420A No spark cylinder 4 only

[Mechlawrence]

Hey guys, need some direction here. Driving yesterday and pulling away from a stop light and car lost power and sounded like driving a farm tractor. Get home and have no spark on cylinder four at coil pack. Swap coil pack with a known good pack and still no love. 1-3 fire as they should but #4 has zero spark and is a dead cylinder. Where do i start troubleshooting this from? Recently replaced crank sensor about a week ago and all was good for about a week. 97 420a 5 speed

 

[silvreclips]

The 420a coil pack is divided into 2 coils. Cylinder 1 and 4 run off one coil. Cylinders 2 and 3 run off the other coil. If all of the cylinders have spark except for #4 then I would look into the spark plug wire/connection to the plug. Swap plugs and wires around and see if that changes anything.

Is the injector firing for that cylinder?

 

[Mechlawrence]

I’ll be home in a little while and check the plug and wire for that cylinder and swap them and see if it follows. I’ve got a noid light set so i can check injector also. It was just weird when i pulled wires loose and nothing was arcing around on #4 but #1 was hitting nice and hard since they share the same coil.

 

[Mechlawrence]

Switched plug and wire with cylinder #1. Problem stayed at #4. Injector is pulsing and plug was wet. No spark for just the #4 half of that #1/#4 coil. Any suggestions?

 

[silvreclips]

Put a meter on the coil and compare the resistance between the pins and the terminals. See if #4 is different. I know you swapped the coil pack but it won't hurt to check. It doesn't make sense why only 1 cyl is missing spark.

 

[VelocitàPaola]

Can you describe in more detail how you're testing the plug? With wasted spark systems, if there's an issue with the coil, it's kind of an all or nothing deal: you'll either get spark in both cylinders 1 and 4, or neither.

 

[Mechlawrence]

Tested the coil harness terminals to each of the 4 plug wire towers and #4 has the same readings as #1 in all combinations. I’m at a dead end on this one. What tells the computer when to fire #4? Is it the cam sensor?