Oil Pressure Sensor and Won't Start

[philte]

Hi All ~

I'm having an issue with my 1990 525i/M20 which just decided to pop-up yesterday morning. The engine cranks over fine but doesn't want to start, this is accompanied by the Oil Press Sensor warning appearing in the display. After about 8-10 10 second crankings the engine will start and run perfectly. I've ordered a new oil pressure switch (12 61 1 710 509, cheap and easy to replace) but would really appreciate any suggestions as I have a gut feeling it's not going to be that simple. Thanks!!

[Ross]

I believe the fuel pump will shut down under zero oil pressure conditions. But it should run for a short period during startup. If you are convinced there is indeed oil pressure try using some ether or carb cleaner etc. in the intake to see if it's fuel related.
Even if your oil sender is bad though it ought to get fuel for start-up. Does it fire up at all?

[philte]

There's no spark at this point. I checked voltage at the coil during cranking, nothing. Is it possible that when sensing zero oil pressure that the ignition system is shut down?

[Ross]

I don't think so. Hopefully some of the experts are lurking, I'm just a dodo.

[BillionPa]

no spark usually means crankshaft position sensor dead

[joshua43214]

all cars have no oil pressure on starting, and take a while to build pressure on starting, and even longer after the oil is changed, ergo, no oil pressure will not cause a no start condition.

[Ausmpower]

No oil pressure can cause a no start, GMH 3.8 v6's (buick to you US lot!) use a 3 pin oil pressure switch which causes the ecu to cut the fuel pump in a no oil pressure situation or 5 seconds after a start if the oil pressure doesn't come up. I don't know if BMW ever used them on the older models but they do on the E60's.

[White535Mtl]

I've had something similar happen to me.
It was caused by the crank position sensor.
I believe the main computer does not send any fuel, unless it gets a reading from that sensor.

Can someone more knowledgeable elaborate on what I just said?

[Bill R.]

down feature. I would suggest you look into the crank position sensor as suggested. Check and see if its loose and has come out of adjustment.

[philte]

Thanks for the suggestions! I'll check the crank position sensor this evening. I have the Haynes manual which provides some fairly detailed spec for testing and will post the results. Thanks again All!!

[philte]

Finally found time to resume diagnostics. I believe you folks hit the nail on the head with the crank position sensor (pulse sensor in my case, part # 12 14 1 720 852). Specs indicate 500-600 ohms between pins 1 & 2; testing showed 2.7M ohms. Ordered from Bavarian Autosport for $74.95US and will keep my fingers crossed that's all it is. Also ordered an Oil Pressure switch since I'm under the 'bonnet' getting greasy anyway.

[wingman]

Is the non start always accompanied by the 'oil pressure switch' gong and readout? I get both of your symptoms but at different times. On the odd occassion the oil switch thing happens and on other occassions it takes 3 goes to start. Both these problems are like a once every 5 trips thing.