e34 535i m30 misfire under load

[leighton 535i]

Hi

Can anyone help I have a E34 535i m30, but it misfires under load if I rev it up slowly it dosnt seam to do it, any ideas ? And where are the timing marks for the cam ?

Cheers leighton

[bsell]

Hi

Can anyone help I have a E34 535i m30, but it misfires under load if I rev it up slowly it dosnt seam to do it, any ideas ? And where are the timing marks for the cam ?

Cheers leighton

Can't help with the cam deal but I would recommend you look at the ignition coil to spark plug connection for each cylinder. If you get crud or oil in that area, you got nothing but trouble.

Oil will cause the spark to go to ground on the outside of the plug instead of across the gap.

If you have crud (resistance) between the coil and the plug, you will burn up the connection between the two (money ).

Edit: I missread the year of your car as a 1998 with coil over plug ignition, sorry. But the point of losing high tension voltage during high loads on the engine is valid either way, you just have more 'stuff' between the coil and each plug. What does the inside of your distributor cap look like? Any faint black lines running from the center to the bottom? These lines are from the high tension zap running to ground along the inside of the cap.

Any oily film on the inside? If so, its time to fix the oil leaking into the distributor. You might could get by for a while by just cleaning the cap with a good solvent but you know the oil will come back causing the same problem .

Either way check it out as it isn't too hard to get to...

Brian

[genphreak]

Pressing throttle sharply (as opposed to gradually increasing revs slowly) creates a lower vacuum in the intake which is changing the mixture from what the computer had previously worked out to be right according to what the O2 sensor is telling it about the exhaust gases. So finding it can be a game of cat and mouse...

As others have said, start by checking your plugs. Then check your leads for loss and the rotor cap and button for excessive wear/damage.

An injector problem will show on the condition of its corresponding plug. If they all look similar you'll need to look further.

When you open the throttle it worsens a leak in the intake to throttle body area. The first thing to do is remove and replace the 2 vacuum lines (one for the Fuel Pressure Regulator and the other that goes to the rocker cover 1" vent pipe) as they have to be replaced on most cars anwyay. Remove and Inspect the other 1" pipe that goes to your ICV from the lower middle of the manifold- and the throttle body to AFM boot. A crack or pin hole in these will cause this issue. Replacing all of them is a good idea unless they are really good. Be sure the connections on all of them are clean, smooth and secure; previous damage from over-tightening or other abuse will also defiantely cause problems here- and is common

[zmuff]

While you're in the area, closely check the distributor cap for small cracks. My 535im did exactly the same as you described about a year ago. Turns out the (cheap aftermarket) cap was cracked. Works great with the new Bosch cap.