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Thread: Retrofit 24x reluctor to early V8

  1. #31
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    Fair enough, I think we need to put this on hold and move on. I will revisit it once I have a chance to do a physical inspection, probably in a few weeks. I'd encourage anyone else who has the chance to also do so. As I said, I'm just as willing to see the results go either way and would in fact favor your viewpoint as it means less work for me. I just want it resolved. I know you think... well, let's not go there right now.

    Anyway, the next step is to set the cam sensor pulse to match the CKP sensor. It will be a wasted effort if I have to change the position of the tone ring but I suppose it's a chance I will have to take. After that I will look at the coil logic outputs. I agree, those should be there regardless of the timing and regardless of the cam sensor for that matter. (It and the coils are presently unplugged.) This should point me to the actual problem.

    How about this, if I can get it to run and the timing light either does or does not match the advance map we should be able to claim we've proven the case one way or the other. Sound reasonable? (This engine DOES have timing marks.)

    Jim

  2. #32
    Super Moderator dave w's Avatar
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    The measurements I have for the L31 Cam Position Sensor Flag is 175 degrees "Flag in Sensor" and 185 degrees "Flag out of Sensor".

    My daily driver has a L31 engine with an aftermarket 24x Coil-on-Plug Conversion, using the original L31 distributor Cam Position Sensor.

    Sensors will trigger on Leading Edge / Trailing Edge of the trigger wheel or sensor flag. The center line of the sensor is the critical alignment point for the trigger wheel or sensor flag.

    GEN III computers have a CASE Learn Procedure for "Timing", mostly for production tolerance reasons. GEN III computers will "Assume" near perfect alignment of the CKP / CMP sensors, because that's the methodology of mass production.

    It can be a challenging question: is success re-engineering the factory mass production methodology, or reverse engineering the factory mass production methodology. Either method will yield success, with measurements, alignments, and parts fabrication as good as the factory mass production tolerances.

    dave w

  3. #33
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    In this case the CMP sensor is mounted to a specially built oil pump drive unit which includes the flag for the sensor. It is essentially a cut down distributor which due to space constraints is in a much smaller package. Since I did not have those measurements it is 180/180 but hopefully that will be close enough. Once I get out to the shop I will backprobe the signal lead at the ECM, run a trace, and then rotate the body of the sensor to get the right alignment, or as close as I can get it given the 5 degree difference. I could probably trim the flag to match your specs but it would require some work with a die grinder. I'll see what the trace looks like first. Given considerations like the sensor lobe pattern, target distance, and overlap, that 180 degree mechanical configuration could certainly result in either a 175 or 185 degree pulse. I'll just have to measure it.

    Sorry, no photo available at the moment.

    Jim
    Last edited by Jim Blackwood; 02-25-2020 at 06:47 PM.

  4. #34
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    Don't align the cam sensor to the crank wheel. Align it to TDC. The signal should transition low to high at TDC #6 and transition high to low at TDC #1. With a meter you should be very able to set it up and test it for accuracy.

    On a similar note, the engine will start without the cam sensor, just might need more cranking or a couple of tries to get it going.

  5. #35
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    A true 1X cam signal is 180*. Look at the posted scope probes and it's clear the cam signal transitions at each full single turn of the crank.

    The distributor Dave used was not from a 24X application, but apparently the PCM can cope with the variance of that sensor.

  6. #36
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    Quote Originally Posted by lionelhutz View Post
    Don't align the cam sensor to the crank wheel. Align it to TDC.
    Should be the same thing right? I'll be using my scope and get a dynamic reading while cranking. I'm headed that way.

    Jim

  7. #37
    Super Moderator dave w's Avatar
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    I opted to build a 1x distributor, non GM application.

    dave w

    IMG_0325.jpg

    IMG_0324.jpg

    IMG_0322.jpg

  8. #38
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    Put a meter on the cam sensor and measure it as you crank the engine past TDC then you'll know it transitions at the right time.

  9. #39
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    Quote Originally Posted by dave w View Post
    I opted to build a 1x distributor, non GM application.

    dave w

    IMG_0325.jpg

    IMG_0324.jpg

    IMG_0322.jpg
    You make some of the coolest parts Dave. The fabrication you do is always impressive.

  10. #40
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    CMP sensor and oil pump drive for Buick.

    Jim
    Attached Images Attached Images

  11. #41
    Super Moderator dave w's Avatar
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    Quote Originally Posted by Jim Blackwood View Post
    CMP sensor and oil pump drive for Buick.

    Jim
    Cool design

    The 1x distributor pictured in post #37 is for the low resolution 4x '0411 system.

    dave w

  12. #42
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    That will work.

    Before I meant to use the meter and hand turn the engine past TDC so you can capture exactly when it transitions compared to the timing marks.

  13. #43
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    After reviewing I think you guys are right. The #1 coil secondary trace on the joecar screen print was something I should have looked at more closely. Sorry bout that.

    Anyway, I worked up a rudimentary bench mockup for the crank trigger and am working on getting a proper scope reading on that before I go back out. Photo below. It runs at 200rpm so is about right for cranking speed. Once I get that going and have consistent results with the scope I'll feel a lot more confident about what I'm seeing in the shop.

    Jim
    Attached Images Attached Images

  14. #44
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    Here's an interesting wrinkle. It appears that below a certain rotational speed the VR signal becomes unreliable. This makes perfect sense if you think about it since it relies on a somewhat similar triggering method as the scope does, which is to say, triggering a voltage state change from 0 to 12v and back depending on the transition of the signal generated by the tooth. The output signal remains a 12v square wave and this tells us that there is indeed signal processing going on in the sensor. It is not a simple VR pickup. If it were the voltage and waveform would vary with the speed and it does not, at least to any significant degree. This further tells us that the pickup probably uses the rear pattern to blank out noise or unwanted pulses from the 24 tooth wheel on the front.

    BUT that also means that detecting the condition changes using a multimeter and turning the crankshaft by hand is likely to prove unreliable or at least inconsistent.

    I see this on the mockup. Giving it a moderately slow spin through 1/4 of the rotation gives a good solid pulse train but I can slowly rotate it through any number of teeth at about the speed you'd be able to do with a wrench on the crankshaft without any voltage change at all.

    I've not tested the cam sensor yet to see if it acts in a similar way.

    Jim
    Last edited by Jim Blackwood; 02-27-2020 at 11:26 PM.

  15. #45
    Fuel Injected! brian617's Avatar
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    This may sound super silly, but are you 100% sure the sensor connector is wired correctly?

    0411 PCM?

    Terminal (A) at connector (drkblu/wht) goes to PCM terminal (12) signal

    Terminal (B) at connector (ylw/blk) goes to PCM terminal (21) low ref

    Terminal (C) at connector (lt/grn) goes to PCM terminal (2) high ref

    All PCM connector C1
    89 K1500 Scottsdale 5.7L 5spd 3:42 RamJet cam Dart iron TBI heads 427 PCM swap
    95 C2500 Cheyenne 6.5L turbo diesel 4L80e 4:10 DB2-4911 Manual pump conversion 0411 PCM trans control 2Bar COS
    05 Outback XT 2.5L turbo gas auto

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