Re: Starting problems (archive)

Minor point of clarification on the reference and speed sensors. The real test is for a pulse signal while the engine is spinning, the ohm test is a static test of resistence, not of operation. My 733i passed the resistance test, but had a bad reference or speed sensor (replaced both at same time). IT ONLY FAILED WHEN IT WAS HOT. Would drive somewhere and the car wouldn't start when I wanted to leave. A couple of hours later it was fine, until it just died.

Was able to borrow a pair of sensors from some friends at local shop (pretty much on size fits all on 80's big sixes) after I'd tested everything else (see below). Bought a used set from Zionville for about $60.

I had previously tested everything else at the Mototronic Box, except the crank position/speed sensors unless you have a DVM that reads square waves. Everyting else is a simple test. The Bentley's 5 series manual has the test procedure. It will tell you what the "brain" knows and the "brain" will know why the car isn't running.
This told me that the idle switch wasn't working correctly and that the colant temperature sensor that tested fine under the hood had dirty contacts and wasn't giving a good signal to the brain. Car idles perfectly now.

Well, I've got a similar problem with my '85 635 and it is driving me nuts. I checked the reference and speed sensors, they should be around 1000 Ohms (spec is 960 +/- 96 Ohms between pins 1 and 2). The connections to these sensors is also important, make sure they are tight and the contacts clean.

Yesterday, I pulled the fuel pump relay apart and cleaned the contacts. I know, "just buy a new one" well, I can't get one this weekend. First try this morning and it fired right up but as we both know, it might just be in a "good mood". Will see how it does this week.

If the relay fixes the problem on my car, I'll post something.

Here's a short list of other possibilities:

- Idle control valve sticking. You can clean it with some carb cleaner.

- Flaky thermo-time switch (replace mine, no better)

- Flaky cold start valve (next on the list)

- Poor ground connections, (and power connections at the battery). Make sure the connections are all clean. If you have a voltmeter, you can look for voltage drops along some of the cables.

- Sounds like you already looked at residual fuel pressure. I also added a check valve in the fuel line, no improvement!

I'm sure there are more things to look at, good luck.

Mike

Ok I'm stumped. Spark; yes. Gas; yes. Starts every time I don't need to go anywhere. When I need to go somewhere it wont. Seems to be more prevalent during hot weather. Eliminated vapor lock possibility by installing a check valve between filter and engine near pump. Checks when hot and pressure is definitely good. Checked wiring to all ECU sensors and looks good. Got it running and disconnected sensors one at a time and each one caused a change in running. I haven't done reference/speed sensor yet. Anyone know a way to test them? My family believes that it just wants to mess with my mind. I am tending to think that also. Electrical manual being delivered on Monday. Any suggestions would be appreciated.

Scott

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