Need some help guys, 325e starts and dies.

[MacBudd541]

Update. It turns out it was a bad AFM.

I am at work now and I cant figure out how to copy and paste from my phone but I made a thread in the m20 subforum. The car is an 87 325e, it was running just fine then died in the driveway. It will start up for a moment then die immediately, if I hold the key in the start position it will run fine but drag the starter. I replaced the ignition switch but it did not fix the problem. Any ideas? Thanks guys.
-Mac

[bmwm42]

Reference sensor

[e30austin]

Reference sensor on bell housing of trans.

[MacBudd541]

There is 2 of those down there, they look to be identical. I know one of them is the crank position sensor but the car starts up so it clearly has spark for a moment and if i keep the key in the start position it runs just fine. What is the function of the second sensor?

[e30austin]

One is the reference (crank) sensor and the other is a speed sensor.

[bmwm42]

Replace it problem solved

[Ryann]

Doubt it's the crank sensor. DME wouldn't be energizing the fuel pump relay. Is the AFM unplugged? Huge hole in the intake boot?

[MacBudd541]

Everything is plugged in, the car was running great. I had actually just replaced the intake boot and the spark plugs and drove the car around the block, when I got back to the house I left it running in the driveway while i tinkered in the garage and the car died. I went back out there and it was acting this way. Starts right up, revs to 1500rpm then falls flat. I tried supplying fuel (brakleen in the intake while cranking) and it made no change at all. The parts that makes it interesting is that if i keep the key in the run position i can rev the engine and it essentially runs perfect with the exception of the starter running the whole time. I did move the car back into its spot this way tho.

[e30austin]

Reference sensor buddy. Worth a shot at least.

[camip]

replace the sensor and tell me if it works I'm to cheap to try it lol

[Ryann]

Check the main power wire where it bolts to the under side of the fuse box and make sure it's not loose. Also check it for power, should be hot at all times unless you've got a fuse link or battery connection issue.

[bmwm42]

Its the reference sensor this shit had been covered many times

[Ryann]

It'd be a strange mode of failure for the sensor then, because without any reference signal the fuel pump relay won't energize the pump and it wouldn't start at all.

[bmwm42]

Could try a new ignition switch

[MacBudd541]

Its the reference sensor this shit had been covered many times

I have one on order for tomorrow but i would like to be confident and not waste $60. Are the 2 sensors in the bellhousing identical? If one is a speed sensor and the other is the reference sensor what/who is it checking speed for? If they are the same part number then if I switch the two plugs the car shouldnt start at all right?

It'd be a strange mode of failure for the sensor then, because without any reference signal the fuel pump relay won't energize the pump and it wouldn't start at all.

It seems strange to me also, every faulty crank sensor i have run into has been a no start.