BMW Repair: Loss of power/misfire around 1500 rpm; no codes., vacuum leaks, electronic thermostat

Question
Hi there John.  Got one for you.

2000 540i (6 speed/Dinan intake/ecu/exhaust)

I've been throwing a CPS code and replaced the correct bank Camshaft Positioning Sensor.  Before replacing started throwing misfire code on #1.  I replaced the bad coil pack and checked the plug (good).  Now I'm having a loss of power/misfire between 1k-1500 RPM.  It's especially noticable under hard throttle and is unnoticable to the driver above 2000 RPM. The only code it's giving is a bad Electronic Thermostat Sensor.  (I don't think this could be the issue.)  If hold the rpms at 1600 for more than 30 sec a whole slew of codes are thrown. Misfire in cylinders #5, #8, #7.  I cleared the codes and used a new coil pack to test all 8 cylinders one at a time.  No change in performance/symptoms.  I've checked 4/8 (1,4,7,8) plugs and all look good. There was a little oil residue on 7 and cleaned that.  I should check the other 4.

Forums say to check for vacuum leaks.  (intake manifold for cracks, gaskets, Throttle body/MAF intake boot)  Could something be wrong here w/o throwing a code (liek fuel trim correction)?

What about ignition module not working correctly?

Fuel filter?

I'm stumped and not interested in letting the dealership run me around yet.  

Any ideas?

Thanks in advance!
Greg  

Answer
Always start with the easy ones.  Are air and fuel filters good?

Next go with the air leaks.  Check them all carefully.  Amazing what a small leak in those areas can do.

Are you running premium gas?  The Dinan chip should force that.

Bad electronic thermostat sensor is an interesting one.  There are two things tied into the thermostat:  A temperature sensor that feeds the temperature to both the dash and the computer.  Use the system to get "KTMP" reading on your dash display to see if the temperature seems to be reading correctly.  (The boards have lots of info about how to get to these codes) The other aspect is these things actually have an electrically operated thermostat.  If the engine is actually getting too hot or not hot enough, it's likely the thermostat. Ignition module unlikely cause.


Any chance your injectors are dirty?

Keep playing the easy ones first.

A final thought....change back to your stock control chip, and see if it goes away.