complete loss of power at high rpms

[jofusfarr]

My 540/6 has had this problem for awhile now. A higher rpms, 5000-6500, there is complete loss of power as if the engine is starved of fuel - it cuts off immediately. This occurs regardless of engine load.

Idle is acceptable with no discernible misses.

Issues that may be remarkable: There is unusually high amount of water vapor in exhaust once the engine is warmed up - more than my 540ia.

There is rather severe oil leakage at both valve cover gaskets and they need to be replaced.

I have done the following:
Thoroughly tested for vacuum leaks.
No oil/coolant in expansion tank/oil sump.
Tested fuel pump/pressure/regulator/fuel filter.
Spark plugs are new and old ones had consistent wear among cylinders.
All injectors functioning and flow is acceptable.
CPS confirmed working.
MAF sensor confirmed working.

Any ideas?

[BMWDriver]

I think you need not look much further than your valve cover gaskets. These play a pretty damned important role, especially at the higher revs you refer to. So you're loosing essential air pressure and probably leaking fuel intake; there is so much air pressure in an engine that in fact the air gets thrown out the leaks you found and unbalance your engine enough for it to die out.

[jofusfarr]

I thought there was a vacuum in the crankcase, which would manifest problems more severely at idle during higher vacuum?

[bubba966]

Change your VCG's and get new coil boots.

High RPM issues are usually ignition related. Coil boots would cause that if they were in need of replacing.

High amount of white exhaust is also a symptom of bad coil boots. Bad boots cause poor combustion which sends raw gas out the exhaust. Raw gas hits the hot cats and burns causing excessive white smoke.

Not only is such a situation bad for your fuel economy, but it'll also kill your cats. Throw new coil boots in there before you need to replace cats, 'cause cats aren't cheap...

[Bill R.]

are you sure you're not hitting the factory rev limiter?




My 540/6 has had this problem for awhile now. A higher rpms, 5000-6500, there is complete loss of power as if the engine is starved of fuel - it cuts off immediately. This occurs regardless of engine load.

Idle is acceptable with no discernible misses.

Issues that may be remarkable: There is unusually high amount of water vapor in exhaust once the engine is warmed up - more than my 540ia.

There is rather severe oil leakage at both valve cover gaskets and they need to be replaced.

I have done the following:
Thoroughly tested for vacuum leaks.
No oil/coolant in expansion tank/oil sump.
Tested fuel pump/pressure/regulator/fuel filter.
Spark plugs are new and old ones had consistent wear among cylinders.
All injectors functioning and flow is acceptable.
CPS confirmed working.
MAF sensor confirmed working.

Any ideas?

[jofusfarr]

Fairly sure since it ranges from 5-6.5k. I didn't know the six speed had a rev limiter.

I have taken my 540ia to 7k redline, I expect my 540/6 to do the same.

I just checked coils/boots on the other car and they check out fine at high rpm.


I forgot to mention that when the engine bogs down, the check engine light comes on briefly. The stomp test reveals no codes.

[compmore]

had a similar probem and my fuel filter was the cause

[bimmo_2007]

had a similar probem and my fuel filter was the cause

+1

I had the same issue many times and it turned out to be either the fuel filters or bad fuel pump.

[BMWDriver]

The rev limiter does not provoke such issues anyhow. What happens with my M50 is that the engine loses a bit of power and the engine stutters a bit and won't rev higher than 7000. It's possible your 540 has another chip that does not limit it.

But all the same, if your engine is not capped, you would loose power somewhere above 7000 rpms, not the 5-6500 you report. The power peak of the M60B40 (http://en.wikipedia.org/wiki/BMW_M60#M60B40) is at 5800 rpms, so 6500 would still yield significant power output.

It's always difficult to pinpoint exactly what's wrong with the engine on a forum.

[Ross]

I can't speak to the water vapor issue as I don't know where you are. Here in cold Chicago cars that do a lot of short trips are boiling off condensation in the exhaust and it's no worry.
If power tails off at high revs look for a fuel delivery problem, if it sputters or misfires look to the ignition.

[632 Regal]

I can't speak to the water vapor issue as I don't know where you are. Here in cold Chicago cars that do a lot of short trips are boiling off condensation in the exhaust and it's no worry.
If power tails off at high revs look for a fuel delivery problem, if it sputters or misfires look to the ignition.

old rule of thumb: if it backfires through the exhaust its electric, through the intake fuel.

You mention valve cover gaskets, if any oil is down around the plug boots that's your problem. Remember not to mix different brand plug boots with the coils, they are specific to each other in resistance. Boots are relatively inexpensive compared to other items so I would consider them a step with the valve cover gaskets a no brainer.

[jofusfarr]

Valve cover gaskets have been replaced.

Swap coils/boots and DME from other 540i, issue remains.

I can't really get it to backfire, though I thought I heard a few smalls pops from the intake...too quiet compared to engine noise at those RPMs.

Power is great until it hits this point, between 5-6k rpm or so. Engine bogs down abruptly similar to a spark arrest rev limit.

Fuel pressure is good at these RPMs, and pump is strong (two different fuel pumps used to diagnose). Only thing I haven't checked that could cause this is TPS and actual fuel flow.

[632 Regal]

Valve cover gaskets have been replaced.

Swap coils/boots and DME from other 540i, issue remains.

I can't really get it to backfire, though I thought I heard a few smalls pops from the intake...too quiet compared to engine noise at those RPMs.

What stumps me is fuel pressure is good at these RPMs, and pump is strong (two different fuel pumps used to diagnose). Only thing I haven't checked that could cause this is TPS and actual fuel flow.

you have everything covered unless i missed something. What plugs are you using? Is it possible (answer no lol) the intake gaskets got fubarred during install? I barely caught a major fcuk up when I did mine, the intake gasket fell out on the back and flipped over, I felt it when the intake was on before tightening, would have sucked.

[632 Regal]

you have been rebooting the computer after each step correct?

[jofusfarr]

Yes, computer has been reset. I have not changed the intake gaskets since owning the car - a thorough soaking with starting fluid led me to rule out intake leaks, especially with an issue at such little vacuum.

Next I suppose I should actually check the wiring to the coils, though I'm not familiar with such a procedure.

[632 Regal]

Yes, computer has been reset. I have not changed the intake gaskets since owning the car - a thorough soaking with starting fluid led me to rule out intake leaks, especially with an issue at such little vacuum.

Next I suppose I should actually check the wiring to the coils, though I'm not familiar with such a procedure.

I really doubt the wiring, boots yes but you said those were changed. If you never changed the intake or end gaskets I could almost guarantee you will solve your problem. My intake gaskets were like dried plastic and the new ones are like a silicone rubber. Spraying juice on our intakes is almost futile as there is no way to get to the inside part.

[Bill R.]

The rev limiter on a stock m60 is 6800 rpm, if you have any tach error then you could be higher than you think.

You could scope the motor and see what kind of firing voltage you are getting. Also you could have dirty injectors that just aren't flowing enough fuel under high demand, pump and filter could be fine. You would have to pull the injectors and flow test them. Mass air flow sensors could be bad, swap your mass air flow sensor from the good car to the bad car and see if it gets better. Dme could be not supplying enough current to the injectors

[jofusfarr]

This is true, there could tach error. Though the way it bogs down with a CEL makes me think otherwise. Would swapping a cluster confirm this or would the tach signal be out of whack further upstream?

MAF is confirmed functional with a known working one.

I'll check the injectors again - I haven't tested injector/fuel flow at all, merely pressure and function.

Intake gaskets will be the last thing I check, since I really don't see a vacuum leak causing such issues near WOT.

One thing I did do was to partially block the return fuel line to increase fuel pressure - more pressure, more flow was my reasoning. Same results, though I could not read tach at the time.

[bubba966]

You said the plugs were new. Which plugs were installed?

[jofusfarr]

NGK BKR6EK plugs

[jofusfarr]

After an oil change the smoking has ceased.

Also, the rev problem has a new update. I let the engine reach normal temperature with the hood CLOSED to thoroughly heat the engine bay. Higher temperatures seem to increase the rpm on which the problem occurs or allows it to red line completely with no CEL or bogging down.

Perhaps it could be intake gaskets as suggested! I'll keep you folks updated - there's been great input so far and I am grateful.

[Ferret]

Crank or cam position sensors?

Cam timing slipped somehow?

[632 Regal]

Cam timing slipped somehow?

Eeek, don't even think like that!

lol