All,

I'm running out of idea's. It all started with a cam sensor code, intake manifold leak (non-internal) and a #3 misfire. I am now trying to fix the #3 misfire. So far I have replaced the wires and plugs and swapped the coils. Next I was going to check for spark and swap fuel injectors.

Am I missing anything else? I thought of using a 3M injector cleaner (rec. by mechanic) but I am fearing it will kill the O2 sensor and catalytic.

1996 3.1 lumina 115k

O.K. I am almost on empty and there is still no change after adding fuel injection cleaner. Can I use the test probe and poke the fuel injection wire to check for a signal or do I need to swap them?
When I first start the car in the morning it will give me a blinking service light. Once I start moving the light will stay on constant. If I am on the highway and I am going up a hill the light will start blinking again and then go back to being constant again. I know that a blinking light indicates a misfire and a constant light indicates an emissions problem (according to the manual). Now when I hook up the scanner it will give me the P0303 (misfire #3) code. after clearing the code it will reappear within a mile or so. Is there a chance that one of the O2 sensors went bad & how can I test it. The car use to get 27mpg 2 months ago I am now at 21mpg.

Any feedback will be appreciated. Inpection is due this month

what i would do is
switch the coil packs around and see if the misfire follows the coil pack
this is easier than an injector

that is i am assuming u have DIS
which is no distrubitor and coil packs with two plug wires coming out of them

its ok to switch them just make sure the plugs go back in the same spot they were in

i hope that helps some
or check for spark

I have a 1997 Lumina that began knocking and then I got a flashing SES light while on the highway, once on the off ramp it switched to a steady SES light but continued knocking. I drove the car to Autozone and got the code read and saw it was a P0303 just like yours. While driving home the light would sometimes be steady and sometimes would flashing. I bought and installed a set of new Spark plugs and wires and the problem persisted. I did some checking of the ignition coil and it seems to be working properly still (besides shocking myself from the plug wire). My exhaust seems to smell like part unburnt gasoline and some other unidentifiable smell. After reading: http://www.obd-codes.com/trouble_codes/generic/p0303-cylinder-3-misfire-detected.php I'm not sure what to try next. Any ideas?

As a follow up, removing the plugs and wires, and even more carefully putting them back and double checking every connection, along with bottle after bottle of injector cleaner resulted in removing the knock, and I haven't seen the P0303 in quite a while now.