Hi all- new to the forum and had my Cayenne S for about 6 months. It's a 2005 4.5 S with 67000 miles on the clock

Pretty sure I noticed the slight roughness at low revs when I bought the car, but since I knew no better thought no more of it.

On tick over it runs rough, and has a rather bad spot at 1150rpm...where you can feel more vibrations.

I had an LPG (conversion done, the symptoms are the same on tick over but there are more noticeable flat spots (missfires?) when you accelerate with any vigour.
Which I've only had a few times on petrol (gasoline)

I have trawled the internet and asked everyone.

I've never had an engine light up, and the only code I've had is the cam angle sensor one.
What I've done so far:
-New plugs...old plugs were all white/brown and all exactly the same
-New coils all round
-Tried a new Air Flow Meter on both sides
-Catalytic convertor/Fuel System cleaner in fuel tank
-Cam andle sensor changed-
-Engine Oil/Filter change

Most specialists say- Oh you need a Porsche Specific Diagnostic Reader...bring it to us
So I go to Parr Porsche local to me, been around for years racing team etc

Plugged in- ''Nothing come up, we don't know what the problem is, that will be £85 please''

Hmmm..thanks for that

''Our next step would be to look down the bores and change plugs''
£400?? No thanks

Any ideas??

Charlie

 

Bump to the top

 

Most of us would suspect the Coil packs for this problem but you indicate yours have been replaced, what version do you have? (mine are .09)
Any possibility of water in your gas?

 

Just looked- Beru 0 0400 012 021

Bought new from EuroCarParts

Does it seem that there are even new coils that are faulty straight away?

 

That's not a Porsche part number so I suspect those are OEM (not OE) parts. No, I would not suspect new coil packs to be bad from the mfgr.

I don't know what the Beru part number was on my .09 coils (Porsche part number) so I can't compare the numbers.

 

Just remembered, Parr Porsche said that their diagnostic reader was showing that two cylinders weren't having the best spark
I've no idea how that can be read?!

 

Am I reading thie correct the car runs on propane? either way I would be interested in your knowing your misfie counter, what cylinders, what your fuel trim numbers look like. The next thing to do would be a compression test of all the cylinders and see if anything jumps out.

 

Hi-
Yes, LPG (liquid petrolium gas, propane) is becoming a common conversion on big thirsty cars in Europe.
You get less to the Gallon, but the pump price is 40% less than petrol (gasoline)
The system has an ECU which piggy backs the cars' original, and you can switch to what ever fuel you want.

Since the rough running is on both fuels I tend think it cant be fuel related

I did see a thread on fuel check/pump....I guess there's a possibilty if the cars ECU uses this it could cause the issue on both fuels!?

LPG is harder to ignite, and therefore usually shows up engine running issues much sooner than when running on petrol.

No missfires were recorded on either the generic diagnostic reader, or the Porsche Specific one

The only error was a once recorded Cam Angle Sensor...which was said not to be a current problem....i.e. just popped up once before


I think the problem is in it's early stages, if someone jumped in the car, with good fuel I doubt they'd notice it, on high octane fuel its fast, pulls like a train and very smooth from 1400rpm upwards
But when you point it out to someone semi mechanic minded, you get the reaction- ''oh yes, now you mention it''....

 

Sorry, I completely missed the LPG part, I wouldn't even want to guess on this.

 

Well pretty sure the car had the rough running before it put the LPG on, and still does it on both fuels

 

Rulling out both fuel systems, which still leaves us with a few common components, and you have replaced coils and plugs. It could be internal engine related.
I think you need to check your compression and leak down and see what you have.

 

Ok hoping to geth compression and leak down check done next week when not so busy using the car

I noticed yesterday that at the bad flat spot of 1150rpm, if you accelerate you get a significant hesitation on petrol, and worse on LPG.

One tuning garage I rang (not Porshe specific) said their bosses wifes' Cayenne had a similar thing, and the workshop ended up changing the Crank Angle Sensor and solving problem

think I forgot to mention, I've had the odd struggle to start, and occassionally when hot, turns over a few times before firing

 

Hard to start is usually related to the canister purge valve, Iive seen a few bad cam position sensors but never a crank sensor (on a cayenne) and always with faults .

 

Hey Charlie,
the problem with the missfires you have (and the camshaft errors in ecu) is caused by the bad installation of the LPG.
The injectors that they drill into your intake manifold, are placed at the wrong position.
So at low rpm it sucks air, but the LPG takes to long before it end up at the valves.

I have had the same problem for 3 years with my cayenne 4.5s on LPG.
The company that installed the LPG system told me there was something else wrong with the car (like coils etc)

After 3 years i ended up at the company that designes and makes these LPG systems that i have installed in my car.
They took a look and saw that the injectors were drilled at the wrong positions.

They took off my intake manifold and put them in the right place, closer to the valves. They send the bill to the garage that installed the LPG in the first place!

Greetings from holland

 

My 08 CS was suffering from a similar issue last few days. I initially thought it was bad gas, ran the tank almost dry, put in Sunoco from a different station, added Techron to no avail. Took it to the dealer (CPO) and it turns out to be the primary fuel pump. They will be changing it tomorrow under CPO (phew!).
Raj