Problem with starting the car

[Leon.stt]

Hi guys,

I'm a bit frustrated at the moment. I'm hoping to find the answer to the problem I'm currently having.
My 1990 318i M40 doesnt want to start. Well, the car starts but dies almost immediately. Sometime when it started, it idles erratically then dies. I tried giving it some gas, the engine revs in an erratic manner then it dies. So far what have been replaced are as follow:

1. Air flow meter
2. Idle control valve
3. Fuel pump (replace with original part)
4. Intake boot (the old one had cracks in it) and yes I triple checked that the small ICV hoses are properly attached
5. Ignition sensor

After all these are replaced the problem is still there.
I'm now super confused and desperate. Any one here have the same problem? What else should I look into?

[somecarguy]

Hey there

Itll help if you tell us what preceded this behavior. Normal running or the car is new to you and always did this? Progressive decline or on/off bad behavior.

[Leon.stt]

Hey there

Itll help if you tell us what preceded this behavior. Normal running or the car is new to you and always did this? Progressive decline or on/off bad behavior.

The problem came all of a sudden. When I first noticed the idle went erratic, I had a look around and found that the intake rubber boot had a crack. So I sealed it with sealant to check that that was the cause. And it did. The car idles well. So I ordered a new original boot from BMW. But when I installed it, the car was not idiling well until now. Also to note, when I, install the boot I made sure I, didnt force anything and made sure that everything was installed correctly

[maxthegearhead]

Pressure test the fuel pump. This sounds like a fuel starvation issue to me. Also check for vacuum leaks.

[Leon.stt]

Pressure test the fuel pump. This sounds like a fuel starvation issue to me. Also check for vacuum leaks.

The fuel pump is brand new sir. I replaced it with an OE unit

[maxthegearhead]

The fuel pump is brand new sir. I replaced it with an OE unit

Sorry I should have read your original post more closely! All I can really point to at this point would be vacuum leaks. Once I got my E30 running it would start and then die quickly and I noticed I forgot to connect the crankcase breather hose. After doing so it idled perfectly.

[95BMWIC]

The fuel pump is brand new sir. I replaced it with an OE unit

I'm assuming the M40 uses the motronic engine management system? If so the fuel pump does not regulate the fuel pressure on this model - the fuel pressure regulator does.

The new fuel pump is probably working fine - but you can still test the pressure. The diaphram could be worn and thus the pressure could be low and low pressure could be causing your starting issue.

[Kumarv]

my m20b25 was doin this and i rewired the crank position sensor and it fixed the problem, im not sure if the m40 has one, it must. wiggle the wires around and see if it changes how the engine behaves, my bet is that it is the sensor.