Ignition module Q's...... - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 01-17-2004, 09:49 PM Thread Starter
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Ignition module Q\'s......

I am trying to figure out the advance curve for the 258 ignition. In my research I have found that the 258 and the 360 use the same ignition module. Doesn't the ignition module determine the amount of non-mechanical advance? Wouldn't the advance requirements of the 360 and 258 be different? I also found that the Ford 300 I6 uses the same module. Maybe someone can explain the role of the ignition module so I can understand what is going on.

Thanks,
Tom
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post #2 of (permalink) Old 01-17-2004, 10:01 PM Thread Starter
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Re: Ignition module Q\'s......

After more reading, I have decided that the reason that the same module works on all these engines is because it doesn't have any effect on the timing. It basically acts as a fancy switch reading the reluctor on the distributor and firing the coil. All of the advance on these engines is controlled by the distributor. If I am correct, then the only available advance is the vacuum advance and the mechanical advance. Can anyone verify my theory? Anyone know the advance curve for the 258 distributor?

Thanks,
Tom
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post #3 of (permalink) Old 01-17-2004, 10:53 PM
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Re: Ignition module Q\'s......

i dont know the advance curve.. but it is handled by the distributor... and not the ignition mod..
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post #4 of (permalink) Old 01-17-2004, 11:18 PM
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Re: Ignition module Q\'s......

1. By Jove, he's got it!
2. Tom, never sell yourself short...
3. You're learning stuff,
4. At a fantastic rate!
5. And sharing it.
6. Good Job, keep it up!
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post #5 of (permalink) Old 01-18-2004, 12:04 AM
 
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Re: Ignition module Q\'s......

correct for advance.
but, actually it depends. On the stock ignition of a computer controlled 258 the reluctor signal is fed to the MCU then to the ignition module. This gives the MCU the ability to retard the timing.

when you do the howell upgrade. you rewire the ignition so that the signals go directly to the ignition module.

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post #6 of (permalink) Old 01-18-2004, 12:25 AM
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Re: Ignition module Q\'s......

</font><blockquote><font class="small">In reply to:</font><hr />
This gives the MCU the ability to retard the timing.

[/ QUOTE ]1. The MCU controlled the timing,
2. Via the Knock Sensor.
3. If a Knock was sensed,
4. The MCU retarded the spark,
5. Thinking the knock was a ping.
6. It makes sense,
7. But I wonder what happened,
8. When a rod or the crank started knocking?
9. But, the MCU only had the ability,
10. To advance or retard about two degrees,
11. Per the knock sensor.
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post #7 of (permalink) Old 01-18-2004, 01:01 AM
 
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Re: Ignition module Q\'s......

</font><blockquote><font class="small">In reply to:</font><hr />
10. To advance or retard about two degrees

[/ QUOTE ]

it cant advance really. to do that it would have to fire the plug before it got the signal from the distributor. ie, it would need to guess.

</font><blockquote><font class="small">In reply to:</font><hr />

7. But I wonder what happened,
8. When a rod or the crank started knocking?


[/ QUOTE ]

this is 100% why I went with the Howell system over the MPI. I think today they could filter the knock sensors signal to detect a real ping, maybe with some DSP. but I think they were just using a band pass filter.
I think I read its about 5K center.
but, on dale Becket's web page he said you can test the knock sensor by knocking on the intake manifold. Which means that the filter doesn't filter much. Which would mean on a tiered old engine, the timing could be wiggling due to lifter noise or any noise.
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post #8 of (permalink) Old 01-18-2004, 04:11 AM
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Re: Ignition module Q\'s......

Yes, two degrees - at a time. But 2+2+2+2, one after the other retards it as needed.
When the knock sensor "hears" what it thinks is ping, it pulls the timing back instantly 2 degrees. But it doesn't immediatly go back advanced again. Another noise, another -2 -- and so on until the "ping" stops.
So the end result is it can pull the timing back fast, but the timing advances slowly.
As you drive the timing's always seeking the most advanced position - most efficient - but too much jumps it back a little at a time.

Yes, since the knock sensor is just a little microphone, a rattle can sound like a ping to it. I've seen several times an unrelated item - like a loose alternator bracket, even a deep socket left on the intake manifold accidentally, cause enough noise so it won't advance - it keeps pulling it back. It cannot retard at all, it cannot go back any further than intitial base timing, it just prevents advance.
Symptoms - low power, sometimes it's intermittant. Sometimes a hair puller!
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post #9 of (permalink) Old 01-18-2004, 06:48 AM
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Re: Ignition module Q\'s......

A long time ago, in the life of this board, TeamRush said that only the 1979 258 cu.in. distributor had a longer slot to allow for more advance.
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post #10 of (permalink) Old 01-18-2004, 08:42 AM
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Re: Ignition module Q\'s......

Also, when you put a gm hei distributor from a 250 the curve is not the correct one for a 258.
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