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Completely confused as to why my engine isn't running right

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kingmanjr00
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Completely confused as to why my engine isn't running right

Post by kingmanjr00 » Mon Sep 18, 2017 11:15 pm

Hello all,

Long time lurker, first time posters, as I finally own my first e24!! I have owned several e30's, but was never able to own a beloved 6er. On to my issues

So I purchased the car from a friend, who used it as a daily for about 8 months. He did a lot of general maintenance work, however while driving the car right before I bought it, it would bog down when the throttle was depressed to 70% or more. It does this under load, and in neutral. It also took a lot of cranking to start. Since I have purchased it, I have installed a new in tank fuel pump, bypassing the in line pump, installed a new fuel filter, and rotor. The cap, plugs, wires, and injectors were replaced last fall and were running right before this issue started.

I have checked everywhere for vacuum leaks, fuel pressure is ok, but the engine sometimes has a really rough idle, cuts out at high RPM, no matter the load, and takes forever to start. I'm at my wits end, and could really use some advice/suggestions on where to look next.

Cheers,
NK

daz635
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Re: Completely confused as to why my engine isn't running right

Post by daz635 » Tue Sep 19, 2017 7:14 am

Coolant Temperature Sensor maybe. Step 7 in the link below

Or perhaps an issue with ECU

Good article on diagnosing faults with the Motronic System http://www.hiperformancestore.com/motronic.htm
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Brucey
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Re: Completely confused as to why my engine isn't running right

Post by Brucey » Tue Sep 19, 2017 8:31 pm

when the engine is started from cold, and when it runs WOT (as determined by the WOT contact closing) the normal 'closed loop' running conditions do not prevail in the usual way. Thus your fault sounds like there is a major error in the 'open loop' fuelling calculations. Since not all the sensors do things at the same time, this narrows down the fault to a small subset of the things that determine/control open loop fuelling.

Specifically

- the CTS
- the FPR
- the AFM

of these I'd agree with the previous post the CTS is a very likely culprit. Measure the CTS resistance at the ECU plug, and see if you are getting sane values. If you are not, check the sensor itself and check the wiring. Some US-spec models have an inline resistor added in the harness, and this commonly breaks off and goes open circuit, giving a fault that sounds very similar to yours.

cheers
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miklilmag
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Re: Completely confused as to why my engine isn't running right

Post by miklilmag » Thu Sep 21, 2017 5:34 pm

Hello,
Looking for,

moisture in ecu, specially if sitting in rain,

Good luck,
Franke

kingmanjr00
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Re: Completely confused as to why my engine isn't running right

Post by kingmanjr00 » Fri Jun 15, 2018 2:07 am

A long due reply. Thank you to those who have responded. Unfortunately work took me away for a while and I have just been able to get back on the car. I have replaced the CTS and CPS, checked the FPR and AFM. Wound up sending in my ECU, it was shot. Sent it to ModuleExperts to be repaired, and it was beyond repair. They sent me a reman unit with a warranty on it. After installing everything, now my car will not start period. I pulled a plug and am getting no spark. It's cranking strong, but no spark. Any suggestions would be great.

daz635
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Re: Completely confused as to why my engine isn't running right

Post by daz635 » Fri Jun 15, 2018 4:00 pm

I have converted the Motronic document linked above into a PDF as the link no longer works. It contains lots on information on tracing no start issues

https://drive.google.com/open?id=1X2hPj ... fDnugVsk9N

I would check
- Speed and reference sensors to see that they have the correct resistance (section eight)
- Check to see if the coil will produce a spark directly from the tower using a plug and spare spark plug lead (will tell you if distributor and rotor are the issue) section 12
- Test to see if there is voltage at the postive side of the coil terminal 15. Section 12

If there is no power to the coil have a look at your main relay (Section 4). Also check you grounds (Section 4). There is also a wire that goes from the ignition switch to the coil

Brucey will probably have more information to add
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cofred
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Re: Completely confused as to why my engine isn't running right

Post by cofred » Fri Jun 15, 2018 6:54 pm

I would also start with what daz635 said but if that all checks out, look at the AFM again. I had a similar no start issue, and the sweep arm on my AFM was "stuck". I pulled the cover and cleaned the contacts, plugged it back in and it started right away.
Heath
'85 M635

kingmanjr00
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Re: Completely confused as to why my engine isn't running right

Post by kingmanjr00 » Fri Jun 15, 2018 10:19 pm

So I had replaced my speed and reference sensors when I replaced the ECU. Went back through that PDF you posted, thanks for that BTW, and when I got back to section 8, almost skipped it. Brand new Bosch sensors on a never before run car. Decide to test any way, and am getting proper resistance on terminals 1 and 2, but an O/L reading on 1/3 and 2/3 on both sensors. If I'm reading that PDF right, I should have somewhere around the 100k resistance reading. Is that correct? If so, is my O/L reading on terminals 1/3 and 2/3 saying my sensor is bad? If that is the case, I'm going to be not happy, because they were a pain to get out, and that means I was sent 2 bad sensors....what are the chances of that?!

kingmanjr00
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Re: Completely confused as to why my engine isn't running right

Post by kingmanjr00 » Fri Jun 15, 2018 10:20 pm

ps. I have no spark directly from the tower, and I do have power on terminal 15. The coil also ohmed out correctly.

kingmanjr00
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Re: Completely confused as to why my engine isn't running right

Post by kingmanjr00 » Sat Jun 16, 2018 12:24 am

I called my dad, and he just left. He owned an e30 for years and years, and thought he may have some insight as well. Of course, we struck out again, but he brought up something I had not thought of yet. Before I replaced the ECU, I replaced the timing and speed sensors, hoping they would be all that was wrong and that the ECU would be ok. The car did not start at all after replacing those two sensors. I then sent the ECU in and it was bad and I installed the new one. Could the bad ECU have done something to the sensors? Neither of us were sure.

Thanks again for those who have responded! I really appreciate all of the help.

daz635
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Re: Completely confused as to why my engine isn't running right

Post by daz635 » Sat Jun 16, 2018 6:16 am

Check that the speed and reference sensors are plugged in the correct way around. If they are reversed that car will not start

It's highly unlikely that you would have two bad sensors
download.jpg
download.jpg (11.41 KiB) Viewed 1295 times
Note the difference in the color of the connector. The gray and black connectors are part of the engine harness and plug into the sensors which push up thorugh the support bracket. . The Bentley manual says the speed sensor is the top one (D) and goes to the black connector and the lower sensor location (B) is the position sensor and it goes to the gray connector.

To check them Bentley says to check the resistance between pins one and two of the three in a row and it should read 960 +/- 60 ohms. The other connections should have over 100,000 ohms resistance

The only other idea I have is that there is an issue with the OBC
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kingmanjr00
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Re: Completely confused as to why my engine isn't running right

Post by kingmanjr00 » Tue Jun 19, 2018 8:43 pm

So I received my two new speed and reference sensors. I tested them and the same thing. They show a resistance of 1k on the first two, and an O/L on the other two. This is the part that I ordered.

https://smile.amazon.com/gp/product/B00 ... UTF8&psc=1

It is the correct the correct part, right? I checked on realoem.

If that is not the issue, is there any way to test the OBC? It looks like it functions correctly and I'm not seeing anything wrong with it. The other questions I had was what ECU should I have? I totally forgot to take a picture of the original one before I sent it to them and don't know to compare with the one they sent to make sure it's the correct one. I have an 85 635CSI.

Thanks again for all of your inputs so far....I cannot tell you how much I appreciate it!

daz635
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Re: Completely confused as to why my engine isn't running right

Post by daz635 » Wed Jun 20, 2018 9:42 am

I have a couple of new reference sensors and tested them with a multi meter and got the same readings as you did so I think we can assume that they are OK

Part looks correct, it is identical to the ones I have.

I believe you should have an Bosch 059 ECU part no 0261200059 BMW part no 12141705619.

Ok So If there is voltage at the coil at point 15 then that circuit from the ignition switch is Ok.

If the reference sensors are new, in the correct position and plugged in the correct sockets at the back of the motor then the ECU should be receiving the correct start signals from them

Next we need to test the OBC relay. This relay passes power from the ignition switch to the main relay. If it is bad no signal will reach the ECU. Does the main relay click when you turn the key to the run position?

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.


If the main relay is old it may be a good time to change it out for a new one and keep the old one as a spare. I have seen them function ok but fail under load. The main relay can cause all sorts of running issues

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. Clean the relay prongs and the sockets in the holder base and plug the Main relay back in.


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.

relay_jumpers_193_114.jpeg
relay_jumpers_193_114.jpeg (53.67 KiB) Viewed 1217 times
The ECU also requires a signal from the starter motor to pin 4 via a yellow and black wire

I would also check your grounds. Section 4 in the above Motronic document
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kingmanjr00
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Re: Completely confused as to why my engine isn't running right

Post by kingmanjr00 » Sun Sep 30, 2018 1:48 pm

Ok, I'm back after a long long trip, and hoping to figure this out over the next week.

Daz,

I double checked both reference sensors and they are in the correct position. From what I can see, there is no way to adjust them on depth, is that correct? If I do have to adjust them, how would I do that?

I have also changed the crank position sensor. Does that have a depth adjustment?

I'm guessing if any of those three sensors are too close or too far from what they are sensing, they won't send a signal.

I have also checked the power to the main sensor, and there is appropriate voltage at the appropriate pins, though I can go double check this if you think I need to now that I have done so much more to it.

The car is cranking very very strong. I have good fuel pressure. I disconnected the wire from the top of the coil, and put a plug wire on it and grounded the plug and am getting no spark, so that is where I am focusing my efforts.

To date, I have replaced the speed and reference sensors, crank position sensor, plugs, wires, coil, main relay, fuel pump relay, converted the fuel pumps into a single in tank pump (walbro 255), coolant sensor, and sent the ecu to Modular Experts. They tested it, and it was bad, so I purchased a rebuilt one from them to replace it.

Thank you so much to all who have already helped so much, and I look forward to seeing what suggestions you have for me.

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Brucey
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Re: Completely confused as to why my engine isn't running right

Post by Brucey » Mon Oct 01, 2018 4:28 pm

Currently you have a no-start? Is that right? Or still the rough running?

For a no-start; Am I right in thinking that you don't say that you have checked the 'start' signal on pin 4 of the ECU yet? This would be one of the first things I would check. Jumpering the main relay (as per my photo that Daz has reproduced above) will be more likely to power the coil, where a dodgy main relay won't.

If you have not done so yet, test the integrity of all the ground wires in the system; a bad ground connection to the ECU will result in a no-spark condition and may result in ECU damage.

If you have spark but no start then you must not have enough fuel. The car should fire on the cold start injector only (which does not require the ECU for operation) but then quit after a few seconds if the main injectors don't fire.

Note that the front crank sensor (on pre 6/87 cars) does nothing at all; it isn't even connected to anything unless you plug in a (now obsolete) BMW service system.

Playing 'parts change bingo' is all very well but some more diagnostic tests are required IMHO.

cheers
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JCS
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Re: Completely confused as to why my engine isn't running right

Post by JCS » Mon Oct 01, 2018 4:54 pm

kingmanjr00 wrote:
Mon Sep 18, 2017 11:15 pm
Hello all,
I have installed a new in tank fuel pump, bypassing the in line pump, installed a new fuel filter, and rotor. The cap, plugs, wires, and injectors were replaced last fall and were running right before this issue started.

I thought the in tank lift pump, did not supply the correct fuel pressure by itself.
Why did you delete the inline pump?
What did you replace the lift pump with?

Best,
Jay
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Read the instructions on page 2,3,4 to view the info panel (CAPTIONS)
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kingmanjr00
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Re: Completely confused as to why my engine isn't running right

Post by kingmanjr00 » Mon Oct 01, 2018 5:31 pm

Brucy,

The car is currently not starting.

I have tested all of the grounds, and will be replacing them with new wire tonight. They tested ok, but making up new wires is not difficult, and an easy preventative step.

The coil has power on terminal 15.

I currently have no spark. The car cranks strong, and the motor sounds good, I just have 0 spark. There is power at the coil, just no signal is my hunch. Fuel pressure at the rail is fine.

How am I supposed to check pin 4 on the ECU? Am I looking for signal while cranking?

JCS, I put an aftermarket pump that eliminated the need for the inline pump.

Thanks for your help.

baders
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Re: Completely confused as to why my engine isn't running right

Post by baders » Tue Oct 02, 2018 8:17 am

You can test the switching action of the ECU with a test light on to terminal 1 of the coil. Test for continuity between coil terminal 1 and ECU terminal 1. Make sure the shielding of this wire is in place and effectively grounded at one end.
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miklilmag
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Re: Completely confused as to why my engine isn't running right

Post by miklilmag » Tue Oct 02, 2018 7:16 pm

relay_jumpers_193_114.jpeg
relay_jumpers_193_114.jpeg (53.67 KiB) Viewed 631 times
Start and run okay

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miklilmag
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Re: Completely confused as to why my engine isn't running right

Post by miklilmag » Tue Oct 02, 2018 7:21 pm

miklilmag wrote:
Tue Oct 02, 2018 7:16 pm
relay_jumpers_193_114.jpeg
Start and run okay
Also over ride's the OBC relay under steering wheel
Good luck
Franke

daz635
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Re: Completely confused as to why my engine isn't running right

Post by daz635 » Wed Oct 03, 2018 10:04 am

OK to review. You have replaced speed and reference sensors, main and fuel pump relays, coil tested Ok, dist cap, plugs and leads replaced

The fuel pump is running and pressurising the fuel lines

You have tested that there is voltage at Pin 86 of the main relay when the ignition is switched to run

To test next

1) Make sure all of you grounds are good including both under the bonnet and in the cabin (left hand side kick panel I believe for LHD cars)

2)As Baders has said test the switching action of the ECU by placing a a test light on terminal 1 of the coil.

3) As Brucey has said test for a signal at pin 4 of the Motronic plug. I believe that pin 4 is grounded at all times except when the starter motor is engaged. Take care when removing the 35 pin motronic plug is is delicate and 30 years old. Disconnect the battery as well before disconnecting the plug. I also place a piece of tape over the socket on the motronic unit.

4)Test for continuous voltage voltage at pin 18 at motronic plug (hot at all times). Check for voltage at pin 35 with ingition in run position

35 pin plug has pins 1-18 on one side and 19-35 on the other
Motronic 35-pin_zpsermxbae9.jpg
Motronic 35-pin_zpsermxbae9.jpg (115.97 KiB) Viewed 603 times

Let us no how you go
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baders
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Re: Completely confused as to why my engine isn't running right

Post by baders » Thu Oct 04, 2018 3:36 am

Other tests to throw in to the mix;

1) Make sure you have continuous 12v at pin 18 of the ECU.Check for ignition power at pin 35.
2) Check operation of injectors with a noid light.
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TN_M6
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Re: Completely confused as to why my engine isn't running right

Post by TN_M6 » Tue Oct 16, 2018 5:49 pm

Back to the crank sensors just in case. About 1000 ohms between 1&2 is correct. Wire 3 is simply a shield with no connection at the far end and you should get >100k ohms or megohms or infinite between it and anything else. Another way to test the crank sensors is with your meter on AC volts between 1&2 while cranking. The reference should generate something less than 1/2 vAC while the speed maybe > 1 vAC. This will help you verify if they are producing a signal the DME can see. You need a scopemeter to be really sure of the pulse and signal but AC volts is a good first check.

The sensor on the crank hub is only for the diagnostic port. Not needed for the car to run.

With good sensors and power to the DME you must see spark and you should test at the coil in case there is a dist cap or rotor problem. A noid light would help you see if it pulses on the (-) side of the coil or if it pulses injectors as well.

Sounds like you have already verified DME and coil power, Main and Fuel relays so it must be something really basic. I was also thinking the crank sensors just got reversed. Have you physically tried that rather than assumption? So easy to test this.

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