Cat's can 'plug' on any car, although it is a bit of a misnomer. The innards work loose, seriously impeding airflow.

Take it off and shake vigorously. If it's shagged you'll here it pronto.

Peter R.

 

My clogged cat produced a lining of cat material on the tail pipe which was obviously on one side when compared to the other. As well as rattling when it was removed.

 

...I think he replaced the plug wires already?

 

Sorry guys, I was not around a computer today. Yes, the plugs and wires were replaced. The car is just sluggish and feels like it cant breathe and/or not getting enough gas. Im also thinking it could be the knock sensors. Hopefully they were able to get the hammer on it today ir tomorrow. I havent spoken to them today. I also dropped off a good used cat froma friends car with a bypass pipe so we can try that.....I will let everyone know.....

 

Maybe a critter got stuck in your intake - ?

When you put you hand in front of the exhaust tips, does it come out forecfully ehn someone blips the throttle???

 

One other consideration: In the Streather book on page 163, it discusses that on non-Varioram engines, the DME (ECU) opens a resonance flap in the intake manifold when the engine speed reaches 5500 RPM. The resonance flap is designed to optimise intake length and induce intake charge oscillations. The result is increased intake air velocity and improved fuel atomization. In your case maybe a malfunction is preventing your car from revving beyond 5500 RPM!

The book further states: To prevent the resonance flap from seizing in the manifold bore due to formation of deposits, the vacum solenoid is activated breifly each time the iginition is turned on. This causes the flap to move and an AUDIBLE CLICKING is heard in the intake manifold.

Your problem is 5400 5500 RPM right? Might want to check this. Also, the 993 does have a potentiometer (pot) in the throttle valve to sense throttle position and it sends this info to your computer.

 

this thread may help clarify on the res flap: https://rennlist.com/forums/showthre...ferrerid=35947

and this post (in same thread) may help on the rpm cutoff... seems like a longshot, but I think that is all that is left? : https://rennlist.com/forums/showpost...1&postcount=31 (check out the preceding posts for more)
It's going to be a cornercase thing and probably really simple.

 

Thanks Mark. I looked at the post and my car has a new battery in it already. I haent checked it though? It is worth a shot. right now Im waiting to see what happens today with the hammer. It has to be knock sensors, o2 sensors, Cat or fuel injectors. At least all my maintenance will be up to date after this!!! The new M3 is really starting to look good at this point though

 

...I have slid my chips across the table to a Resonance Flap problem. See page 163 in the Streather book - for tose few of you that have it:^)

 

I dont have that book but there was a post in the link MarkD gave that said if it was the resonance flap it would still pull to redline. My chips are still on cat or knock sensor. Then when it isnt either of those, I will have to switch to something else........or just tell mthe wife that "I dont know why the 911 is slower than your X5? I guess BMW's are just better ....

 

The thread I posted above had 2 problems. One was solved by a new batt (not your issue) the other was a kinked fuel line. That did solve his 5500 rpm limit problem that sounds a lot like yours.
I am still betting on fuel delivery issue of some sort. I doubt it is another kinked fuel line but who knows...

 

Kinked - fuel line. It's possible to 'twist' a stainless fule line if the installer does not double wrench it.

True Story: as a CH-53E pilot we had to start a little turbine engine that drove ancillary electrics and hydraulics before starting the main engines: it is called an APU. (Aux Powe Unit). Anyway, the maintenance guys had done some work on the main fuel line and in the process actaully twisted it a turn or two, but nobody knew it yet. We could start the APU and as it was winding up to operating RPM, it would just 'die'. Took a while to figure it out, but the rsidual fuel pressure would allow the APU to light off and begin winding up, but then die from fuel starvation.
Could have a similar situation here. Kinked or twisted would allow the engine to operate ok in a lo-power regime, but unable to keep up with the demand as power rqmnt increases.

If the car has been jacked up recently and the jack put in the wrong place it could have smashed the fuel line from the pump, or a myriad of other possiblities relating to reduced fuel delivery.

 

Ok, Update, cat is ok. fuel flow is over factory spec (when measured after fuel filter). Not sure about the engine harness. Havent heard back yet. Im thinking possibly clogged injectors? Im also thinking the BMW dealer wont even feel the miss on the test drive if he stays under 5k so it wont affect trade in value............