Citroen SM MAP sensor 0280100036 not working

Howdy all,

I'm currently assessing the remaining few tasks. One of these is engaging with the company that rebuilt the ECU (for around $1400) 14 months ago.

While it is claimed that around 80 Citroen SM's have been imported to Australia & New Zealand - few are D-Jetronic. SM Australia imported many of these, just about all from the USA - where D-jet SM's were never sold. They, therefore, have limited expertise in this area and no I.E.parts to speak of (based on my conversation with them a month or two ago).

I know of a couple of D-jet SM's 1000's of Kms away. These strangers would be as reluctant to lend me a ECU, as I would be ....in their place. An unknown performing ECU (if I could find one), is no big step forward. But I'll still try and source one.

Still some checks to be made in the mean time.

Regards,
Rhys

Hi Rhys,

now I understand why you find no SM ECUs in down under. When I read the repair prices for ECU repair 1400 AUD or 950 €, I am shocked. Maybe I should emmigrate to Australia What I can offer as help: I'll try to find an ECU for you here in Europe, verify it and then send it to you.

Hi Volker,

Yes - you immigrating to Australia.....would work for me. But you would make a better living teaching Latin - than selling d-jet services in this part of the world.

I checked the operation of the cold-start valve tonight, and re-check fuel pressure. All ok.

A colleague (experienced Volvo mechanic) encouraged me to try a used Volvo P1800 MAP sensor we had lying around and demonstrated that adjusting the rear screw of the MAP sensor - at idle- affected the running.

Out of interest we hooked up the gas analyser while the car was idling, and found that via the MAP sensor, we could adjust the CO from 7-8%, down to around 2%. While still at idle, we could Adjust the potentiometer on the ECU down to almost 0. This event is consistent with my colleagues extensive experience with Volvo D-jets.

This is the first time I've had the car running within these lean parameters.

This experience seems at odds with D-jet theory. What are your thoughts?

Regards,
Rhys

Hi Rhys,

first of all: Latin was my performance course in highschool, I even learned ancient Greek as well: Australia insula est. Ceterum censeo D-Jetronicum conservandum esse ! So where can I sign to become a rich man in Australia ?

With your Volvo MAP sensor now you are raping your D-Jetronic. You abuse that wrong MAP sensor like a potentiometer. Why? Potentiometer is only active when idle-run contact is closed. Then it overlays the effect of MAP sensor transformation with a steady voltage level. What you and your firend are doing is a bit strange. You are abusing a totally different type 3 MAP sensor to replace your type 1 MAP sensor. I am not sure about your specific MAP sensor, but if I compare other type 3 sensors to other Citroen type 1 MAP sensors, type 1s have a much shorter tuning range (max vacuum 0,5 Bar) and they have a lower transormation level. Now you come with a type 3 sensor and on top you change its adjustment dramatically. A few degrees of screw turn shift the armature drastically. That is why you use the poor type3 sensor like a potentiometer now. It's a bit like raping the system.

Your friend can forget his Volvo sensor. It lef unusable now.

Hi Volker,

Rape? - I say the D-jet system asked for it.

The Volvo MAP sensor (type 2 not 3) was to just try something different......no-one is getting married. As offensive as the brief mating might be, it caused flexibility in mixture adjustments not experienced to date. Actually a refreshing change.

With the idle circuit enacted on the ECU and tangible adjustment achievable via the potentiometer......why was the MAP sensor having an effect ....as well? The adjustment from the MAP sensor should have no effect at idle?

Would not adjusting the original SM type 1 sensor achieve a similar result as the loan type 2? (or send it to Bosch for rebuild) Is this any demonstration that my existing MAP sensor may be the cause of the rich mixture?

Cheers,
Rhys

Hii Rhys,

no your D-Jetronic system did not ask for rape

I assumed you had a type 3 as you can only adjust a type 2 after you remove the potting. Type 2 and type 3 MAP sensors have a higher transformation level. I alwasy use the word supersede when I talk of the idle-run potentiometer overlaying the effect of the MAP sensor transformation. A type 2 and type 3 MAP sensor has a higher level of transformation than a type 1. Additionally you change ist setting heavily by changing the zero position of the armature. That has the effect that you now create a different level.

There is a 5% chance that your MAP sensor has a broken aneroid cell or spring inside so that it heavily deviates. But generally type1s are very robust. And as yours is with rivets and still originally potted, I have always stated that it should be 95% okay.

Having said that one can never be 100% sure if it is not verified.

Hi Rhys,

interesting subject though. I have followed here what Bosch and others like PB Anders have proclaimed and I saw the electrical circuit that causes the overlay and prioritization with the potentiometer. So it seemed to confirm what has been proclimed for so long. However, I will do a test these days where I will do an experiment. How far does a broken MAP sensor influence idle-run CO setting via potentiometer. You made me curious.

So far the cases I had in my hands where idle-run CO would not fit were either broken ECUs or mostly false air in intake manifold. Now a completely broken diaphragm in a MAP sensor would of course also be a source of false air. But it will be intersting to see, how far a mistuned of completely false sensor can effect idle-run CO.

I will let you know.

Hi Volker,

While I do not understand the MAP sensor theory in the detail that you and some others do - I appreciate the concept of the relationship between MAP sensor and ECU.

My colleague describes how over 20 years at a Volvo-only workshop (at a time when D-jet 140, 164 & P1800-s were common) that it was typical that when they uncovered defective MAP sensors - that those vehicles allowed simultaneous mixture adjustment at both ECU and MAP sensor at idle. Defective cars were returned to the road where that car & service client were maintained satisfactorily for many years. He has a recollection of 20+ exact scenarios like this. I unreservedly believe his word and his real-life experience trumps ......my readings.

So, it would seem sensible to send my MAP sensor to Bosch for repair & verification. I have some document (here somewhere) that explains the Bosch procedure to do this. I feel like I aught remove the epoxy potting covering the adjuster and do some CO tests first (is the epoxy "factory sealed" or has someone re-filled it with araldite after some tampering years ago?)

Cheers,
Rhys

Hi Volker,

I removed the potting from the end of my MAP sensor. It is difficult to see through the aperture, but there are some signs of irregular marks within the unit.

The potting on the end of the sensor looks neat - and I presumed factory. Do you thinks this is the case?

Regards,
Rhys

Hi Rhys,

well that is hard to say from a picture. Original potting is of a dark yellow and it is half transparent. You can see the screw underneath through it. It seems that Bosch used a ring which they set on the MAP sensor to fill it. the potting does not contain air bubbles and it is not straight but slightly convex.

Hi Rhys,
it looks like this one isn't originally sealed to me.
The bubbles inside, the height - two indicators for this,

One wanted to create a 'looks like originally sealed' look.

Have a look at the rivets, too. There should be a stamp (three digits) on one of the heads showing the year and month of production.
Missing stamp would mean it has been opend before, in my opinion.

Regards
Norbert

That is how a 0 280 100 048 looks like in new. Looks different than yours.

So looking at your picture in comparison, I believe it is no original potting and it is mistuned. I know someone in Switzerland who has such a sensor. Unfortunately customs is an issue for both his and your MAP sensor. Otherwise I would have offered to take a sample reference and adjust yours accordingly.

So if anyone in Germany has a SM MAP sensor 0 280 100 036 that he could borrow for a reference measurment, please let me know. It would really help Rhys.

Auf Deutsch: Hat irgend jemand einen 0 280 100 036 Druckfühler, den ich kurz vermessen könnte, um Rhys in Australien helfen zu können?

Hi Volker + Norbert,

Yes, it would seem that this MAP sensor has been raped (using the term in the correct context now Volker), and re-sealed.

A booby-trap to steal precious hours of diagnostic time that I'll never get back.

But all is starting to make sense now.

It would be nice if another MAP sensor did materialise.

Regards,
Rhys

Hi Rhys,

Chris from Switzerland has Xmas gift for you . He has the requested MAP sensor and will send it to me for reference measurements.

Hi Volker

I like this Chris fella - and a MAP sensor is as good, as a Xmas gift ever gets.

I look foreward to hearing when it arrives..... and it being measured.

Please advise when I need to send funds to someone.

I wish the best over the festive season to all your forum members.

Regards,

Rhys

Hi Rhys,

Chris will send it to me 2nd week of January. Could you - after removing your potting - post a picture of the look inside your MAP sensor? That would give a hint whether yours is complete. After I measure Chris sensor, I will also be able to judge whether I can retune another one like 011 to fulfill the specs.

Best regards,
Volker

Hi Volker,

Not the best photo - but all that my phone can achieve.

Regards,
Rhys

Hi Rhys,
you posted the wrong photo???

Regards
Norbert

Hi Norbert.

The photo is correct......in that it is a close-up of the MAP sensor aperture with the potting/epoxy removed (from directly above).

Regards,
Rhys