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Thread: Timing control with GM large cap HEI.

  1. #61

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    Yeah, I'm talking about those two wires. I just found instructions from MSD and it also says Green to Green and White to Purple, so maybe it is correct. If you disable the fuel pump you can set your cranking timing to 15°, so you can check the timing without starting it, and see which way the timing goes when you swap the wires.

  2. #62

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    But that's my problem. When I set everything up and go to start the truck, it goes to 50°. Even if I set static timing at 15°, it seems to do the same.
    '73 K5 Blazer, built 350 SBC 375 HP/425 TQ, 12" F/18" R suspension travel. Deaver springs with King shocks, D44/12 bolt, 3.73 gears, lunchbox locker F/Auburn Posi R, crossover steering, 35" BFG Mud Terrains, Vintage Air system, PRP suspension seats, lots of custom work, all built by me.

  3. #63

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    I was just suggesting that you check the timing while you're cranking it, with the fuel pump disabled, so that the car won't start. Then you can test it with the wires swapped, and see how the timing changes compared to the original way.

  4. #64

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    Got it. I'll try that.
    '73 K5 Blazer, built 350 SBC 375 HP/425 TQ, 12" F/18" R suspension travel. Deaver springs with King shocks, D44/12 bolt, 3.73 gears, lunchbox locker F/Auburn Posi R, crossover steering, 35" BFG Mud Terrains, Vintage Air system, PRP suspension seats, lots of custom work, all built by me.

  5. #65

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    Also, see this on Reference Angle & Phasing: http://www.chevelles.com/forums/89-e...nce-angle.html

  6. #66

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    That's basically what I did, just maybe backwards, but achieved the same end goal. I set my phasing so the rotor & cap contact are aligned throughout the timing sweep, 15 to 36°. Then turned to my Reference Angle of 50°, and used the locked out vacuum advance to move the reluctor points to line up, making sure the rotor did not move.

    So everything should be set right. When I start the engine, set the static timing on the handheld at 15° to do my timing check and dial it in, the timing mark on the balancer is all over the place. And best I can tell, it's at 50°. Almost seems like the computer is not controlling my timing, even though I set it up in the Wizard to do so.
    '73 K5 Blazer, built 350 SBC 375 HP/425 TQ, 12" F/18" R suspension travel. Deaver springs with King shocks, D44/12 bolt, 3.73 gears, lunchbox locker F/Auburn Posi R, crossover steering, 35" BFG Mud Terrains, Vintage Air system, PRP suspension seats, lots of custom work, all built by me.

  7. #67

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    Well I put everything back to normal in the distributor until I can figure this out. I started having some backfire issues through the exhaust on the drivers side. So yesterday I started looking into it and found that my #5 & #7 wires had burned through on the headers and were arcing out. They had actually burned through the protective heat shields and then the wire. So now I have to replace the wires and find a better way to keep them off of/away from the headers as best I can. Then I can go back to trying the timing control.
    '73 K5 Blazer, built 350 SBC 375 HP/425 TQ, 12" F/18" R suspension travel. Deaver springs with King shocks, D44/12 bolt, 3.73 gears, lunchbox locker F/Auburn Posi R, crossover steering, 35" BFG Mud Terrains, Vintage Air system, PRP suspension seats, lots of custom work, all built by me.

  8. #68
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    637

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    I was using a large cap HEI at one time. It can be a pain to get the rotor phasing correct. Get yourself a spare cap and drill it on either side of the #1 post. Then you can see where the rotor is by shining your timing light in the hole and see the rotor. Having the pickup wires reversed can cause the problems you are seeing. It happened to me. It has to do with the wave the ECU sees, the wave is reversed and not where it should be. If the ECU is looking for the point that the volts go from + to - (which is the point the reluctor is lined up) to trigger the spark, and you reverse the wires on the pickup, you just put that point somewhere between the two pickup points on the reluctor. And that point will change with RPM. Causing all kinds of problems. On a side note, there's nothing like a crank trigger for timing stability.

  9. #69

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    When I dig back into it, I'll check it as is, and then again with the wires swapped if it doesn't seem right. I had bought a MSD plug to use, but after reading a few places that it should be green to green. I swapped the wires around so that it would be that way. Maybe that was a mistake? But with the issues I was having trying to get it to fire, I swapped them to see if that would help, unbeknownst to me that I had other issues with the way I originally wired the coil.
    '73 K5 Blazer, built 350 SBC 375 HP/425 TQ, 12" F/18" R suspension travel. Deaver springs with King shocks, D44/12 bolt, 3.73 gears, lunchbox locker F/Auburn Posi R, crossover steering, 35" BFG Mud Terrains, Vintage Air system, PRP suspension seats, lots of custom work, all built by me.

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