Engine test stand

[Dave WM]

5 hours ago, Zed Head said:

Here's the diagram of the distributor dual pickup wires.  Looks like if you connect the two outside wires, Green and Red, (Edit - I screwed up here. The out side wires would be Red and Brown)m to your module you could get double voltage pulses maybe.  Not sure.

The easy way to check that you have two correct wires might be to measure resistance.  If you're on one pickup coil you'll see ~720 ohms.  Green is the shared wire, red and brown are the independent wires.

 

1978 ign module.pdf

[Dave WM]

So if I read this right the large eye off the distributor is the Green lead per ZH attachement so that connects to G lead on the module in the attached PDF and either of the small eyes would go to the red on the module.

think I got that right. could not figure out how to get the pdf to show an image for clarity.

 

[Dave WM]

and that is how I have it

:)

testing tomorrow will include switching those around to reverse polarity  to see if I get the chuga chuga chuga jungle juice effect.

 

Edited April 29, 2019 by Dave WM

[Dave WM]

possible smoking gun! guess that is what happens when you start hooking up things from scratch.

So the working theory was it was trigging on one of the trailing positive going bounces, and not the larger square wave (neg going with incorrect connections).

Edited April 29, 2019 by Dave WM

[Zed Head]

I think that Nissan might be going positive.  If I read their description right.  Funny that they don't just tell you to switch the wires if you get the dashed line.

 

[Dave WM]

you know I was thinking of the wave form from something else, a square with trailing oscillations. have to go back and review.

ok I remembering the wave form at the neg side of the ignition coil...

Edited April 29, 2019 by Dave WM

[Zed Head]

I'm really only aware because it's a common problem when people do the GM HEI swap.  Watching the timing light flash is how you tell if you got it right, if you don't have a good writeup.  If it's steady, it's right.  If it jumps around and gives an unstable idle, it's wrong.  N.G. as Nissan would say.

[Captain Obvious]

I also believe that the original ignition modules are looking for the negative to positive going transition.

And as Zed Head mentioned, if you get them hooked up backwards, you end up with a lot of spark scatter and unpredictability.  It's because you are spending a whole lot of time in the transition zone with a slow changing signal. Kinda like a very slow ramp on a CMOS input. They don't like it and can go indeterminate. You want the slope as vertical as possible and if you get it hooked up backwards, it can go metastable.

The only predictable area is physical transition when the reluctor stops approaching and starts retreating. At that point, the magnetic field change reverses, and the induced current will reverse as well. And... If that's not all... (we talked about the amplitude before being proportional to the speed of rotation) When designed correctly, the signal slope at the transition point is relatively unaffected by the rotational speed unlike the slope elsewhere which is very dependent on rotational speed.

If I haven't beaten this to death yet, here's a pic showing the waveform with the polarity switched. Note that the important positive going transitions are that flat indeterminate area with almost zero slope. Bad. What you really want is infinite slope on the positive going transitions. Here's the wrong polarity:

And here's what the waveform should look like. Note that the positive going transitions are the vertical slope areas. Correct polarity:

[Captain Obvious]

4 hours ago, Dave WM said:

testing tomorrow will include switching those around to reverse polarity  to see if I get the chuga chuga chuga jungle juice effect.

Can't wait. Hopefully we have a smoking gun. It's always a great feeling when that happens!

[Dave WM]

Bingo, and the award goes to polarity. started this morn right up, swapped polarity , back to chuga chuga, swapped back , smooth again.

Clearly the smoking gun

Next up will be to hook up the gauges, color code the distributer wires, work on the vacuum advance, get some new plugs, just refine the over all status.

I would like to do something about the carbon build up on the pistons, not sure if I buy all the hype of sea foam, don't want to hydro lock with water. Don't want to pull the heads right now. I am sure they needed it even before the rich running the borescope showed a LOT of build up.

Maybe use the CSV hooked up to a bottle of water under pressure then some very short burst? that CSV real atomizes well which may help with avoiding hydro lock. some before and after picks to show the effects?

[Patcon]

1 hour ago, Dave WM said:

Bingo, and the award goes to polarity. started this morn right up, swapped polarity , back to chuga chuga, swapped back , smooth again.

Clearly the smoking gun

Next up will be to hook up the gauges, color code the distributer wires, work on the vacuum advance, get some new plugs, just refine the over all status.

I would like to do something about the carbon build up on the pistons, not sure if I buy all the hype of sea foam, don't want to hydro lock with water. Don't want to pull the heads right now. I am sure they needed it even before the rich running the borescope showed a LOT of build up.

Maybe use the CSV hooked up to a bottle of water under pressure then some very short burst? that CSV real atomizes well which may help with avoiding hydro lock. some before and after picks to show the effects?

If it ain't broke, don't break it. Premium fuel might remove the deposits over time

[Zed Head]

I think that time and a correct tune are probably the best for cleaning up carbon deposits without taking the engine apart.  There are a bunch of before and after videos out there showing that Seafoam and the others don't do much.  It will bake and flake off over time.  Bake and flake.  Gives you a reason to drive it hard.  Cleaning the carbon off.

Did you take some pictures with your borescope?  How bad is it?