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355 Cam phase sensor malfunction

Discussion in '348/355' started by taz355, May 11, 2019.

  1. taz355

    taz355 F1 Rookie
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    Just hooked up scope to the pin 21 pink wire and car would not start this time, maybe battery is getting low?
    I got nothing on the scope it was set to 5volts and 2 ms but without it starting now. Am wondering if i should lengthen the time frame.

    Interestingly enough the trigger light did flash a few times but i could nit see a wave form.
    I also took off the cover and inspected the triggering piece onthe cam and it was tight, i could not budge it and the cam does turn but quite slowly. Maybe 1 to 2 rev per second when cranking
     
  2. taz355

    taz355 F1 Rookie
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    Yes thats the one. I reinspected it but it kinda looks good. I think 1 wire goes to fuel pump because my fuel pump was not working when i finished the major due to that i think.
    I created a thread on it to let others know
     
  3. taz355

    taz355 F1 Rookie
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    I forgot to take a pic of the wire colors for you as well Ian. Will get that tomorrow.
     
  4. taz355

    taz355 F1 Rookie
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    #279 taz355, Jun 11, 2019 at 12:23 AM
    Last edited: Jun 11, 2019 at 12:31 AM
    Everything looks good.
    I could continuity test each pin I guess if i knew their numbers tomorrow
    Maybe that was not the problem with my fuel pump
    Nope the problem withthe fuel pump was a pin in behind passenger seat for a plug that feeds the fuel pump
     
  5. Qavion

    Qavion Formula 3

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    I doubt the fuel pump wiring goes through there, Grant. All the pins on that plug are accounted for in the wiring diagrams. The pump has a solid wire between itself and the relay panel. If plug 40119 was disconnected, however, the car would not start. The starter motor solenoid wiring goes through there. The speedo sensor signal is also critical to engine management. The fuel pump or injectors may have been inhibited by the Motronics ECU because it was not getting the right signals from the sensors.

    Well, if that plug is ok, it's back to the drawing board. Not having a waveform is a worry, but then how does the other bank fire if the ECU is not getting a cam signal?

    Interesting. Could you see how many lobes it had? Google tells me that the camshaft rotates at half the crank speed on a 4 stroke engine, but does this apply to an 8 cylinder twin cam per bank engine?
     
  6. m.stojanovic

    m.stojanovic Formula 3
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    Yes it does. The cam/crank turning ratio of 1:2 is related to the engine being 4-stroke (cylinder fires once in every two crank turns), not to the number of cylinders or anything else.
     
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  7. Qavion

    Qavion Formula 3

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    Ah.. ok, so on a standard 4-stroke engine, the intake valves (for example) have to be opened once every two crank turns. Does this mean that, on a wasted spark igniton system (found on the F355), the cam needs to trigger the spark once per (cam) turn? If so, this means there only needs to be one lobe (or whatever it's called) on the end of the cam to trigger the cam sensor.

    So, if spark frequency is the same as engine rpm on a wasted spark system and assuming 1200rpm at idle, the spark will be triggered 1,200 times per minute, or 20 times a second. I guess the timebase on the oscilloscope needs to be at least 50 milliseconds to show two pulses on the screen.

    Please feel free to correct me :p (I lost the plot several times compiling this logic)
     
  8. m.stojanovic

    m.stojanovic Formula 3
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    On a 4 cylinder engine, there are two sparks per each crank revolution (per rpm) or 2 sparks per half cam revolution or 4 sparks per one full cam revolution. However, the cam sensor does not directly fire the sparks. The cam sensor "fires" once per cam revolution and it only tells the engine ECU what is the rotational position of that one cam. The ECU then calculates from there where the other 3 cams are and, also using the crank sensor pulse, calculates when to fire the coils and when to fire the injectors.

    348 also has wasted spark ignition. Whether the ignition is normal or wasted spark type, does not make any difference as to how the ECU works using the cam and crank sensors. The wasted spark ignition was invented in order to eliminate the need for a distributor.
     
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  9. Qavion

    Qavion Formula 3

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    Thanks Miro, I got a lot mixed up there, including my terminology. Anyway, what I was trying to calculate was the number of "cam sensor pulses". They should be at the same rate as cam speed (which equals engine rpm). Somehow I ended up with the right value.

    I hope the owner of the oscilloscope didn't want it back in a hurry :p

    If the left bank is working normally, doesn't this mean that the cam sensor is ok? Since the crank sensor is in the spark equation, could we be looking in the wrong area?
     
  10. m.stojanovic

    m.stojanovic Formula 3
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    On both, the 348 and the 355, the cam sensor produces one pulse per one cam rotation or one pulse per two crank rotations. At 1200 rpm there will be 600 pulses per minute or 10 per second.
     
  11. fatbillybob

    fatbillybob F1 World Champ
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    Grant,

    Is the car in Indio? Stoogapollusa is this Saturday. Have AAA drop the car and we will get it running. Then you will get the Ketel award too!
     
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  12. Qavion

    Qavion Formula 3

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    Ugh... Got it. So engine "rpm" is based on 2 crank rotations and not one.
     
  13. taz355

    taz355 F1 Rookie
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    No its not its up here in the rockies.
    May have to pick up Henry in the fall, bring the car down, and have another one.
    Iwill supply the beer and food for you guys.
    Iknow you all like a challenge.

    On another note Alberta is following Californias leed and burning up. Work is busy and really gettin in the way of getting my car up and running.
    Thank you all for the help so far.
     
  14. taz355

    taz355 F1 Rookie
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    Does the cam revolution not seem slow though if its only 2 rpm when cranking. I thought the engine turns over at about 300 rpm
     
  15. taz355

    taz355 F1 Rookie
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    K8nda looks like 2 lobes one large and one small as in the pic above
     
  16. Qavion

    Qavion Formula 3

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    Probably that smaller lobe is too far away for the sensor to pick it up. It may simply be there as a counter balance.

    I assume you mean two revs/sec, not rpm )

    If the starter motor produces 300rpm (indicated engine rpm), that's 1/4 idle speed, so 2.5 cam pulses/sec. Sounds pretty close.
     
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  17. fatbillybob

    fatbillybob F1 World Champ
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    From page 1 I have liked crank sensor and associated wiring.
     
  18. Qavion

    Qavion Formula 3

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    I think a few of us have thought about that (as it's such a common problem), but I think we ignored it until now because we presumed that it would affect the ignition on both sides (as should the cam sensor). However, the engine seems to be running so poorly now, it's hard to say if even the left bank is working properly.
     
  19. m.stojanovic

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    #294 m.stojanovic, Jun 12, 2019 at 1:43 AM
    Last edited: Jun 12, 2019 at 1:50 AM
    Engine "RPM" is based on 1 crank rotation. The camshaft rotates at half speed of the crankshaft, thus the pulse from the cam sensor comes once per 2 crank rotations.

    On another subject, Hall Effect sensors are also used to directly trigger the ignition when mounted inside the distributor. In that case, the sensor will "fire" 4 times per 2 revolutions of the crankshaft on a 4 cylinder engine. The reluctor for the sensor has 4 "lobes" or slots and the reluctor rotates one full turn for every 2 turns of the crank.

    The cam sensors are actually not directly the ignition triggers but are "camshaft position sensors" and triggering of the ignition, at correct times and sequence, is all done by the ECU based on its calculations by reference to where the crankshaft and the camshafts are and, of course, taking the engine speed (the rpm-s) into account.
     
  20. m.stojanovic

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    2 revs/sec means 120 rpm of the camshaft and 240 rpm of the crankshaft. Somewhat lower than the spec probably because of a bit weaker battery or a bit tired starter motor.
     
  21. Qavion

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    Tattooing that on the back of my hand now so I don't forget.

    So, to pick up more than one cam pulse on the oscilloscope with the cam rotation between 2 per second (slow cranking) and 10 per second (idle), Grant probably needs to set his oscilloscope TIME/DIV at 50mS or greater.

    Should we now be doing tests on the crank sensors (despite what the diagnostics told us... and despite that broken cam and crank sensors should affect both sides)?
     
  22. m.stojanovic

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    It is possible that one of the sensors (crank or cam) is on the way out, or its gap has "grown" to near the limit and that this, for some reason, affects one bank but not yet the other. Certainly worth checking/replacing the sensors.
     
  23. johnk...

    johnk... F1 Veteran
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    #298 johnk..., Jun 12, 2019 at 4:58 AM
    Last edited: Jun 12, 2019 at 5:06 AM
    The car would not run at all if the crank sensor was bad. It tells the ecu that the engine is turning over. Without that signal the ECU will not turn on the fuel pump.

    I think you are chasing the wrong tail. It's an IC engine; fuel compression, spark and it runs. I referred back to my older post because you all seem to be forgetting that the ecu is grounding the coil correctly, but the wave form is not correct. I repeat what I said before. The shape of the wave form typically indicates that the coil is discharging through a finite resistance. Grant, Have you pulled the plugs and checked them? Have you pulled the ignition wires and check them? I asked before but don't recall a response.

    I found this on the web. Please see Figure 9 and the related text.
     

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  24. Qavion

    Qavion Formula 3

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    Not forgetting. I think we had trouble understanding how a single fault could affect all four plugs. What would happen if one of the 2/3 plug leads were shorting to one of the 1/4 leads. Would it kill all four?

    There have been cases where the gap wasn't quite right. There were pulses, but not 100% of the time depending on the engine temperature.
     
  25. fatbillybob

    fatbillybob F1 World Champ
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    I do not think you are correct. A wonky crank sensor or wiring to it can give inconsistent signal to the ecu. You can get weird misfires as an example.

    I'm not the one with boots on the ground so it is very difficult to be an internet mechanic except to speak in generalities.
     

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