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Broken down on the way home...

Scubadiver

Well-known member
Joined
3 Jun 2017
Messages
49
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!
 
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
 
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?
 
isysman said:
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?
 
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 :(
 
MisterCorn said:
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:
 
Demort said:
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 :(

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!
 
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 .
 
Scubadiver said:
MisterCorn said:
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
 
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
 
MisterCorn said:
Scubadiver said:
MisterCorn said:
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:
 
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 :?
 
Welcome to the forum. Sorry for your bad start but best of luck for tomorrow. Let us know how you get on.
 
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!
 
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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