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  1. #1
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    HELP!!!!: faulty thermostat(s) and running rich!

    Hello guys new to the list just bought my car and am trying to get it on the road. I need some help getting the thermostat to work correctly in the air ventalation system as the onboard computer reads that it is 3 degrees out when it is really 45 (degrees F). I know that there is a sensor built into the dash that tells the onboard computer what temperature it is and is used for the automatic climate controll, but is this the same as what is being displayed on the onboard computer? Also I don't know how to test it or bypass it or even get to it for that matter. My second problem, that I think may or may not be intereconnected, is that the car is running really rich and sometimes will not start when it is warm after you shut it off for aobut 5 minutes. I am thinking that maybe the problems are interconnected but someone told me that the problems shouldn't be because the temperature sensor and the engine temperature sensor are run by different computers? Maybe it could be a diffrent sensor then? I have had problems passing emissions as well and I had the exhaust re-worked recently so I know that it isn't the catalatic converter.

    Thanks for all of the help!
    Jeff


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    Re: HELP!!!!: faulty thermostat(s) and running rich!

    The outside or ambient temp. sensor for the OBC is in the front air dam below the bumper on the driver side. The engine temp. sensor for the ECU is mounted on the passenger side of the A-housing. Next to it in the center is the temperature time switch which controls the on-off time of the cold start valve (among other things and depending on the model car we're talking about). The sending unit next to that, or on the driver side if you will, is for the temperature gauge in your instrument cluster. Suspect the temp. time switch for your warm start problems, or possibly the temp sensor for the ECU.

    As for HVAC, what are your symptoms? There's tons of info in the archives.

  3. #3
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    Re: HELP!!!!: faulty thermostat(s) and running rich!

    i just bought the car so i am going on what the previous owner said and what i am seeing. it is an 85 bmw 735i. my problems are that the car is running rich, and the temperature sensor for the display on the dash, the digital one, not the radiator temperature is displaying many degrees below what it should be. With the HVAC my problems are that the switches arn't staying in anymore, like when i first bought the car the switches would stay in and it all worked fine, but now the switches don't stay in. i might have blown a fuseor relay but i don't know how to check relays. also if the on board computer reads the interior temperaturefor the hvac that could complicate the problem, because then the automatic climate controll is off significantly. in my owners manual they say that the button looking type thing right below the other retangular button on the drivers side dash is for the interior temperature, so what does the computer output, the outside temperatur or the inside temperature?perhaps both of them are faulty, but still interconnected?

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    Re: HELP!!!!: faulty thermostat(s) and running rich!

    What about the volume control for the HVAC? Do you hve fan for all speeds? You might get the push buttons to work by trying different buttons quickly. It sounds like the spring in the push button control is bad. Also could be a vacuum leak causing the problems. the temp for the OBC is from the temp sensor Bob was talking about. it has no bearing on the HVAC system. it only measures outside temps.
    Searcxh the archives for HVAC or vacuum for tips to fix these issues. There is one fuse up above the glove box, but if you have any power to the HVAC system, it should be good. I'll send you a vacuum diagram to help trouble shoot the vacuum system.

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    Re: HELP!!!!: faulty thermostat(s) and running rich!

    another way to try and get the push button to respond is to gently push two in simultaneously. Once one begins to grab, let up on the other and go with the one that is grabbing. They work on vacuum not relays.


    The way to manipulate the computer showing temp/time/mph depending on the year is by a little pin hole on the lower right of the computer. By depressing it with a fine point pen 3 or 5 times, (I forget) you will clear the computer and can set time and adjust from kilometers to miles. I am wondering if you are reading celcius vs. F

    hope this helps you out. and easy on yourself. You'll be on this board quite a bit. The car is a great car, you just need to get to know it a bit. Indeed take time to search through archives, you'll see the current issue with your car is common.

    enjoy
    Marguerite

  6. #6
    CV Stancampiano['84 733i]
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    Re: HELP!!!!: faulty thermostat(s) and running rich!

    The outside air temp sensor can be broken and not influence anything else. Mine said -40F for a few years before I got around to fixing it. There is info on how to deal with the pushbutton assembly. Be careful taking it apart; I've heard the pieces tend to fly apart!

  7. #7
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    Re: HELP!!!!: faulty thermostat(s) and running rich!

    okay guys, i got the push buttons to hold, and the defroster works, and the up/down heating, and the air volume works, and the heat selector works, but i still have no a/c and no automatic heat. any suggestions? I also was looking at the temperature sensor for the computer in the air dam, how do you get that thing out?! I just took the car for a drive around and them stopped at the mall a few blocks from here, and about 7 mintues later when i came out it refused to start, i got out and the exhaust smell was strong, like it is rich. now earlier before i started it when i was tinkering around with things, i had the key on and the big black round thing that is attached to the air induction tube, (i think that it is the cold start injector?) was running and therefore pumping fuel into the thing, so if it is opened up all of the time what could i check to fix it? I will seach the board, but help here would be nice too, thanks.

    Jeff
    your right it is a great car, i do need to learn more about it, and fix things on it though.

  8. #8
    Maury 86' 735i
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    Re: HELP!!!!: faulty thermostat(s) and running rich!

    If I understand your description, the big black round thing that runs with the key on is the ICV (idle control valve). Does it hum or vibrate with the key on? If so, thats ok. The cold start valve is a small injector under the intake. If its gone bad or leaking, you could be getting extra fuel causing a rich condition. A symptom of a bad ICV is humping (up and down) idle. Don't worry about the temp sensor in the air dam now. Get the thing running properly first. I'm sure you can roll down the window to tell how cold it is out side LOL:). <br>Maury

  9. #9
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    Re: HELP!!: Running Rich: (doesn't start when hot)

    yeah i have forgot about it. thanks for telling me if that is the cold start injector or not, it definatly isn't. it hums well. Hmm what are some other things that could cause it to not start when it is warm, i got stuck today not having it start when it is warm.previous owner told me also that it wasn't passing emissions. i know that it is running rich because it needs extra fuel to run when it is cold, and i can smell it running rich in the exhaust. MY best guess is that the cold start injector is stuck on, isn't it only supposed to run for a little while, like 1 minute? is there a relay for it if so does anyone have the relay #, how bout this, anyone selling a book for a 85 bmw 735i?!! LOL :) hmm i know that this problem has turned up before. Is there a temperature sensor for the engine at fault? I ahve forgot about the temp sensor for the OBC, and I figured out what is wrong with the HVAC. I just need to figure out what is with this running rich constantly thing! I bet the extra fuel adds a nice bit of power though :)

  10. #10
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    New Main Relay / 02 sensor wiring connection...

    I had a hard-start problem on my 635 about 1 1/2 year ago. Changed the Main relay (5 pin connector adjacent to your fuse box - pull off rubber boot to access) and never had a hard start problem hot or cold again. $15-$20 from the dealer. [Bob Duckworth's posts on the E24 board]

    If you're running rich, have a look at your 02 wiring and connections (locate the 02 sensor off the downpipe from your manifold and follow wire up to its connector) If this isn't connected properly, engine management might not be able/permitted to turn off the "choke". Most obvious indicator that you're running rich - black sooty tailpipe and black smoke out the back end (indicator that the actual 02 sensor is shot and needs replacing] as well as black spark plugs or fuel soaked (on top of lousy gas mileage). Check all your connections, make sure they are fairly clean (a bit of sandpaper and WD40 or something of that nature will do). Next thing I would do is take off your air filter housing, clean with soap and water and dry, put in a new air filter, and spray a can of carb cleaner (with rags to clean) up your throttle body, throw in a set of Bosch (gap pre-set [BMW dealer will have them pre-gapped - not much $$ more]) copper plugs.
    As far as the HVAC is concerned, you've got your defrost working (the almighty bypass) which will give you heat, including the up/down which will also give you heat. Auto and Air C - depends on just how important these two functions are to you. You're system's condition sounds to be similar to mine. It doesn't bother me much - I know how to get heat when needed. Tiny springs in the buttons are shot - have to play with them to get one to stick down from time-to-time, etc. Sometimes its like a lottery in my car finding just which of the buttons will work (ha,ha) - makes my daily drive to work that more interesting. Great car, safe and reliable.
    First thing I would do is change your Main Relay, see if that fixes your hard start problem.
    Intermittent Hard Start (hot or cold) == Main Relay (most of the time).
    Good luck.

    Ralph/Toronto 735i -392,000 KM.

    P.S. Before I joined this board, I knew nothing about these cars...

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