Motronic 1.3 - no oxygen sensor - fault code 54?

[RABen 6]

Hi all,

 

New here, proud new 205 GTI 1.9 (1989 DKZ, motronic 0 261 200 162) owner/driver.  This forum is super!

 

The car is very solid and looks great. It starts/runs but pretty rough like it runs on 3 pots at times. Supposedly the engine is recently rebuilt and somewhat upgraded (pistons), no cat anymore.

 

The RPM was quite high on cold start but not too bad. When warm it was running 2k rpm and very rich by the smell of the exhaust and the really bad MPG. I have reduced the warm idle RPM  using the big brass screw on the throttle housing this improves the warm idle revs but it is not very stable. Still smells badly like gasoline on cold start.

 

The handling and driving is quite fine by the way.

 

Notably there is no oxygen sensor installed which strikes me as odd. The exhaust manifold is non-stock spagetti with no mounting hole for the oygen sensor.

 

I did check for ECU fault codes using the wire/bulb method and it produces 54. It is ECU error - I found some general remarks that this fault code can be caused by (sensor) wiring or a bad supply voltage.

 

Could the 54 code be caused by the complete lack of an oxygen sensor?

 

Any other information/suggestions on causes and/or how to dig into this fault 54 on a running car?

 

All help much appreciated!

Edited March 6, 2022 by RABen

[SRDT 182]

A chipped ECU can do this.

At startup the ECU is checking the EPROM content by calculating a checksum with it and comparing it with a value stored inside the EPROM. When programming a performance chip the reference value should be altered to match the new checksum.

Some tuners don't know where it is or simply don't care, others use it as a proof that they "worked their magic" on the ECU when in fact they just raised the rev limit.

[RABen 6]

Thanks  a lot SRDT - This is a likely cause then as the car has been remapped on the dyno - I know that for sure.

 

Do you happen to know if it is a (common) mod  in 205 country to omit the oxygen/lambda sensor?

[SRDT 182]

Maybe the tuner deleted the lambda control inside the EPROM or tricked the ECU, it's hard to say.

[RABen 6]

Thanks a lot - will try to find out who did the tuning.

[petert 588]

My experience is they don’t run very well without a functioning O2 sensor, exhibiting symptoms exactly as you describe. 

[Thijs_Rallye 87 4 Cars]

Code 54 is a bad checksum fault. (failed EPROM memory self test) I don't know if you are able to dump the EPROM otherwise I could have a look at the binary file.

 

 

[RABen 6]

Thanks petert and Thijs_Rallye. Most helpful!

 

Aiming to get a O2 sensor and mounting  added.

 

Will have a look at what is needed toolingwise to read the eprom quite new to this ...

[Thijs_Rallye 87 4 Cars]

A 10mm socket, a screwdriver and an EPROM reader would suffice . I am not exactly near you otherwise I could dump it for you, the ECU needs to come apart for this. If needed I can provide you with a dump from the original EPROM, or correct the checksum for your current EPROM content.

 

Only thing is you'll need to source a blank EPROM since most of these are only able to be written to once.

[Tideee 3 1 Cars]

you say "the ECU needs to come apart" ....do you mean that you have to open up the ECU ??...if so, can you please advise how you do that, as looks like you will need to bend tabs and need more than a 10mm socket and screwdriver 

Thanks 

[petert 588]

Correct. Only open the tabs enough to clear the lid. Too much and they’ll work harden and snap off.

[Tideee 3 1 Cars]

Thanks Petert 

[RABen 6]

Thanks Thijs.

Next week I'll first look at the O2 sensor / rich mixture issue - I may take up you offer on the checksum later on.

Socket 10mm - check
Screwdriver - check
Guess I am half way there in getting into the EPROM domain ;)

 

Would any simple EPROM reader such as this cheap one do or should I look for a specific type / software support?

 

[Thijs_Rallye 87 4 Cars]

It is a 28 pin EPROM, (27C256) so the reader you've posted is on the small side . If you are willing to travel I can dump it for you, if you are interested drop me a PM.

 

I am also curious to see what ROM modifications are done

[RABen 6]

Quick update:

- O2 sensor indeed missing.

- Taked to the tuner and he said they never remove the o2 sensor for uncontrolled cats - even if the cat goes.

- ECU with modified software throws 54 as the only fault.

- Got my hands on an stock ECU.

- Checking the fault codes after driving for a while with the stock ECU I get 51 which refers to the Lambda sensor electrical circuit (as expected).

 

Careful conclusion is that the ECU stopts throwing faults if it has a 54 (checksum after modified software).

 

Next week the exhaust is getting a brand new o2 sensor after the mounting hole is welded in.

 

Will then first check with the stock ECU and if that is all ok try again with the tuned one ...

 

@Thijs_Rallye when all is resolved I'd like to get the checksum (fault 54) issue fixed on the tuned ECU - mainly to get it to report gaults again - would be great if you could help with that. Good opportunity to have a look at the mods then.

 

Will follow up with results.

Edited April 9, 2022 by RABen

[RABen 6]

"Careful conclusion" should read "Cautious conclusion" ...

[SRDT 182]

I think you can have other faults on top of the checksum (54) one, at least the ML1.3 on my 309 GTI16 can do that with the knock sensor.

[Thijs_Rallye 87 4 Cars]

20 hours ago, RABen said:

Careful conclusion is that the ECU stopts throwing faults if it has a 54 (checksum after modified software).

I think it can spew out more codes even if code 54 is present. I think they "hacked" out the lambda fault setting criteria.

 

If you weld in the lambda bung it might be wise to have a look at the wideband lambda probe mounting instruction: ( https://www.bosch-motorsport.com/content/downloads/Raceparts/Resources/pdf/Data sheet_69086859_Lambda_Sensor_LSU_ADV/ADV_pre_Turbo.pdf )

If you even plan to start messing around yourself with a wideband you will have the bung already fitted correctly for a wideband sensor. For the functioning of the narrow band sensor it doesn't matter if it is fitted as per wideband instructions.

 

 

 

[RABen 6]

Thanks for the feedback on 54 and additional fault codes - makes sense indeed that they changed or removed lambda criteria.

 

Also good advice on the bung position. Will pass that on to the welder. No plans yet re. wideband sensor - first goal is to get it running decently - maybe at a later stage.

 

 

[SRDT 182]

Some software revisions for XU9JAZ and XU9J4 are pretty close so the same generic code must be able to run with or witout lambda, idle valve or knock sensor.

The no lambda mode should need to use the CO pot inside the AFM but I don't think it is wired on the 205 and the AFM may not have it either if it's the original one.

[petert 588]

Even if you fit a 158 or 161 chip into the 8V case, it will fault because there isn’t a knock sensor present. Ignition timing will be severely retarded.

[Thijs_Rallye 87 4 Cars]

4 hours ago, petert said:

Even if you fit a 158 or 161 chip into the 8V case

Just out of curiosity but is the knock signal processing present on the PCB of an eight valve ECU? I would think not, but the late eighties were still the good times in the automotive world, before it was being rules by solely bean counters.

 

@Baptiste, I need to have a close look at the ...202 AFM, maybe it still has the air bleed screw similar to the Jetronic ones for setting the CO vol%. From what I've read there is a map in the software which needs to be set to a certain value (dec 128?) to disable lambda feedback. (6x1 from that I've read)  I haven't found it yet though.

[SRDT 182]

You should find a daughterboard inside the ML1.3 ECU with knock sensor so I think the best the 8V can do is adjust timing depending on intake and engine temp.

 

Directly using the 16v chip on a 8v ECU can't work well without knock sensor and idle valve. However you can find the exact same maps at exactly the same place (with different values and rpm points) on both XU9J4 and XU9JAZ chips. That means that the software was made to run with or without lambda / knock sensor / idle valve depending of the engine.

The guys at PSA must have started by selecting those options before working only on the revelant maps.

[petert 588]

23 hours ago, Thijs_Rallye said:

Just out of curiosity but is the knock signal processing present on the PCB of an eight valve ECU? I would think not, but the late eighties were still the good times in the automotive world, before it was being rules by solely bean counters.

All I know, is that if you put a 16V chip in an 8V case, maximum advance is around 16º and it throws up a code 44.

[RABen 6]

Lambda/O2 sensor bung welded in, installed a brand new Bosch 0258003074 4-wire lambda/02 sensor.

 

The stock ECU now throws 51 instead of 52 before installation of the sensor.

The code 51 suggests to try another ECU (?).

The car still smells like it is running very rich.

>> Could this be because of non-stock pistons not playing well with the stock ECU/map ?

 

Will try the modified ECU tonight.  As this one did not throw 52 before, I doubt if it will throw the 51 or anything else related to the mixture. Will have to rely on the smell of the exhaust gasses .

Will post back any findings.