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Thread: E32 750iL questions to electronic gurus (long)

  1. #1
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    Default E32 750iL questions to electronic gurus (long)

    Have tried to help a friend here in Japan yesterday.
    The VIN is DC55265, it is a Japanese model E-G50. Built 05/1990.
    Here what he posted on roadfly:

    This afternoon for the first time, I started my car and the engine had this vibration and it sounded low pitched. I thought maybe I was in limp mode so I popped the hood to check. Both sides were running. So I shut the car off.
    Now a little history:
    Just prior to starting I checked the fluids and added about a liter of water to the resovoir tank. (Note: I had recieved a check coolant level in the past couple months and have been topping up) I can not see any coolant leaks and I am afraid it could be a head gasket? The oil level hasn't changed nor is there any usual signs of coolant and oil mixing (ie white sludge under oil cap, frothy oil on dipstick)I couldn't smell any coolant burning nor was there any on the ground. I started it up again and noticed a little bit of white exhaust (I live in Tokyo and the temp is above 0 celcius but still a little cool) After warm up the white exhaust disappeared. I think this is normal. The engine still has the vibration, and after driving around the block and letting the engine warm up the temp gauge reads normal (12 o'clock), with no overheating problems prior.
    In the past month I changed the catalytic converter on the left side, from the exhaust manifold to the muffler with a non OEM part (BMW after market part bought from ArizonaAZ)The catalyizer did not have a spot on the pipe to insert the exhaust temp sensor. I doubt however, this could be the problem as there have been no instances of this vibration until today. The funny thing is that I drove the car this morning and aside from it being cold from the night before it ran normally.
    Does anyone have any ideas on what I should be looking for? I know I have to find the coolant leak, but is that the probable source of the problem?
    -----------------
    I have driven the car and could compare it with my 750iL. There is almost no power, hardly can climb up a small hill, engine revs up very slow.
    Checked with the PEAKE: left side bank (drivers side LHD) says OA = emission (lambda) control.
    It looks to me the engine runs in limp mode, but I have never had my car in limp mode, so I am not sure.
    The temp. sensor on the new cat from USA has not been connected and hangs loose, see pic. The next pic is the other old oroiginal cat on the right (pass side) with the temp sensor connected.

    We have a query for all the experts
    is the exhaust temp sensor within the engine control loop?
    nothing shown in Bentley Repair Manual


    Car occasionally runs well but most often it sounds like its dieseling, vibration does not disappear with higher revs, is worse when cold, better when warm
    intake manifolds look to be tight
    the exhaust smells very rich and fuel consumption is poor
    very little power.

    Also posted question on the German board. One comment was, that maybe the cat(s) are partly blocked and we should remove the exhausts from beg. of the cats and then rev the engine to see if any change.
    That we will do asap.
    But apparently no one knows about the function of this temp sensor and what effect it has when it is not connected.
    Any advise and comment is welcome. Thanks for reading the long posting.
    PS: The leak in the cooling system we found apparently. It has nothing to do with the power problem of the engine, just a leak at a place difficult to find.
    Last edited by shogun; 11-21-2013 at 11:14 PM.

  2. #2
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    have you looked at any spark plugs yet? our cars don't have temp probes just 02 sensors, i would carefully pull plug wires while it's running looking for which holes aint firing (another way without possibly getting zapped is to pull injector wires), i am not up on all of the v12 tricks and tips so i can't be too specific on how to check it out without getting my hands dirty
    all america wants is cold beer warm cat and a place to take a poop with a door on it

  3. #3
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    Default it has, Winfred, I was also surprised to see it

    and there is nothing on the Bentley book about this temperature sensor.
    look at number 28 http://www.realoem.com/bmw/showparts...44&hg=18&fg=05

    Did not pull yet the spark plugs, as it is a pain in the a** on the V12, especially the number 12 plug. Started to get dark in the evening. Will do that next Saturday. Removing all 12 spark plus on a V12 takes more than 2 hours (and ones wishes to have the arms 3 times broken or rubber arms to get to all these places in that packed engine room).
    As you know, I know the V12 M70 very well, and also Mike (Hairywithit) from roadfly was here. He is also not that unexperienced on the V12, as we usually wrench on that car together. But we could not yet solve it.

    Will continue next week. Just need some opinions and ideas what to check next.
    We are now somehow fixed to that temp sensor, because we do not know what effect it has on the Motronics. As you know, there are DME 1 and DME2, and all is somehow supervised by the EML.
    Both throttle valves are synchron in running, so that was checked by us already, as this is often the case that the car goes into limp mode.
    EML light comes on at the beginning and goes off after 2 seconds as it should do. Battery voltage and alternator also o.k., enough charging voltage.
    One DME has now the signal from the one side temp sensor, the other side does not have this info. But does that have so much effect, that the car runs like in limp mode like a 50 HP car? So the one DME now always gets the signal "cat cold" we assume. So the DME will change the fuel air ratio so that the cats reach the required temp of at least 300 degree Celsius.
    Well, lets see, maybe someone has the correct wiring diagrams and knows to which pin this temp sensor sends the signals and what it does with it. The online wiring diagrams do not have it. I already checked that.
    Thanks, Winfred
    Last edited by shogun; 11-21-2013 at 11:05 PM.

  4. #4
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    you don't need to pull all of the plugs, just a few from each bank just to get a idea of how it's doing, fuel filter/filters? plugged cat? nasty burned up cap/rotor?
    all america wants is cold beer warm cat and a place to take a poop with a door on it

  5. #5
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    Thanks, will do so. No misfire at all.
    That is why the assumption of blocked cats is an issue. Will do that checking as suggested next Saturday, as it is too cold here to do the job outside and we can only get into the garage of a friend next Saturday. Till then, any new idea welcome, gents.

  6. #6
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    i've come across a few cars that the fuel pump has gotten real weak and is only mantaining 20 odd psi, if it's running smooth look for common shared systems, had a 95 740il with one plugged cat and a blown pcv plate that was a pisser to figure out, it wouldn't get out of it's own way the computer was trimming the mixture 50% lean on one bank and 50% rich on the other among other weird readings (damn i am getting to hate the later cars, they get pissed off and then over correct and snowball) the early cars are easyer to figure out when things get weird
    all america wants is cold beer warm cat and a place to take a poop with a door on it

  7. #7
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    Default Here is what Real wrote after further tests

    -quote-

    ECT readings

    I was able to (finally!) get to the ECT a little tight in there. I tested it and I had the 5 VDC and 4.9 VDC (from both sides of the connector) and on the sensor itself I got a proper reading (I don't have my Bentley's in front of me right now). I then checked the sensor itself, the coolant temp, was tested with thermometer in resovoir and was 106.6 F and the reading I got, I can not remember at the moment, was right in the middle of the two readings in the Bentley chart, 11 ohms maybe?

    I have recieved corrensondence about a possible CAT blockage as being the problem. As I just replaced the left side and the right is the original, should I try the orginal one (on right side) even though a PEAKE check gave a 0A fault for the left side?(probably because the exhaust temp sensor is not attached) In my opinion the new one should be good, so I'll try the old first. Should I notice the difference in the idle if I just disconnect the CAT from the manifold to the resonator (ie before CAT)? If I do this the O2 sensor will probably not work seeing as the exhaust is not travelling trough the pipe. Will that still cause a problem and an inaccurate idle? If there is an increase in RPM I will completely remove the CAT and clean it out.

    Furthermore, I checked the engine cold and when I first started it (running for about 10 seconds) I tried to rev it up and it hestiated climbed to about 2500 RPM then almost stalled.

    Looking into an electrical issue further I tested the coils with the key in the stop position. As per Bentley's I tested the ohms across terminals 1 and 15 and I got a good reading on both (I'll send the numbers later,(I am at work now), however, when I tested the 15 and 4 terminals and when I put the multimeter leads to the top of the coil point #4 I didn't get any readings, when I placed it deeper inside on the bottom of the pin I recieved a reading of 10.4 and 10.35 Kohms. This didn't seem right to me, any ideas?

    My apologises for the unclear numbers in the readings, however at the time I checked them my Bentley was there and the readings were within range except the coil reading as mentioned above.

    -unquote-

    Any comments on this which I can pass on?

    Thanks to all for reading.

  8. #8
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    Is he getting a good spark at each plug? The old fashioned way is to pull one boot with plug in it and hold it near a good ground (insulate the boot or wear a rubber glove or something), you can pull it first and crank the engine or just do one at a time while the car is running. You should get a nice blue spark. Do it for each plug. If you don't have spark on one side or you have a weak-looking spark on some plugs, it could be one bad (or failing) distributor. Not sure about my 750il, but I have fixed my old muscle cars with this test. Heck, there are two distributors on this car--maybe one is dying. It could also be gummed-up plugs or a bad plug wire set on one side put in by a previous owner.
    The O2 sensor should be working, however. Can you set up (or splice or rig or beat with a hammer) the inputs from both O2 sensors, so that they will read from only one side or the the same exhaust cat? Just to test? Seems like you could trick the computer into working that way if it is just an O2 sensor issue. My in-laws own an engine shop and they say most of the "drivablity" problems that they encounter are from disconnected or bad O2 sensors. I would think that you should get that thing working first, just to eliminate it. A good muffler/exhaust shop could tap in a bung or at least a place for that sensor to sit and read properly. Maybe they could repair the connection to the old 02 sensor. Just throwing out ideas...
    Last edited by Whit; 03-07-2005 at 03:36 PM.
    Whit
    1988 750il (whoops, tricky title--probably not a 1994!)

  9. #9
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    Whit,
    it is not the O2 sensor which is not connected, it is a temperature sensor at the end of the cats. The cat from USA does not have a connector for this. See top the link with the pic to item 28.
    The japanese owners manual says, that if the cat is overheated, there will come a warning signal. Switch engine off and let cool down and then drive to the next available dealer with max 50 kmh. There is danger of fire.
    I still do not know if this temp sensor is connected to the DME and the DME reads cat cold/warm/etc., or if it just gives a signal to the check control as a warning.
    Not sure, if this is only on versions for Japan specification but not for other countries.
    Will report later when Real has done further checks at night.

  10. #10
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    Well, I guess my idea/question still stands:can both temp sensors be rigged to read only one cat? Or can one temp sensors send the signal to both sides? you know? Just to test?
    By the way, what is the actual temp involved? Can you measure each with an infrared/laser temp checker or something else? Is it really hot? If you cannot find a way to check temp, when a cat is blocked and the exhaust manifolds are actually getting hot, check them at night (along with the head exhaust pipe) they might glow red-hot. I had a blocked cat on a Jeep once and it glowed red at night on the exhaust manifold. New cat & new muffler, no red glow. Not a BMW, just my experience with a different vehicle.
    What about the distributors and the spark at each plug wire?
    Whit
    1988 750il (whoops, tricky title--probably not a 1994!)

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