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MAF Sensor problem in '84 318?

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    MAF Sensor problem in '84 318?

    After installing a new head on my M10, I am unable to start my coupe. Fuel delivery is fine (cold start injector dumped plenty of fuel into the air hose), getting spark, but I don't think I'm getting air to the system which is unexpected as airflow was not a problem before the blown HG and cracked cylinder head.
    I pulled the airbox out of the engine bay and wonder how to get access to the MAF sensor. It appears adhered in place on the airbox. I wonder also if a relay could go bad for this system. What else might I be missing? I don't see that I have missed a ground wire anywhere.
    The flap inside the airbox is pivoting freely - no binding - and the spring that controls it seems fresh enough. I suspect that the flap is not opening due to an electrical issue.

    Thoughts? Sage advice?

    #2
    The flap opens and closes based on airflow- if it moves freely, you're good.
    It's a sensor- the throttle plate is the air controller.

    How's your timing? You need fuel, and spark at the right time. It's not hard to
    be off 90 or 180 degrees, and this is something that would be disrupted by a head swap.
    Also, are your main injectors squirting? The cold start dump is just meant to be an enrichment,
    not a way to get the car to run...

    those are my thoughts so far. It has been a very long time since I messed with LJet on
    an M10...

    t
    now, sometimes I just mess with people. It's more entertaining that way. george graves

    Comment


      #3
      Synching

      Timing is spot on - marked TDC on the pulley, and we double-checked the cam and the distributor.
      Injectors are new and are squirting. (No leaks either, fortunately). There was quite a puddle of fuel from the cold start injector. Too much, I figure, for ignition.
      When cranking it just sounds starved for O2. Won't turn over. Batt is plenty strong, starter is good.
      I need an ohmmeter to check the circuits of the sensor. Anything else I can do in the meantime?


      Originally posted by TobyB View Post
      The flap opens and closes based on airflow- if it moves freely, you're good.
      It's a sensor- the throttle plate is the air controller.

      How's your timing? You need fuel, and spark at the right time. It's not hard to
      be off 90 or 180 degrees, and this is something that would be disrupted by a head swap.
      Also, are your main injectors squirting? The cold start dump is just meant to be an enrichment,
      not a way to get the car to run...

      those are my thoughts so far. It has been a very long time since I messed with LJet on
      an M10...

      t

      Comment


        #4
        When you're cranking the engine, is it close to starting or is it totally flat?



        Just to be safe, I'd verify the engine grounds on the oil pan and the valve cover and that there aren't any large vacuum leaks. Make sure you don't have the water temp sensor and the water temp gauge plugs reversed. They have the same connector and are next to each other.




        Are you getting spark to the plugs? If you unplug one of the spark plug wires, put a spark plug on the end of it, and ground the electrode (touch to unpainted metal surface), does it spark when you try to crank the engine?

        Check the changeover relay (number 2 on that realoem page). On the driver side of the engine bay, there are the 3 relays near the AFM. The It should be the largest relay of the 3.

        I unplugged the connecter from the bottom of the relay. I popped it open, cleaned, and reseated all of the pins. The car has been driving flawlessly for months since.

        Take care to label, draw diagrams, and take pictures of where all the wires go! There are nearly no images online and when you pop the connector open they have a tendency to all go everywhere.




        Any clicking sound from the relay when you're trying to crank is usually a bad sign.

        Comment


          #5
          1) It's close to starting (seems I routed the plugs to the cap incorrectly last week - wasn't 1342 but 1243)

          2) Grounds appear sound. Yes, checked grounds to/from oil pan, injectors/manifold, and oil pan. Sensors are connected correctly - checked that as well.

          3) I'll check the relay tonight - thanks!

          Comment


            #6
            Will it start if you open the throttle plate a little?

            Comment


              #7
              When you say its close to starting what exactly do you mean? Does it backfire now out of the exhaust or start then cough out the intake and die? Does it spin over differently?

              For reference the motor itself wouldn't be starved for o2, it wouldnt know how to properly meter the fuel for the oxygen if it wasn't getting a air flow reading. At its very basic core you need three things for a motor to start spark, fuel, and compression. Air isn't mentioned in the equation because its almost a given. As I understand it the car hasn't ran since you changed the head gasket I would say its more then likely something to do with something you worked on then not an entirely new problem.

              My personal guess would be timing but thats just going off the fact we know already you routed the cap incorrectly. It could even be as simple as you routed them in the wrong direction. How exactly did you mark the crankshaft and verify the cam and distributor after install?

              Comment


                #8
                Throttle plate

                Originally posted by Pavane View Post
                Will it start if you open the throttle plate a little?
                Unfortunately, no. No start. Just cranks.

                Comment


                  #9
                  Timing

                  Originally posted by rommaster2 View Post
                  When you say its close to starting what exactly do you mean? Does it backfire now out of the exhaust or start then cough out the intake and die? Does it spin over differently?

                  For reference the motor itself wouldn't be starved for o2, it wouldnt know how to properly meter the fuel for the oxygen if it wasn't getting a air flow reading. At its very basic core you need three things for a motor to start spark, fuel, and compression. Air isn't mentioned in the equation because its almost a given. As I understand it the car hasn't ran since you changed the head gasket I would say its more then likely something to do with something you worked on then not an entirely new problem.

                  My personal guess would be timing but thats just going off the fact we know already you routed the cap incorrectly. It could even be as simple as you routed them in the wrong direction. How exactly did you mark the crankshaft and verify the cam and distributor after install?
                  I marked the crankshaft position with some red paint - lined up with the peg on the front of the block. After reassembly we then advanced the crankshaft to TDC and the distributor was reinstalled. My coworker did the cap and rotor work so I am not entirely sure how that was done but he was confident he'd done it right. He had an 02 and had rebuilt it a few times, and has rebuilt his old M20 cars a few times.

                  The day after reassembly I noticed the plug wires appeared to be in the wrong order - though 1342 is stamped on the valve cover, somehow it was wired incorrectly. I don't know which one of us did that. Oh well. After re-organizing the wires, the starting noise seemed much more promising. (The rotor does spin clockwise, right?)

                  Oxygen as not part of the equation seems sound....
                  Just back in from the garage - I propped open the flap in the airbox and tried to start it - no difference: no start. So my lack of O2 theory is kaput.

                  The damnedest thing is that it was running before the HG blew... it ran a wee bit rich but it ran. And I was getting well over 20 MPG. (IP is a little wonky so I'm going off of refueling intervals, not the MPG gauge.)

                  Comment


                    #10
                    The m10 has two distributor types depending on what year the m10 is from. Earlier ones if i remember correctly spun clockwise (a 2002 for example like your friend had) the later ones spin counter clockwise. To confirm which direction yours is spinning take the cap off and bump the starter then see what direction it turns.

                    Also just to note your test with holding the VAM flap open wouldn't be a valid way of checking oxygen flow to the motor as the VAM does not meter the oxygen it measures how much is being sucked in while the throttle body is doing the metering. Essentially using the gas pedal is what controls the amount of air your getting the air meter just moves farther open as you suck more air in telling the engine your sucking more air in so the computer can provide fuel.

                    Comment


                      #11
                      Counter to the clock

                      So this is a later-era distributor. It spins CCW. Thanks for the help!

                      I was able to start 'er up this weekend. Just gotta adjust the timing. I began to sort it out - the analog way by rotating the distributor - but then i noticed the wire to my O2 sensor had frayed to the point of failure. So I'll re-wire that this week and try again. I think I'll be on the road in days!

                      Originally posted by rommaster2 View Post
                      The m10 has two distributor types depending on what year the m10 is from. Earlier ones if i remember correctly spun clockwise (a 2002 for example like your friend had) the later ones spin counter clockwise. To confirm which direction yours is spinning take the cap off and bump the starter then see what direction it turns.

                      Also just to note your test with holding the VAM flap open wouldn't be a valid way of checking oxygen flow to the motor as the VAM does not meter the oxygen it measures how much is being sucked in while the throttle body is doing the metering. Essentially using the gas pedal is what controls the amount of air your getting the air meter just moves farther open as you suck more air in telling the engine your sucking more air in so the computer can provide fuel.

                      Comment


                        #12
                        I'm glad to hear you got it running i was almost ready to pm you and ask if that was it since it piqued my curiosity. Thankfully these motors are pretty simple and theres only so many reasons they wouldn't start.

                        Comment


                          #13
                          Got it running, now electrical gremlin

                          Originally posted by rommaster2 View Post
                          I'm glad to hear you got it running i was almost ready to pm you and ask if that was it since it piqued my curiosity. Thankfully these motors are pretty simple and theres only so many reasons they wouldn't start.
                          One step forward, two steps back. So I got the coupe running a few weeks ago but when we worked to get the timing set, the battery ran down from all of the cranking. Had the battery recharged, and went back to setting timing the next night. Same problem - battery was depleted after about a dozen cranks. Took the battery back to get recharged and I also had the alternator checked - and it is fine. Tonight, tried to fire it up and it won't idle, and again I ran the battery down. I checked the resistance across the terminals on the coil and it's reading a little high at 1.1-1.2 (Bentley states 0.82 as spec). But feel skeptical that is the culprit. I feel there must be a bad ground somewhere, or maybe the starter is drawing current. But that seems unlikely to me as well - I DID get it started a few weeks ago, and even took a quick spin up the street.
                          What do you think? There are only a finite number of grounds to check.

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