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Hey Guys,

 

Desperately seeking your help and knowledge on this one. 

 

I have a 2003 Cayenne turbo, the car is running very rough on idle also while driving if your gentle with the throttle it's ok, but when accelerated harder it hesitates and sounds like theres a backfire through the intake. After about 5k rpm it settles down and pulls hard. what i am seeing is multiple random misfire codes from cylinders 5,6,7,8 so it's only from the one bank. This is the only code thrown, absolutely nothing else. 

 

I've been to 2 Porsche independents who have both had a look but nothing concrete. One seemed to think its the variocam adjusters or variable cam timing for that one bank. The thing is i applied voltage to the actuator/solenoid and it adjusted the timing and the car ran rough while voltage was applied, this was the same effect on both banks. Seems to me that the variiocam adjusters and the solenoid is working?

 

The following has been done:

Compression & Leak down test

checked fuses between the windscreen and engine bay

Checked battery and fuses in that area

Checked earth points under the bonnet and battery area

Checked fuel pressure 

Swapped injectors from a good cylinder to a misfiring one and the problem did not follow

installed 8 Brand new plugs and coils. Old coils tested OK anyway with a coil tester

Smoke tested the intake system, there were some small leaks which have been fixed

Applied voltage to the cam adjuster solenoids, both seemed to advance timing and the engine speed was reduced while voltage was applied. (same effect on both banks)

 

Me and a mechanic friend will be checking timing by pulling the valve covers off, thats the only thing we have not done just yet. 

 

Any advice is appreciated as I'm coming to a loss of ideas.......Thank you!

 

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Sure, sorry i forgot to add them, the only fault codes i'm getting are as follows which were from a few weeks ago, i cleared them and will have to recheck for codes later today:

Random/Multiple Cylinder Misfire Detected - P0300 - 002 - Intermittent
Cylinder 8 P0308 - 002 - Misfire Detected - Intermittent 
Cylinder 7 P0307 - 002 - Misfire Detected - Intermittent
Cylinder 6 P0306 - 002 - Misfire Detected - Intermittent
Cylinder 5 P0305 - 002 - Misfire Detected - Intermittent
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Coil packs on that model years cars were known to cause misfires. Make sure you are using the latest coil packs.

Look for obvious signs of cracks in the coil packs and/or remove each one and test with an ohm meter.

 

Since you do not have camshaft deviation faults I would not go there yet.

 

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Coil packs on that model years cars were known to cause misfires. Make sure you are using the latest coil packs.
Look for obvious signs of cracks in the coil packs and/or remove each one and test with an ohm meter.
 
Since you do not have camshaft deviation faults I would not go there yet.
 



Thanks for that however I purchased brand new coil packs from pelican parts along with new plugs, the old and new coils were tested with a coil tester and they all still work.

The car not throwing camshaft deviation faults is the strange one, however I don't have durametric I'm using VCDS which works with this ecu to read faults as it's the same used on some VW's.

I've purchased durametric and awaiting its arrival. However the workshops are Porsche specialists and they checked the specifics but couldn't pin point it for sure, other then one thinking it's the variocam adjuster, even in this case I would suspect a camshaft deviation code.
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Have you checked the fuel pumps for volume and operating pressure? Sometimes misfire codes can lead you down the garden path, you have misfire codes for certain cylinders but it might actually be the paired cylinder at fault. Example would be a four cylinder engine with firing order of 1-3-4-2. Cylinder 1 and 4 are common to each other as is 3 and 2. Engine fault code P0304 but actually cylinder #1 is at fault..... just something to be aware of. Also carefully inspect the ground path and wiring harness for the coils on the bank in question. Age/Heat can deteriorate the harness and cause issues. 

 

Can you monitor Mass Air Flow Sensor with VAGCOM?

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5 hours ago, rjt86 said:

Is there any other suggestions on what to look at that hasn't already been checked?

Durametric won't give me any additional info that the shops have already seen, so I'm not feeling to confident even if I did have it.

Seems like something common to this bank, so my thinking is knock sensor bank 2 or wiring like the earth or signal of the coils loom on bank 2. 

You can easily probe the coils from the rear and check for +12v and earth. There is four pins but I haven't got the pin info to hand. One is a feed back to the Ecu on how the coil is performing. 

 

I also don't think it is cam related and the maf is not used for idle so if misfires are at idle as well forget the maf sensors for now. 

 

 

Edited by lewisweller
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Probably too simple, but since you have no other error codes are the plugs torqued correctly? First time I changed my plugs I didn’t have the nerve to go to 20 ft/lbs, seemed way to tight for an expensive aluminum head, but I got the same error codes and rough running too (just a bit rough though). Went back and re-torqued them to spec and all was fine. Was really surprised it made a difference.

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Have you checked the fuel pumps for volume and operating pressure? Sometimes misfire codes can lead you down the garden path, you have misfire codes for certain cylinders but it might actually be the paired cylinder at fault. Example would be a four cylinder engine with firing order of 1-3-4-2. Cylinder 1 and 4 are common to each other as is 3 and 2. Engine fault code P0304 but actually cylinder #1 is at fault..... just something to be aware of. Also carefully inspect the ground path and wiring harness for the coils on the bank in question. Age/Heat can deteriorate the harness and cause issues. 
 
Can you monitor Mass Air Flow Sensor with VAGCOM?



Thanks for that fuel pumps were tested and pressure checked to ensure it's getting what it should be.

Interesting point about the cylinder grouping, earth points were checked and new ones run for testing.

I think I'll need durametric to check the airflow sensors but the shop tested it
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Seems like something common to this bank, so my thinking is knock sensor bank 2 or wiring like the earth or signal of the coils loom on bank 2. 
You can easily probe the coils from the rear and check for +12v and earth. There is four pins but I haven't got the pin info to hand. One is a feed back to the Ecu on how the coil is performing. 
 
I also don't think it is cam related and the maf is not used for idle so if misfires are at idle as well forget the maf sensors for now. 
 
 



I'll have to test the coil wires more closely now as it seems the issue is not a simple one. I'll try dig up a wiring diagram to see what wire is doing what.

Thanks for the point on the MAF sensors I didn't realise they are not important at idle. The shop I took it to did test these out and didn't find any faults with it.
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Probably too simple, but since you have no other error codes are the plugs torqued correctly? First time I changed my plugs I didn’t have the nerve to go to 20 ft/lbs, seemed way to tight for an expensive aluminum head, but I got the same error codes and rough running too (just a bit rough though). Went back and re-torqued them to spec and all was fine. Was really surprised it made a difference.


I did torque then down correctly as I had access to the workshop manual at the time, however having said that it's been to a Porsche Indy who had to remove and refit the plugs to do the leak down test. Still the same issue unfortunately.
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