No crank No start

[Snowspeeder]

Hello all,

I have a 1996 bmw z3 automatic which will not start in warm weather. It will not even crank. When the weather dips below freezing, the car will generally start.

when I put the key in and try to start I hear a click. The overhead light will not come on, and the windows will not work. But the dash lights up and the radio works.

Some things I have done:

1. replaced battery with a new battery.
2. Checked and replaced all blown fuses.
3. Found an article about the EWS might be faulty. So I followed a troubleshooting article that had me short two pins on the EWS. At this point the car would crank but not start. (The short has been removed)
4. if I put the key in, then turn it as if I am starting the car, I can reach into the engine compartment with a screwdriver and crossover the engine to the starter and the car will start. However, even running, the windows will not work. When it turn the car off, it will not restart on its own.

 

[t-tony]

Recently another member had this issue and if I recall correctly he found a broken wire under the drivers front carpet area. This was on a RHD car.

Tony.

 

[IanA]

The cable from the battery to the busbar under the fusebox had corroded away under the driver's (RHD) seat. The larger cable from the battery to the starter was intact. I'd be checking the voltage at the battery and then at those two points at the front of the car. That would establish the integrity of supply from the battery to the control electronics and the starting circuits. Any codes showing on OBD?

 

[mrscalex]

We usually fish around in the area of the EWS when there's a no crank. The EWS is responsible for checking a valid key is in the ignition and releasing the starter. Although an early car like that has a more basic EWS than the later one I have done all the work on and usually try to help with.

But to be honest there's so much other weirdness going on I think you need to be looking elsewhere first along the lines of an electrical fault as already indicated by the previous posts. I'm no electrics whiz but I think @t-tony is right about having the interior out to exam in-particular the big fat wire from the battery that runs under the driver's seat - unless your car being early has the battery in the engine bay? But perhaps before going to that trouble as per @IanA I would be checking voltage drops at key points.

 

[IanA]

Bitter experience showed me two fat wires from the battery. The 30mm2 one feeds the fusebox and the 40mm2 one feeds the starter. They are fused independently close to the battery. The former by fuses under the green cover and the latter by the "explosive" pop-out link on my MY2000 2-litre 6cyl Z3.

 

[mrscalex]

Bitter experience showed me two fat wires from the battery. The 30mm2 one feeds the fusebox and the 40mm2 one feeds the starter. They are fused independently close to the battery. The former by fuses under the green cover and the latter by the "explosive" pop-out link on my MY2000 2-litre 6cyl Z3.

You got it. Can confirm this from our adventures here. That's where I would be starting by checking voltage drops around those 2 cables as between them they feed the whole car. The explosive link/"blow-off" can go bad and may trigger an SRS/airbag issue. Reason being it's the SRS/crash module that monitors the resistance there as it needs to be in a good way to blow the charge if it detects a crash situation. Blowing the charge cuts all the main circuits except for eg lights. Imagine being upside down in a ditch fuel pumping through and leaking out with compromised electrical circuits ready to cause a spark. But you do need lights as a beacon to the car and to see around inside.

Wiring loom replacement project

Well after a couple of false starts the project has now started in earnest. Story so far: 2.2 bought as a project with damaged wiring loom Caused by boot loom of doom Short circuit. Fuse blew. Fuse replaced with cheap Chinese fuse. Fuse didn't blow next time and loom heated up and melted in...

zroadster.org

 

[mrscalex]

Btw again being an early car I would not say 100% the blow-off is present or the same 2 chunky wire set-up is present but I would tend to think so.