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Thread: Runs badly after time - resetting ECU seems to help?

  1. #1
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    Runs badly after time - resetting ECU seems to help?

    I have an M52B28 from an E39 in my E30 and it seems to develop issues over time, but then runs okay if I leave the ECU unplugged overnight.


    The symptoms develop to become jerking half the time (as if I'm messing around with the throttle), lumpy idle, and lack of power. It almost seems as if one cylinder intermittently turns off and on. I could be cruising at 40mph with the car jerking and bucking then instantly it'll just purr like a dream for a few minutes. Then it'll begin bucking and jerking again.


    Unplugging the ECU overnight seems to solve it, until the symptoms develop again.


    I was advised maybe the O2 sensors are plugged in the wrong way around, so it was reading emissions wrong and constantly trying to correct itself. But I've had a look and i'm sure they're plugged in correctly.


    Tried two MAFs and tested the TPS - all seems fine.


    I've had my codes read but I sent the ECU off to do so as my port doesn't work. This means that some of these faults are triggered when the ECU was plugged in, and are therefore unreliable. The O2 sensors for example have only been triggered once and it was the most recent switch-on, meaning they probably only triggered because the ECU was switched on without being plugged into a car. They came back as follows:


    Code - Description - Times seen - Countdown





    Any ideas?
    Last edited by ACJJ619; 07-11-2018 at 02:58 AM.

  2. #2
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    Alas, I can't see the codes.. The image doesn't load..

    What I personally do in this type of cases, is just have the ECU reset all adaptation values with a laptop with INPA (not sure if disconnecting it overnight accomplishes that) and then disconnecting MAF sensor AND both O2 sensors. Then it will run without any feedback from the O2 sensors and will use the TPS angle and RPM (it's called Alpha-N) to roughly calculate the mass of the air going in the engine. It works surprisingly well with the M52 engine/DME. If the car regains all its power and runs perfectly fine, also in the long run, then you know it's either the O2 sensor or the MAF.. You will probably notice that it runs a bit rougher at idle, and take-off from idle, but for the rest it should run very well, almost impossible to distinguish it from the stock way (with MAF).

    Then retest, by reconnecting the MAF.. See what it does.
    Then retest, by disconnecting MAF and only one O2 sensor. See what it does.
    Then retest, by disconnecting MAF and only the other O2 sensor. See what it does.

    If it's one of the three sensors (MAF, O2 bank 1, O2 bank 2), then you'll know which one it is.
    Then you can do more tests, for example, if you think O2 sensor of bank 2 is bad, then reconnect MAF and O2 sensor of bank 1.. If it runs perfectly fine then, then you're 90% certain you've find the cause.

    One little risk that you have, is that because there is no feedback from the O2 sensor, and if, say your fuel pressure regulator isn't working fine and gives a too low pressure, you will run lean and the DME will have no way of telling (except knock sensors).. So, if you feel it hesitates a lot at wide open throttle (WOT), then be a bit careful, and go and test fuel pressure at the rail first. On the other hand, no need to be really anxious about it, because all (at least in Europe) pre-1986 BMW's had no oxygen sensors and ran perfectly fine without it.
    Last edited by ed323i; 07-10-2018 at 06:07 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  3. #3
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    Doh, I tried to attach the image but it didn't work and now my post has disappeared? You can find the codes here: https://i.imgur.com/j091R55.jpg

    I wouldn't be surprised if it's an O2 sensor issue to be honest. My previous engine (I only swapped this in recently) burnt through an awful lot of oil and I dread to think the state of the O2 sensors.

    I've tried two different MAFs and they don't seem to make a difference. The engine also seems to change note with the MAF unplugged so I'm sure it's not that.

    I'll try your unplugging method - thanks for the suggestion.

  4. #4
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    ed323i has a very good grasp of the e36 engine management systems. Excellent. I hope you don't mind but I'm going to save your username.

    I'm not sure about e36. I have owned US e30 obd1 and US e36 obd2 cars but never a obd1 e36. It is my understanding that in Europe there was only ever one O2 sensor in the manifold/header for A/F ratio and the post-cat sensor in USA markets was for emissions only. (obd2)


    I *think* that we should have persistent memory in our ECU/DME and therefore "unplugging it" should not make a different for adaptation values. You must manually/physically clear codes and adaptation via software. (I know OBD2 e36, not obd1)


    acjj619 --randomly... my sister and her husband (and 3 kids) are living in Wokingham at the moment... (is that right? wok-ing-ham) Anyway, On US cars the DME is a little different than in Europe. Regardless, Do you have anything running Windows XP or 7? Or W10 that you are comfortable running legacy software on? If you do INPA. If you have an old laptop that you can repurpose it would help.


    I have no clue what UK ECU/DME is (europe or usa) so can't really help. have done a lot with usa cars but zero on European cars. Only Europe e36 I own is e36 touring diesel.

  5. #5
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    Quote Originally Posted by 1215 View Post
    ed323i has a very good grasp of the e36 engine management systems. Excellent. I hope you don't mind but I'm going to save your username.

    I'm not sure about e36. I have owned US e30 obd1 and US e36 obd2 cars but never a obd1 e36. It is my understanding that in Europe there was only ever one O2 sensor in the manifold/header for A/F ratio and the post-cat sensor in USA markets was for emissions only. (obd2)


    I *think* that we should have persistent memory in our ECU/DME and therefore "unplugging it" should not make a different for adaptation values. You must manually/physically clear codes and adaptation via software. (I know OBD2 e36, not obd1)


    acjj619 --randomly... my sister and her husband (and 3 kids) are living in Wokingham at the moment... (is that right? wok-ing-ham) Anyway, On US cars the DME is a little different than in Europe. Regardless, Do you have anything running Windows XP or 7? Or W10 that you are comfortable running legacy software on? If you do INPA. If you have an old laptop that you can repurpose it would help.


    I have no clue what UK ECU/DME is (europe or usa) so can't really help. have done a lot with usa cars but zero on European cars. Only Europe e36 I own is e36 touring diesel.
    Yeah, Wokingham is right! I live about 5 minutes away. I've got a PC running W10 but could easily acquire a separate XP laptop. Why, what are you thinking?

  6. #6
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    Quote Originally Posted by ACJJ619 View Post
    Yeah, Wokingham is right! I live about 5 minutes away. I've got a PC running W10 but could easily acquire a separate XP laptop. Why, what are you thinking?
    I have the wife's old Tohsiba laptop from uni that I use as a dedicated BMW laptop. I think it came with Vista and I put Windows 7 on it. It is painfully slow but I only use it for BMWs.

    Here is a link local to you:
    https://www.scantool-direct.co.uk/bm...els-369-p.html

    (maybe not local but at least on your island


    Then buy one of these:


    https://www.aliexpress.com/item/ACI-...363746154.html

    Look over on the Z3 forum. There is a really good (here it is: https://www.bimmerforums.com/forum/s...xperimentation ) thread... Any old 20-pin to OBD converter will do but you need to get the right chip on the OBD to USB for it to work properly. I think it's the one that works on VW's as well. The exact chipset is mentioned in that thread.


    The only windows machine I have is that laptop so not very familiar with W10. I know you can do VMs inside W10 and it has a legacy mode that does either XP or W7 compatibility. Laptop is MUCH easier because you can bring it out to the vehicle. In that Z3 diagnostics thread there is a link to download the software (free, legal, legit). Then get rom raider (software) that you have to pay for (one time, it's cheap) and you'll be able to do anything you want... flash your own ECU, read/reset codes, change your gauges back and forth between 'Merican miles/Fahrenheit and km/Celsius... It is a pretty powerful tool and will tell you a lot about what is going on. It'll give you all your codes too. You can also clear codes easily or just clear adaptations, etc.


    The software will also show you real-time what is going on with knock sensors, etc.


    Do you know what ECU you have? (the numbers on the actual ECU) And also what codes are coming up? I assume you kept your e30 gauge cluster. How much of the e39 wiring harness did you put into the e30? Your OBD port may or may not work the same but the round 20-pin from the e39 should have gone into the e30 so that should let you talk to the ECU/DME (car engine management computer). Not sure if guys have figured it out or not yet. The INPA software is OLD and at one time was not running on Windows 10. Everyone was running it on old XP or Windows 7 or inside a virtual machine running on Windows 10. This is another reason why an old, crappy laptop is good.

    In the US we had two sets of o2 sensors, we had one up at the manifold and then a second pair back behind the cat converters. I forget how the codes read: bank one is cylinders 1-3 and bank two is cylinders 4-6 I believe... And then the codes were numbered differently for the engine/manifold sensors and the post-cat sensors. I think that might be the only difference between US and other cars. The rest should be the same but when you install INPA it'll let you pick your country and it'll pick up your car's VIN... or at least the VIN of the e39 that the ECU came with. You must have a CEL (check engine light), you probably can't see it because you didn't change over all of the wiring, but you should at least get a code reader and see what codes the car is throwing.

    Hope that helps. Cheers!

  7. #7
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    Thanks so much for the detailed reply!

    I've already got a 20 pin to 16 pin adapter and an OBD2 scanner but it wouldn't work. I guess my engine is OBD1?

    I had an old Windows laptop but I binned it literally three days ago!

    I've booked the car in with a local BMW specialist so I'm hoping they'll be able to figure out what's wrong once and for all. I use the car daily and it hasn't worked properly since January. It's wearing me down now.

    I have two O2 sensors but no CAT. As far as I know, one controls air/fuel mixture and the other only reads emissions. New symptom today too - the car stalled whilst sat in a traffic jam. I think it's Crank/Cam sensor.

  8. #8
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    I think somehow his diagnostic port isn't working properly, but indeed, INPA would be a great help diagnosing this kind of problems.

    The European cars have no CEL light (though it can be wired in easily if wanted). Also, no OBD2 port on the "OBD2" newer BMWs, 1996+. Again, can be wired in if wanted.
    OBD1 E36 has only one oxygen sensor pre-CAT in the exhaust pipe. And OBD2 has two oxygen sensors pre-CAT (one per bank) in the exhaust manifolds. The European E36 never had oxygen sensors after the CAT as far I know.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  9. #9
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    My engine is from a June 1996 528i Auto. The ECU was flashed by an expert to be suitable for my manual E30. Does that change anything? Reg of the donor car was TKZ5710.

    The exhaust was custom made for an E30 M52 swap and has two O2 sensors in it.

    The problem definitely seems to be getting worse. Unplugging the ECU overnight doesn't seem to be doing anything any more, it's taking more cranks to start and today it stalled in traffic.

    I'm going to fill it up with fuel as it's getting kinda low and see if it changes anything. If it's a fuel delivery issue, just having that added pressure of a full fuel tank may smooth things out and help diagnose the issue.

    Thanks again for the help and advice. Truly appreciated.

  10. #10
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    I'm sorry. I know enough to be dangerous with US cars but don't know enough about Euro cars to help. ed323i seems to be much more knowledgeable than I about the differences. The only thing I can suggest is that you wire in the 20-pin port properly so you can see what is going on. If you had the ECU flashed by someone suitable/reputable, can you look at the fuel mapping? Do you know why it is stalling? I have several 1997 (all US [except diesel car] built late 1996). Happy to flash an ECU and see what happens --or at least take a look at the mappings and see what it looks like.


    Who did the swap?

  11. #11
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    Have you tried driving without MAF and without both O2 sensors (remove black fuel rail cover and disconnect the o2 sensor connectors there) ? I think disconnecting the MAF also resets all adaptation values (for the time you're running without MAF), and disconnecting the O2's will stop the dynamic live adaptation.
    If the problems persist, then I would check the fuel pressure at the rail. Perhaps your fuel pump, fuel pressure regulator is dying, or your fuel filter is stuffed.
    But, like 1215 writes, best would be to do a proper INPA read-out..
    Perhaps it could also be crank or cam position sensors going bad.

    1215: Really great, the link to the Z3 forum.. A wealth of information and downloads. Thanks!
    Last edited by ed323i; 07-13-2018 at 09:05 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  12. #12
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    A friend of mine did the swap. He was a BMW techie when E30’s were built and he’s done plenty of swaps in the past so I trust him.

    I tried disconnecting the MAF and O2 but only for for a minute or two. Made no difference but maybe I need to try it for longer.

    The behaviour has changed somewhat now. As of yesterday morning I’ve driven 8 miles and it’s driven okay, except it struggles to start. It cranks for quite a while before spluttering into action but once in action it seems okay.

    I’d like to say this was when I filled it up with fuel but it was fine on the way to the fuel station.

    I’ll try a different fuel pump and then I think I’ll just have to wait until the garage can see me and do some tests.

  13. #13
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    If disconnecting MAFs and O2s made no difference, then those are probably not causing the trouble..
    Fuel pump or fuel pressure regulator might be causing it (measure fuel pressure at fuel rail to diagnose). Otherwise crank or cam position sensor, but best to first do a proper INPA read-out, because otherwise you might spend lots of money swapping the wrong parts..

    Good luck, and let us know the results!


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  14. #14
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    My battery was drained so the car would not start, it took me a few days to recharge it. When it started it ran like crap. This went on for a few min so I shut it off. At first I though the charging may have damaged something. The 2nd start everything ran fine. Did the ECU get reset? Was it a poor connection?

    Are you willing to try a ECU reset but Unplug battery for 15 min. not just remove the ECU. (or do you remove battery power when you swap ECU)

  15. #15
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    Update!

    The last few days it's been running okay, but struggling to start. It cranks for quite a while before starting but when it eventually does, it seems to run fine.

    Until today, where it couldn't start after a short drive. I drove 3 miles to the shop and when I came out, the radiator fan was on and the car wouldn't start. It was cranking and trying to start, but not quite getting there. Went back a couple of hours later and it started up fine (albeit with the usual lots of cranking).

    Coolant temp sensor maybe?

  16. #16
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    If I'm correct you can disconnect the coolant sensor, especially when the engine is already warmed up.. The DME will 'assume' some temperature and I think when the engine is warm this will work ok.
    So, next time with a warm engine, and it doesn't want to start, just find the coolant sensor and disconnect it. It's below the intake manifold, so not that easy to reach. It's double-temp sensor, one output for the instrument cluster and one for the DME. If it does start then, then you know you've found the cause. No difference, then it's probably not the cause.

    Also, this is something INPA can instantly show you, if it's reading wrong temperatures or not. You can watch all DME-related sensor values live, in actual human readable format (like, for example, 80 degrees C).


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  17. #17
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    I think it's working okay based on the fact my radiator fans comes on and off. I've sorted out a spare car for now and we'll see what the mechanic says next Tuesday...

  18. #18
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    Quote Originally Posted by ACJJ619 View Post
    I think it's working okay based on the fact my radiator fans comes on and off. I've sorted out a spare car for now and we'll see what the mechanic says next Tuesday...
    OK.. Good luck. I hope you selected a mechanic that has software or tools to read out the DME error codes. Otherwise, it might get very expensive quickly (just swapping new parts until he finds the cause).

    Coolant sensor can still cause the symptoms:
    Coolant sensor signal goes to the DME, which then uses it to calculate fuel enrichment for when engine is still cold (up to 60 or 70 degrees C).
    The aux fan is controlled by a temperature switch, which is mounted on the passenger side of the radiator. So, the DME doesn't control the fan (perhaps only to turn the low speed fan on for the A/C), and the coolant sensor in the head (below the intake manifold) in no way influences the aux fan.
    Last edited by ed323i; 07-17-2018 at 02:29 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  19. #19
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    Update:

    I've had the codes read (this time in the car) as follows:

    3 - Ignition #6
    8 - MAF
    25 - O2 sensor 1-3
    52 - Solenoid valve
    55 - O2 sensor 4-6
    68 - Tank vent valve
    83 - Crankshaft sensor

    I thought finally! The crankshaft sensor is throwing a fault and the symptoms are textbook crankshaft sensor issues. So I replaced it with a brand new OEM one...no difference. I tried another MAF too...no difference.

    Grrrr!!

    It's booked in with a specialist on the 2nd to see if he can make any sense of it.

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