going great until around half way back when during an overtake on the highway (I floored it), there was a complete loss of power. I managed to limp to a safe place and took a look. It will start and tick over perfectly, but when trying to rev nothing happens except some backfiring. It is possible to drive very slowly by just touching the throttle, but any further pressing causes spluttering, jumping and dying.

My initial thought is that I have popped off or split an intercooler hose. I can't see any problem in the visible areas (near the intake plenum), and can't hear any unusual sucking or blowing noises when I try to rev it but had no tools with me to strip things down further to investigate.

I'm returning tomorrow (Sunday) to where I left it (2+ hours away) with tools, but I guess what I'm asking for is a little insight to whether you guys think I' m guessing the problem right (or any other alternatives?) and whether there are any common weak areas on the boost hose/intercooler side of things to check first?
I did have a little bluetooth OBD device with Torque with me, but no errors are shown as stored (in this limited way!) and no warning lights appeared on the dash. I will have an iCarsoft with me tomorrow to check further.

Would a catastrophic boost leak like a popped hose cause the symptoms described and also not throw up an error or engine warning light?

Any thoughts would be hugely appreciated!
 
  
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MisterCorn
Zolder


Joined: 08 Jan 2011
Posts: 5291
Location: Nottingham, England

2004 Porsche 996 Turbo

PostPosted: Sat Jun 03, 2017 4:10 pm    Post subject: Reply with quote

I can't help on your fault I am afraid, just wanted to say welcome and wish you the best of luck. Not a good start.

MC
 
  
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isysman
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Joined: 22 Apr 2011
Posts: 5469
Location: Cheshire


PostPosted: Sat Jun 03, 2017 4:49 pm    Post subject: Reply with quote

Sounds like Mas air flow sensors. It's a common problem, and I had it on my Audi a few years ago. Soon as you trying and give it any throttle is refuses to go.

Did you get the check engine light on the dash?
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Scubadiver
Newbie


Joined: 03 Jun 2017
Posts: 29
Location: Norfolk, UK


PostPosted: Sat Jun 03, 2017 6:01 pm    Post subject: Reply with quote

isysman wrote:
Sounds like Mas air flow sensors. It's a common problem, and I had it on my Audi a few years ago. Soon as you trying and give it any throttle is refuses to go.

Did you get the check engine light on the dash?


Good shout, it was the fact that I didn't get a check engine light on the dash (and because I floored it when it happened) that made me think (or hope) that it might be a popped hose.
I'm guessing a MAF sensor would always throw a fault code up?
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
Posts: 3343
Location: Sussex


PostPosted: Sat Jun 03, 2017 6:02 pm    Post subject: Reply with quote

From how it happened and the symptoms you have now then i would think an intake pipe has come off .. so i would start with that but getting to the turbos is going to be a bit of a pain on the floor .. its removeing the under tray that will cause you grief .

Basically high intake pressure has caused a pipe to blow is what im thinking when you floored it .

Maf sensors .. a good call but there should be some sort of fault code and there are 2 of them .. in a desperation mode and i have no idear if it would work with this but i would unplug both and see if it could be driven .

Only time i have fixed a car like this was a non porsche it would idle but not rev up and i had a hunch it was the maf so unplugged it .. car was able to be driven then .

There are problem areas but not for this that im aware of .

Sad start to Porsche ownership Sad
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Scubadiver
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Joined: 03 Jun 2017
Posts: 29
Location: Norfolk, UK


PostPosted: Sat Jun 03, 2017 6:03 pm    Post subject: Reply with quote

MisterCorn wrote:
I can't help on your fault I am afraid, just wanted to say welcome and wish you the best of luck. Not a good start.

MC


Thanks! I am a car enthusiast and ex-mechanic, so I certainly wasn't expecting a purchase of this kind to be trouble-free motoring. It would have been nice to at least have got it home though Sad
 
  
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Scubadiver
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Joined: 03 Jun 2017
Posts: 29
Location: Norfolk, UK


PostPosted: Sat Jun 03, 2017 6:17 pm    Post subject: Reply with quote

Demort wrote:
From how it happened and the symptoms you have now then i would think an intake pipe has come off .. so i would start with that but getting to the turbos is going to be a bit of a pain on the floor .. its removeing the under tray that will cause you grief .

Basically high intake pressure has caused a pipe to blow is what im thinking when you floored it .

Maf sensors .. a good call but there should be some sort of fault code and there are 2 of them .. in a desperation mode and i have no idear if it would work with this but i would unplug both and see if it could be driven .

Only time i have fixed a car like this was a non porsche it would idle but not rev up and i had a hunch it was the maf so unplugged it .. car was able to be driven then .

There are problem areas but not for this that im aware of .

Sad start to Porsche ownership Sad


Thanks for the response. I'm hoping that due to the way it happened, and the fact that the two banks are joined at the plenum so all boost from both sides will be lost wherever on the system a hose pops off or splits would point to this as a likelihood.
I've only had a similar thing happen on a Mercedes turbo diesel which also didn't bring up a check engine light, but the difference was it was still perfectly driveable and the change in engine noise (from quiet to loud induction noise) meant I immediately knew what had happened.
In this case, it's absolutely fine on tickover but not driveable without kangarooing down the road and I'm not hearing either induction or blowing noise. I'd be interested if anyone's ever heard how a petrol Porsche of any flavour behaves when an intercooler hose pops off. Once home I can do most things, but at the side of the road 2.5 hours away I'm trying to give myself a clue so I can at least get it back!
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
Posts: 3343
Location: Sussex


PostPosted: Sat Jun 03, 2017 6:23 pm    Post subject: Reply with quote

Im leaning towards it being a blown pipe as it ticks over ok ..

If the mafs are disconnected then in theory the car would drop to defaults , it wont know how much air is being drawn in so it should just drive on the throttle / pedal sensor .. if a pipe has blown off then this will allow the car to drive.

Not something ive ever done before but in theory it will work if you cant get at all the system .
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MisterCorn
Zolder


Joined: 08 Jan 2011
Posts: 5291
Location: Nottingham, England

2004 Porsche 996 Turbo

PostPosted: Sat Jun 03, 2017 6:28 pm    Post subject: Reply with quote

Scubadiver wrote:
MisterCorn wrote:
I can't help on your fault I am afraid, just wanted to say welcome and wish you the best of luck. Not a good start.

MC


Thanks! I am a car enthusiast and ex-mechanic, so I certainly wasn't expecting a purchase of this kind to be trouble-free motoring. It would have been nice to at least have got it home though Sad


I usually get new purchases home on a trailer for this reason.

MC
 
  
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Harv
Suzuka


Joined: 18 Sep 2014
Posts: 1074



PostPosted: Sat Jun 03, 2017 6:57 pm    Post subject: Reply with quote

I'm with the feeling that it's intercooler pipe related but if failing that and by weird chance tomorrow it starts and drives fine then probably a failing fuel pump (had it on our old mk1 S and the symptoms you describe are identical).

Make sure there's at least some fuel in there and one trick you can do is pull one of the fuel pump fuses out which forces the other one to run constantly (rather than how the system works in practice), of course you need to establish which fuse kills the good/bad pump and remember that as the tank is humped and you are only sucking off one side the range will be very reduced.

The system should prime when you open the drivers door regardless if ign is turned on or not and you will hear it the pump in the o/s of the tank go bzzzzzzt.

With our car the pump in the o/s worked and gave the prime to pressure the system when the door was opened and the engine would start and run but as soon you tried to add power there was nothing there and it would die, the n/s pump was faulty.

If it is the pumps don't by Porsche ones as the VW Touareg is the same and they are avail for about $50 each from eBay in the USA


Good luck with it Thumb

Edit: Also if it is fuel pumps then they give no error codes or check engine light

Last edited by Harv on Sat Jun 03, 2017 8:05 pm; edited 1 time in total
 
  
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Scubadiver
Newbie


Joined: 03 Jun 2017
Posts: 29
Location: Norfolk, UK


PostPosted: Sat Jun 03, 2017 7:48 pm    Post subject: Reply with quote

MisterCorn wrote:
Scubadiver wrote:
MisterCorn wrote:
I can't help on your fault I am afraid, just wanted to say welcome and wish you the best of luck. Not a good start.

MC


Thanks! I am a car enthusiast and ex-mechanic, so I certainly wasn't expecting a purchase of this kind to be trouble-free motoring. It would have been nice to at least have got it home though Sad


I usually get new purchases home on a trailer for this reason.

MC


Might still happen Damn
 
  
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Scubadiver
Newbie


Joined: 03 Jun 2017
Posts: 29
Location: Norfolk, UK


PostPosted: Sat Jun 03, 2017 7:53 pm    Post subject: Reply with quote

Thanks for taking the time to respond with your thoughts on this guys, between confirming I might be on the right lines with a blown hose plus the MAF and fuel pumps to try, this gives me a little preparation for tomorrow.

Being totally unfamiliar with this model, it's always great to get input from those who know them. I have a feeling I'll be learning a lot quickly however....

I'll let you know how I get on tomorrow Confused
 
  
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nigel99
Suzuka


Joined: 16 Jul 2015
Posts: 1132
Location: Surrey

2009 Porsche 997 Carrera 2S

PostPosted: Sat Jun 03, 2017 8:24 pm    Post subject: Reply with quote

Welcome to the forum. Sorry for your bad start but best of luck for tomorrow. Let us know how you get on.
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Scubadiver
Newbie


Joined: 03 Jun 2017
Posts: 29
Location: Norfolk, UK


PostPosted: Mon Jun 05, 2017 9:30 am    Post subject: Reply with quote

It's home.

Firstly a big thank you for all responses and in particular to isysman and Demort for steering me toward the MAFs.

The first thing I did when I got there was start it to find the problem was still the same. The second thing was to disconnect the o/s MAF. Problem gone. Well, pretty much anyway, I drove it to a nearby car park and disconnected the (harder to access) n/s MAF too for good measure and then drove home, in this state I would say the car drove 90% normally. It makes boost (so no popped hose) and the power is there but it is less smooth as perhaps one would expect with no MAFs connected, but surprisingly good and perfectly driveable. The only obvious difference is the 'PSM off' light is now on and associated warning to attend a workshop and the 1-6 gear indicator no longer works and instead illuminates P R N and D all at the same time.

So to the problem.... After getting home I reconnected the o/s MAF expecting the problem to return. It didn't. I reconnected the n/s MAF and it still didn't. I connected my iCarsoft and cleared all the codes (there were many). The PSM dash warning went away and the gear shift indicator returned to normal and the problem came back. Disconnected the o/s MAF again and it went away and the dash warnings returned.

That was as far as I got before rain and darkness stopped play!
 
  
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grbspeedster
Nürburgring


Joined: 11 Nov 2007
Posts: 469
Location: Rugby


PostPosted: Mon Jun 05, 2017 10:09 am    Post subject: Reply with quote

Glad you managed to get home ok, and for posting may help others if they get the same problem. Hope you get to the bottom of this and can start enjoying the car👍
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Scubadiver
Newbie


Joined: 03 Jun 2017
Posts: 29
Location: Norfolk, UK


PostPosted: Mon Jun 05, 2017 2:05 pm    Post subject: Reply with quote

Thanks Geoff.

I've carried on looking at it today and it's a little inconclusive. Having cleared all the old fault codes, with everything plugged back in it still does the same, starts, ticks over, but won't rev. Scanning it afterwards reveals no new codes at all so nothing pointing to the problem.

I have ordered a new pair of genuine Bosch MAFs that I hope will arrive tomorrow as they're not a bad thing to renew even if they're not at fault and I found a place selling them at a very reasonable price.

Fingers crossed that will solve the issue, but I have a nasty feeling that I'm going to end up chasing electrical gremlins due to the strange behaviour of the PSM and gear shift displays and lack of 'check engine' light or fault codes.....
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
Posts: 3343
Location: Sussex


PostPosted: Mon Jun 05, 2017 8:17 pm    Post subject: Reply with quote

The systems are interlinked , with no mafs then it will throw up faults in the gearbox as its doesnt know the engine load ( dme tells the tip control unit that data ) .. mafs disconnected and it kinda goes into limp mode .. it uses the data from other sensors and trys to work out what the failed sensor should read from any other sensor reading but the gearbox is just left in the dark so to speak .

It may well just be a faulty maf .. you can depending on the tester read the voltage of each maf , that will show different readings i would have thought .. im actually working on a similar fault atm but i have different readings on the maf voltages and am leaning towards an air leak .. which is going to be a total bitch to find !

This car drives but with a stutter though .

If a sensor fails but fails inside of its normal limits then there will be no eml and the car will still work on the assumption that the sensor data is correct even though its faulty .
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Scubadiver
Newbie


Joined: 03 Jun 2017
Posts: 29
Location: Norfolk, UK


PostPosted: Tue Jun 06, 2017 9:00 am    Post subject: Reply with quote

Perfect, thanks Demort that's reassuring. I think electrical problems of the kind I've read about caused by water ingress would be the absolute worst to diagnose and repair so good to know that the behaviour is normal.

I did have a look at the o/s MAF with a meter, of the four wires one is negative earth, one is full 12v +ve and the other two read around 1v +ve and 5v +ve. I would expect one of these last two to give a higher voltage when more air is moving (higher revs), but revving the engine had no effect on the voltage displayed so I'm pretty convinced it's faulty.

The car you're working on, are you suspecting an air leak between the MAF and the turbo? Or is it normally aspirated?
 
  
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Demort
Paul Ricard


Joined: 21 Mar 2015
Posts: 3343
Location: Sussex


PostPosted: Tue Jun 06, 2017 8:23 pm    Post subject: Reply with quote

The one i have is an air leak .. found several leaks on the system today .. not easy to pressurise each intake but a combination of smoke and a rigged up tyre pressure gauge confirmed it.

On a tester i was seeing 1.23 volts for 1 and 1.33 volts for another .. on a rev up the sensors where too far appart and it logged a fault on full boost .. but thats not your issue Smile

This is a turbo im working on .

The car looks at the volume of air passing over the MAF sensors and then compairs it to the amount of pressure seen on the MAP sensor .. this should be inside of a certain range and mine wasnt due to an air leak .. if yours has a failed MAF but its reading inside of limits then im guessing the car is reacting to the live reading and running according to the wrong value.

Yours could be a MAP sensor fault as unplugging a MAF will drop the car to default values and it will only look at throttle pedal / throttle valve and substitute a set value that it thinks is correct for the MAF .. getting complicated here aint it lol .

On a turbo then the max boost pressure is at 2500 rpm .. higher rpm and it actually lowers the boost .

Strange that we are saying a MAF failed just as you where giveing it some beans though .. thats the bit that bugs me and makes me think of a blown pipe / air leak .. but then you should have a fault code for that .. i have lol .

MAF first and see what we get after that before continuing i think .


EDIT ..

Btw .. remind me after this and ill tell you about water leaks .. and the main places that cause problems .. your ok atm though .. your car still starts !!
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Scubadiver
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Joined: 03 Jun 2017
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Location: Norfolk, UK


PostPosted: Wed Jun 07, 2017 8:45 am    Post subject: Reply with quote

All absolute gold, thanks Demort.

Yes, the car was making boost (and showing on the car's gauge), so I eliminated a popped off hose, although if I'm understanding you correctly, it could still have a leak or split which could mess with the sensors and confuse them. I can't hear anything, but it is hard to get away from the fact that it happened when I floored it, seems too coincidental!

The MAFs should arrive today, so I'll fit them and see where we're at.

Thanks again for taking the time to help, this kind of knowledge is invaluable.
 
  
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