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Delete dizzy advance for efi or not?


Henning
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So I’m planning to install a modern engine management into my car. It is called Universal Motor Controller -UMC1- and is based on Megasquirt.

Now I’ve read and also one of those tuning porls told me to set the mechanical ignition advance of the dizzy shaft out of order. Means to freeze the shaft to a one-piece by welding, lock bolts or however. This is necessary because the advance is done in the ECU and no longer in the dizzy.

But I think this is wrong. I have a different theory. Here we go:

When the shaft is stiff the dizzy finger will always point to the same spot in the dizzy cap at any rpm in a certain crank position. Not regarding the spark here yet. When cylinder #1 is in TDC, the finger will always point to pin #1 in the cap- totally indepentent from rpm, due to the welded shaft. OK?

Now when the engine is running at higher rpm the spark wants to pass finger and cap earlier than in TDC due to the programming in the ECU. But the finger will not fit to the cap’s pin since it can not move forward any longer. The spark wants to pass when the finger has not arrived at the pin yet.

So I think it doesn’t matter where the advance is done and the dizzy should be untouched- except of maybe removing the points. There will be no longer an ignition advance but a finger advance what will still be needed. And yes: the dizzy finger curve and the programmed ignition curve will not match 100% but it will be better than with a frozen shaft.

I really do hope that I have described my problem here understandable. What do you think?

Thanks in advance for input,

henn

 

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What you are talking about is called 'Phasing' of the distributor...making sure the low and high tension parts are synchronised. I think allowing mechanical advance for HT is OK as long as your TDC signal for ECU is not coming from the distributor. Part of the reason for the end of the rotor arm being an arc (& not a pointer) is to deal with the issue you describe.

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This all depends on *how* you are setting up the new ignition control with the UMC.  Since it has 2x ignition outputs (though I'm not sure whether they're high current or just logic drivers), you have the option of going wasted spark and not using the distributor at all.  The other option would be to keep the distributor, but with its ONLY job of sending the spark to the correct cylinder.  In this case, with the UMC controlling the timing of the coil, you want the distributor locked down so that it doesn't change timing at all by itself. The 'finger' on the rotor is wide enough to cover the full range of timing that you need, but you want the computer doing all the control, and not complicating things with computer timing PLUS distributor timing.  Make sense?

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Rotor phasing:

https://www.haltech.com/support/309315000033092751

 

From the logic presented in the Support article, the rotor should be locked.  At low rpm the spark advance is low and the mechanical centrifugal advance is at its minimum point.  As speed increases, the with the rotor unlocked, the mechanical advance mechanism advances the rotor relative to a post in the cap.

 

At the same time the ECU advances the timing from the timing map.  So the when the spark event occurs at high rpm, low load, the rotor moves relative to the cap terminal, the mechanical degrees of advance plus the ECU timing map advance and cross fire will probably occur (30 degrees mechanical advance + a probable and often normal +40 map advance = 70 degrees total rotor position ahead of the terminal.)

 

If you don't believe, leave the distr advance mechanism unlocked and hope for the best on a crossfire.

Edited by jimk
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11 minutes ago, HBChris said:

You need to lock the dizzy, this is a common mod when using a Motronic ecu in an m30b35 motor.  I did this in my e9 as I wanted the tradional dizzy and not the Motronic dizzy.  The ecu controls everything.

As was said.

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Thirded.

 

You don't want the distributor messing up the advance, because your ECU won't

know what it's doing.   And it's not all that precise.

 

Let the chips do the work- the mechanical advance is only for analog  ignition.

 

t

 

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So thanks to all of you for the input.  And sorry for not mentioning that the dizzy points will be removed. It will not have anything to do with the phasing in the future. It will only distribute the sparks to the correct cylinders like Guy said. Ignition will be done in the ECU.

But nevertheless I'm not entirely convinced yet. I do understand that the rotor's tip contact is wide enough for all the range. But if the ignition phasing is programmed to spark earlier with rising rpm, why should the rotor not follow this phasíng? @Jim: there will be no addition of mechanical and mapped advance. You have to lay them parallel, so there will be a difference of 10 degrees in your example what's not that much. 40 degrees from the mapping and 30 degrees from the rotor.

I just don't want to spend time and effort to lock the dizzy if it's needless.

 

henn

Edited by Henning
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Locking would be necessary if you put a trigger in the dizzy, like I have done with optical trigger. But I get your point. Haven't thought about it before. I have had some trouble syncing the trigger with rotor tip that isn't that wide. Your thinking might work, it's just not that common case. Usually people either use dizzy for trigger or go wasted spark or full sequential COP system. 

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2 hours ago, Henning said:

But if the ignition phasing is programmed to spark earlier with rising rpm, why should the rotor not follow this phasíng? @Jim: there will be no addition of mechanical and mapped advance.

Keep the spark advance and rotor position separate in you mind.  Spark advance is relative to crankshaft and will be per the ECU.  Rotor position is just that, and locates the rotor when the ECU triggers the spark to occur.  The mechanical advance only adjusts the location of the distr rotor at the time of spark and will not affect when it occurs (because points are not in there).  So if you want to keep the mechanical advance mechanism, you will have to account for it when phasing the rotor if it gives trouble.

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On 9/19/2021 at 7:30 AM, jimk said:

30 degrees mechanical advance + a probable and often normal +40 map advance = 70 degrees total rotor position ahead of the terminal

 

Isn't 30 degrees of advance at the crank due to 15 degrees at the rotor?

 

e21 rotors have a wider tip than the e2002 rotors and less resistance built into them.

 

BMW 2002 320i (1975-1979) Ignition Rotor Bosch OEM 1 Year for sale online |  eBay

Rotor for Golf 1 with Bosch distributor 055 905 225 B - Mecatechnic.com

 

How do people go about blocking out centrifugal advance?  I've seen one example where someone ran a screw down through the points plate, but I don't remember the details.


Tom

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2 hours ago, '76mintgrün'02 said:

Isn't 30 degrees of advance at the crank due to 15 degrees at the rotor?

Spark happens when the ECU says it happens, the rotor has nothing to say about it.

 

2 hours ago, '76mintgrün'02 said:

How do people go about blocking out centrifugal advance?  I've seen one example where someone ran a screw down through the points plate, but I don't remember the details.

 

Arc welder does a good job.

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11 hours ago, Henning said:

. 40 degrees from the mapping and 30 degrees from the rotor.

You can't add these together, they are happening in parallel, one is not dependent on the other.

 

34 degrees crank advance is 17degrees at the dizzy rotor. 

 

Dizzy rotor position alone does not affect ignition timing, it either fires correctly or it misfires (if it's too far away, or pointing at wrong cylinder).

 

You can check it by aligning trailing edge of rotor tip with No1 at TDC, then turn crank backwards 34degrees and see where the leading edge of rotor points.

 

I don't think it's an issue on a 4 cylinder, but on a V12 you only have 30degrees between cylinders and it's quite easy to get a misfire situation.

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Use a trigger wheel and run wasted spark. Let the ECU control spark  Then use a locked dizzy as a cam sensor to allow the ECU to better control the fuel

Not sure about the capabilities of your ECU but it may be able to produce sequential fuel injection rather than just a batch/flood approach  

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