85 635 No Spark!

[ybyless]

Hi! I just bought an 85 635csi. I bought it not running (with no spark). I noticed that the coil was geting power, but not putting out any spark. I bought a new coil, wires, plugs, distibutor cap and rotor, but it is still doing the same thing. Would this motor have a CPS? If so, could this be bad?
Thanks in advance for your help!

[Captain Bavaria]

Aye. Teh reference sensor must be sending the signal of the crankshaft's angle for the car to start. It is connected to the bellhousing and the electrical connection is up on the engine brace-between the intake mani and the valve cover-closest to the cabin. It's the gray connector. To test it- just disconnect it and nab the resistance of two pins right next to eachother- two should show 100k+, and the other two should be round 960 (give or take 96). Anything over or under that ohmage means it's toast.

[ger doody]

I had the same problem, I checked sensors at bell housing,relays,wiring etc..
It ended up as a faulty ECU.(water damaged)
Check it out!

Ger.

[CW6er]

It is probably the Main relay or the sensor on the bell housing as mentioned (Let us know if you need info about the relays), but here is a step by step trouble shooting guide:
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Break down of components needed to get spark to the engine:
Ignition Switch, OBC Relay, Main Relay, Coil, Reference Sensor, ECU
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First check for spark:

Pull a plug wire and get an extra spark plug* and plug it in. Position the plug so that the metal shell is grounded and try to start the car. Watch the plug to see if you are getting a spark. If you are getting spark, skip to the next section to check for fuel.

If you are not getting spark at the plug, test again at the coil tower. if you get spark at the coil but not the spark plug, check the Distributor Cap and Rotor.

(* or use a spark tester, these can be had from an auto parts store. You may also need an extra plug wire to plug in and test at the coil tower.)

If no spark from either the Coil or Spark Plug:

Checking the ignition Switch and Coil:

• Check, with the key on, for voltage at terminal 15 (+) on the coil. If no voltage, the ignition switch or wires to it may be bad. Wiggle the ignition switch to see if it is intermittent**.
  
  Check the resistance between Terminals 1 (-) and 15 (+), of the coil. It should be 0.50 Ohms. The resistance between terminal 15 (+) and the high tension center tower should be 6000 Ohms. Replace the coil if it has higher readings.

Checking the OBC Relay:

• Next, pull the Main relay and with the key on, check for voltage at pin 86 in the relay holder (the numbers are molded into the bottom of the relay).
  
  If there is no voltage at pin 86, check the OBC relay box under the driver's side kick panel, by jumping the two green wires (pins 3 & 4) in connector C2. If there is no voltage at pin 3 of C2, the ignition switch may be bad (both terminal 15 on the coil and pin 3 of C2 are powered from pin 15 of the ignition switch).
  
  If voltage is present at pin 86: It is easiest to just swap in a new/good main relay and then skip to the check for the Speed and Reference Sensor below, otherwise check the main relay as in the next steps.

Checking the Main Relay:

• Check the circuit diagram on the side of the Main Relay to see if it has two separate contacts for the output pins 87 and 87b or if it just has one contact going to two pin 87's. Plug the Main relay back in.
  
  If there is just the one contact: With the key on and the Main relay plugged back in, check for voltage at the RD/WH wire in an fuel injector plug (or use a "noid" light on the injector plug).
  
  If there are two contacts: With the key on, check for voltage at BOTH terminals 87 and 87b of the Main relay. (You have to wrap a wire around each pin and plug the relay back in and test for voltage at each wire. Don't short between the pins!! One terminal can be good, suppling power to the fuel pump, and the other bad, not suppling power to the ECU, or vice versa.
  
  • Alternately, to check both relay contacts and the Start Input: With the key on, check for voltage at Pin 4 (Start Input) and Pin 35 in the ECU harness plug, and at the RD/WH wire in an fuel injector plug (or use a "noid" light on the injector plug).
  
  
  If there is no voltage in the tests above: replace the Main Relay. As stated, it might be easier to just replace the Main relay out of hand in the first place, instead of doing the testing. It is also a good idea to keep a spare Main relay in the trunk Tool Kit and just replace it (and the Fuel Pump Relay) out of hand if the car stops out on the road.

Checking the Speed and Reference Sensors:

• Check the plugs to the sensors first, the plastic can get brittle with age and they can crack around the wire locking bail leaving them loose. Then check their resistance as below (won't hurt to check them both hot and cold if the car's hard starting is temperature sensitive):

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The resistance test above is simpler, and gives you info on the condition of the crank sensors, but the AC voltage output test below is a bit more conclusive, as it also checks for the rare instance of a missing Ref. pin in the flywheel:

• 1. Pull rubber boots back off the two sensor plugs. Pull the main relay & fuel pump relay to disable the FI system.
  2. Set your voltmeter to AC volts and probe the black and yellow wires while cranking.
  
  • Speed Sensor (Black Connector) -- 4.0 AC volts max at crank.
    Ref. Sensor (Grey Connector) ------ 0.4 AC volts max at crank.
  
  

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** (To start with a bad ignition switch: run a jumper wire direct from the battery to term 15 (+) of the coil and jump pins 11 and 14 in the diagnostic plug to engage the starter.)
__________________________________________________ ________

[Luis135a]

My car had be running perfect the last few weeks. Then last week I was idling and the car just randomly died. I tried starting it and it would just crank but not start. After a few minutes and some more cranking attempts it finally started. A few days afterwards I was driving on the highway and the car just dies, no power at all. I pulled over to the shoulder and tried starting and it would just crank. Again after a few more attempts it finally started. I had a full tank of gas during these incidents. I checked out the Bosh Motronic Troubleshooting website, and my main relay and fuel pump relays are all good. I then checked for power going to the coil and there was no power. I then tried checking that OBC relay for power at pin 86 at the main relay and theres no power there either. I am confused to where I need to check that pins 3&4 at the OBC relay. As of now the car does not even crank over. Please help this is my Daily Driver.

[RSheiman]

No expert by any means but if the car just dies, ie the tach goes straight to zero in an instant , then it's just starts up like nothing happened a few min's later....it's usually the relays.

[Luis135a]

Well the car won't even start with the relays jumped.

[CW6er]

......... I checked out the Bosh Motronic Troubleshooting website, and my main relay and fuel pump relays are all good.

What is the "Bosh Motronic Troubleshooting website"? Link?

I then checked for power going to the coil and there was no power. I then tried checking that OBC relay for power at pin 86 at the main relay and theres no power there either. I am confused to where I need to check that pins 3&4 at the OBC relay. As of now the car does not even crank over. Please help this is my Daily Driver.

It sounds like the ignition switch is bad. Pin 15 of the ignition switch supplies power to both the coil (pin 15) and to the OBC, which in-turn passes power to the Main Relay (Pin 86). Since neither Pin 86 of the Main Relay, nor the coil have power, it is a good bet the ignition switch is bad. The electrical portion of the ignition is replaceable separately without having to replace the key and tumbler :

Ignition switches with prices and sources:
http://bigcoupe.com/phpBB2/viewtopic.php?t=8478
http://bigcoupe.com/phpBB2/viewtopic.php?t=8716

[Flash635]

What is the "Bosh Motronic Troubleshooting website"? Link?

Lots of hits on Google, I didn't look at any though.

[ldk]

Probably this one: http://www.hiperformancestore.com/Motronic.htm.

[Luis135a]

Yes its that one that "IDK" posted.

Today I checked the car over again, and I am getting power to the coil. But the car is still not starting. When I jump the fuel pump relay, I hear the pump buzzing, I have the access panel to the pump thats in the fuel tank off, but i hear nothing coming from that pump. But i feel fuel at the fuel lines going to the fuel rail. Would the transfer pump supply fuel like that? Do i have man fuel pump issue?

[Taylor Marshall]

You'll never know until you get a fuel gauge on the line (at the fire wall) feeding the fuel rail. I'm assuming here that the engine still actually cranks / turns over and that it is no longer true that there is no spark.
A failed or failing in tank pump with a fullish tank of gas will usually not affect engine performance. Have you checked the fuel filter yet ?

[CW6er]

+1 on Taylor's question ... Are you now getting spark?

Are you jumping both the Fuel pump and the Main relay when trying to start?

Have you tested the Ref and Speed Sensors as listed above?

Have you gone through the steps in my post #4 above?

[doc ock]

This happened to me once, the car just died. I was a loose neg. battery cable. Yes the battery was new and alt was ok.

[bimas]

I must say that I had a similar issue, where the starter cable loosened itself enough not to engage. Silly, but true. Reconnecting the wire fixed the car instantly.

[anastasio]

I had a bad reference sensor, and a bad main relay, it did the job, thanks for the help of the guys in this forum, they are amazing

Anastasio

[Bert Poliakoff]

I had a bad reference sensor, and a bad main relay, it did the job, thanks for the help of the guys in this forum, they are amazing Anastasio

Hey Anastacio, where in Scottsdale. I am close to the 101 and Cactus.

[Luis135a]

Okay on the speed sensor I had 1005 ohms between Terminals 1&2 (yellow and black wires) but between the terminals 1&3 and 2&3 I had and open. On the reference sensor I had 1011 ohms between terminals 1&2, but between the terminals 1&3 and 2&3 I had and open. Were talking about checking ohms at the terminal side of the sensors right? Not where the sensors plug into the harness?

Im limited on tools right now so i can't check for spark. All my tools are at work.

+1 on Taylor's question ... Are you now getting spark?

Are you jumping both the Fuel pump and the Main relay when trying to start?

Have you tested the Ref and Speed Sensors as listed above?

Have you gone through the steps in my post #4 above?

Where can I get these at? Seems like no one carries them here locally.

[CW6er]

Okay on the speed sensor I had 1005 ohms between Terminals 1&2 (yellow and black wires) but between the terminals 1&3 and 2&3 I had and open. On the reference sensor I had 1011 ohms between terminals 1&2, but between the terminals 1&3 and 2&3 I had and open.

Sounds normal, terminals 1&3/2&3 are 100Kohms MIN, so infinity (Open) is Ok.

[quote] Were talking about checking ohms at the terminal side of the sensors right? Not where the sensors plug into the harness?

Yes, you are checking the sensors

Im limited on tools right now so i can't check for spark. All my tools are at work.

I try to keep a spare (old) spark plug in the trunk tool kit so i just have to pull a plug wire and use the spare plug to check for spark.

Where can I get these at? Seems like no one carries them here locally.

Are you talking about the relays?

How to jump the relays and sources for relays, the Audi-VW (OEM)/Stribel Main Relay may be had locally:
http://bigcoupe.com/phpBB2/viewtopic.php?t=9180&

[Luis135a]

Okay so i just checked fuel pressure with a gauge and I have about 45psi-47psi. Is this normal or high?

+1 on Taylor's question ... Are you now getting spark?

Are you jumping both the Fuel pump and the Main relay when trying to start?

Have you tested the Ref and Speed Sensors as listed above?

Have you gone through the steps in my post #4 above?

[quote=CW6er;25002644]Sounds normal, terminals 1&3/2&3 are 100Kohms MIN, so infinity (Open) is Ok.

[quote] Were talking about checking ohms at the terminal side of the sensors right? Not where the sensors plug into the harness?

Yes, you are checking the sensors

I try to keep a spare (old) spark plug in the trunk tool kit so i just have to pull a plug wire and use the spare plug to check for spark.

Are you talking about the relays?

How to jump the relays and sources for relays, the Audi-VW (OEM)/Stribel Main Relay may be had locally:

I was talking about the speed and reference sensors. Because they are pretty much terminals now. They don't have any connectors anymore. I went to unplug them and they fell apart in my hands lol

[anastasio]

Bert Poliakof:
My house is in deer valley rd, between scottsdale rd, and hayden, but right now I'm in Mexico city, and keep some cars down here, along with a business

yes jump the relays, since you have fuel pressure, it can be the main, mine had a bad one, it was getting power, but not making any contacts, even though it would click.

[Luis135a]

I am not getting spark at the plugs. But I am getting voltage at the coil and to the distributor.

So im guessing a new cap and rotor?

[Taylor Marshall]

To Luis135a:

Your fuel pressure is fine.
Your dizzy cap & rotor could be pooched and that would indeed cause stalling, very hard cranking and, ultimately, a no start situation. However, a failing one will usually be indicated by back firing and wet plugs and an exhaust that stinks of unburnt fuel...real bad for the cat con too.

My first suspect in your case are those crumbling reference sensor connectors as intermittency here will really raise unpredictable hell with driveability. I just went and disconnected one of mine (see pics) to double check what type of connector it is and it seems to me to be p/n 12521706068 which is the 3 pin connector in the attached pdf extract from RealOEM. This will almost certainly be a dealer only supplied item but hopefully the price won't be too ridiculous.
Hope this helps
Taylor

[Luis135a]

Thanks a lot Taylor. But the cracked part is the sensor side. The harness side is fine. I'll try to look for it on that site.

[CW6er]

I am not getting spark at the plugs. But I am getting voltage at the coil and to the distributor.

Wait, are you saying you are getting Spark (voltage) at the coil center tower and to the distributor, but not at the plugs? If so, then yes a new cap and rotor is called for.

or are you saying you are getting voltage at Terminal 15 of the coil, but if this is the case, what voltage are you measuring for at the distributor?

If this is the case, then It sounds like the ECU is not firing the coil, which it would not if the Ref. Sensor were bad.

I don't think they sell the sensor plugs separate, they are a molded part of the cable, If your 'car is pre 5/'87:
Speed and Ref. Sensor: BMW Part # 12 14 1 708 619 - (Bosch Part # 0 261 210 002)

$73.47 - Free Shipping at AutoHausAz.com ("Under Crankshaft Position Sensor", the other one is for later cars after 5/'87)
$62.27 - Plus Shipping at bmwmercedesparts.com/


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The Harness plug (12 52 1 706 068) that Taylor shows is $$7.38 at bmwmercedesparts.com/