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internal88
internal88, BMW Mechanic
Category: BMW
Satisfied Customers: 2526
Experience:  I have an Automotive Engineering Degree and also work for an Automotive engineering company since 2003.
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1999 540i. p1343, p1351, p1341. Replaced all the ignition

Customer Question

1999 540i. p1343, p1351, p1341. Replaced all the ignition coils, the car seems to be misfiring. what else could be the issue?
Submitted: 1 year ago.
Category: BMW
Expert:  internal88 replied 1 year ago.

Hi, I'm Brandon - BMW TECH.

1999 540 have a crankcase ventilation valve that provides a constant low level of vacuum to the crankcase, no matter what the level of vacuum in the intake manifold. If the diaphragm in this valve fails, there will be too much vacuum applied to the crankcase, and there will often be a whistle or hum caused by air being drawn into the engine past the rear main seal. Often the PCM will have codes for the O2 sensor or a lean fuel mixture as well. If pulling the oil dipstick or removing the oil filler cap stops the noise, the crankcase ventilation valve is bad and should be replaced.

Expert:  internal88 replied 1 year ago.

The pressure control valve is centrally located in the rear end cover of the intake manifold and is connected directly to the cyclone-type separator via an aluminum pipe.

Expert:  internal88 replied 1 year ago.

For the best quality part try to get the BMW OEM version.

Please rate me positive for the prompt service, thank you!

Customer: replied 1 year ago.
Already replaced them. It seems like the cylinders are losing compression on the 1 and 5 cylinders. What do you think would cause this?
Expert:  internal88 replied 1 year ago.

Losing compression on these BMW could be two things. Cracked cylinder head gasket or damaged compression rings in the combustion chamber.

Customer: replied 1 year ago.
but why would the two cylinders lose compression on 2 of the cylenders one opposite sides of the engine
Customer: replied 1 year ago.
could it be a rod bearing?
Customer: replied 1 year ago.
its misfiring on 5 and 1
Expert:  internal88 replied 1 year ago.

No, I doubt is the bad rob bearing. You will have low oil pressure and low knocking noise coming from the engine.

Expert:  internal88 replied 1 year ago.

Who tested the engine compression. What were the pressure reading?

Customer: replied 1 year ago.
most had about 150 psi but the two front less then 30
Customer: replied 1 year ago.
there is still compression but not much
Expert:  internal88 replied 1 year ago.

Yes, I believe the cylinder head has a cracked in both banks. 30 PSI is very low.

Customer: replied 1 year ago.
how would that happen at the exact same time?
Expert:  internal88 replied 1 year ago.

overheating is one of the biggest cause and lack of coolant change.

Expert:  internal88 replied 1 year ago.

Please rate me positive for the prompt service, thank you!

Expert:  internal88 replied 1 year ago.

Any updates?