Bosch ign module on VN,VP V8 driving other ign box

[Circlotron]

Well. today I picked up an ECU from the wreckers for the princely sum of $41. It was one of those wreckers where you take the parts off yourself, and some turkey had already knocked off the memcal. Didn't matter so much because it was a V6 one but I still would have liked to have it so I could convert it to a V8 one. Anyhoo, put my memcal into this new ECU and it started up and seemed alright so I took it for a drive. After about 15 minutes I pulled up and let it idle and dingbust it, it started missing just as before. So it's not the ECU.

[VL400]

Going back to basics, and not sure if its been asked already, but does it misfire using the standard V8 module?

[blownvp]

i think the delco has a variable where it changes the dwell with accelleration.5d.xdf or 12p.est params-dynamic correction factor.est params-dynamic correction delta ref deadband.try zeroing est params-dynamic correction factor.

[Circlotron]

Going back to basics, and not sure if its been asked already, but does it misfire using the standard V8 module?

No it doesn't, unfortunately. At least that rules out all the high voltage side of things. The standard module does have a single electrolytic cap inside and they are probably the most unreliable type of component. 20 years of heat and time may be taking it's toll. It also has a pair of 85 deg C rated 4011 chips. Maybe if I replaced them too. Or if I could just get a lend of another module somewhere.

Has anyone ever traced out the circuit of one of these modules?

[Circlotron]

i think the delco has a variable where it changes the dwell with accelleration.5d.xdf or 12p.est params-dynamic correction factor.est params-dynamic correction delta ref deadband.try zeroing est params-dynamic correction factor.

So if there is no acceleration this parameter has no effect? I get a miss at steady idle so I can't see how this would have the right effect. Of course, my inability to see something is hardly a sound basis for any given point of view.

[Circlotron]

Today I hooked up my poverty-stricken "datalogger" to the Hall effect pulse and went for a drive. The car was on it's best behaviour of course and it took a while to play up but finally it did. Here's a short wav file snapshot of it idling in gear and missing. The Hall effect waveform is well behaved, simply tracking the erratic changes in engine speed as you can hear plainly.

[VL400]

I guess you also need to know if the hall effect tone change is the result or cause - it will change when the engine stumbles but was it the first thing to change tone? However if it works fine on the standard module its pretty unlikely and is more pointing towards the output driving your ign box.

Not getting any EST fault codes reported by the ECU?

Back to your dynamic dwell here is a data log (its about 40Hz so so shows a reasonable representation) showing dwell at idle on a V6 - it was cold and about 1 second after starting it so idle is a bit higher. Dwell is the green trace in monitor 2, the red in monitor 2 is spark advance showing the idle spark control...

idle dwell.png (32.97 KiB) Viewed 5103 times

[Circlotron]

Yeah, the dwell certainly jumps around in a hurry, doesn't it? Maybe it's making life difficult for me...

Spent the evening having a close look at the Bosch module and the Hall effect input has a 1K5 pullup and a 4V7 zener to ground. That's awfully interesting because the waveform I was looking at before was definitely 9 volts peak on the scope, not 4.7V as clamped by the zener. Just had a further look at some notes of mine and the tooth in the distributor is pretty close to 40 deg wide so the Hall effect waveform should go high for 40 deg but is actually going LOW for 10/24 mS x 90 = 37.5 deg. I must have read the wrong waveform. Dear oh dear.

[VL400]

I would have thought there should also be a series resistor to limit current through the zener, so will still see > 4.7v on the hall signal but its clamped further in.

I think you have read the correct waveform too, ECU triggers on the falling edge so should be low for 40deg. This is also the cranking dwell when in module mode before switching to EST mode

[Circlotron]

I am just wrong in so many ways
The 9 volts I thought I read from the Hall effect was exactly half that because I read the scope wrong.
The waveform I thought had the wrong mark-space ratio was in fact inverted by my laptop as I mentioned several posts ago but subsequently forgot, so it is in fact okay.

Current limiting is by the 1k5 pullup (that the Hall effect pull down) that can only go as far up as the zener voltage.

I have got a spare Bosch module I just put back together after tracing out part of the circuit. I'll try that one and see what happens. Tell you what; those modules look like the inside of a two dollar transistor radio, and the board layout looks like it was done by a schoolboy on work experience. Not only that, there is one transistor that it's collector to to a 100k resistor and 100nF capacitor in series and then to the internal +5v line and that's it. The transistor does NOTHING AT ALL! The R & C go nowhere except to the supply rail. And the snubbing cap and overvoltage clamping zeners are all connected wrong too. Amazing.