help e34 intermittently failing to start

[steve sport]

BMW E34 1995 Sport Auto 525i

Problem:- Occasionally, once/twice a week having arrived somewhere and switched off car. Locked it, popped into somewhere and gone back to car, unlock it, get in and it won't start. Lock it and leave it for half an hour, then unlock as usual and it starts!

It sounds like a flat battery, it doesn't try to turn over though and the battery is fine. I wonder if it might be something to do with the immobiliser/central locking system. It's almost as if it is shutting down because the immobiliser thinks someone is trying to steal it!

Help - any ideas before my wife kills it!! :(

[pingu]

Does it only happen when the engine has run for long enough to warm up?

If so then I've had this on both a 525 manual and my 540 auto. In both cases, the battery and starter were both fine so do your diagnostics fully before shelling out for something new. I got rid of the 525 but on the 540 I put in a jumper relay to increase the voltage to the solenoid terminal on the starter motor - there was a drop of about 2V in the wiring loom. It wasn't the fusible link. If you do a search on my posts you'll find what I had to do to fix things.

[steve sport]

Yes it only does it when its hot.

after reading you posts what did you end up doing. fitting a relay or replacing the ignition switch?

[shogun]

http://www.bmwe34.net/e34main/maintenance/electrical/fusible_link.htm
http://www.bmwe34.net/e34main/trouble/535ihot_start.asp

[Fred/Houston]

BMW E34 1995 Sport Auto 525i

Problem:- Occasionally, once/twice a week having arrived somewhere and switched off car. Locked it, popped into somewhere and gone back to car, unlock it, get in and it won't start. Lock it and leave it for half an hour, then unlock as usual and it starts!

It sounds like a flat battery, it doesn't try to turn over though and the battery is fine. I wonder if it might be something to do with the immobiliser/central locking system. It's almost as if it is shutting down because the immobiliser thinks someone is trying to steal it!

Help - any ideas before my wife kills it!! :(
This happened to me a few months ago on my 94"/540i and it drove me nuts. It ended up being the cam sensor.
Good luck
Fred/Houston

[myles]

Had this problem myself. It was a worn starter and solenoid.

[pingu]

I did replace the ignition switch (and the battery) but that was a waste of money. On the 525, replacing the starter motor was a waste of money.

What fixed it was putting in a relay to ensure that the starter motor solenoid got the full battery voltage (without the relay some sort of fault in the wiring loom was dropping about 2 volts, which was just enough to stop the solenoid from working).

Putting in the relay was less time consuming than trying to deduce what/where the actual fault was. I think the fault might have been in the E box but I never got that far.

[steve sport]

Hi

I have a couple of questions about the starting relay.

pls see attached pic

many thanks

steve

[pingu]

I've got some photos (I think!) of what I did - I'll see if I can dig them out - I'll hopefuly post them tonight.

Off the top of my memory, I think the relay was the one that you have numbered 6 (which, rather confusingly, also seems to be embossed on the relay itself with number "3"!).

[pingu]

Alas no photos - you might have to wait till the weekend before I get a chance look into this to work out which relay.

[steve sport]

thanks any help would appreciated.

steve

[pingu]

I'm about to post a piccy but with regard to your photo, my car is different.

On mine, the starter relay is directly between the relays that you've marked 1 and 2 - but in your relay box that's a vacant spot without a relay!

I'm not sure how you get access to the relay - my Indy did this for me. I wonder if it's quite tricky as they basically levered up the relay socket (the socket is now loose) rather than undoing the screws etc.

P.S. It might be worth completing your profile in more detail - we can't tell what sort of car you've got.

[pingu]

To answer your question, the starter relay has two wires: they're both black with a yellow stripe and quite thick (thicker than the other wires that go to the starter relay).

One of the black/yellow wires goes to the ignition switch. The other goes to the starter motor solenoid.

If you splice in a wire to the black/yellow solenoid wire, then by connecting the other end of your splice wire to the B+ terminal, you'll be able to energise the starter motor. Make sure your engine isn't in gear!

[pingu]

Although using a spliced wire to connect the solenoid to the B+ terminal works, I got fed up with that after a while (especially when it was raining).

To banish the problem once and for all, I used a booster relay.

The "original" (I fitted a replacement relay from the dealer but this didn't have any effect on the starting problem) relay is marked "1" on the photo.

The booster relay is marked "2" on the photo.

The original relay 1 is now only used to energise the coil of the booster relay 2 (the original relay 1 is no longer connected to the starter motor solenoid).

Of the switched contacts of the booster relay 2, one now connects directly to the B+ terminal. The other switched contact of the booster relay 2 is connected via the black/yellow wire (the one that previously connected the original relay 1 to the starter motor solenoid) to the starter motor solenoid.

Of the two wires that you can see leaving the relay box, the red one is the wire to the B+ terminal. The black wire provide an electrical path to chassis for the coil of the booster relay 2. I had to make a small notch in the relay box to allow the black and red wires to exit the relay box. The brown gunk is sealant to stop moisture from getting in to the relay box.

Good luck!