Quiet does not mean that a diode hasn't died....

I will try to find that thread - it has a test!!!

Also, www.gordonkillebrew.com - he is the MAN when it comes to these cars. It ain't cheap, but I suspect he will have you running for about $20.00!!!

 

What he is implying is if there is signal to it there should be a signal out to the coil.Basically he is trying to see if a signal is coming from the ECM.
A good idea. It will also let you look at the amplitude of the signal in/out of the module.It is possible that a weak signal is triggering the old one but not the new one.Only problem here is to figure out what amplitude it is supposed to be.It could go back to the ECM have you got someone who you might swap yours with?

 

Tom, I spoke with one of the EE's here at work and his comment was unless you know what the wave form is suppose to look like there would be no way of determining what your seeing. Could be a sine way or a square wave, and then the frequency values are unknown.

Lani

 

The frequency will change with engine rpm.
Four cylinders fire per revolution of the crankshaft -- so, 4 x rpm / 60 (divide minutes into seconds) = frequency in hertz.

The input signal to the ignition module (which is the output from the ECM) is going to be a "trigger" signal which will be only a spike -- I think the output of the ECM has an amplitude of 5 volts peak-to-peak.

The output from the ignition module (which is the input drive to the primary of the ignition coil) will look like a square wave with an inductive dampened oscillation (ringing) on it -- this is also the signal that is sent to the tach filter; the tach filter filters out the ringing so there is a square wave to drive the tach. This signal is about 12 volts peak-to-peak.

These signals are all common signals to any "Kettering" ignition system.


Tom Piper

 

Tom,

Kewl thanks for that info. I'm going to borrow a 4-chl portable scope and my EE friend. We will check this after work.

Lani

 

Here is the link:

http://forums.corvetteforum.com/show...56&forum_id=48

 

That is certainly an interesting read. Although I couldn't get to the link he posted, something about a firewall. Not sure if that is an issue from here or their server. I'll try it again from the house. That would be interesting to see what my relatively new alternator is doing. Thx Bogus.

Oh BTW, I have a new ECM, new coil and new ICM being overnighted.

 

Sorry here about your problem as you had been helpful to me in your advice on how to replace my coil (installed the MSD coil and no other changes and the car runs better). Here is an idea out of left field that you might try (no basis other than instinct). I would unhook the PCM totally and let it sit for a while so that any programming is lost. Then hook up again with a new coil module and see what happens. Maybe the computer had adjusted its program for conditions associated with the old module and is stumped when it sees the new one. Again, this is just a total guess without any basis in fact but at least it is something to try. Good luck and let us know what happens.

 

I thought Gordon was a minimum of $100.? For $20. I'd call him. I'll get this info this evening with oscillascope, this should be interesting.

I was just describing what my old alternator was doing, it was just making all kinds of noise and when I replaced it was so quiet you barely hear it now. I wasn't even aware of this diode thing until you posted.

 

Hey Doug thanks. What is a PCM?

Oh you betcha I will keep this going until I resolve it. If anyone ever has this condition happen to them, I would dearly pass on all information to help someone who experiences this.

 

That's what they call the main computer (or sometimes the ECM?). Anyway, on my 95, this is the large shiny metal box with fins on the rear of the driver's side of the engine compartment--easily accessible. On earlier years I believe this is inside the car.

 

Might be worth a call to Gordon Killebrew. With the detailed description you have he may be able to help. I just took his Corvette 101 & 102 and he really knows the electronic on these cars. Good luck!

 

I was thinking 5V on the signal too pretty comon voltage on computer signals.

I read the Alt thread too and I bet everyone who did will run out and check for AC on the alternator.

It does not matter square or sine(my bet is square) you should be able to see the signal and amplitude.It is not that hard to adjust a scope if you know what you are doing.Hope you get it straight soon but my bet right now is the ECM dc signal is low voltage.Guess you will find out shortly.

 

His min is 10.00, and 3.00 for every minute after that.

 

Oh ok, yes its ECM. Early 93's were a plain black box mid year (eng compartment driver's side) they switched to the newer computers.

I have one on order should be here in the morning. Its being over nighted.

 

Ok we scoped it. It appears ok, at least from what we saw but of course neither of us had a reference to work from other than your message that I printed. I can post a picture tomorrow as I don't have a floppy drive on this computer. We snapped a couple images.

What was interesting which I have no explanation for: Just shortly after we stop the trace and got a couple images, the trigger signal went away. At first my friend thought he just lost the connection with the probe but we could never get it back. I looked at the temp and it was up to 158 at that point. I don't know if that means it went from one mode to another or not. Electronics is sometimes above my head. And I shut it off, then restarted just to see if it came back but it did not.

Of course I showed him how instantly it starts with the old module, then I plugged the new one in and it would not fire over.

I guess one nice thing about it all, I got a compliment on how clean my engine is, my friend was shocked when he put his hands on my engine and was so surprised his hands were still clean LOL.

 

What was the peak to peak voltage?

Did you have the scope on when you tried the new ones and did it show a signal going to it?

You shut it off and it did not come back.What the trigger signal while it was running?

 

Bogus, I ran that alt diode check. I got an instant of 2-3 volts AC but it would run back down to .06 or so.

So does that mean I'm ok or not?

 

It is not your aternator causing this.Keep your eye on the ball.

Now what did you see on both modules with the scope on input and output?

Are you sure you were reading the signal for the coil since you said" it went away"but the car still ran or am I reading this wrong.

FYI an alternator works on a rising and falling magnetic field and any wires close enough to it will get some induced AC voltage in them. 14VDC in a rectified circuit equates to around 28VAC pre-rectified.

 

Darn it was replying and electric went off, stupid thunderstorm.

First I wanted to say thank you to everyone for standing with me through all this, I sincerely appreciate everyone's help.

No we didn't scope the new module. Of course now I'm in territory I am clueless about with this stuff. I didn't think it would show anything since I couldn't start it with the new module. I'm a little hesitant to crank that long on it when it won't fire off. I don't need to burn up my starter or wear down my battery. I have enough problems with this beast.

I'll try to describe better, wish I had a floppy I may run back to work here its not far there are still people there I can pull the images off. But in the mean time...
I started it up, he had the probe in the white wire, terminal B, which comes from the ECM and the other white wire terminal D to the coil. The probes are really thin and sharp, so he just penetrated the wires.
I believe he had the scale for the B terminal set to 5 volts and the D terminal to 50 volts. I need to post the image so you all can see.

He was making some adjustments with the scope to get a clean reading. It was probably about 5-10 minutes I guess. Everything seemed to be looking good then as I mentioned near the end of that time period just after we got some images it just went flat. While he was checking to ensure the probe was still in there good, I looked at the temp gauge to see where it was at. It was something like 158 and climbing. But the signal would never come back. I shut it off and restarted and no it never came back. My best recollection was the square wave covered peak to peak that block for 5 volts. So it was there while running then went flat.