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

[Circlotron]

Nah, not using a "proper" driver, just a PN100 and 2k2 pullup resistor to the gate. I have used this setup with great success on many other boxes I have made. What I might even try is put 100nF across the trigger wires to the opto. Will make about 10uS or so delay but it might give me some kind of indication.

[Circlotron]

So today the weather has cooled down a bit (low 20's) and the thing runs just perfectly.

[Circlotron]

Today is about 30 deg C. Pulled the box out and put 100nF between the trigger wires as per 2 posts ago. Voila! Reduced the problem by about 95%. Sat still for about 5 minutes with the a/c on and watched the water temp go up and up as it does, and there was on the average 1 misfire per minute. Before, there was one every several seconds when the thing got hot, sometimes several in quick succession.

[Circlotron]

Well, I =thought= I had it fixed...
Time to get a bit more scientific. I dug out this old laptop running Ubuntu + Wine + CoolEdit 96, an ancient Windows graphical sound file editor. A poor man's data logger. I ran the wires from ground and trigger (collector output of Bosch box) via an attenuator to the microphone socket of the laptop. The low frequency response is pretty awful so the rectangular pulsed waveform ends up being differentiated but is still quite usable. Set things going and went for about a 10km drive along the Freeway - enough to make things happen. Pulled up and sure enough there was the missfire every 5 seconds or so, on the rough average. See the screen capture. The upper part of the waveform is the Bosch box trying to make dwell and the lower part is the offtime. Before it misses the time between pulses is around about 24ms, so pretty close to 600rpm. "Dwell" time is about 7mS. Then all of a sudden "dwell" jumps to about 12mS for a single cycle and so finishes 5mS late and the spark is about 19 deg retarded for that cycle. My ignition box sees this and thinks whoa! very sudden step change in rpm and so for a variety of well understood reasons it gets caught out on the next cycle with insufficient dwell and misfires.

In the screen capture right in the centre and again 3 pulses later you can see clearly the Bosch/Delco setup changing it's mind abruptly. Why would it do this??? Only when fully warmed up and running a while too.

[VL400]

The delco does some wonderful things, one of them being able to output EST pulses even with no reference input - so it outputs a rise and fall but has no idea the engine has changed RPM and gets it all wrong. Its possible that the issue is actually the the reference pulses from the dizzy to the module or from module to ECU that is causing it. Could be a failing hall effect sensor

[Circlotron]

Oh no!!! The Hall effect sensor! Why does it have to be that??? Why can't it be something easy like replacing the whole vehicle body shell? Damn, I wish I had a Ford with the distributor up the front.

At least that would go some way toward explaining the apparent temperature sensitivity. If the sensor transition is a bit sloppy it would certainly make the trigger point poorly defined. It is somewhat speed sensitive too – above ~800 rpm it doesn't miss because presumably the transition sharpens up barely enough.

After I got home from my datalogging drive last night I copied it all the the desktop pc and put the headphones on and listened to the entire 27 minutes of buzzy captured waves. (That has GOT to give me a shred of credibility around here). Two things - at a constant ~1900 rpm 100kph every now and then there was a bzzt that didn't quite fit in; the mark-space ratio jittered about momentarily like when it idles and misses but you couldn't feel it when driving at speed. Secondly, the droning of the waveform was not entirely uniform even at a constant rpm. You could clearly the harmonic structure changing randomly, again as the mark-space ratio changed it's mind.

I might see if I can post some relevant sections of the file. The original is a wav file so I'll have to change the sections to MP3 to squeeze it down a bit but I hope any compression artifacts don't mask the kinds of sounds I am talking about.

[VL400]

I would be looking at the ref signal on your sound card scope (or datalog the ECU, might see it there as a spike/drop in RPM) before changing it though, may not be it and like you say its a prick of a job to change out.

[Circlotron]

Yep, looking at the Hall output is definitely my next trick. Should give me a bit of an idea what is going on.
That logic analyser screenshot of the 808 continuing to give output pulses is pretty weird. The last word in redundancy. I can imagine that with a 6 cyl setup with two sensors but is it actually possible with a VN/VP V8 single sensor?

[Circlotron]

Here are several zipped wav files taken under different circumstances.

[Circlotron]

Had a look at the Hall effect signal today. Good clean edges, about 9.5 volts peak level. About 40% duty cycle at a guess. The diagram I have shows the signal wire from the dissy to the Bosch box as light blue/white and the best I could find was what looked like a light blue. The wires all had bits of other colours on them from being bundled together in the heat for the last million years. The output signal wires going from the box to the ECU all had totally different colours to light blue so I don't think I made a mistake. I probed the wire by peeling back the tape on the wiring loom where it goes along the LHS inner guard just before it branches off to the Bosch box etc. What now? Try another ECU?