Tried this question in scan and tune, but no response. Just not enough traffic there.

 

Funny you asked. I just happened to be measuring waveforms on my 94 the past 2 weeks and reading up on that stuff. I believe the reference pulses from the opti are 5 volt but I haven’t personally measured this. I have read it, and makes sense because it’s probably TTL signals. I have read about some test setups on the bench to check the optical part pulses using a 5 volt pull down setup. But I can tell you for sure that the signal from the PCM to the ICM is a 4 v p-p square wave real clean looking. This drives the ICM, get amplified to about 40 v p-p and drives the coil. I’m in to process of making my own book of waveforms so if the day comes when I krap out, I have something to look at. Let u know when I get more.

 

Doesn't that pulse come from the pickup coil? might check that.

 

Are you seeking a clean source for RPM from an L98 HEI?

I needed a signal for a device rated for 12VDC square wave at 50%
duty. An MSD 8913 Dis-Tach Adapter delivers.

 

Well got to read the post better answered the question for the wrong system, sorry. However I have written this whole thing up in word and I'm not going to trash it. So this is for operation of the opti system just in case anybody is interested.... or not

Just verified the pulses from the opti are 5 volt. The way the whole system works is the reference pulses from the opti tell the ECM/PCM what the crankshaft position is and what cylinder next to fire. Then the ECM/ PCM takes all the sensor inputs from the engine (MAP, TPS, temp etc) and determines spark timing. It then sends a pulse to the ICM. This will advance or retard as needed. Since the pulse is real small at 5 volts it can’t drive the coil. So it’s function in life of the ICM is to amplify this pulse to a level big enough to drive the coil. There is about 40 volts applied at the same frequency to the primary of the coil and hence the secondary produces the 25K volts which goes to the cap of the opti. The rest you know, the rotor is at the correct position and fires to that plug like any other system.

It’s really a neat system and the precision is with in 1 degree error in timing. The reference pulses are 720 per camshaft revolution or 360 per crankshaft. I use to wonder why they put the darn thing on the front of the engine. But now in my opinion it was for accuracy. There is to much slop in a regular shaft and gears and direct off the cam takes the error out. Charge on

 

Yes. I want to pick up my RPM and TPS wideband inputs at the ECM. The ECM recieves a pulse input from the distributor, thats the line i hope to tap into. The wideband software has the ability to change how many cylinders so i can manipulate the info to get the right RPM, as long as it is a 12 volt pulse wave.

 

TTT

 

I plan on doing this soon with my Innovate Motorsport WB. I understand the white lead (TACH) wire is the place to hook up. Make sure its a high impedence type connection. This I've read at their forum.

 

I'm trying to avoid running a wire from the outside in. I"m pulling the TPS signal at ECM so i thought it would be cleaner and easier to get the RPM signal there too.

 

GRX. The white wire from the dist Tach terminal MAY work for
the Innovate item (LM-1, Aux Box?). However, it did NOT work
for my G2X. I tried several approaches - but the MSD 8913
was the eventual winner.

Agent 86. Valid point. A previous owner had a cable run into
the interior from the engine compartment so I had a ready-made
opening in the firewall. Otherwise, this would have had a different
dimension for me, too.

When I was on the quest for a signal, the suggestion was made to
tap into the ECM source. I received information and a link to the
schematics. I expect these also appear in the FSM. Speak up
if you need this and I'll look it up.

The 8913 is installed in series between the module and the coil.
I don't think you can avoid routing a wire into the cockpit if the
ECM hookup does not pan out for you.

.

 

Still no definite answer

 

Scan & Tune: Apr 27 - May 1 = zero replies
Tech & Perf: Apr 28 - May 1 = no definite answer

My vote, don't hold your breath.

Can you get someone with an oscilloscope to test the output?

While automotive shops would be one place to start looking, there
are also electronics repair facilities and perhaps vocational schools
in your vicinity which might have the equipment, ability and interest
in helping you find an answer.

I was prepared to buy an oscilloscope and found these for $200 US
new. But I came across a solution before purchasing the instrument.

.

 

This is not the definitive answer you're looking for-but, I don't think it can be hooked up directly to the ECM. The reason I say that is from just looking at different wiring diagrams on my 87. I can't see where you could hook up without interferring with another component.

Anyway it got you to the top again.

 

the tach filter is used cause the signal was as square wave...

at least that's what I think is going on.

Get up with TJ Wong or Tom Piper.