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Thread: Odd Fire TBI

  1. #61
    Fuel Injected! Willys43's Avatar
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    Quote Originally Posted by 1project2many View Post
    I learned that Maserati's approach to odd fire was to use dual coils connected to a single distributor. The 225 will likely never see the same RPM as the Maserati and will likely never have a dwell issue. But we have a solution should there be a need for 5k+ rpm revs in the old Willys.

    It appears the MS2 code can use an option bit for odd fire engines and a user entered value for "small angle" to help differentiate the pulses. However, this solution is not universal. Several posters on the msextra board used dual pickups in a single distributor and a special input mode in MS that took the input from the dual pickups. One poster even ran dual MS systems.

    GMECM's actually average the crank pulse signal some. It may be possible to rewrite the GM code so it will do the same. There are also changes needed to the dwell computation to account for small / large time variations. I suppose we could determine a window of time representing maximum possible engine acceleration and determine that any substantial change in time less than that window must represent the switch from "large" to "small." It would follow that the next pulse is a "small" to "large" transition. I really wish I had time to play with this stuff. It would be an interesting excercise.
    It's not even a 225, it's a 198 Fireball, just too damn cool to throw out. I checked my gear ratio chart and the highest RPM I used was 4000 to get 82 mph, which it will never see with this nut behind the wheel. I'm going to try to use two ign modules and 1 HEI coil and see if it will work. Do you think I'll have a dwell issue? I thought dwell was adjust in respect to fuel burn time in each Cyl rather than when the Cyl burns it(odd fire). The Odd fire HEI distributor didn't have any provision for adjusting the dwell,(outside of the initial setting). Please shed some light on this. While reading in the MsPro manual I found a very good explaination of IAC stepper motor operation, I understand the 4 wire system now.
    Last edited by Willys43; 04-19-2016 at 07:02 AM.

  2. #62
    Super Moderator Six_Shooter's Avatar
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    Quote Originally Posted by Willys43 View Post
    It is the Ms3Pro, I didn't see any documentation for odd fire in the other models, but that doesn't mean it isn't supported. I think the Ms3 pro is primarily directed at racing. Cool system.
    Yes it is, I have one sitting here to go into a friend's car where we're replacing the FAST system that never worked right. The engine in s a built Pontiac 496. We're also going from TBI to MPFI.

    Quote Originally Posted by Willys43 View Post
    It's not even a 225, it's a 198 Fireball, just too damn cool to throw out. I checked my gear ratio chart and the highest RPM I used was 4000 to get 82 mph, which it will never see with this nut behind the wheel. I'm going to try to use two ign modules and 1 HEI coil and see if it will work. Do you think I'll have a dwell issue? I thought dwell was adjust in respect to fuel burn time in each Cyl rather than when the Cyl burns it(odd fire). The Odd fire HEI distributor didn't have any provision for adjusting the dwell,(outside of the initial setting). Please shed some light on this. While reading in the MsPro manual I found a very good explaination of IAC stepper motor operation, I understand the 4 wire system now.
    Dual ICMs and single coil will not work. Keep in mind how a coil is triggered. The negative side of the primary is held low to charge the coil and sparks on the secondary when that signal is removed. Using dual ICMs in the way you propose will cause the negative to always be held low or possibly spark at the wrong time. Shortening dwell (which is not something normally supported in tuning software for GM ECMs) MIGHT make it work ok, but as the RPM rises I see it being more of an issue. This is one of the big reasons why I've been saying stay away from the dual ECM route. You need two completely separate ignition systems, and isolate the fuel and air intake of each sets of cylinders COMPLETELY to make this work, like I said treating it like two completely independent engines that happen to share a common crank.

    To even give it a chance of working you will need two coils and a dual coil isolator (usually found in endurance and NASCAR racing}. The isolators are usually used to switch from one ignition system to another in the case of an ignition failure situation, but I don't see why it can't be used with two active ignitions systems.
    The man who says something is impossible, is usually interrupted by the man doing it.

  3. #63
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    Dual ICMs and single coil will not work.
    They should as long as RPM isn't too high. Minimum angle between cylinders is 90 degrees just like a V8. Six cylinder dwell is 30-35 degrees so if spark advance is limited to 30-35 degrees max I would not expect a problem.

    two coils and a dual coil isolator
    Years ago I tried to build a non-computerized HEI for high RPM use. I used a high voltage diode in each coil wire. Each coil was controlled by an independent HEI module connected to a four cylinder pickup coil. It seemed to work ok.

  4. #64
    Fuel Injected! Willys43's Avatar
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    It started this morning. Yehaaaa. Hittin on all six

  5. #65
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    what route did you end up taking?

  6. #66
    Fuel Injected! Willys43's Avatar
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    Two 1227747 computers, both modified for chip flashing, one controlling odd # cyls and IAC, initial spark set to 0* in computor, the other one controls even # cyl without IAC, with initial spark set to 90*, 1 odd fire hei distributor with three of six pickup points ground off, 2 ignition modules, all shared sensors except engine temp and O2 sensors
    Last edited by Willys43; 08-08-2016 at 01:41 PM.

  7. #67
    Super Moderator dave w's Avatar
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    Quote Originally Posted by Willys43 View Post
    Two 1227747 computers, both modified for chip flashing, one controlling odd # cyls and IAC, initial spark set to 0* in computor, the other one controls even # cyl without IAC, with initial spark set to 90*, 1 odd fire hei distributor with three of six pickup points ground off, 2 ignition modules, all shared sensors except engine temp and O2 sensors


    dave w

  8. #68
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  9. #69
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    Congratulations!!! How long before you can start driving and tuning?

  10. #70
    Fuel Injected! Willys43's Avatar
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    Quote Originally Posted by 1project2many View Post
    Congratulations!!! How long before you can start driving and tuning?
    2nd fuel regulator is bad, 11lbs. New adjustable regulator due in about Wed or Thur. Hope to try driving maybe this weekend. I'd hate to proceed knowing the fuel pressure was marginal.

  11. #71
    Super Moderator dave w's Avatar
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    I'm curious about your data logging and tuning plans? Identical VE Tables in both '7747's? Identical Spark Table in both 7747's? Two Laptops with two ALDL cables? One Laptop with two TunerPro RT sessions running?

    dave w

  12. #72
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    Very interested, lots of cool factor. what's the firing strategy,IE: will tach signals be right? is three cylinder firing possible on 7747? curious to learn how those things are gonna share fueling/mapping. I love oddball stuff, especially bringing it into the modern age........

  13. #73
    Fuel Injected! Willys43's Avatar
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    Im planning on staying with idntical tables, spark and ve. The laptop i have isnt much. I'll start without the ability to compare one ecu to the other. The harness has an extra injctor wire in it so I can change 1 wire and run both injectors off the same ecu if nescesary. I'm probably just going to drive the same route twice and log both just for grins and see what I get. Really accurate comparison isnt it? I lke the idea of 1 laptop, 2 cables, running to copies of Tunerpro RT. I just hate to buy another laptop. I could tune it ith 1 ECU controlling the fuel the prgram both ECUs the same and switch the injector back. Actually I don't think it should matter much which way I do it.
    Last edited by Willys43; 08-08-2016 at 05:19 PM.

  14. #74
    Fuel Injected! Willys43's Avatar
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    Quote Originally Posted by skandolis View Post
    Very interested, lots of cool factor. what's the firing strategy,IE: will tach signals be right? is three cylinder firing possible on 7747? curious to learn how those things are gonna share fueling/mapping. I love oddball stuff, especially bringing it into the modern age........
    Tach signal is picked up off of the distributor which still has six pulses so i think it will work. 1227747 ECU is software programmable for 3 cyl engine. I am using mapping for a stock 4.3. My 198 is a 3.2 which is almost exactly 74% of a 4.3 so I've reduced the base fuel pulse width of the 4.3 to 74%. It starts and I haven't got the foggyest idea what will happen next. Time will tell.

  15. #75
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    Quote Originally Posted by Willys43 View Post
    It starts and I haven't got the foggyest idea what will happen next.
    I love the 1 step at a time approach. No matter what system you're working with you've got to get it running before you can worry about doing anything more. It's the only way to learn and you're doing a good job on such an oddball system.

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