The car has been tough to start and I've found that there is poor spark on the rear leading plug.

I put a timing light on it and it is intermittent. It sparks ok for a second and then cuts out, then ok again. When I rev the engine, there is no spark on the rear leading at all.

The front leading sparks fine under all conditions.

New plugs, new wires.

Would this indicate a bad coil or bad wiring?

I'm leaning towards the coil, since the front leading is working fine and they are fed by the same 2 wires, which go to the same coil.

I made a repair to that harness, so I'm going to check the wiring now.

 

Check the coil resistance on the two connectors. If it's 1 ohm or above (iirc), it's bad. Mine are good when they're cold, but once they warm up, they go out of spec.

 

I checked the wiring and there was a problem. The shield wire (grounded) had been contacting the wire it goes around, which goes to the leading coil.

I fixed that and the rear leading spark still sucks. Again, the front leading spark is great.

 

That's really strange as both rotors share the coil. Have you checked inside the contact of the rear leading coil? There could possibly be corrosion or some other foreign matter...

 

Tell me about it.

When I had the engine apart, I checked the coil resistances with a multimeter. It's clean in there. I remember checking that.

 

The coil resistances check out fine.

When I pulled off the wires one of the terminals came off at the coil. I temporarily fixed that and checked resistance on the wire. Wire is good.

I checked the spark at cranking and the rear leading sparks during cranking, but once it starts up the spark is intermittent.

I tried switching the leading wires at the plugs and whichever plug gets the L2 wire does not spark properly.

Then I put them back to normal.

I also tried switching them at the coil and the L2 didn't put out a spark on the L1 wire. Meanwhile, the L2 wire was sparking fine on the L1 output. What the hell? I'm gonna check the plug I guess..

 

I ordered a new coil, harness, and plug wires. I'm 99.9% sure it's the coil.

Does anyone know if you can replace the leading coil by just taking off the throttle body, or do you DEFINITELY have to take off the UIM?

 

If I remember correctly there are 4 8mm nuts holding it on, you will have to take the uim off to get to them.