M62 engine problem

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   11/98 540i. 65000 miles. Bought 2 months ago, passed with a clean bill of health just after purchase, and a good MOT with good emissions, just 500 miles before, since it stood at the dealer for a few months.
One month later, after going through a deep watersplash a couple of days previously, it stutters  and dies, but will restart after a few minutes. After a couple of days like this, take to BMW specialist who diagnoses Camshaft Position Sensor failure. Replaces, but engine now runs really roughly, with no power.
�700 pounds worth of diagnostic time and 2 weeks later, the pronouncement is the cats are blocked. Remove cats, find they were changed 10,000 miles and 2years 4 months ago. Broomhandle the cats, replace and run car.
All seems OK, but fuel consumption down by about 15% compared with my 96 740i, with slightly lethargic feel, and it only really goes when you wind it up. Not what you expect from a 540i.
For the MOT, I put some non-BMW cats on. Exhaust note was terrible, with rasping on power, and crackling on the overrun. Not sure if this is the non-BMW cats, or another manifestation of the poor running.
What is the most likely cause? There are no fault codes in the DME. all things like compression, ignition, fuel pressure, plugs, MAF, ICV have been checked, substituted. except for the ECU, which passes all self tests. The BMW main dealer says the car is right, because the computer says it's right, but I know by direct comparison with the same engine in a 740i, it's not right. Anyway, why would the cats have been changed at 50k miles and just 4 years old. The dealer explanation is that an ECU programming error, corrected in July 1999 may have shortened the cats life, but I would have expected BMW to have coughed up for new cats when they were changed.
All suggestions welcome, although ones that involve taking it to a dealer might not be accepted too keenly. So, M62 experts, tell me what's wrong.
TIA John Newell

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johnn635 Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 17-May-2004 Location: United Kingdom Status: Offline Points: 6	Topic: M62 engine problem Posted: 14-September-2004 at 18:41
	11/98 540i. 65000 miles. Bought 2 months ago, passed with a clean bill of health just after purchase, and a good MOT with good emissions, just 500 miles before, since it stood at the dealer for a few months. One month later, after going through a deep watersplash a couple of days previously, it stutters and dies, but will restart after a few minutes. After a couple of days like this, take to BMW specialist who diagnoses Camshaft Position Sensor failure. Replaces, but engine now runs really roughly, with no power. �700 pounds worth of diagnostic time and 2 weeks later, the pronouncement is the cats are blocked. Remove cats, find they were changed 10,000 miles and 2years 4 months ago. Broomhandle the cats, replace and run car. All seems OK, but fuel consumption down by about 15% compared with my 96 740i, with slightly lethargic feel, and it only really goes when you wind it up. Not what you expect from a 540i. For the MOT, I put some non-BMW cats on. Exhaust note was terrible, with rasping on power, and crackling on the overrun. Not sure if this is the non-BMW cats, or another manifestation of the poor running. What is the most likely cause? There are no fault codes in the DME. all things like compression, ignition, fuel pressure, plugs, MAF, ICV have been checked, substituted. except for the ECU, which passes all self tests. The BMW main dealer says the car is right, because the computer says it's right, but I know by direct comparison with the same engine in a 740i, it's not right. Anyway, why would the cats have been changed at 50k miles and just 4 years old. The dealer explanation is that an ECU programming error, corrected in July 1999 may have shortened the cats life, but I would have expected BMW to have coughed up for new cats when they were changed. All suggestions welcome, although ones that involve taking it to a dealer might not be accepted too keenly. So, M62 experts, tell me what's wrong. TIA John Newell

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�bermensch Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member I Joined: 14-April-2004 Location: Oswald Penitentiary Status: Offline Points: 112	Posted: 20-September-2004 at 17:29
	you probably damaged the cat (which tends to run extremely hot) while going through that standing water, and when replacing \ retrofitting an aftermarket item the car has reverted to running on lambda1 which is a default setting for lambda sensor \ probe or catalytic converter problems.. you could try fitting (temporarily) the 740i cat & sensors to see if the problem disappears ?

autofix Members Profile Send Private Message Find Members Posts Add to Buddy List Really Senior Member I Joined: 23-August-2003 Location: Kildare Status: Offline Points: 294	Posted: 28-September-2004 at 09:46
	Hi, Well where to start on this one, I just wish I could get 700 quid to diagnose blocked cats, especially after hearing about the water splash. That would equate to about 1400 per hour :) Aftermarket cats can sometimes cause problems. Basically the engine breathes through the exhaust and if the cats will not allow enough flow then you can have power output and fueling issues, the latter often causing the demise of the new cats. Exhaust back pressure can be measured to check this. Also, when cats break up, bits often find their way downstream and lodge in the rear boxes so restricting exhaust flow. HTH Alan