318i lacks power over 4000 rpm

[mattg]

[FONT=Optima][SIZE=14][COLOR=blue][B]my j reg bmw 318i looses power at 3500 revs and starts to missfire around 4000 rpm if i ease off the gas then the missfire will clear at around 3000rpm.
The problem is consistant and is the same in all gears, i have changed the ignition coil, leads, spark plugs, distributor cap and rotor arm, tappets, all filters and the oil but still the problem persists does any one have any ideas any help in this area would be much appreciated.

The options i have left are to check the catalytic converter as suggested by a friend or to have a diagnostic test performed which could prove expensive as the obd1 appears not to be working when i have tried the accellerator method.

thank you to anyone who can help as i am getting a little annoyed as you might expect.

[Furious]

hmmm, sounds to me like you already covered the possibilities that i could be , but what grade gas have you been using? and also did you have any DME work (chip install, possible replacement etc).

[Autotechnica]

Maybe you're losing vaccum pressure. Did you check to see if all the vaccum hoses are in good shape? Check the throttle body sensor plug, it may have gone bad as well.

Another common problem is the black intake boot right after the throttle body and right before the MAF unit. This black rubber boot is quite fragile. If you bend it too much or haven't replaced it in a while it's a good bet it could be cracked or punctured. I've exeperienced the same problems you had before, usually it has to do with air leaks in some old rubber hoses that needed replacing.

good luck,

Bry

[dutchbmw]

It sounds to me like an air leak at first sight...... How many miles are on your car and from which year it is? I don't think but it could be a worn-out engine.

[dutchbmw]

One more:

-Bad fuel pump