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Thread: Camshaft Sensor

  1. #1
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    Question Camshaft Sensor

    The infamous check engine light started to come on on my 1994 B4000 Mazda 4x4 4.0L V6 Manual truck about four years ago. My truck seemed to be running fine, so I simply ignored it. It wasn't until I moved to a town where it was required that I get an emissions test done that I discovered I couldn't pass the test when my check engine light was on. I brought my truck to an auto shop to have my computer plugged in to figure out what was wrong. My camshaft sensor was to blame, and the mechanic found a shop with a replacement part for $400. As a poor college student, such an expense was out of my league at the time, so I figured I'd take my chances and hope no one caught me driving around without an I/M sticker on my windshield.

    A couple friends of mine had their cam sensors replaced before, but they said it only cost them $50 or so for a new sensor and they said that their gas mileage even went up by like 4 miles/gallon after fixing it. One of the guys said his engine actually wouldn't even start with the broken sensor. I started to wonder whether the dealer I had inspect my truck's computer was trying to screw me, since my part was supposed to cost $400.

    A little bit of net searching led me to discover that the sensor my friends may have had to replace were actually crankshaft sensors, which for my model of truck does indeed cost around $50. But then I found camshaft sensors, which did indeed cost around $400 for a replacement.

    My net searches seemed to infer that crankshaft and cam sensors were interchangeable terms. Indeed, they're not. They're different things. But I'm confused as to what a camshaft sensor even does? How is it different from the crankshaft sensor? My truck seems to be running just fine without it working.

    I'm also wondering if I might get improved gas millage if I replaced my camshaft sensor. With the soaring cost of gas these days, I'm wondering if that $400 will eventually pay for itself in gas savings. At the moment, my truck averages 21 miles/gallon on the highway (I've measured this by dividing my odometer mileage by the amount of gas in gallons it takes to refuel my tank). I'm not sure if that's good or bad mileage for my particular make and model.
    Last edited by duckshepherd; 03-18-2008 at 11:30 PM.

  2. #2
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    the cam shaft sensor basicly tells the computer what cylinder is near tdc, so it knows when to fire that injector. without it your truck will get bad gas mileage.

    if it was a bad crank sensor, then your buddys are right, your truck would not start. the computer would have no idea where the pistons were in the engine.

    sorry if it is kinda vauge(sp), but i just woke up and have a hard enough time remembering their purpose when i am awake.
    <----just your average 5.3

  3. #3
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    Welcome to the forum duckshepherd
    What was the actual code that caused the light ?
    Here's some light reading for you, just for fun.

    The Crankshaft Position (CKP) sensor, located on the front cover (near the crankshaft pulley) is used to determine crankshaft position and crankshaft rpm. The CKP sensor is a reluctance sensor which senses the passing of teeth on a sensor ring because the teeth disrupt the magnetic field of the sensor. This disruption creates a voltage fluctuation, which is monitored by the PCM.
    The CKP sensor (A) is triggered by the teeth which are machined into the crankshaft damper (B)



    TESTING

    Navajo and B Series Pick-up Models

    Using a DVOM set to the DC scale to monitor less than 5 volts, measure the voltage between the sensor Cylinder Identification (CID) terminal and ground by backprobing the sensor connector. If the connector cannot be backprobed, fabricate or purchase a test harness. The sensor is okay if the voltage reading varies more than 0.1 volt with the engine running at varying RPM


    Camshaft Position (CMP) Sensor
    OPERATION
    The CMP sensor provides the camshaft position information, called the CMP signal, which is used by the Powertrain Control Module (PCM) for fuel synchronization.

    The following vehicles do not utilize a CMP sensor:
    • 1994 B Series Pick-up equipped with 2.3L engine and automatic transmission.
    • 1994 B Series Pick-up equipped with 4.0L engine.
    • All 199495 MPV models.
    • Navajo models.
    1994 2.3L engines equipped with a manual transmission, all 199597 2.3L and 1998 2.5L engines utilize a CMP sensor that is located on the oil pump cover assembly, on the left-hand lower side of the engine block.

    On the 1994 3.0L engine in the B Series Pick-up and 199698 MPV, the CMP sensor is an integral component of the distributor assembly, and it is a Hall effect magnetic switch.
    On 199598 3.0L (B Series Pick-up) and 4.0L engines, the CMP sensor is mounted on an auxiliary shaft drive assembly, located towards the rear of the block. it is also a single hall effect magnetic switch and it is activated by a single vane, and is driven by the camshaft

    Typical auxiliary drive mounted Camshaft Position (CMP) sensor used on 3.0L (B Series Pick-up) and 4.0L engines


    TESTING

    B Series Pick-up Models

    THREE WIRE SENSORS
    1. With the ignition OFF, disconnect the CMP sensor. With the ignition ON and the engine OFF, measure the voltage between sensor harness connector VPWR and PWR GND terminals (refer to the accompanying illustration). If the reading is greater than 10.5 volts, the power circuit to the sensor is okay.
    2. With the ignition OFF, install break-out box between the CMP sensor and the PCM. Using a Digital Volt-Ohmmeter (DVOM) set to the voltage function (scale set to monitor less than 5 volts), measure voltage between break-out box terminals 24 and 40 with the engine running at varying RPM. If the voltage reading varies more than 0.1 volt, the sensor is okay
    TWO WIRE SENSORS
    1. With the ignition OFF, install a break-out box between the CMP sensor and PCM.
    2. Using a Digital Volt-Ohmmeter (DVOM) set to the voltage function (scale set to monitor less than 5 volts), measure the voltage between break-out box terminals 24 and 46 with the engine running at varying RPM. If the voltage reading varies more than 0.1 volt AC, the sensor is okay
    "camshaft position information, is transmitted by the CMP sensor, installed in place of the distributor (engines with distributorless ignition), or integral with the distributor"

  4. #4
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    You know, that's really weird. I was just looking through my Chilton Repair manual today and I noticed what crabtruck had highlighted in red; apparently my exact year and engine type don't even utilize a cam sensor. Could the book be wrong? Or could my mechanic have been mistaken?

    My truck was inspected two years ago, but still remember a bit of what the mechanic told me about the diagnostic. I still have the receipt from that visit with a quote on my part needs and cost. Unfortunately, I wasn't informed on what the code actually was, and it's not printed on my quote. My quote simply states: needs cam sensor.ecm/ . I remember the mechanic telling me that the diagnostic revealed that there was no sensor input coming from the cam sensor, that it was flat lined. Could that be because there is no cam sensor for my particular make and model? But why would there be info on a scan of a component not even included on my truck? Plus, my check engine light still signifies something must be wrong. And that's what the mechanic found.

    I did find a forum where someone made a post a few years back with the exact same model and year of truck as me with the exact same problem with the exact same response from the mechanic after doing a diagnostic test: 1994 mazda b 4000 engine light stays on - Mazda Forum - Mazda World.org Alright, so I'm not alone!

    Yeah, now I'm confused. Only way to know if I even have a cam sensor is to locate the darn thing on my engine. I peeked under the hood today trying to find it, but the description of it's location in my Chilton Repair manual didn't help much. Let me take some photos of my engine, and maybe you guys can help me locate it.

  5. #5
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    A scanner is dependant on the mechanic to tell it what truck it's hooked up to.
    If it asks the computer for the readout on the sensor input it will get the flatline.

    Per autozone "Under hood, center, upper engine area, mounted behind rear of intake manifold, in the engine block"
    But if you try to buy the part...
    "Camshaft Position Sensor
    We're sorry, but there are no results in this parts category for your 1994 Mazda Truck B4000 4WD 4.0L MFI . "
    Parts America will sell you one for $379/list $618 if your truck uses it
    Standard Motor Products Engine Camshaft Position Sensor
    http://www.partsamerica.com/productd...rtNumber=PC137

    Suggest you try to pull codes as a first step regardless of light, method should be in your Chiltons book.
    In the original shop manual the pages F3-170 through F3-172 are missing
    "Camshaft position Sensor Adjustment Proceedures"
    then released in early 94 as being for Navajo's. Love those papertrails.

    If you like following wires around under the hood...
    PCM. located by the fender well I think, pin #24 DkBlu/Org is CMP.
    Ground (Blk/Wt) side may be sliced to the O2 sensors, hot (red) spliced into the PowerTrain control Relay.
    That was the 3 wire setup, some were 2 wire.

  6. #6
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    I tried to pull codes off a free scan at NAPA today, but they didn't have the right scanning device to attach to my truck. They recommended I go see this other shop in town that might be able to help me out.

    So I talked to the guy at the other shop. I told him about my visit at the mechanics shop a couple years ago and about the cam sensor that was to blame. I asked him if fixing it might give me better gas mileage, and if it was even worth replacing at all. He basically said it didn't really do or affect much. He said that the only thing the cam sensor is any good for is to help at start up, so you can get the best kick out of your crank. But after that, the sensor really doesn't aid in the timing, the crank sensor pretty much takes care of that. I also informed the guy of the fact that my truck manual said that my particular make, model, and year was labeled as not even including a cam sensor. I told him about the flatline that the first diagnostics test showed two years back and how I thought it might be because I don't have a sensor in the first place.

    At that shop I went to a couple years back, they also tested me for emissions anyway just to see if I'd pass; I didn't. So something is definitely screwy, causing me to have bad emissions. Who knows, maybe my engine is just old; 171,000 miles, but still running great. I've done pretty good maintenance since I bought it used four years ago, and the person who owned it before had good maintenance records on it too.

    Doing another full diagnostics scan would cost me $65. With the new information I have at hand, I might be able to deduce and solve this problem once and for all. I think I'm gonna go for it.

    I'll let you guys know what I find. I'd have to wait 'til next week to get the scan done.

    Thanks much for your help crabtruck

  7. #7
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    What does your code plug look like, there were at least two styles. Best I can tell, you will only need a jumper(paperclip), or a voltmeter at worst to read them yourself.
    These are the only codes I can find so far, nothing for cam:

    Diagnostic Trouble Codes - 1994
    Mazda

    02 Crank Position Sensor 2 (NE 2 Signal).
    03 Crank Position Sensor 1 (G Signal).
    04 Crank Position Sensor 1 (NE 1 Signal).
    05 Knock Sensor.
    08 Air Flow Sensor.
    09 Engine Coolant Temperature Sensor. 10 Intake Air Temp. Sensor (Air Flow Sensor).
    12 Throttle Position Sensor.
    14 Barometric Absolute Press. Sensor.
    15 and/or
    23 Heated Oxygen Sensor (Inactivation).
    16 EGR Function Sensor.
    25 Pressure Regulator Control Solenoid Valve.
    26 Purge Control Solenoid Valve.
    28 EGR Vacuum Solenoid Valve.
    29 EGR Vent Solenoid Valve.
    34 Idle Air Control Valve.
    41 VRIS 1 Solenoid Valve.
    46 VRIS 2 Solenoid Valve.
    67 Coolant Fan Relay No. 1

  8. #8
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    I have an older style EEC connection that actually connects from under my hood next to my power distribution box. The following year, 1995, my same model was released with the more modern parallel type connector.

    And what do you mean I can use a jumper or a voltmeter to read my codes? I'm completely new to this whole code reading thing; is there a way to read them without a code reader?

  9. #9
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    For some basic general info (not specifically your truck) regarding reading OBD-I:
    Auto Repair - how to read codes yourself without scan tools
    One of the mazda connector styles:
    Connector Photo Gallery - Mazda Connector 5
    OBD-I and OBD-II on mazdas:
    Mazda Engines - diagnostic connector locations with pictures
    More than you want to know about OBD from the national clearhouse:
    OBD Clearinghouse
    How to on type 5:
    Mazda Engines - auto tune up using codes, Example models: 100, Familia
    How to on type 10:
    Mazda Engines - auto tune up using codes, Example models: Mazda 6, MX-3, RX7
    Do look in your manual, there should be an explanation there as well.
    Last edited by crabtruck; 03-21-2008 at 02:57 PM.

  10. #10
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    Oh wow, that's awesome! Thanks a lot! I can easily whip up an LED tester. I believe I have the Connector 5 connection.

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