Motronic 1.3 - no oxygen sensor - fault code 54?

[RABen 6]

Modified ECU now throws 54 and 52.

(Actually the stock ECU also threw 52 rather than the 51 - contrary to the post above.)

 

I am a bit puzzled and wondering if I do have the correct O2 sensor (Bosch LS 3074 / 0 258 003 074).

 

Without O2 sensor:

    Modified ECU throws 54 (only)

    Stock ECU throws 51 (only)

 

With O2 sensor:

    Modified ECU throws 54 and 52

    Stock ECU throws 52 (only)

 

From the smell of it the car runs rich with and without O2 sensor.

 

Fault 52 suggests to try again with a new ECU - any idea what may be wrong with both ECUs in this context?

Any tips where to look next?

 

Planning to

1. Check if the O2 sensor heater plug has 12V

2. Test and/or replace the ECU temp sensor

 

All help/direction is much appreciated!

 

PS - just found this info on 52 (from post by kevins dd Thu Dec 04, 2008 10:36 here):
52: Mixture control, supply voltage, air or exhaust leak

 

So I guess the O2 sensor supply voltage is a good place to start?

Edited April 14, 2022 by RABen

[petert 549]

The pins do corrode. A cold sensor could well be your issue.

[RABen 6]

Thanks Peter - up for the test this weekend!

Do you happen to know if the O2 sensor heating gets a continuous 12V or is it regulated by the ECU - in other words - could I bypass the ECU and connect directly to battery for test?

 

[petert 549]

It’s just switched 12V.

[welshpug 1,621]

I doubt  the 12v comes from the ecu!   Haven't  got the diagrams to hand, they tend to be supplied by the management  system relays.

[SRDT 146]

Yes it's 12V from one of the relays with a fuse in the engine compartment near the battery.

[petert 549]

It would appear that +12V for the lambda sensor (4) on wire #96, comes from the distribution block near the battery & PAS oil tank. I've never personally traced it, so can't vouch for the accuracy of Mr Haynes. It doesn't make a lot of sense as it would be permanently live.

 

Edited April 16, 2022 by petert

[welshpug 1,621]

This Mi16 M1.3 diagram appears to have a separate  relay for the Lambda supply.

 

[SRDT 146]

[RABen 6]

Thanks all - much appreciated!

 

The heater supply shows 13.8v on running engine. Close to nothing with only ignition on.

 

The search is still on ..

[welshpug 1,621]

How was the earth side?

[RABen 6]

Hi Welshpug - what do you mean by the earth side? I measured over the 2 poles of the supplying connector which is what the sensor "sees".

 

Also measured the lambda signal directly on the sensor side connector and that read up to 1V on revving so I guess that is ok (given it is a new sensor).

 

Will need to check the resistance of the lambda signal wiring to the ECU - aiming to do that tomorrow with an additional set of hands.

Edited April 17, 2022 by RABen

[SRDT 146]

Was the heater pluged when you checked?

Maybe you can only find 13.8v as long as there is no load.

[RABen 6]

No - the sensor was out - will check with sensor connected as well - a bit of a cramp without lift .

 

I read someplace that a good way to test the power supply is to put a bulb in place of the heater element - need to find out the watts the heating element takes. Guess that is a matter of measuring the resistance.

[RABen 6]

The bulb method for testing the heater circuit:  https://www.motor.com/magazine-summary/diagnosing-o2-sensor-heater-circuit-failures/

[welshpug 1,621]

I think most bosch narrowband lambda are 10w.

[RABen 6]

Tested the O2 sensor power supply with a 10w bulb and that glows happily once the engine is running.

 

Signal cable from under car to ECU - both wires ok and connected to the correct pins ECU side per: https://www.e30zone.net/e30wiki/index.php/ECU_Pinouts#Motronic_1.3

 

Power connector terminals (female, car side) are not tight an possibly partly broken. Can imagine this causes disturbances so will replace those and post back.

[RABen 6]

Thorougly cleaned, sanded, reshaped the original car-_7side/female lamda terminals inside the connectors and now the stock ECU is without errors - yeah. Still plan to replace the terminals as they are not in top shape but did not have this type readily available

 

The modified ECU keeps thowing 52 next to 54.

 

The car seems to run smoother on the modified ECU but for now I'll stick with the stock one go see what the impact on milage is.

 

Will test the modified ECU again with new connector terminals in place and post back results.

 

Thanks all for your help!

 

@Thijs_Rallye if you are still interested in the software modifications I'd be happy to see if we can arrange to meet some time.

[Thijs_Rallye 86 4 Cars]

2 hours ago, RABen said:

if you are still interested in the software modifications I'd be happy to see if we can arrange to meet some time.

Sure, drop me a PM.

[RABen 6]

Problem returned somehow with extremely jerky behavior on low loads and code 52 reoccurred in the stock ECU after some harder driving.

 

Really need to get new connectors soon.

 

Opened up the AFM to see if the track is worn as it is listed as a cause for jerky behaviour.

 

How would the experts qualfy the state of the track from the picture? Is it a suspect?

 

 

[Thijs_Rallye 86 4 Cars]

Hard to tell on that picture. It seems like there is some wear around where the cable runs in the picture. I've seen worse but this picture may be misleading. Best way to check these is measuring the signal with a scope whilst manipulating the flap angle, the signal should be fairly smooth.

[RABen 6]

Thanks Thijs.

 

It has been a while since posting here. I have been cleaning (ground) contacts and did re-fit the ignition module which appeared to be lacking thermal paste. Sometimes some of these actions seemed to help, to be back at square 1 after restarting the car the next day.

 

Last Friday decided to replace the fuel filter. After that the engine ran very stable on idle. Added some injector cleaner to the fuel and since drove 250km. Cleared the fault codes later -  about 150km ago - and it is still fault free om the modified ECU (apart from the 54 /checksum).

 

A cautious ¡YEAH!

 

Fuel consumption still quite stiff but that is likely correlated to the right foot trying to give the injectors a workout with the cleaner.

 

I assumed the engine rebuild would have come with a fresh fuel filter although it looked old from the outside ...

 

Fingers crossed the 52 stays away now - will monitor it for the time to come and will mark the issue resolved if the fault stays away.

 

Thanks all for the advice and for thinking along!!

 

Edited June 6, 2022 by RABen

[RABen 6]

In the mean time replaced the injectors with new genuine Bosch 4hole ones (0 280 150 962, according to bavarianwerke.com identical spec to  the original 0 280 150 762).

 

Seems to help and faults have not returned since on both standard and modified ECUs.

 

Idling not perfect but OK.