Intermittent starting problem:

[Dash01]

Sometimes the '85 635csia will crank, but not start. Opening and closing the door while the key is in crank position lets the car start. Perhaps the jarring of the door shutting jiggles a loose connection nearby, allowing continuity in some part of the start circuit, so she then starts. Also, the plastic steering column cover gets warm or even hot.

I suspect the ignition switch has a bad connection.

Given these factors, where is the fault most likely to be, in addition to the ignition switch?

[EuroGeorge]

Sometimes the '85 635csia will crank, but not start. Opening and closing the door while the key is in crank position lets the car start. Perhaps the jarring of the door shutting jiggles a loose connection nearby, allowing continuity in some part of the start circuit, so she then starts. Also, the plastic steering column cover gets warm or even hot.

I suspect the ignition switch has a bad connection.

Given these factors, where is the fault most likely to be, in addition to the ignition switch?

Your column cover should never get "hot" If it's in the area of the switch, I suspect you have a problem there.

[CW6er]

It could be several things; the electrical portion of the ignition switch (it is replaceable and you keep the key cylinder), the OBC relay, The Main relay, etc. You need to narrow it down. Here is a list:

This "No Start" procedure is for '83 to '87 cars; the '88/'89 cars have their main relay wired slightly different and different Ref. and Speed Sensors.

Break down of components needed to get spark to the engine:
Ignition Switch, OBC Relay, Main Relay, Coil, Reference Sensor, ECU
____________
• The Engine Cranks Over

First check for spark:

Pull a plug wire and get an extra spark plug* and plug it in. Position the plug so that the metal shell is grounded and try to start the car. Watch the plug to see if you are getting a spark. If you are getting spark, skip to the next section to check for fuel.

If you are not getting spark at the plug, test again at the coil tower. if you get spark at the coil but not the spark plug, check the Distributor Cap and Rotor.

(* or use a spark tester, these can be had from an auto parts store. You may also need an extra plug wire to plug in and test at the coil tower.)

If no spark from either the Coil or Spark Plug:

Checking the ignition Switch and Coil:
• Check, with the key on, for voltage at terminal 15 (+) on the coil (voltage will appear at Term 1 also). If no voltage, the ignition switch or wires to it may be bad. Wiggle the ignition switch to see if it is intermittent**.

• Check, with the key off, the resistance between Terminals 1 (-) and 15 (+), of the coil. It should be around 0.50 Ohms. The resistance between terminal 15 (+) and the high tension center tower should be around 6000 Ohms. Replace the coil if it has high or infinite readings (Open) or little or no resistance (Short).

Checking the OBC Relay:
• Next, pull the Main relay and with the key on, check for voltage between pin 86 & Ground and pin 30 & Ground, in the relay holder (the numbers are molded into the bottom of the relay).

• If there is no voltage at pin 30, check the Red wires at the Positive Battery terminal (Clean and tighten them regardless).

• If there is no voltage at pin 86, check the OBC relay box under the driver's side kick panel, by jumping:


◦ New Style OBC (10/'84):
◦ the two green wires (pins 3 & 4) in connector C2.
◦
◦ Old Style OBC:
◦ pins 14 (GN) and 15 (GN/RD) in the black connector C1 (See page 116/117 in the ETM for pin locations).

• If there is no voltage at pin 3 of C2 (New Style), or pin 14 of C1 (Old Style), the ignition switch may be bad (both terminal 15 on the coil and the OBC pins above are powered from pin 15 of the ignition switch).

• If voltage is present at pins 86 and 30: It is easiest to just jumper the Main Relay as in the Photo below or swap in a new/good main relay and then skip to the "Checking the Speed and Reference Sensors" below. Otherwise check the main relay as in the "Checking the Main Relay" steps after the Photo.


Jumping the Main and Fuel Pump Relays:

• http://bigcoupe.com/phpBB2/files/relay_jumpers_193_114.jpeg
_________


Checking the Main Relay:
• Check the circuit diagram on the side of the Main Relay to see if it has two separate contacts for the output pins 87 and 87b or if it just has one contact going to two pin 87's. Clean the relay prongs and the sockets in the holder base and plug the Main relay back in.

• If there is just the one contact: With the key on and the Main relay plugged back in, check for voltage at the RD/WH wire in an fuel injector plug (or use a "noid" light on the injector plug).

• If there are two contacts: With the key on, check for voltage at BOTH terminals 87 and 87b of the Main relay. (You have to wrap a wire around each pin and plug the relay back in and test for voltage at each wire. Don't short between the pins!! One terminal can be good, suppling power to the fuel pump, and the other bad, not suppling power to the ECU, or vice versa.


◦ Alternately, to check both relay contacts and the Start Input: With the key on, check for voltage at Pin 4 (Start Input) and Pin 35 in the ECU harness plug, and at the RD/WH wire in an fuel injector plug (or use a "noid" light on the injector plug).
•
• If there is no voltage in the tests above: replace the Main Relay. As stated, it might be easier to just replace the Main relay out of hand in the first place, instead of doing the testing. It is also a good idea to keep a spare Main relay in the trunk Tool Kit and just replace it (and the Fuel Pump Relay) out of hand if the car stops out on the road.

Checking the Speed and Reference Sensors:
• Check the plugs to the sensors first, the plastic can get brittle with age and they can crack around the wire locking bail leaving them loose. Then check their resistance as below (won't hurt to check them both hot and cold if the car's hard starting is temperature sensitive):


http://forums.bimmerforums.com/forum/attachment.php?attachmentid=349802&d=1284959685
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The resistance test above is simpler, and gives you info on the condition of the crank sensors, but the AC voltage output test below is a bit more conclusive, as it also checks for the rare instance of a missing Ref. pin for the Ref. Sensor in the flywheel (Automatic transmission only):

• 1. Pull rubber boots back off of the two plugs on the sensor lead side (not the harness side). Pull the main relay & fuel pump relay to disable the FI system.
• 2. Set your voltmeter to AC volts and back probe the black and yellow wires while cranking the engine.

◦ Speed Sensor (Black Connector - reads flywheel Teeth) -- 4.0 AC volts max while cranking the engine.
◦ Ref. Sensor (Grey Connector - reads flywheel Ref. Pin) ------ 0.4 AC volts max while cranking the engine.

____

** (To start with a bad ignition switch: run a jumper wire direct from the battery to term 15 (+) of the coil and jump pins 11 and 14 in the diagnostic plug to engage the starter.)

[Dash01]

Thanks very much, George and Chris, I'll follow up on these diagnostics asap.

First, will remove the lower half of the steering column plastic housing, and source the heat. Could be, the problem is burned contacts in the ignition switch, which is simple and inexpensive to replace if not disassemble and clean.