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Thread: Pickup coil wires p & n

  1. #1
    Fuel Injected! S.O.B.B.'s Avatar
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    Pickup coil wires p & n

    After much searching and reading I've found a fair bit of info on this.looking at new large cap hei distributors I see which color wire goes to which pin on the 7 pin icm.my understanding of the pickup coil is that the rotation direction affects the output signal for triggering a spark event.it puts out a wave that is converted to square wave and the trigger should come from the later side just before it drops again.and having the p and n wires backwards would mean it gets the trigger signal from the beginning of the square wave rather than the end where it's desired.I hope I understand this correctly. My question is looking at a corvette large cap hei the icm pickup is wired the same as my cadillac 4.5 distributor but they rotate in opposite directions. Which has left me confused. Is it the ecm that configuration that decides which signal or at which part of the square wave is the trigger. I also found a diagram for megasquirt and it shows the pickup coil wired opposite of the factory wiring.so more confusion. So which way should my set up be wired.my distributor rotates ccw and is wired like factory.but my ecm came from a sbc that rotated cw.the symptom I've had since day one has felt like the timing just isn't right and no matter where it's adjusted or how well it runs it just feels like it has this miss to it.in checking plugs I don't have any that stand out looking different from each other.if anyone with knowledge of this can help that would be great.
    Jeeper
    87 sjimmy 4.5L /nv1500/ 8.8 3.55 rear/disc brakes.

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    20171109_210509.jpgew7hei.gif the pic is wired same as factory.second pic is wired opposite
    Last edited by S.O.B.B.; 6 Days Ago at 10:20 AM.
    Jeeper
    87 sjimmy 4.5L /nv1500/ 8.8 3.55 rear/disc brakes.

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    Can someone point me in the right direction.my engine call for 10° initial advance.at what degree of Crank rotation should the reluctor line up with the tabs on the pick up coil.should it be at 10°btdc that they line up?or more like 30°btdc?as in initial set up of a new to me distributor.any help would be greatly appreciated.thanks
    Jeeper
    87 sjimmy 4.5L /nv1500/ 8.8 3.55 rear/disc brakes.

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    Well today I played with my distributor. I tried setting the distributor to 0°TDC and changed it in my bin aswell.felt same.I also swapped back to smaller injectors and did a few logs to get the fuel close again.I also tried a chip with all spark latency set to Zero and entire timing table to 20° of advance.I went through the rpm range in the latency table and marked what I got.it said I was getting 30°and the timing light confirmed it.I was trying to figure out if the latency table I'm using is way off.the laptop agreed with the data.but it's not what was requested in my bin.I was getting lots of knock count at higher rpm and map.seems I also get a count when I shift. Anyway it still has a felling of a slight miss.like something not firing at the right time and this has bend a problem since day one of this conversion.so I looked at a few pics I took b4 of the small cap and large cap distributors.I think I'm onto the problem but just need to rest my brain and bit and figure out how to rectify this.small cap dizzy the rotor does not point at and plug terminal when the pickup coil is aligned.it's kinda in the middle of two plug terminals.on the large cap the rotor is aligned with a plug terminal when the pickup coil is aligned. So I'm figuring this is the cause of my miss feeling. Any input would be good input.
    Jeeper
    87 sjimmy 4.5L /nv1500/ 8.8 3.55 rear/disc brakes.

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    Jeeper
    87 sjimmy 4.5L /nv1500/ 8.8 3.55 rear/disc brakes.

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    If you have the positive and negative backwards it will retard timing as rpm rises and will misfire and carry on no matter what you do tuning wise

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    Thanks.I neglected to mention.I did try to reverse the wires this morning but it would hardly run so i put it back the way it was.same as is wired in a pic of a new distibutor.I had the dizzy at 10°advance and my bin b4 i started messing with it as thats the cadillac spec.put the crank at 0°TDC on #1 compression stroke and aligned the reluctor tabs on the pickup coil.changed initial advance to zero in my bin.then started it with bypass disconnected.it was at about 2 or 3 ° atdc.so I advanced distributor till timing tab at zero.reconnect bypass.unplug ecm to clear codes.start it and ran Decent.I then did the testing to try and figure what spark latency should be which is when I saw that at the crank I was getting about 30 and tprt sa hack says same.but that was with a chip with entire timing table at 20°.so I'm kinda stumped.went back to the garage to compare distributor to pics.still unsure if the difference I see makes much difference.I did the zero setting to see if that would change the miss feel.I did end up changing my main spark bias from 0 to 10 and that changed what tprt reports for timing.less that ten. I didn't get the chance to look again with the light to see if it was 10 less at the crank but id bet so because i could feel it and hardly any knock count.as compared to b4 the main sa bias change.
    Last edited by S.O.B.B.; 1 Day Ago at 11:03 PM.
    Jeeper
    87 sjimmy 4.5L /nv1500/ 8.8 3.55 rear/disc brakes.

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    From some bins I looked at from f body and y body tpi cars with large cap hei none are initial sa zero.they have 6° advance for most.one f body had 10°.so I'm thinking a reason for this.I don't have 2 distributors on hand to verify if there is any phasing difference. Anyone know for sure? Or why the difference in initial advance from large and small cap?back to reading and searching. No adjustable rotor for hei that I see.only way I can think of getting phasing adjustment is to use a hei vacuum advance style housing with all the parts from cc hei and make an adjuster for the pickup where the vacuum was.I don't know if that could work.
    Jeeper
    87 sjimmy 4.5L /nv1500/ 8.8 3.55 rear/disc brakes.

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    Found some cam specs for 4.9 which I believe is identical to 4.5.Screenshot_2018-05-29-02-29-28.jpgScreenshot_2018-05-29-02-29-08.jpg can anyone tell me how different this is compared to a stock 305 tbi
    Jeeper
    87 sjimmy 4.5L /nv1500/ 8.8 3.55 rear/disc brakes.

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