2001 Saturn missfire

The fuel filter and the O2 sensors shouldn't be isolating the misfire to one cylinder.

What did the plug look like from that cylinder compared to the other?

It looked the same as the other.

All the spark plugs were a little black but the electrodes were not excessively worn.
I replaced the wires as well becuase they were the original wires and I thought it couldn't hurt.

Also I had removed the throttle body and cleaned it with a spray carb cleaner. there were a lot of carbon deposits. However I am told that is normal

Carbon build up in normal (typical)-yes, but leads to problems.
Cancer is typical (normal?) but lead to problems.
Do you know what I mean? Normal is relative to the situation. This is my carbon removal technique that works for me:



Air induction service:
I like to use castle hydroblast. You spray it into a vacuum line such as the brake booster line if nothing else is accessible. Full spray for 3 minutes, stall the engine with it or have someone kill it while your spraying. Let it set for a few hours then take for a short drive in low gear, revving the rpms to help break it up. First use Castle cleansrite to clean the throttle bore. Try to get the throttle plates scrubbed good with a brush, while your spraying. Use a rag to wipe the carbon out between brushings. Seafoam is another good product, but smokes a lot.

IF you can't find Castle, here is my rep's email:
robw@castlepackspower.com


I am trying to find out why just the # 4 cylinder is the problem. Was the number 4 cylinder coil "electrode" any differnet than the others?

I looked at the electrodes on the coil and they all looked about the same. their was some sort of brown substance (I am guessing rust or corrosion).
I used a small metel wire brush and cleaned all the electrodes on the coil, but that did nothing.

I checked the resistance on the plug wires and the coil and they were all in specs.

I am starting to think about the fuel injectors.
I checked the resistance on one injector (I could not get the other three connectors off) and I came up with 15.4 Ohms.
What do you think?

I really appreciate your help with this problem.
It is good to find experenced techs to get advice from.

Try swapping the number 4 injector with the number one injector. If the mis fire moves to the number one cylinder, you have your answer :)