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

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kingmanjr00
Posts: 6
Joined: Mon Aug 14, 2017 5:15 pm
Location: Indiana

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
Posts: 64
Joined: Sat Jul 20, 2013 7:26 am
Location: Brisbane, Australia

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
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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miklilmag
Bigcoupe supporter
Posts: 522
Joined: Mon Dec 21, 2009 5:01 am
Location: Minneapolis Minnesota usa

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
Posts: 6
Joined: Mon Aug 14, 2017 5:15 pm
Location: Indiana

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
Posts: 64
Joined: Sat Jul 20, 2013 7:26 am
Location: Brisbane, Australia

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
Posts: 50
Joined: Wed Jul 24, 2013 5:38 pm
Location: Frisco, Tx

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
Posts: 6
Joined: Mon Aug 14, 2017 5:15 pm
Location: Indiana

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
Posts: 6
Joined: Mon Aug 14, 2017 5:15 pm
Location: Indiana

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
Posts: 6
Joined: Mon Aug 14, 2017 5:15 pm
Location: Indiana

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
Posts: 64
Joined: Sat Jul 20, 2013 7:26 am
Location: Brisbane, Australia

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 387 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
Posts: 6
Joined: Mon Aug 14, 2017 5:15 pm
Location: Indiana

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
Posts: 64
Joined: Sat Jul 20, 2013 7:26 am
Location: Brisbane, Australia

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 309 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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