E34 engine loses power @ 4500 RPM

[e34fun]

Engine runs strong til 4500 RPM, then power fades abruptly.
Running thru the gears (5 Speed Man. Trans), engine runs superbly, then at 4500 it hits a wall. What has been replaced in the last year; new fuel pump, fuel pres regulator, oxygen sensor, & catalytic convertors. Rebuilt engine has 20,000 miles on it, in a 92 525i with 95,000 miles.
Has anyone experienced a similar problem or have an idea what might be causing it?
Thanks in advance!

[shogun]

Fuel filter, rotor+disty cap come to my mind.

[BM-BOY]

check the injectors as well... mine had a slight blockage in one... also check HT leads, distributor and rotor arm...

[Dan in NZ]

Could just be something simple like the air filter.

[brodee]

Fuel filter, rotor+disty cap come to my mind.

No rotor and cap on an M50

[Bill R.]

coils for poor output, someone else had that same problem with an m50 and it turned out to be a couple of bad coils....







Engine runs strong til 4500 RPM, then power fades abruptly.
Running thru the gears (5 Speed Man. Trans), engine runs superbly, then at 4500 it hits a wall. What has been replaced in the last year; new fuel pump, fuel pres regulator, oxygen sensor, & catalytic convertors. Rebuilt engine has 20,000 miles on it, in a 92 525i with 95,000 miles.
Has anyone experienced a similar problem or have an idea what might be causing it?
Thanks in advance!

[Kalevera]

coils for poor output, someone else had that same problem with an m50 and it turned out to be a couple of bad coils....
That's what I was thinking....restricted flow at the cat. best, whit

[brodee]

That's what I was thinking....restricted flow at the cat. best, whit

He replaced the cats. Coils should cause a miss at idle if they are going bad.

[Bill R.]

problem such as unburnt fuel it will kill the new cats very quickly. And typically a weak or bad coil will have more than enough energy to light the mixture at idle when with the throttle bore is closed. But not so when accelerating under load.









He replaced the cats. Coils should cause a miss at idle if they are going bad.

[632 Regal]

yep the old blow the spark out in high wind theory.

I would check them (coils) first because even if you replace the cats your gonna dump more raw fuel in there and kazam! just like magic youll be asking the same question a month from now.

OT: I used to be on a forum where guys would have super powerful ignition systems getting high speed miss...chasing things and spending thousands of dollars and of course I wouldnt get the credit for being nut on in the first place. You have high compression and a miss at 7000rpms...lets see here, whats the plugs gapped at .045...LOL Try .030...that would start all kinds of stuff going. I dont need to gap them that small I have 30 bazillion volts...whatever man.

[Anthony (M5 in Calgary)]

yep the old blow the spark out in high wind theory.

I would check them (coils) first because even if you replace the cats your gonna dump more raw fuel in there and kazam! just like magic youll be asking the same question a month from now.

OT: I used to be on a forum where guys would have super powerful ignition systems getting high speed miss...chasing things and spending thousands of dollars and of course I wouldnt get the credit for being nut on in the first place. You have high compression and a miss at 7000rpms...lets see here, whats the plugs gapped at .045...LOL Try .030...that would start all kinds of stuff going. I dont need to gap them that small I have 30 bazillion volts...whatever man.

I agree with your OT Jeff, but have experienced different: The plugs on the M5 are spec'd to be 0.028" and when I first pulled them for replacement shortly after purchase, the gap had eroded to at least 0.060", maybe more. The car ran fine right to 7K+ and there was no noticeable change with the new plugs.

Here's a picture of the worn plug next to another gapped at 0.028". BTW, the Champions were listed as a direct replaement for the Bosch Y6DC but you can see they are not a proper match. I ran them for about a week...
http://img.photobucket.com/albums/v11/interalian/BoschvsChampion.jpg

[632 Regal]

I was talking about 500-1200hp drag race engines with 15-17:1 compression.

you rev that thing to 7k? sweet!!!!


I agree with your OT Jeff, but have experienced different: The plugs on the M5 are spec'd to be 0.028" and when I first pulled them for replacement shortly after purchase, the gap had eroded to at least 0.060", maybe more. The car ran fine right to 7K+ and there was no noticeable change with the new plugs.

[Anthony (M5 in Calgary)]

I was talking about 500-1200hp drag race engines with 15-17:1 compression.

you rev that thing to 7k? sweet!!!!

A day without 7K is like a day without sunshine. Here's the stock dyno chart - you need to rev it to make it go...

http://img.photobucket.com/albums/v11/interalian/Dyno_0709.jpg

I try to not bounce off the rev limiter though - the S38B36 is a happy engine provided you stay away from the ~7500RPM harmonic that blows out the keyway on the harmonic damper mount.

Note the added photo - I just put it in.

Cheers,

[632 Regal]

saw the plug pics, what I noticed is a lot of plugs straps try to straighten along with the electrode burning...no doubt then plugs are "used" LOL. I havent changed mine in 40k...I should think about picking up a new set one of these days.