Joep
Member
Sharing experiences with the E9 is one of the goals of this forum. As such, I wanted to share with you one, I had with my 75 3.0 Csi. The problem I was having with my D-jetronic csi just recently, was that the engine would stall after warming up (10 min), almost not starting unless you waited a couple of minutes, firing only on a couple of cylinders, running very very rough and requiring a lot of action on the accelerometer. Never had my bimmer leave me stranded due to engine troubles so what was wrong?
Examining the spark plugs showed that they were black/carbon fouled denoting either bad ignition but, more likely, too much fuel. They did have a spark, so my basic analysis was that it was a fuel metering problem.
It took me a while but I finally managed to solve the problem, which turned out to be two fold and indeed fuel related.
The first and main one, was the fact that the coolant temperature sensor (the one used as input for the D-jetronic ECU and located below the inlet manifold) was faulty. It turned out that the resistance went from roughly 2500 Ohm down to 200 Ohms with increasing temperature and around 70 degr C it went to infinity all of a sudden, thus not good. As such, I replaced it with an old one which I happened to have and which did follow the right path to lower resistance with increasing temperature after testing this with a pan of water in my kitchen. This to my understanding was the main cause of the initial problem.
However, it seemed that this fault had resulted in another component going bad as the engine would still run very badly after replacing the coolant temperature sensor. This was my Manifold Pressure Sensor (MPS) located above the main brake servo cylinder in the engine compartment. It turned out that this was leaking thus providing the ECU with the signal that the engine was at high revs and requiring lots of fuel even when running at idle. So the engine was basically being drowned in fuel and running way too rich.
I happened to have an old MPS lying around which had cracks in the diaphragm which I discovered after dissasembling it. It did however, provide me with a good tool,to check whether the MPS I currently had in the car was ok. Main indication that the MPS is not good, is the fact that it will not hold vacuum, which was the case here I noticed. Easy check is to suck on the rubber tube connected to the inlet manifold and feel if it keeps the vacuum or not. If not, it is leaking, most probably a cracked diaphragm.
Anyway, back to the problem, after connecting the disassembked MPS to the connector, I depressed the LVDT in the MPS which is normally driven by the decrease of pressure in the inlet manifold. This resulted in the fact that my engine would run far better than before and confiming my anaysis that the MPS was also faulty. So Iwent out to look for an replacement MPS.
If anyone is having a problem with their MPS, I can now recommend the reman service provided by Koller&Schwemmer in Germany, authorised by Bosch for this work.
(http://www.koller.de/oldnew.jetronic,103_344,81157660365041840287478772660118.html)
I sent in my old MPS and they returned it after 2 weeks in perfect condition, the engine now runs like a charm, far better than previously. It is not cheap (aro 450€), but then again this is a "as good as new" part.
Anyway, recapping: if anyone wanted to be further enlightened in D-Jetronics in general and the associated MPS in particular, a very good write up can also be found here:
http://members.rennlist.com/pbanders/manifold_pressure_sensor.htm#MPS Diagnostics
regards,
Joep
Examining the spark plugs showed that they were black/carbon fouled denoting either bad ignition but, more likely, too much fuel. They did have a spark, so my basic analysis was that it was a fuel metering problem.
It took me a while but I finally managed to solve the problem, which turned out to be two fold and indeed fuel related.
The first and main one, was the fact that the coolant temperature sensor (the one used as input for the D-jetronic ECU and located below the inlet manifold) was faulty. It turned out that the resistance went from roughly 2500 Ohm down to 200 Ohms with increasing temperature and around 70 degr C it went to infinity all of a sudden, thus not good. As such, I replaced it with an old one which I happened to have and which did follow the right path to lower resistance with increasing temperature after testing this with a pan of water in my kitchen. This to my understanding was the main cause of the initial problem.
However, it seemed that this fault had resulted in another component going bad as the engine would still run very badly after replacing the coolant temperature sensor. This was my Manifold Pressure Sensor (MPS) located above the main brake servo cylinder in the engine compartment. It turned out that this was leaking thus providing the ECU with the signal that the engine was at high revs and requiring lots of fuel even when running at idle. So the engine was basically being drowned in fuel and running way too rich.
I happened to have an old MPS lying around which had cracks in the diaphragm which I discovered after dissasembling it. It did however, provide me with a good tool,to check whether the MPS I currently had in the car was ok. Main indication that the MPS is not good, is the fact that it will not hold vacuum, which was the case here I noticed. Easy check is to suck on the rubber tube connected to the inlet manifold and feel if it keeps the vacuum or not. If not, it is leaking, most probably a cracked diaphragm.
Anyway, back to the problem, after connecting the disassembked MPS to the connector, I depressed the LVDT in the MPS which is normally driven by the decrease of pressure in the inlet manifold. This resulted in the fact that my engine would run far better than before and confiming my anaysis that the MPS was also faulty. So Iwent out to look for an replacement MPS.
If anyone is having a problem with their MPS, I can now recommend the reman service provided by Koller&Schwemmer in Germany, authorised by Bosch for this work.
(http://www.koller.de/oldnew.jetronic,103_344,81157660365041840287478772660118.html)
I sent in my old MPS and they returned it after 2 weeks in perfect condition, the engine now runs like a charm, far better than previously. It is not cheap (aro 450€), but then again this is a "as good as new" part.
Anyway, recapping: if anyone wanted to be further enlightened in D-Jetronics in general and the associated MPS in particular, a very good write up can also be found here:
http://members.rennlist.com/pbanders/manifold_pressure_sensor.htm#MPS Diagnostics
regards,
Joep
