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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20376
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a 2004 4.5 v8 porsche cayenne, it ha an engine rebuild

Customer Question

I have a 2004 4.5 v8 porsche cayenne, it ha an engine rebuild 40000 miles ago , runs very smoothly when cold as soon as it is up to temperature, it is very jerky when pulling away , it is tiptronic semi automatic!!it does not feel like a transmission problem , but the engine.
it has had two new fuel pumps, two front catalytic converters, two air mass sensors, new sparkplugs, woould very much appreciate your thoughts.
Submitted: 1 year ago.
Category: Car
Expert:  Shantal-Mod replied 1 year ago.
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Expert:  Matt replied 1 year ago.
hello I see that you've had a fair bit of engine work done but has the transmisson fluid been checked at all? as if low or worn out then you'll get a juddering on take off I'd take a look at the colour of the transmission oil it should be a dark red colour if its black then its needs changing together with its oil filter. Also check its level with the gearbox warm and just after you've moved the selector through all the positions leaving it for a few seconds in each one and then back to park. You can top up the box through the side fill plug if required and make sure you use the correct oil for your car as the fluids are not all the same. Some manufacturers recommended a change of the type of fluid - Speak to the local dealer and parts dept - they will advise you on the updated fluid to use.. If that’s all OK then check all the electrical connections of the gearbox, remove each connector in turn and spray with contact cleaner. Check that the wiring to the gearbox is in good condition with no chafing or frayed wireand if all of this is OK then This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running. Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
Expert:  Matt replied 1 year ago.


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