New owner with no spark issue

[jonah111]

Hi everyone,

I am the new owner of a non-running 84 633csi 5spd and was hoping for some advice on tracing a no-spark issue. I’ve read through many excellent posts on what to check (including Rick’s no-start page) but still can’t figure it out.

Battery is new. Ignition switch is bad- it will work through the first 2 positions, but feels like it is binding when cranking the starter. Starter will crank when I jump pins 11 & 14 on the diagnostic plug but I do not have spark. Before I spend $140 on replacing the ignition switch, I was hoping to see if I had any other big issues. What I’ve checked so far:

· 12v at terminal 15 of the coil with the key on.
· 12v at the #30 main relay connection with the key off.
· 12v at the #86 main relay connection with the key off- I soldered the two wires at the OBC harness just to be sure.
· 12v at the 2 #87 main relay connections with the relay plugged in.
· Installed spade connections to bypass the main & fuel pump relays.
· Checked reference sensors.
· Cleaned cap & rotor.

Still no spark. I’m starting to wonder if it’s the ECU, but I was wondering if a faulty ignition switch could prevent the engine from starting while jumping the pins at the diagnostic plug- even if I were getting 12v at the coil?

Thanks for any advice on where else to check.

[e24mpwr]

Try Rick's No Start Page (http://my.att.net/p/s/community.dll?ep=16&groupid=160912&ck=)

[smaglik]

(OP already tried that...its in the post)

wish I could help.

[CW6er]

Looks like you have checked everything but the ECU. You could try re-flowing the solder on the transistor controlling the coil. There is a thread on here somewhere showing the transistors in ECU.

[Seeker]

Looks like you have checked everything but the ECU. You could try re-flowing the solder on the transistor controlling the coil. There is a thread on here somewhere showing the transistors in ECU.

This one?

http://e28-535i.com/technical/e28-ECU_Repair.php

[Prairieman]

My son and I worked through a problematic no-start on his 535i recently. We checked or changed everything in the ignition system without success. A lot of research on the internet ended up driving us to the OBC relay module.

Symptom was no spark out of the coil wire to the distributor, but there was 12V on the + side of the coil with power on.

Try cranking the engine with a test light connected to the + side of the coil. The test light must "pulse" (rapidly flutter between brighter and dimmer) while the engine is being cranked.

In our situation, the test light did not pulse, until we replaced the OBC relay module - and the car started right up.

[e24mpwr]

(OP already tried that...its in the post)

wish I could help.

Oops - sorry. Reading fails me tonight :(

[jonah111]

thanks for the link! I'll pull the ECU tonight and see if I notice anything.


This one?

http://e28-535i.com/technical/e28-ECU_Repair.php


My son and I worked through a problematic no-start on his 535i recently. We checked or changed everything in the ignition system without success. A lot of research on the internet ended up driving us to the OBC relay module.

Symptom was no spark out of the coil wire to the distributor, but there was 12V on the + side of the coil with power on.

Try cranking the engine with a test light connected to the + side of the coil. The test light must "pulse" (rapidly flutter between brighter and dimmer) while the engine is being cranked.

In our situation, the test light did not pulse, until we replaced the OBC relay module - and the car started right up.

I was hoping to bypass the OBC relay issue by jumping the harness wires- described on this page:

http://my.att.net/p/s/community.dll?ep=87&subpageid=110934&ck=\

I'll see if I can get a test light on the coil though

thanks

[CW6er]

· 12v at the #86 main relay connection with the key off- I soldered the two wires at the OBC harness just to be sure.

Is this really with the key OFF or did you mean with the key ON?


I was hoping to bypass the OBC relay issue by jumping the harness wires- described on this page:

http://my.att.net/p/s/community.dll?ep=87&subpageid=110934&ck=\ (http://my.att.net/p/s/community.dll?ep=87&subpageid=110934&ck=%5C)

I'll see if I can get a test light on the coil though

thanksThe OBC relay passes power to the Main Relay, so by testing for power at pin 86 of the Main Relay, you have already confirmed that the OBC relay is Ok.

The flashing light** on the coil simply indicates that the ECU is controlling the coil (making/breaking the path to ground), and since the ECU gets it's power from the Main Relay and the Main Relay in-turn gets it's power from the OBC relay, replacing the OBC relay fixed the problem in Praireman's case, but in your case you have already confirmed these are relays good.

You might try checking for power at Pins 18 & 35 in the ECU harness plug, this would check the OBC relay, the Main Relay and the wiring to the ECU.
___


Break down of components needed to get spark to the engine (at the coil):
Ignition Switch, OBC Relay, Main Relay, Coil, Reference Sensor, ECU


**Using an incandescent bulb on the coil like this is not recommended in the Bentley, they suggest using an LED test llght.

[jonah111]

Is this really with the key OFF or did you mean with the key ON?

The OBC relay passes power to the Main Relay, so by testing for power at pin 86 of the Main Relay, you have already confirmed that the OBC relay is Ok.

The flashing light** on the coil simply indicates that the ECU is controlling the coil (making/breaking the path to ground), and since the ECU gets it's power from the Main Relay and the Main Relay in-turn gets it's power from the OBC relay, replacing the OBC relay fixed the problem in Praireman's case, but in your case you have already confirmed these are relays good.

You might try checking for power at Pins 18 & 35 in the ECU harness plug, this would check the OBC relay, the Main Relay and the wiring to the ECU.
___


Break down of components needed to get spark to the engine (at the coil):
Ignition Switch, OBC Relay, Main Relay, Coil, Reference Sensor, ECU


**Using an incandescent bulb on the coil like this is not recommended in the Bentley, they suggest using an LED test llght.


From what I can remember, I tested for power at pin 86 of the main relay with the key off.

Is there a digram of the ECU harness plug somewhere? I was trying to check it, but couldn't find any numbers to identify the pins. Do I need to open up the harness plug?

I asked in the original post, but didn't get a response: If the ignition switch is faulty, should I still be able to start by jumping pins 11 & 14 at the diagnostic plug if I'm showing power at the main relay & coil?

thanks

[CW6er]

One more thing, on the back of the cylinder head, on the drivers side, there is a cluster of brown wires. This is the ground for the ECU (and injectors). Remove, clean and retighten these grounds. While you are at it, do the one next to the battery on the inner fender and the ground cable from the battery to the engine block also.
____________


Is there a digram of the ECU harness plug somewhere? I was trying to check it, but couldn't find any numbers to identify the pins. Do I need to open up the harness plug?Do you have your ETM or the Bentley Manual?

ETM (Electrical Troubleshooting Manual, aka "wiring diagram"). It is a very good manual, and everyone needs to have this. You really can't work on the car without it. Here is a Site with free downloads of ETM's (PDF files -13 to 20 MB) for various years ('82 to '01) and models of BMW's (3/5/6/7/8/Z):
http://wedophones.com/BMWManualsLead.htm

Hmm ... the '84 nor the '85 ETM shows the 35 pin ECU connector pins, but it is the same as the ABS ECU plug shown. Well .... here:

One row of pins is longer than the other, position the longer row with 18 pins at the bottom of your view. Pin 1 is the first pin to the right in the bottom row and they number across to the left to pin 18 on the left. Pin 19 is, again, the first pin to the right in the top row (shorter, 17 pin row) and they number across to 35 at the left.

So pins 18 & 35 are the two end pins to the left, with the wiring harness going off to the right.


I asked in the original post, but didn't get a response: If the ignition switch is faulty, should I still be able to start by jumping pins 11 & 14 at the diagnostic plug if I'm showing power at the main relay & coil? My first reaction would be, yes, it should start if you are getting power to the Main relay and the coil, but it would take a bit more study of the ETM for a more definitive answer.


From what I can remember, I tested for power at pin 86 of the main relay with the key off.

Also, pin 86 of the main relay should only have power when the key is in the "run" or "start position" so something is screwy with your ignition?

[jonah111]

One more thing, on the back of the cylinder head, on the drivers side, there is a cluster of brown wires. This is the ground for the ECU (and injectors). Remove, clean and retighten these grounds. While you are at it, do the one next to the battery on the inner fender and the ground cable from the battery to the engine block also.
____________

Do you have your ETM or the Bentley Manual?

ETM (Electrical Troubleshooting Manual, aka "wiring diagram"). It is a very good manual, and everyone needs to have this. You really can't work on the car without it. Here is a Site with free downloads of ETM's (PDF files -13 to 20 MB) for various years ('82 to '01) and models of BMW's (3/5/6/7/8/Z):
http://wedophones.com/BMWManualsLead.htm

Hmm ... the '84 nor the '85 ETM shows the 35 pin ECU connector pins, but it is the same as the ABS ECU plug shown. Well .... here:

One row of pins is longer than the other, position the longer row with 18 pins at the bottom of your view. Pin 1 is the first pin to the right in the bottom row and they number across to the left to pin 18 on the left. Pin 19 is, again, the first pin to the right in the top row (shorter, 17 pin row) and they number across to 35 at the left.

So pins 18 & 35 are the two end pins to the left, with the wiring harness going off to the right.

My first reaction would be, yes, it should start if you are getting power to the Main relay and the coil, but it would take a bit more study of the ETM for a more definitive answer.



Also, pin 86 of the main relay should only have power when the key is in the "run" or "start position" so something is screwy with your ignition?

I was wrong- I've got power on the #86 pin of the main relay with the key ON.

Checked the ECU harness with the help of your description- 12v is at pins 18 & 35.

I've cleaned the main battery grounds earlier- I'll go through the cluster for the injectors & ECU tomorrow.

[jonah111]

I managed to track down a 733i ECU for $25 shipped and tried it out last night- I had spark, but no start. I guess I'll start looking at the fuel system.

[jonah111]

Just thought I'd give an update on this thread. After hot wiring the pumps for a bit, I got it started with the new ECU. After a few minutes of old-gas fumes, it idled nicely. If it weren't for all of the snow I would have taken it for a first drive down the street.

Now I need to look into the brake fluid, power steering, and oil leaks that popped up during it's 20 minute idle.....

thanks for the help & advice

[Taylor Marshall]

I love happy endings. Well done !