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Discussion Starter · #1 ·
Hi guys,

Its been a while but I really need some help with my 1993 Firehawk. About a year ago I had a no run condition with my car, which the engine builder said the ECM was bad. Had a second ECM tested which was fine and I replaced the coil and icm at the same time. Problem solved.

Couple of months ago I was driving the car and it started missing, almost like a plug wire which I discovered once it was home was the case. In the process though the car shut down and had to be towed home.

Once home, it looked like a no spark condition as fuel pressure was fine and I got nothing when checking a plug. As of this time, I’ve replaced the icm and coil. I checked the coil wire for resistance and tested the injector pulse which I have.

The car has an MSD Opti and I heard sometimes the rotors come loose so I pulled the front of the motor apart. All appears fine there.

I bought an oscilloscope which I am unsure of how to use. There are also no codes set. Any ideas here? I am at a total loss right now and would really like to get the car back on the road. Any help is appreciated.

Thank you,


Global Moderator
13,559 Posts
Learn to use the scope. Start by checking a simple DC voltage. Adjust the voltage to have 12 volts in it's range. Then you adjust the time control to get the straight line in view.

Next hook scope leads up to opti low resolution wire. Have assistant crank engine Adjust voltage so 5 volts will be in center of scope view. Then you adjust time setting so you can see the square wave low res signal.

Also check high range signal. You will have to adjust the time control to get it into view. What you are looking for is a vell formed square wave. With no drop outs or crazy wave form pattern. If you have either of these optical sensor is toast.

If a new optical sensor is needed, you must buy a complete opti.

Only buy Delco, Delphi, or GM opti. I've heard the Petris opti is good also, but have never used one myself. And they're about $600.
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