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George
George, BMW Technician
Category: BMW
Satisfied Customers: 1861
Experience:  BMW Master Technician over 20 years BMW Dealership Experience. BMW Auto Repair Shop Business Owner
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bmw e34 does not start. i have changed the crank position sensor

Customer Question

bmw e34 does not start. i have changed the crank position sensor and swapped the ecm already...car cranks but no start. strangely, the fuel pump relay never closes the fuel pump circuit, yet the fuel pump works fine with the relay bypassed._
Submitted: 4 years ago.
Category: BMW
Expert:  AMEDEE replied 4 years ago.

Hello!

 

It sounds like you have a bad new crank sensor or maybe even a bad computer.

Check for battery power on the RD/WH and BL/RD wires to terminals 87 and 87A of the main relay. If OK, verify that there is 10v or more on the terminals with the engine cranking. Trace the wire harness of the Crankshaft Position sensor back to the sensor 3-wire connector. Unplug it to allow for testing at the sensor side of the connector. Test for continuity between pins 1 and 2. Pin 3 connects to the ground shield, so there should not be continuity to pin 3. Test the resistance between pins 1 an 2. It should read close to 500 ohms. Switch the Digital Volt Ohmmeter (DVOM) to A/C voltage (low range) and then crank the engine. It should read from 2-3v A/C (higher is OK). Connect a lab scope to the pins 2 and 3. Crank the engine and look for a saw tooth pattern with a space in it.

Customer: replied 4 years ago.
Thanks for the info. The ac voltage for the crankshaft position sensor when cranking is in fact 2-3 volts (~2.9 Vac), which seems alright, although the resistance between pins 1 and 2 is not in range and is around 700 ohms (should be 540 with a 10% tolerance). I have checked the sensor connector and wiring from the DME harness, so no problem there, wiring is continuous as I expected. This is the second sensor, by the way, the first sensor had a resistance reading of around 580 ohms. I have checked the main DME relay and it seems to be working just fine. Having said that, how would I test the DME? I have 2 identical Bosch modules, which I've interchanged, and the car still does not start.
Expert:  AMEDEE replied 4 years ago.
Hello!

If the crank sensor tests out ok, then check to be sure the main relay has power to it on the RD/WH and BL/RD wires to terminals 87 and 87A.

If all powers check out good top the main relay and there is still no activity coming from the computer to the main relay to activate, then you will need to check all powers and grounds going into the computer. If all checks out good, then the computer is bad and will need to be replaced.

Obviously, be sure the crank sensor signal is getting to the ECU.
Customer: replied 4 years ago.
I have checked the main relay and it test out fine. I have also checked the resistance of the crank sensor from the ECU harness, all is well there also. Is there a test I can run for the ECU, because I have 2 modules and cannot imagine both are bad.
Expert:  AMEDEE replied 4 years ago.

Hello!

 

YES... you can check the inputs.... turn the key on and check to see how many powers and how many grounds you have. If in fact the computer is not bad, I have a feeling you will find you problem when you run this test.



Edited by AMEDEE on 8/9/2010 at 5:05 PM EST
Customer: replied 4 years ago.
The inputs to the ECM seem fine. I can manually ground to the chassis terminal 85 of the fuel pump control relay and it closes the circuit, the fuel pump runs, the ECM fan runs, the engine will not start. The on-board diagnostic test, however, reveals error code 1261, fuel pump control. I don't know why the ECM will not turn on the relay. Can I definitively test the ECM, and if so, how? I have 2 modules and I am having a hard time believing they are both faulty, and want to be sure before I buy a new one.
Expert:  AMEDEE replied 4 years ago.
I will leave this question open for other experts.

Expert:  George replied 4 years ago.

Depending if you have a late starter immobilizer or early production the obc (On Board Computer) the obc can be cutting out the fuel pump signal for some reason.

Pin # XXXXX is the input signal from the obc to the dme you are going to have to check this to make sure it is ok.

___

 

If I answered your question I ask that you please accept.

Customer: replied 4 years ago.
George,

Pin #66 is the OBC drive-away protection enable (would the engine really crank if this were the problem?) How do I test this input, and better yet, how do I disable this protection for good?
Expert:  George replied 4 years ago.
Yes it will still crank the later production vehicles will not they have the starter enable system. You can test it for voltage on that pin # XXXXX while trying to crank it now the way it is. And then activate the code function by inputing a code and then try cranking it again and see what your voltage is on pin # XXXXX It is either high or low voltage signal depending if code function is set or not. If you have the same voltage with and without the code function set, there is your problem.
Customer: replied 4 years ago.
Wow, great info, thanks. How do I activate the code function and what does it do? Also, can I just remove the obc for the purpose of troubleshooting? Will the engine start with the obc missing, or is there another way to disable the drive away protection?
Expert:  George replied 4 years ago.

The best way to start out is by doing the below listed procedure for Emergency start procedure if code has been lost.

____

 

If I answered your question I ask that you please accept.

 

 

The '80s and '90s BMW models (E23, E24, E28, E30, E32, E34) that have the separate On Board Computer units (OBC), such as your E30 chassis (3 series 84-91), have an anti-theft feature available within the OBC. If this feature is activated, the pre-set 4-digit code must be input. When activated, the starter will turn, but the engine will not start. After 3-attempts, the horn will sound for 30-seconds.

It's likely that accidentally activated the anti-theft by pushing the OBC CODE button while the key was in the #1 position (perhaps listening to the radio). They may have just been lucky enough to push the buttons in the sequence that ended up storing a code and activating the system.

The owner's manual for your 325ic gives the sequence and instruction for activating, using and de-activating the system, but there is no mention of what to do in case you "forget" the code you input. However, the owner's manual for a later model E34 chassis (5 series 89-96) does mention an emergency procedure for the system. So, give it a try. If this does not work try just disconnection the battery for 15-minutes, or so.

 

 

EMERGENCY START PROCEDURE - IF CODE HAS BEEN LOST:

* Disconnect battery for 5 minutes, or more.

* Reconnect battery.

* Turn ignition key to position 1 (alarm should sound).

* A time display will appear and run down to zero (for 15 minutes).

* After 15 minutes, the engine can be started.

During the waiting period of 15 minutes, the code can be re-entered.

* Press CODE button.

* Input desired code.

* Press the S/R button.

* Start the engine.

Customer: replied 4 years ago.
no code was set...i did disconnect the battery and reset the code, but still no luck there. any other suggestions?
Expert:  George replied 4 years ago.
I would like you to make a 3 wire jumper cable and jump pins # XXXXX 87, 87a of the Main relay. And then with a 2 wire jumper cable jump pins # XXXXX and 87 of the fuel pump relay. Leave both jumper cables hooked up at the same time and then try to start the vehicle, and let me know what happens after doing this.
Customer: replied 4 years ago.
The main relay gets battery voltage on 30, 87, and 87a, so there's no problem there. The fuel pump relay is functional, but I have to manually ground 85 to turn on the pump, otherwise no flow, no ECM fan. I tried to crank with the fuel pump running (both in relay bypass and 85 grounded manually), but the car still did not start. Is there a way to test the ECM? It's a Bosch 0 261 200 404, I believe.
Expert:  George replied 4 years ago.
I know you have jumped the fuel pump relay, but I need you to do the Exact test I suggested above so I can determine some factors. If you don't perform this test with the jumpers as I suggested I will not be able to give you any further advise or testing to do. Everything has a purpose that I ask you to do even if it might not make sense to you at this time.

Edited by George on 8/20/2010 at 5:39 PM EST
Customer: replied 4 years ago.
I've performed the test you described and it yielded the same result - cranks, but no start. The fuel pump and the ECM were running, however, with the fuel pump relay jumped from 30 to 87. Do you think the ECM needs to be reprogrammed? Any other suggestions would be greatly appreciated. Thanks, George.
Expert:  George replied 4 years ago.
I want you to pull the spark plugs out after cranking the engine a few times, then let me know if they are wet with fuel and what color the tips are.
Customer: replied 3 years ago.
plugs are not wet with fuel, tips are black. tried spraying starter fluid into the intake, still no luck. What's the best way to check for spark?
Expert:  George replied 3 years ago.
You can remove one of the ignition coils from each side along with the spark plug, then install the spark plug into the coil and ground the spark plug threaded portion to a vehicle ground. Then crank the engine and see what happens.
Customer: replied 3 years ago.
i removed one coil and plug, there is a regular spark when cranking.
Expert:  George replied 3 years ago.

I will opt out so that another Expert might be able to assist you.

Customer: replied 3 years ago.
sure, thanks. any other advise appreciated.
Expert:  George replied 3 years ago.
You cannot answer otherwise it will come back to my mailbox, you must wait for another Expert to reply to you 1st.
Customer: replied 3 years ago.
when is this expert going to get around to it?
Expert:  George replied 3 years ago.

If another Expert has not responded to you it means that they either did not have any further information that what you were being supplied with already.

Or it is possible that they felt the amount of time and effort that will be needed to get to the bottom of your problem is not worth the question value, I cannot state for sure what other Experts reasons are for not responding to your question.

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