can't rev over 5500 rpm

[colin86325]

Ok, a strange little problem developed recently.
I can't really rev the car past 5500-6000 rpm, regardless of whether the engine is under load or in neutral.

It definitely feels like a fuel cut as there is no bucking/jerking at this limit.  The engine tries to increase in rpms when I have the pedal at WOT, but it very, very slowly creeps to 6000 rpm.  I didn't want to damage anything by trying too hard past this point.  It just feels like fuel is being cut.  The car does seem slightly down on power above 4500 rpms or so.

Some maintenance background:

I replaced the fuel pump about 3 weeks or so ago because the car wouldn't start one day (but did start after I banged on the pump), so the pump should be good.  

• The catalytic converter is about 4 months old.
• I'm running COPs with about 13,000 miles on them.
• The engine was rebuilt about 16,000 miles ago.

The Check Engine light is not displayed while the car is running.

I'm going to replace the fuel filter tomorrow and also see if any codes are stored.  I'm going to also test the cam and crank sensors (which have at least 150,000 miles on them).

Has anybody had a similar problem?

Thanks,
Colin

[ziedas nr 1]

what engine in yours bmw m42 or m44?

[colin86325]

I have an M42 engine.

I pulled the coils (I have a COP conversion) and the spark plug wells were full of oil.  I replaced the valve cover seals and the coils, along with the cam sensor and the car still cuts out above 5000 rpm.

The problem gets worse once the car sits in traffic and gets hot.

I'm going to replace the crank sensor next.

[DesktopDave]

What codes did you get from the stomp test?  I have an original crank sensor with 276k miles on it, they're too expensive to toss a good one.  I'd suspect you have a sensor problem too, but the crank sensor will stop the fuel pump if it's bad.  I had to clean it recently, might just be you have oil & rust interfering with the crank trigger signal.

You're getting this at wide-open throttle, I'm guessing?  If so, the DME ignores the O2 sensor (goes open-loop) and guesses what you need from the coolant temp & AFM flap.  When the motor is fully warm the cam PS gets to be more important too...sets aggressive timing.  If you have an e36 you might also have trouble with the knock sensor.  If either are retarding the spark timing you'll have a noticeable power loss.  Test the TPS too - might not be sending the WOT signal to the DME.

If this isn't at WOT, I'd go down the list for all the stuff that leans out the mixture closed-loop (warm engine, partial throttle) from easiest to hardest:
stomp test, test any component it flags
ohm out the crank & cam PS
ohm out the coolant temp sensor
ohm out the AFM flap and temp sensor

If that's all OK, look for vac leaks
clean the ICV
check the throttle cable & linkage

If they're all OK, try the fuel system next.
dirty injectors
bad fuel filter
weak fuel pump connectors or relay

[colin86325]

Problem solved.

While messing around yesterday, I noticed some water come out of the harness that goes to the AFM. There is an intermediate connector that goes between the AFM and the main wiring harness, and this had collected water and was corroding the pins.
After cleaning and drying the connector I was able to rev to 7200, so I was very happy.

Usually I'm pretty diligent if I wash under the hood, but I think on this day I was asked to move my car and then received a phone call immediately afterward. I forgot all about taking harnesses apart and checking for moisture.

Anyway, hope this can help somebody in the future.

Cheers,

[DesktopDave]

Good to hear you solved it.  That is a resistor pack that BMW installed as a TSB campaign.  I pulled mine because I was having trouble with a 1215 code, it's run fine ever since.

[colin86325]

Thanks Dave.  i neglected to add that the water was the result of washing the engine and not properly disconnecting and drying the electrical components.