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

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kingmanjr00
Posts: 5
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: 60
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
'86 Euro 635 #1887204 Schwartz (086) Buffalo Schwartz Interior
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Brucey
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Location: Cambridge, UK

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: 5
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: 60
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: 47
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: 5
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: 5
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: 5
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: 60
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 40 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
'86 Euro 635 #1887204 Schwartz (086) Buffalo Schwartz Interior
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