The Starting Saga, PTII

[borderchris]

Well, it still goes into a no crank condition after several starts, tooling around town, etc. I would assume heat soak is contributing to this, but how?

When I run a jumper from the 10MM bolt on the starter to the jumper post, she starts just fine. So it's not the starter or solenoid. I would assume not the relay either, since the relay clicks off and on when I have somebody move the shifter in and out of neutral or park (which tells me the neutral switch is good also). Any ideas? Maybe ignition switch? But how would heat or multiple starts affect it? Arrrrghhhhhh!!

Any ideas? Someone had suggested bad wiring, but this is not intermittant; it occurs on the nose every time the motor heat soaks.

Chris

1989 535iA, 170K

[joshua43214]

I seem to remember folks making alot of good suggestions on the last thread you started on this, did you cover all the bases suggeted? Hearing a realy click doesnt mean alot. It could be a different relay than the starter relay, and if it is the starter relay, all that means is the exciter circuit is working.

Relays can fail on heat soak as well, they close but will have burned contacts that prevent power from flowing through it. usualy a sharp tap on the top of the relay will bring it to life.

Also, just to make sure we are on the same page, when you say 10mm bolt on the starter, do you mean the 10mm wrench size nut that the small wire attaches too (this is a 6mm stud)?

[borderchris]

The bolt below and between the two main ones on the solenoid. Starts up fine. Is the starter relay the same P/N as a bunch of others, or is it individually spec'd?

[joshua43214]

The bolt below and between the two main ones on the solenoid. Starts up fine.

huh?

Does it have a BIG wire ging to it, or a small wire going to it?

No idea what "the two mains ones" are.

[joshua43214]

I'll assume the place you are jumping to is the small wire that goes to the "s" terminal.

here is my memory of the starting circuit, I don't have a diagram in front of me, so forgive any mistakes.

When you turn the key on, power flows from the fuse box to the neutral switch, then to the winding side of the starter relay closing the relay.( I know sounds backwards)

When you turn the key to crank, power flows from the front fuse box to the ignition switch to terminal 30 on the relay, if the car is in park, the relay will already be closed allowing complete circuit to the "s" terminal on the starter. the solenoid will then engage spinning the starter and moving the gear forward, power will flow from the other small terminal to the GM, and other stuff telling the car it is is "crank mode" so that it will turn off the blower and the like.

If you have a factory alarm, the alarm module replaces the starter relay.

The starter relay is in the power distribution box under the hood(I think), should be a DIN standard square relay, or something that looks like it.

If someone has a wiring diagram to verify this that would be cool, But either way, as I've stated, hearing a relay close when you crank, doesn't mean a relay is good, or it could easily be a relay for a totaly separate item.

Once again forgive any mistakes as I don't have a diagram in front of me.

[pingu]

OK, you've confirmed that the starter motor and its solenoid are both fine(and that the autobox starter inhibit and its relay are also both fine).

Last time you posted this, both me (I've had this problem on two different E34s) and cshollum suggested you look into the ignition switch (cshollum also suggested a rather neat idea using a "bypass" relay to avoid the hassle of changing the ignition switch - did you ever ask cshollum for further details of his idea?). You'll recall that I gave you the voltage measurements I obtained, which showed that the ignition switch was dropping 2 volts, with the result that the starter solenoid wasn't getting enough voltage (and hence not enough current) to operate properly.

Have you actually checked ignition switch for voltage drop?

On both E34s on which I've had this problem, the symptoms were just about exactly as you've described. After about 30-60 minutes of driving, the engine wouldn't crank. Winter was better than summer (in winter, took a good hour, or on a very cold day even longer, to get sufficient heat soak to cause the problem). Mine was maybe not quite as bad as yoursd but occured just about every time there had been heat soak.

As I said before, on mine the problem was a marginal battery in combination with a bad ignition switch. As for why heat soak should affect things, I could only come up with one idea (heat soak of the ignition switch doesn't seem likely!): car batteries have a voltage coefficient of -2mV per degree Centigrade, per cell. So if the battery warms up by, say, 10 deg C (and bearing in mind that there are 6 cells in series), it's voltage will drop by 0.1V. Not much, but maybe enough to make a difference. I guess the battery will warm up as it's being recharged by the alternator.

Good luck!

[joshua43214]

As for why heat soak should affect things, I could only come up with one idea (heat soak of the ignition switch doesn't seem likely!):
Good luck!

Any part with voltage running through it is subject to heat soak failure. Ignition switches can get hot enough to feel uncomfortable to touch in many cars. They even have been the subject of recalls as a fire hazard on atleast one American car. Parts that have a circuit board with solder joints are especialy prone ie. multi-position switchs, relays,computors etc. But even plain wire can fail from heat soak. This is why resoldering printed circuit boards fix's so many problems.

[borderchris]

Hmmmmmmm. Interesting, guys. Well, ignition switches are pretty cheap on ebay- I may just pay 20 or 25 bucks for one and see what happens. For now I'll check the wiring inside of the dash and steering column for pinched or poorly routed wires. BTW, the battery is fine- it's a good quality, spec battery that is about 1 year old. The previous owner stated that the original lasted 15 years!!! Anyway, she cranks super strong when I jump the starter from the jump lug, and dosen't drop volatge with brights on, radio, full fan and flashers on. Well, let me start running down the wires.

One question- which is the starter relay? Is it the same spec as a bunch of others, or is it the one blue one (the rest being yellowish)

Chris