form94

I have no spark out of the coil. The module is newer and i had it checked to make sure its good. I bought a new coil because its cheap and it was old i guess. I have an extra harness and pcm so i swapped them out to still have no spark. That leaves the opti which i had bad luck with recently and i have a bad feeling i bought another bad one. Makes me sick if thats the case. Will a bad opti cause no spark out of coil and if so how and why? If it can how to check it?

moparman

There's a sticky on checking the opti at the top.

Guest47904

A 42 concerns the IC line from the PCM to the ICM. This is the white wire that fires the coil. A 42 indicates it is grounded.

You need to check it from one end to ground with an ohm meter and be sure when you do, both ends are disconnected.

The PCM connector is the black one and the white wire is on pin 5.

form94

Thanks guys. Speedy I did do the checks that people talked about in other posts but it seemed ok. So i had another engine harness from another car and i hooked it up along with the pcm and still no spark. Thats why i wanted to know if the opti could cause no spark out of coil.

form94

What should the resistance be between on white wire?

Guest47904

The code informs you that the white wire may be shorted to ground.

When you measure a wire with an ohm meter. You either want a measurement of 0 ohms or you want infinite ohms. If you are measuring from one end of a wire to the other to see if there are breaks in the wire. You want the meter to read 0 ohms. That means there is no resistance. No break in the wire.

If you suspect the wire is shorted to ground. You measure from the wire to a ground point. What you want is the meter to read infinite. High resistance. So the wire is not touching ground.

In your case, the PCM is reporting that the white wire is grounded. So you disconnect both ends of the wire and ohm it to ground. Put one meter lead on the wire at one of the connectors and the other meter lead on a ground point.

If it reads low ohms, you wiggle the entire length of the wire until the meter reads open (infinite) or high ohms.

Never ohm a wire to ground unless both ends are disconnected. If it is still connected, the device may give you false low resistance reading to ground. Try it with a light bulb sometime.
Understand?

form94

Yes that makes complete sense. thank you for explaining clearly.

Guest47904

What I should have clarified a little better was if you check it and it reads infinite. That is obviously what you want when checking a wire for contact with ground. But, suppose the problem is intermittent. With a vehicle that has both engine and road vibration, that is a very good possibility. So if you check it for a short to ground, it may not be evident at first.

So my clarification is whether it shows 0 OR infinite ohms, you should wiggle the entire length of the wire to see if the reading changes. Don't just check the wire for contact to ground, and stop if it reads infinite (high resistance). It just may not be touching at the time you checked it.