frustrated 528e

This darn thing is becoming a money pit..but I've spent too much to give up now..I gotta know what it is that is causing my issues....so far I've replaced:

Airflow sensor
temp sensor
fuel pumps
plugs,wires,cap,rotor
fuel pressure regulator
vacuum hoses
Air intake boot for airflowe sensor

....I have 36psi fuel pressure and volume is more than adequate. When you pinch off the return it will make as much as 80 psi. Durring cranking it will spit ands sputter. occationaly it fires off and goes to 2000 rpms...smooth at 2000....eventualy after about 5-10 sec. it drops down and sputters into a stall. restricting the return to produce 50 - 60 psi makes it start easier and it will stay running...but it runs/idles over 2000 rpms....durring sputtering it sounds like some minor backfiring into the intake....plugs are black after just a few minutes of running......Could the idle air valve cause this...it seems to be constantly hunting for a good position.....

Originally Posted by mrbbchevy

This darn thing is becoming a money pit..but I've spent too much to give up now..I gotta know what it is that is causing my issues....so far I've replaced:

Airflow sensor
temp sensor
fuel pumps
plugs,wires,cap,rotor
fuel pressure regulator
vacuum hoses
Air intake boot for airflowe sensor

....I have 36psi fuel pressure and volume is more than adequate. When you pinch off the return it will make as much as 80 psi. Durring cranking it will spit ands sputter. occationaly it fires off and goes to 2000 rpms...smooth at 2000....eventualy after about 5-10 sec. it drops down and sputters into a stall. restricting the return to produce 50 - 60 psi makes it start easier and it will stay running...but it runs/idles over 2000 rpms....durring sputtering it sounds like some minor backfiring into the intake....plugs are black after just a few minutes of running......Could the idle air valve cause this...it seems to be constantly hunting for a good position.....

Pull the Idle Air Control valve and clean it and the passages connected to it. Check it for smooth operation. They can get sticky. What year is your 528e? Up through 1987 they have a cold start valve that can cause problems. Your injectors themselves or the o-rings may be leaking or malfunctioning. They're not terribly hard to remove and replace. The easy way is to remove the valve cover and then the fuel rail. Have your valves been adjusted recently? Your speed sensor or crank position sensor may be faulty. Have you ever had a compression test? Are you sure the coil and its wiring is OK? Do you have a strong blue spark? Did you replace the fuel filter?

So, this only happens when starting from cold? Thermo Time switch could be the culprit and is cheap enough.

Here's a link to a motronic troublshooting manual I posted on the E28. This should help you narrow down a few things. http://www.bimmerfest.com/forums/sho...050&highlight=

The cold start valve is known to cause these kinds of problems. Also, you could have some injectors stuck open, which is common for the E28 at this stage in it's life.
www.okinjectors.com= flow testing and injector overhaul, specializes in BMW and a great value.

There are a number of culprits that could be the cause however. Try to the troubleshooting.