Mysterious non start problem

[Radical Racing]

1988 BMW 635 Csi automatic

The problem has baffled my mechanic, the battery shop, friends and myself. With a new battery the car started every time for a while. Then it gradually starts less frequently until is requires a jumper box and then not even then. They only thing that will get the car to start every time is if I hook up jumper cables to the battery from running vehicle.

Two days ago I put a brand new 750 CCA Interstate battery in it. Wouldn't start. The Interstate battery people hooked up a huge 900 CCA battery. Wouldn't start. Though they were dubious I asked them to bring over their shop truck and hook it up with jumper cables. Car started immediately.

All the battery connections and grounds have been cleaned. Still only a jump from a running vehicle will start it.

Any thoughts would be greatly appreciated. We are baffled in Chico.

[bakemono]

What happens when it doesn't start? Does it still crank? Does the solenoid click?

[Radical Racing]

Nothing happens. No click no rotation of starter when there is an attempted start now with a brand new battery, a 900 CCA battery jumped into the system. The ONLY thing that works every time is a jump from a running vehicle.

[bakemono]

Hopefully someone who knows well the electricals on later cars can answer, but I think autos have a relay under the dash which delivers power to the starter solenoid. I would look there.

[Radical Racing]

Bakemono: Interesting. Can anyone post a photo of the relay in place and/or a section in an electrical diagram? My '88 is an automatic.

[bpoliakoff]

All automatic cars of all manufacturers have what I call a neutral safety switch that prevent a car from starting in gear and your foot on the brake. I know the 6s have it as well and believe it is mounted on the shift mechanism. Put a dvm on that and check for continuity. Start simple first and then work your way backwards

[Radical Racing]

What I just can't fathom is why a jump from a running vehicle works and a jump from a jumper box designed to start cars or a monster of a 900 CCA truck battery do not even cause the starter to move or the solenoid to click. Baffling. What could be the difference? Electricity is electricity. In all three cases I am sitting in the car with it in Park and turning the key. The dash lights come on but no response whatsoever unless I am jumping it with a running vehicle. Sometimes my 1993 Chevy truck. Sometimes my 2010 Ford Edge.

[marc79euro645]

I had a no start about 2 weeks ago. A wire had all but broken, but was still able to send voltage ,until amps were required. I'd start with how much voltage is getting to the starter, then work back.
good luck!

[baders]

What I just can't fathom is why a jump from a running vehicle works and a jump from a jumper box designed to start cars or a monster of a 900 CCA truck battery do not even cause the starter to move or the solenoid to click. Baffling. What could be the difference? Electricity is electricity. In all three cases I am sitting in the car with it in Park and turning the key. The dash lights come on but no response whatsoever unless I am jumping it with a running vehicle. Sometimes my 1993 Chevy truck. Sometimes my 2010 Ford Edge.

The only thing I can think of here is that the slightly higher alternator voltage is breaking through a bad connection, but that's a reach. More than likely just co-incidence though. You need a methodical approach with a multimeter to solve this.

[pgh880]

I had this problem for 14 years . I have replaced the ignition switch , starter relay , neutral safety switch , starter solenoid and even had the starter serviced . To no avail . I just had my tech install a push button switch ,that’s how I’ve been using it for 14 years , a couple of weeks ago a forum member advised me just to run an extra wire from terminal 87 of the start relay located under the dashboard . He instructed my tech to run the wire directly to the starter solenoid together w/ the original yellow black wire that is connected to the solenoid . And it worked , no more push button starter needed . Car starts via the ignition switch even if it’s hot or cold .
Hope this helps .

[Radical Racing]

pgh880: Thanks so much for this solution. However how do I identify the start relay? There is a lot of stuff under the dash board. Can I trace a particular colored wire(s) from the ignition switch? What gauge was the new wire you ran?

[Salawada]

You can install the Bosch WR1 Starter Relay. Get it from Amazon.

It provides direct voltage from battery to the solenoid via the WR1 Starter Relay. Its an additional starter relay.

[pgh880]

Here is a picture of the starter relay located under the dashboard driver side . You remove the kick board (cover)
There are several cube relays underneath . The one of the starter relay had a yellow/black wire , same color as that of the yellow/black wire that is connected to the solenoid of the starter . I think my only used a gauge 14 or 16!am not sure . From terminal 87 of the starter relay he ran a direct wire towards the yellow / black wire of the starter solenoid .
We did not trace the wire from the ignition switch , since I knew were the starter relay was located .

[pgh880]

Here is the picture .

[hornhospital]

Please direct-upload the picture. Photobucket not only blurs the photo but they plaster their logo across the face of it, further interfering with viewing.

[86_6series]

Page 7000-4, figure #1

https://www.millerperformancecars.com/f ... Manual.pdf

[pgh880]

Please direct-upload the picture. Photobucket not only blurs the photo but they plaster their logo across the face of it, further interfering with viewing.

I hope its as easy as that but Im no techie and Idont know how . I found this picture in this forum . I'm too lazy to go to my parents home were my 635 is garage to take a picture of my starter relay .

[Radical Racing]

pgh880: Thanks for the photo and info. Going to my warehouse tomorrow to see if I can find the relay and them the the BMW dealer. First replace the relay and them the secondary wire through the firewall to the stater.

[pgh880]

Good luck . Tell us how it turns out .

[Radical Racing]

OK back on this problem after dealing with family issues. Removed the drivers side kick panel and could see ONLY two black large size relays. Could not see any black/yellow wires. So to the person that said the starter relay is there I wonder if the configuration is different for the 88 - 89 cars compared to the earlier cars. I have printed out the entire BMW 635 Csi electrical troubling shooting manual. There is single start relay ashown but no part number or location to be found or 87 pin. I went to my local BMW dealership and even they said they could not help me. They also said they called BMW national office and they said they could not help. Unbelievable!!!!!!!!!!!! I am so frustrated. Please help! Car will only start if jumped from a running vehicle.

[Radical Racing]

Can someone please post a photo of some sort of diagram showing where the start relay is located on a 1988 635 Csi. Another poster put up photos of relays from and 1985 and mentioned running a second black/yellow wire to the starter solenoid but search as I might nothing in my car looked the same as his. Over a year now fighting this non start problem.

[86_6series]

Did you open the link I sent you? The location is on PDF page 153 and printed page #7000-4.
The upper left photo shows the location on a 1988.

https://www.millerperformancecars.com/f ... Manual.pdf

[Radical Racing]

I have had a complete printed version of the 1988 Electrical Troubleshooting Manual for five years. All I can find is a wiring diagram showing how the relay is hooked up to the system but no actual info as to where its physical location is within the car. Maybe I am missing something but currently at a loss as to what to do. As per your suggestion I removed the drivers side kick panel. There was no single purple relay and no black/yellow wire at the kick panel OR at the solenoid.

[86_6series]

There is a picture of the starter relay on page #7000-4 of the link I gave you.
Are you saying that you looked in that location
and the relay isn't there?

[Ralph in Socal]

Hopefully these pics can help

First is the Ignition Switch. Maybe not the same as yours but wiring is similar. Large Red Wire is +12V coming from Battery and C101 connector. It provides constant voltage to Ignition Switch at all times. You can see solid black wire also. That wire only gets +12V when switch is in start position. You should be able to see that black wire enter the white connector. Black wire from Start Relay plugs in and connects to that black wire. The connector can be found along the outer side of the steering column under/behind the kick panel

BF3761C3-9526-4E0F-8B37-28B9AA605F2C.jpeg (75.5 KiB) Viewed 7281 times

Next pic is start relay. Solid black wire connects to Ignition Switch connector. Black/Yellow comes out of relay and goes to starter. Location varies with year but it’s also under the kick panel.

12ECE4DD-EEEE-4FD7-979F-507D2C434D7E.jpeg (100.73 KiB) Viewed 7281 times

Ralph