Page 1 of 2 12 LastLast
Results 1 to 25 of 32

Thread: Ever wonder what all those sensors actually do?

  1. #1
    Join Date
    Jun 2009
    Location
    Vermont
    Posts
    30,864
    My Cars
    97 328i Vert, 98 M3 Vert

    Ever wonder what all those sensors actually do?

    We see it every day here. Someones engine isn't running smooth and fast or it won't start. Then there is the gauranteed response to "swap your Crank Sensor" or "It was the ICV on my car". I've been working on cars since the 70's and all this computer control and sensor stuff has been a bit of a mystery to me so I did some research. A lot of it I already knew but some of it was a learning experience.

    Before you throw money at a problem you should always do as much diagnostics as possible. Diagnostics is usually free or very cheap. The one thing this thread is missing is info on testing the different sensors. That info is available if you search. This thread is already very very long. I won't get into a ton of testing procedures.

    NOTE: This is intended to be a very basic description of the most important sensors, what they do and some basic symptoms. If I'm way off base on any of this, I welcome anyone to correct me. Hopefully this will help to point someone in the right direction when they have a problem.

    Here it is in a nutshell, details are below:

    Crank Postion Sensor (CPS) - controls when the plugs fire
    Cam Postion Sensor (CMP) - controls when fuel is injected. fuel injection
    Note: These two are tied together so it all happens at the right time

    MAF - Measures the volume of air entering the intake. Controls air/fuel mix
    ICV - Not a sensor but controls idle by opening and closing to allow controlled amounts of air to bypass the throttle plate. It acts like a choke that can be adjusted by the DME.
    Air Intake Temp Sensor (IAT) - Measures incoming air temp. Cold air is more dense, dense air needs more fuel
    O2 Sensor - Precat - Measures exhaust gases for proper combustion. Controls air fuel mix during Closed Loop.
    O2 Sensor - Postcat - Measures how well the cats are working. Doen't control anything but can indicate problems.
    Coolant Temp Sensor - Measures temp of the engine. DME uses it to switch to Closed Loop at proper operating temp.
    Throttle Position Sensor (TPS) - Measures changes in the throttle position. Controls RPM's.

    Open Loop vs Closed Loop - 2 common terms used a lot here. Open Loop usually only happens when the car is NOT warmed up to normal operating temp. Until all the sensor readings are within their normal operating range the DME pretty much ignores the sensor readings and uses some default settings for stuff like fuel injection and air fuel ratio. Once the sensors are all reading in their normal operating range it switches to Closed Loop. Generally in Open Loop the engine is running rich. This allows it to operate smoothly and allows the engine to warm up a bit faster. In Closed Loop the DME uses the sensor readings to control spark, fuel, air, timing etc. Closed Loop is a very fine tuned computer controled environment compared to Open Loop.

    Vacuum Leaks - Its not a sensor but it is a vey common problem and it absolutely contributes to a host of issues. We tell people all the time to check for vacuum leaks but few people know all the places to look or how to properly test for leaks. The best test is a Smoke Test. This uses expensive equipment to send smoke into the air intake under slight pressure. If any leaks are there the smoke will exit out the leak. The smoke test is great but you have to take it to shop to get it done. The DIY method takes a bit more time.

    Start with a physical inspection. The boot between the MAF and throttle body is clamped in place. Make sure the clamps are tight. Look for cracks on the intake boot. They will most likely show up on the outside bend first. If you have a ribbed boot then look at the ribs. Cracks will be pretty visible on the top of these ribs. The best inpection of the boot is to remove it. When its installed you can only see half of it. Look at where the tube from the ICV attaches to the boot. That tube and that connection are well know for cracks and splits. Look at any tubing that attaches to the fuel rail. On M50 engines there is a small diameter tube that runs from the fuel pressure regulator to the underside of the intake maninfold. There is also a small tube at the front of the engine. These get dry and brittle over time. Check where the second tube for the ICV attaches to the back/underside of the intake manifold. Its held into the manifold with a plastic clip/connector. This can break allowing the tube to slip out. it should be located in the center of the intake directly opposite the throttle body. On M50 intake manifolds its very visible through the slots in the intake tubes. I use a screw driver to push it back in place if it comes loose. On M52 engines there are more small tubes that feed to the vacuum storage, vacuum canister, muffler flap etc. I've never worked on an M52 so Im not 100% familiar with all of them.If any tubes are cracked or broken then replace them.

    To test for vacuum leaks without a smoke test get a can of carb cleaner. Start at the MAF and give each connection and each tube etc a quick shot of carb cleaner then wait a few seconds and listen for any RPM change. If you have a leak it will most likely surge a bit then settle back. work your way up the intake to the manifold. Move up and down the manifold so you can test the gaskets. Finally spray a few good shots on any other tubes you find including the brake booster tube that connects to the intake manifold.

    Now for all those sensors:

    Crank Position Sensor (CPS) - The crank sensor is located either at the crank pulley on the front of the engine or further back in the engine block. Its main purpose is to measure the engines rpm's and the position of the pistons. When the pistons are in the correct position, the CPS tells the DME to fire the spark. The DME uses computer precision to fire the spark.

    The CPS can get dirty or contaminated or it can fail altogether. Since the CPS is telling the DME when to fire the spark its easy to see that a faulty CPS can cause rough idle, misfire, loss of power, backfire and if it fails completely then the DME doesn't know what position the piston is in and the car will crank but it won't start.

    Cam Position Sensor - (CMP) - The cam sensor (I'll use CMP) is mounted at the cam gear or further back in the head. It measures the position of the cam and is used to control when fuel is injected. Each piston comes to the top of the cylinder twice in each rotation of the engine. During the ignition stroke all of the valves are closed and the air is compressed. Fuel is injected and the plug fires. The ignition stroke only happens every other stroke so the cam sensor is used to tell the DME which stroke the engine is in and when its time to open the fuel injectors and fire the spark. Since it measures the position of the cams its easy to see that a faulty cam sensor can cause extended cranking to start, rough idle, idle bounce, back fire, loss of power, misfires.

    The CMP works together with the CPS to tell the DME when the piston is in the correct postion and the correct stroke to inject fuel and spark so essentially they both control spark and fuel injection.

    MAF - The MAF is located between the air filter and the throttle body. Its usually a large box with a cable going to it. The MAF uses a delicate sensor inside to measure the volume of air passing through it. This info is sent to the DME and the DME adjusts the amount of fuel injected into the cylinder for the correct fuel/air ratio. Since the MAF is on the vacuum side of the engine it's easy to see that all vacuum hoses and connections need to be tight for it to work propely. If air enters through a leak in a hose or connection then its entering after the MAF and its not being measured. The DME only measures what passes through the MAF. If 10% of the air is getting into the engine after the MAF then you'll get 10% less fuel and the engine will run lean.

    A faulty MAF can cause rough idle, poor performance, poor gas mileage, idle bounce.

    The MAF is easy to test. If your engine is idling/running rough, unplug the electrical connector for the MAF. This will cause the DME to use default values like it does in Open Loop. If the engine smooths out after a second or two then the MAF has a problem. If it stumbles and tries to stall then the MAF is probably ok. That sensor inside can get coated with dirt and oil (especially if you use a filter that requires oil). Remove the MAF and use MAF cleaner only. It cleans instantly, evaporates very quickly and doesn't leave a film. soaking it in rubbing alcohol works but takes longer. Reinstall the MAF and pug it in. If the idle doesn't improve then clean it again and reinstall. If cleaning it twice doesn't improve things then its probably time to replace the MAF.

    Idle Air Control Valve (IACV or ICV) - The ICV opens and closes while the car is at idle and adjusts the idle speed. It consists of a motor and a vane/door that opens and closes a small window. A tube runs from the intake elbow to the ICV and another from the ICV to the intake manifold. Note that all air used by the ICV is metered air so air fuel mix is maintained. The ICV allows air to bypass the throttle body. It acts just like an auto choke in older cars. Air comes into it from the intake elbow and passes through a small window then out to the intake manifold. That window has a metal vane that is moved by the motor to open and close the window just enough to maintain a steady idle.

    The vane and whole ICV assembley can get dirty which causes the vane to stick. Removing it is a bit of a pain since its located under the intake manifold. Spray it with carb cleaner until its completely clean. Inspect the little vane for scratches that could cause it to malfunction. Once its clean you should be able to spin the body back and forth and see the vane move freely. If its cleaned properly it will take almost no effort to get the vane to move.
    A dirty/faulty ICV will cause rough idle, mild to sever idle bounce and if it gets stuck completely open it can cause the car to stall, misfire, backfire at all RPM's

    Intake Air Temp Sensor (IAT) - Very simple sensor. Its installed in the intake manifold and measures the temp of the air passing through the manifold. Cold air is dense, warm air is less dense. Denser air has more air molecules so it needs more fuel for the proper fuel air ratio.
    Failure of this will tell the DME to add more or less fuel (rich/lean) depending on how it failed. Loss of power, poor fuel consumption, poor idle are all possible symptoms.

    O2 Sensor - Pre cat - 92-95 M50's and M42's have only one O2 sensor and its located just before the cats. 96-98 M52's have two precat sensors and two post cat sensors, 96-98 318's and 323's have one precat and one post cat sensor.

    O2 sensors are used to measure all the exhaust gases. They are made up of a sensor and a heater. They need to be at the correct operating temp to work properly. This operating temp has very little to do with the temp of the cats. The precat sensor heats up and tells the DME its ready to switch to Closed Loop. Until it heats up the engine will operate in Open Loop even if all the other sensors say its ok to switch to Closed Loop. This is why a bad precat sensor causes such poor gas mileage and poor overal preformance. The internal sensor can fail or the heater can fail. In either case the entire sensor needs to be replaced. On M52's there is one precat sensor for cylinders 1-3 (bank 1) and one for 4-6 (bank 2). All other e36's have one precat sensor. Under normal operation it sends the DME specific voltage or resistance readings. These have to be within a certain range. The DME will adjust fuel air mix acording to the readings to get them to their optimal range. If the readings are at the top or bottom of the range for too long and the adjustments the DME makes have no effect then you get a Check Engine Light and a Error Code.

    O2 Sensor _ Post Cat - As disscussed above..92-95 cars don't have a post cat sensor. 96-98 cars will have one post cat sensor for each cat. The post cat sensors measure the gases comming out of the cat. Nothing changes because of there readings. It is only a sensor. if the readings are in the wrong range for too long you will get a Check Engine light and an Error Code. This doesn't mean the cats are bad or the sensor is bad. It simply means the readings were out of acceptable range for too long. If the car is running too rich or too lean because of another issue its very possible to get a post cat error code. Chances are if you get a post cat code you'll have more than one code indicating multiple problems. Just like the pre cat sensors, the post cat sensors need to heat up. Faulty Post Cat sensors generally won't affect performance. They only measure the output of the cats.

    Coolant Temp Sensor - This is located in the head and sends a signal to the DME that the engine is up to correct operating temp so it can switch from Open Loop to Closed Loop. Failure of this sensor can cause the car to remain in Open Loop.

    Throttle Position Sensor (TPS) - this is located on the throttle body. On cars with ASC there will be one located on the Secondary Throttle Body in addition to the Primary Throttle Body. These are a simple vairable resistor. The DME compares the voltage going in to the voltage comming out so it knows exactly what position the throttle is in. The DME measures changes in this reading to make the RPM's drop or increase. There are specs available for the correct Ohm readings for these. A faulty TPS will cause high/low engine rev, poor performance and generally anything you might associate with things like a loose or faulty throttle cable.

    Here is the test procedure for the TPS

    Harness connector disconnected, ignition on:
    Terminals - 3 and ground in harness connector = 5 VDC
    Harness connector disconnected, ignition off:
    Terminals - 1 and 3 at sensor terminals = 4k ohms
    Throttle plate rotated from idle to full throttle position:
    Terminals - 1 and 2 at sensor terminals = Variable from1-4k ohms without interruption
    Last edited by flyfishvt; 11-28-2011 at 08:56 AM.

  2. #2
    Join Date
    Nov 2009
    Location
    Madison, WI
    Posts
    732
    My Cars
    '98 M3 'Vert '07 328xit
    On the subject of open loop vs. closed-loop; I would assume that something like a CPS is not subject to the logic change due to operating conditions. The car needs to rely on that sensor regardless of whether it is warmed up or not.
    So, if someone were experiencing the apparent failure mode of a bad CPS, yet other respected people were arguing a failed ECM, would the fact that the failures occur both when the engine/systems are arguably cold and warm have any impact on estimating which item is actually bad? As I write this, I'm thinking no...
    I'm beginning to wonder if my recently replaced CPS isn't my problem...EJT
    Last edited by shogun; 01-14-2016 at 10:01 AM.

  3. #3
    Join Date
    Jun 2009
    Location
    Vermont
    Posts
    30,864
    My Cars
    97 328i Vert, 98 M3 Vert
    Open Loop vs Closed Loop has more to do with air/fuel mix than anything and that cant occur unless the engine is running. A dead Crank Sensor will absolutely prevent the car from starting. the problem comes in when you try to diagnose it any further. The CPS and CMP are 100% tied together like twins. Just like the ASC system uses the ABS system to do part of its job and the fact they both use the wheel speed sensors. its hard to separate one from the other in a lot of cases.

    This was meant as a VERY basic explanation of what these things do. Its not the final word on any of it by any means.

    There are ways to test the CPS and CMP and there are ways to tell if your DME is at fault. That's beyond the scope of what I was trying to accomplish.

    I'll tell you three things I got out of doing research for this. Crank Sensor has more to do with spark, Cam Sensor has more to do with Fuel Injection and One symptom of a bad Cam Sensor that doesn't seem to show up anywhere else is "Long Crank Times" before it starts.

    There are plenty of very smart people on this forum. And each one has had a different set of experiences with their cars. We aren't sitting in your drivers seat, we aren't looking in at the engine from your radiator. We can't hear what you hear of feel the vibrations you feel.

    We can only go by the info we are given. to be honest...sometimes that info comes out in dribs and drabs..."oh yeah...I forgot to mention". Sometimes it doesn't.

    We can only use the info we are given and try to help. I'll say that DME issues display some pretty specific symptoms. If you're being told its the DME then its worth at least considering. If, in your gut, you think its something else then by all means try something else. We love to hear new solutions to old symptoms.

    In the end we are all just trying to help each other solve problems and save some $$$$.
    Last edited by flyfishvt; 07-31-2011 at 04:38 PM. Reason: Automerged Doublepost

  4. #4
    Join Date
    Aug 2011
    Location
    Richmond, VA. USA
    Posts
    43
    My Cars
    2000 323i E46 Sedan
    For what its worth I WOULD like to know how to test the sensors themselves.. I almost replaced a MAF $$$, but after cleaning this and that it didn't shut my car off like it was. Had I been able to ohm or volt drop test or something the sensor I could have eliminated it from the start...
    Last edited by shogun; 01-14-2016 at 10:25 AM.

  5. #5
    Join Date
    Jun 2009
    Location
    Vermont
    Posts
    30,864
    My Cars
    97 328i Vert, 98 M3 Vert
    sorry but it will have to wait for someone else or until I get some spare time to research it.

    I can tell you that in the course of the research I did for this thread I found many sites that had full descriptions of each sensor, what it did and how to test it. The testing procedure would have made this thread at least three times longer than it already is.

    I only intended this to be a very basic quick reference. Not a copy of the Bentley manual. So I left the testing stuff off. Plus...before I do anything like this for testing I will have to take some time and try out the test procedures myself.

    Someday...

  6. #6
    Join Date
    Jun 2009
    Location
    Vermont
    Posts
    30,864
    My Cars
    97 328i Vert, 98 M3 Vert
    Just thought I would update this a bit. Since there were requests for testing procedures of these sensors I add the one for the TPS. I will add more as I find them.

  7. #7
    Join Date
    Sep 2011
    Location
    Silly Wisconsin
    Posts
    148
    My Cars
    88iX, 97 328is, 96 328is
    Quote Originally Posted by flyfishvt View Post
    thanks...I guess my next project should be a sister thread on how to test all those sensors.

    Someday.....when I'm bored
    Testing a sensor is usually pretty straight forward; ohm it out, or grab a scope and scope it. The first one is easier and much cheaper for the average DIY'r, as a multimeter can be had for 10 bucks at menards
    I have an E36. Like a baus

  8. #8
    Join Date
    Jun 2009
    Location
    Vermont
    Posts
    30,864
    My Cars
    97 328i Vert, 98 M3 Vert
    Not all sensors can be tested with a meter. "hall sensors" generate an impulse usually as a magnet passes by it or if they see a mark on something like the crank pulley. These need an osciliscope to test them properly. Examples of "hall sensors" would be the crank sensor, cam sensor, wheel speed sensor, and a few others. Most of these can be tested for continuity by an ohm meter but you don't get a true picture of whether they are working correctly or not with just an ohm meter.

  9. #9
    Join Date
    May 2009
    Location
    Belgium
    Posts
    2,609
    My Cars
    '97 328i
    I have a question about the IAT (intake air temperature) sensor. Why is this there? I thought the advantage of a MAF like the one in our cars (I'm assuming it is of the hot filament type) was that it does not simply measure air velocity like a vane-type sensor, but the cooling capacity of the incoming air, which automatically takes air density into account and would therefore eliminate the need for an IAT. I'm not a mechanic, I'm just piecing together the information that I have gathered from reading tech articles on the internet for a few years, so educate me if I'm missing something.
    Last edited by shogun; 01-14-2016 at 10:07 AM.

  10. #10
    Join Date
    Jun 2009
    Location
    Vermont
    Posts
    30,864
    My Cars
    97 328i Vert, 98 M3 Vert
    Quote Originally Posted by xlDooM View Post
    I have a question about the IAT (intake air temperature) sensor.

    Why is this there? I thought the advantage of a MAF like the one in our cars (I'm assuming it is of the hot filament type) was that it does not simply measure air velocity like a vane-type sensor, but the cooling capacity of the incoming air, which automatically takes air density into account and would therefore eliminate the need for an IAT. I'm not a mechanic, I'm just piecing together the information that I have gathered from reading tech articles on the internet for a few years, so educate me if I'm missing something.
    The MAF in our cars does not measure temp. It only measures velocity which is converted to volume. The temp sensor is needed to adjust that for density. If the MAF was capable of measuring temp like you said then there would be no need for the IAT.

  11. #11
    Join Date
    Jan 2009
    Location
    Long Beach, CA
    Posts
    265
    My Cars
    1995 BMW 318is
    Quote Originally Posted by flyfishvt View Post
    The MAF in our cars does not measure temp. It only measures velocity which is converted to volume. The temp sensor is needed to adjust that for density. If the MAF was capable of measuring temp like you said then there would be no need for the IAT.
    As an interesting note for the M42 that you could add to the main sensor thread, I was looking for the intake air temperature sensor on mine the other day and couldn't find it, then I read in the Bentley that the M42 engine has the IAT integrated into the air flow sensor, so there is no separate IAT. The M42 also has a volume air flow sensor and not a mass air flow sensor like later cars, which measures, not surprisingly, volume and not mass.
    Last edited by jereisluke; 01-10-2012 at 11:36 PM.

  12. #12
    Join Date
    May 2009
    Location
    Belgium
    Posts
    2,609
    My Cars
    '97 328i
    Quote Originally Posted by flyfishvt View Post
    The MAF in our cars does not measure temp. It only measures velocity which is converted to volume. The temp sensor is needed to adjust that for density. If the MAF was capable of measuring temp like you said then there would be no need for the IAT.
    I thought a MAF (mass airflow) sensor was called like that because it responds to the mass of air passing a hot filament, by measuring the cooling capacity of the passing air. This cooling capacity is determined by the mass of the air, and this what you need to know for the fuel mixture. So why have an IAT at all? You don't need to know the temperature if you already have the mass.

    I believe older cars had something called AFM, air flow meter. They only measured air volume, and therefore needed to know the temperature from the IAT to calculate air mass.

  13. #13
    Join Date
    Jan 2009
    Location
    Long Beach, CA
    Posts
    265
    My Cars
    1995 BMW 318is
    Quote Originally Posted by xlDooM View Post
    I thought a MAF (mass airflow) sensor was called like that because it responds to the mass of air passing a hot filament, by measuring the cooling capacity of the passing air. This cooling capacity is determined by the mass of the air, and this what you need to know for the fuel mixture. So why have an IAT at all? You don't need to know the temperature if you already have the mass.

    I believe older cars had something called AFM, air flow meter. They only measured air volume, and therefore needed to know the temperature from the IAT to calculate air mass.
    Why would you not need the air temp if you know the mass? It's obviously not getting a temp reading from the MAF sensor, or it wouldn't have the separate IAT sensor.

    I just looked it up on Wikipedia, here's what it says:

    A hot wire mass airflow sensor determines the mass of air flowing into the engine’s air intake system. This is achieved by heating a wire with an electric current that is suspended in the engine’s air stream, like a toaster wire. The wire's electrical resistance increases as the wire’s temperature increases, which limits electrical current flowing through the circuit. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit. As more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The amount of current required to maintain the wire’s temperature is directly proportional to the mass of air flowing past the wire. The integrated electronic circuit converts the measurement of current into a voltage signal which is sent to the ECU.
    If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow. Unlike the vane meter's paddle sensing element, the hot wire responds directly to air density. This sensor's capabilities are well suited to support the gasoline combustion process which fundamentally responds to air mass, not air volume.


    http://en.wikipedia.org/wiki/Mass_fl...nsor_.28MAF.29

    It may be possible to get a temp reading from the MAF sensor, but it would be my guess that it's not too accurate since it's suited to reading air mass instead. So there is a separate IAT sensor installed. And yes older cars measured air volume, not air mass (see my last post). So flyfish's main posting is a little off when it talks about the MAF sensors reading air volume. According to the Bentley, only the M42 engine used a volume air flow sensor, the M44, M50, M52, & M-engines all used mass air flow sensors (a hot wire sensor for the 1992 M50 and then a hot film sensor for all the later engines).
    Last edited by jereisluke; 01-10-2012 at 11:54 PM.

  14. #14
    Join Date
    May 2009
    Location
    Belgium
    Posts
    2,609
    My Cars
    '97 328i
    Quote Originally Posted by jereisluke View Post
    Why would you not need the air temp if you know the mass?
    In order to know how much fuel to inject in the combustion chamber, you must know how many oxygen molecules are in there. You know this from the air mass directly. There is no need to also know the temperature as far as I can tell with my basic understanding of chemistry.

    I love this kind of theoretical questions

  15. #15
    Join Date
    Nov 2011
    Location
    NW mississippi
    Posts
    131
    My Cars
    '99 328i cabrio?
    i wonder if the temp has a formula that coincides with the MAS due to cold air being more dense??

    E

  16. #16
    Join Date
    Feb 2008
    Location
    Bay Area, CA
    Posts
    262
    My Cars
    1999 M3, 1993 RX-7 R1, 2006 CBR600RR
    So my car pings from idle to almost 3k and hesitates from about 3.5k to 4.5k Only seems to happen under high throttle positions and definitely is worse in higher gears when the car is revving slower. Do you think I need a cam or crank sensor? I have recently changed: coolant, air intake, knock and o2 sensors along with fuel injectors. Also cleaned maf and tested a known good one in my car. It was a lot worse with shark injector and intake. Thanks
    '99 Cosmos M3 - all US options w/ M3 GT LTWs, CD43, lots of Euro options, DICE, BSW Speakers

  17. #17
    Join Date
    Jun 2009
    Location
    Vermont
    Posts
    30,864
    My Cars
    97 328i Vert, 98 M3 Vert
    I would say cam sensor but if its that bad you should have a code. It could be vanos or cheap gas. Are you running 91 octane? Most of those DME programs require 91
    Last edited by shogun; 01-14-2016 at 10:14 AM.

  18. #18
    Join Date
    May 2010
    Location
    South Africa
    Posts
    17
    My Cars
    1995 BMW 320i
    Nice write-up, my e36 320i doesn't spark but it has fuel, does it mean the CPS is dead or possibility that the DME/ECU/ECM is faulty?
    E36 320i M50TU20
    ANGEL EYES
    E87 5 STAR MAG RIMS
    OTHERWISE ALL STOCK AND OEM

  19. #19
    Join Date
    Jun 2009
    Location
    Vermont
    Posts
    30,864
    My Cars
    97 328i Vert, 98 M3 Vert
    Quote Originally Posted by msesing View Post
    Nice write-up, my e36 320i doesn't spark but it has fuel, does it mean the CPS is dead or possibility that the DME/ECU/ECM is faulty?
    Sure sounds like one of those two. My money is on the crank sensor. Its becomming a fairly common failure item on these cars as they get older.

  20. #20
    Join Date
    Oct 2012
    Location
    Aurora, IL
    Posts
    12
    My Cars
    1998 BMW 328I 4door
    this just told me exactly what was wrong with my car. props for putting up the info

  21. #21
    Join Date
    Jan 2013
    Location
    Fairdale, Ky
    Posts
    1
    My Cars
    1992 BMW E36

    Question

    help: Im goin NUTS trying to fix this
    Hello, I have been reading for days and days, quick summary of what I have done and what has happened. Last Friday I was driving down expressway and all of the sudden the car just died, plain and simple like it ran out of gas.I had it towed and brought back to my home, this car has ran great and really for the year I have owned it, 1992 BMW 318i E36 with just now 100000 miles as of last week. I have changed the Main Relay (waste of money) Fuel Pump Relay (" ") Fuel Pump, Plugs, Fuel Filter. I have Spark, I also have fuel, but no start. Every 10 attempts of a start I get a Poof out of the engine, but no start, I have laid all plugs on the engine for ground and tested them, and for what I know I have spark from all 4, (note just in case it helps, spark starts fast for like 3 or 4 sparks, then slows down but all 4 keep sparking no stop in that, I have read that spark should be blue in color, well so far it is. The plugs tho are still getting drowned with fuel and like I said every once in a while I get a pop and thats it. Now I can fix just about anything, heck I wasted my money on all the parts so far I have bought (after learning how to test a fuel pump, the old one is still great, so a waste of money, but oh well my baby has a new one now, so oh well, but really guys, I have 9 kids and a wife and spending any more wasted money is not in the scenario, although its nice my car has all these shiny new parts, but still no start. I downloaded the Haynes manual and the bentley version as well, I have learned where all the parts are but nothing tells me why this thing after running everyday without a hitch all the sudden just died and wont start and I have been at it for a week as of today, I took the Cam sensor out and it had oil on it, so I cleaned it and put it back, like I said though,I have fuel and I have spark, also since the vehicle has sat around for this week with no start, I also now have no pressure on my clutch pedal. When you push the clutch down now, its like theres no clutch at all, it just drops to the floor no pressure. this has happened a few times, but only when its not driven after it warms up, pressure is back, I replaced the tranny fluid a month ago, and there hasnt been a problem till now. Any help would be great.
    Last edited by shogun; 01-14-2016 at 10:19 AM.

  22. #22
    Join Date
    Jun 2009
    Location
    Vermont
    Posts
    30,864
    My Cars
    97 328i Vert, 98 M3 Vert
    LKYWHOLESALE I bet you have a massive vacuum leak. Probably one of the hoses that comes off the Idle Control valve fell off. I can't remember much about the intake manifold of the M42 but on my M50 one of those hoses plugs into the rubber elbow between the MAF and the throttle body.

    You're plugs are wet so you're getting fuel, you definately have spark. I had this same thing happen on my 328 and it was a large hose that fell off the intake.

    With all that fuel on the plugs dont be surprised if it spits and sputters a bit when you first get it started.

    Your clutch sounds like the clutch Master Cylinder is failing. It really shouldn't make any difference if the car is running or not. You should be able to get pressure on the pedal. The clutch doesn't care if the car is running. Its not connected to the engine in any way at all. Eventually the seals inside the master will fail completely and it wont build any pressure at all. Just to confirm the master is the issue you neeed to look at your brake fluid level. The cluch and brakes use the same fluid reservoir. If your fluid level is normal then its the clutch master cylinder. if the fluid level is low then its probably the clutch slave cylinder that is attached to the tranny. The slave is much easier to replace. If its the slave cylinder you should also see fluid leaking out from where the tranny bolts to the engine.

    Good luck

  23. #23
    Join Date
    Feb 2006
    Location
    Denver, CO
    Posts
    22
    My Cars
    1995 325i Convertible Boston Green
    Will these sensors reliably throw a fault code if they have failed?

  24. #24
    Join Date
    May 2013
    Location
    Sydney, Australia
    Posts
    619
    My Cars
    1998 328i Convertible
    I had a bad cam shaft sensor and crank shaft sensor. Both appeared with computer scan, but nothing on obc.
    "You must learn from the mistakes of others. You can't possibly live long enough to make them all yourself."

  25. #25
    Join Date
    Jul 2012
    Location
    lauderhill,fl,usa
    Posts
    64
    My Cars
    1995 325i s50 swap
    hey guys I have a question does anyone know what sensor goes in the radiator

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •