rs/ss 67

Is there a way of testing the optispark when it is out of the car ?

Steve

MikeC4

You would need a power supply and DVM. I suppose an oscilliscope could also be used to check the high and low resolution pulses if you have something to continually spin the Opti driveshaft.

Here is an On Car method of testing. You could extrapolate what is needed to do this off car as well.


The opti has two functions in the spark process. The first thing that happens is as the cam turns, the optical section of the optispark picks up the signals by the rotation of the shutter wheel. The pulses are sent to the PCM via the optispark electrical harness. The PCM processes the signals along with other sensor input and determines the proper time for the coil to fire. The PCM sends a signal to the Ignition Control Module (ICM) and it, in turn, causes the coil to fire. The spark from the coil travels through the coil wire back to the secondary ignition section of the optispark (cap and rotor), to be distributed to the proper cylinder.

If the opti is never sending the signal to the PCM, the PCM will never send a signal to fire the coil.

Here is some testing you can do. Refer to this diagram:



Disconnect the ICM connector. Leave coil connected.
Turn key to ON.
Check for dc voltage with a digital meter at harness terminal "A" to ground and and also "D" to ground. Note: Use a high impedance meter (at least 10 megohm) when dealing with the PCM.
Result should be 10v dc or more on both terminals. If you get no voltage, use the diagram and chase back toward the coil and the ignition fuse. Power for the ICM comes from the ignition fuse and through the coil, so any of that could be bad.
If you have good voltage, switch the meter to ac scale and connect test leads to terminal "B" and to ground. Observe meter while cranking the engine. You should see between 1 and 4 volts ac (those are the pulses that trigger the coil to fire).
If you don't see the proper ac voltage the problem could be the optispark, the harness to the optispark, the PCM or any of the wiring in between. Visually inspect all the connections you can get to for poor contact or corrosion.


If you are successful using an oscilliscope, this is what the pulse train output should look like from the high and low resolution timing wheel:

rs/ss 67

Mike,
Thanks, I will reinstall it on the engine tomorrow and get to testing.

MikeC4

Since you have the Opti off, did you open it up and inspect the cap and rotor for carbon tracing, coolant or water intrusion ?

These units are easy to disassemble using a deep inverse torx socket. You can get a cheap set at Harbour Freight.

What symptoms lead you to believe that your Opti is bad ?

rs/ss 67

I have a spare Opti that I wanted to check before I did the upgrade to the later style vent system, My son was helping chase down an oil leak and he gunked the engine without my knowledge and now it is popping thru the passenger side exhaust and it is very hard to start and keep running, I checked for water under all the injector harnesses and pu;;ed all the wire conectors on the manifold and blew them out with air--same systems are present so I will be tearing into it I guess.

stephenpen

I know its old but I have a quick question.

I have spark at my coil but no spark at any of the wires. Is this a case of the rotor coming off ? Is the optical side working by telling the coil to fire ? But the distributor side is not distributing spark because the rotor is floating around behind the cap.

TWISTERUP

If you're also talking LT1 (can't tell by your profile)--the rotor is held on by two screws --the rotor sandwiches the opti trigger wheel in place so if the screws /rotor had come loose--the shutter/trigger wheel would most times also be loose and you likely would have no spark period.

The rotor could be broken in another way-cap could be bad or coil wire may be bad. If the coil wire is good remove the dist. cap-shouldn't be hard to see the problem if you have no spark at the plugs.

stephenpen

I think the 2 little screws backed out causing the rotor to come off. This opti only had a couple hundred miles on it. This is what happened with my last opti. I'm hoping I can install a new cap and rotor it will live again.

If the opti was not working at all I would not have any spark at the coil. If I've read everything right the opti has to functions.

First is to pickup timing off the cam to send spark to the coil.

Second is to take the spark from the coil and ditribute it to the 8 spark plugs.

TWISTERUP

Just trying to answer your question -- as i said if the rotor came loose and the shutter wheel became loose (not turning) or damaged the opti decoder no spark at the coil--if the shutter wheel continues to turn with the dist. shaft--spark at coil-none at spark plugs. Try some Loctite on the rotor screws when you go back in the opti.

BTW there's nothing unique about what the opti dist.does the majority of distributors be they -points and condenser--HEI--hall effect--directly or indirectly (via ICM) collapse the field in the coil creating spark then the cap and rotor send the spark to the correct cylinder

ScaryFast

You can easily test the opti off the car by plugging it into the car wiring harness and spinning the shaft yourself.

You'll hear the coil popping as it tries to fire the igntion. Just spinning the shaft makes the ECM think the motor is turning over and it will fire the coil. If you don't hear the coil popping you can put a spark testor on it or a plug wire.

Obviously ignition has to be in the "on" position...