My car has 45,000 miles on it right now. I had the car at 42,000 ran perfectly fine. I bought some Lucas Fuel Injector Cleaner in it and it started misfiring the EXACT same day like 2 hours later. I replaced the spark plugs with Bosch 4501, I took the plugs to a mechanic shop and he said they looked fine. The car ran better after the change but now its getting worse and I have ran maybe 3 gas full tanks of gas since the injector cleaner was added. The service engine light poped up once and flashed for maybe 5 seconds and went away not codes showed up when I had it read. Does anyone have any idea of what the problem is? I am replacing my spark plugs wires with GM parts I just feel its not the plugs or wires. Maybe coils?

 

I'm thinking ignition coil or the ICM itself. How about the spark plug wires?


On another note, I had the same issue on a Grand AM and I changed the plugs, wires and coils and it ended up being a plugged cat. A plugged cat can cause a random misfire too.

 

I was looking into the ICM. Wires will be changed but I dont think that is a problem. Would you really think the cat would be plugged up with so little miles? Would checking the O2 sensor show me if its clogged by it being blackened?

 

Considering the age of the car, yes your cat could be plugged. A blackened O2 sensor isn't a good indicator since it can take only a few days for it to be blackened. Here's some things you can do to check for a plugged cat:


1. Compression test
2. Excess condensation in the exhaust when the car starts cold
3. From a cold start, little to no exhaust from tailpipe
4. Pipe before the cat hotter than pipe after the cat
5. Glowing or red cat after driving the car for awhile (severe)


A plugged cat can also cause you to blow your LIM, UIM or Head gasket too. After I fixed the plugged cat in the Grand AM, I ended up doing the LIM, UIM and TB gaskets a few months later.

 

Ill check to see if the cat is plugged. Would there be a way to test the ICM?

 

Cat check is a pressure test and when they fail they do not cause a miss. The complaint is normally something like, idles fine, no power or won't go over 3000 RPMs. I have replaced dozens of plugged cats and I have yet to see one cause a miss. On the other hand a miss can cause a plugged cat over time.

I believe the parts store can test a ICM but that test is not 100%. Give them a call

Plug wire a time sensitive more then miles. If your plug wires are more then 7 years old that is where I would start, old plug wires tend to take coils with them. As the wire ages it takes more spark to fire the plug. By the time the coil can not longer fire the plug it has internal shorts, new plug wire may fix the issue but it common for the car to be back a week later needing a new coil.

I hate tank fuel cleaner. Why? Because it should be called Fuel filter cleaner. If you put a cleaner though a dirty filter it will break up dirt smaller then the filter can filter. Next stop the fuel injector. If you want to use in tank cleaner only do it right after you install a new fuel filter. Pros shoot cleaner through the rails with a fuel injection cleaning system.

Miss with no codes, Might want to try running the car with the MAF sensor unplugged to see if the miss goes away.

 

I know I'm new here but thought I might be able to help. I had a similar problem on a firebird and chased my tail for weeks. Here the run down. Like you I assumed plugs or wires. And so you know, a #3 misfire is common for many reasons apparently (don't Google it lol) and NONE were the problem.
1. Changed plugs, zero change

2. Changed wires, still misfired, &
3. Swap the coil packs around to see if the misfire followed the pack, had the code rechecked.

**I did #2&3 together without testing the new wires first. I figured it was quick an easy to move a pack around and I didn't think a pack was bad... I also didn't expect a bad wire new out of the box.

The fun started when the misfire code just happened to follow the pack, it's a 1-n-3 shot & my bad NEW WIRE was one of those cylinders.

In the end it was a bad wire. Point is chase the problem 1 step @ a time. Don't just throw money at it.
FYI: I also looked at the Crank & Cam sensors, fuel filter, fuel pressure, fuel injectors, intake problems, lower coil mount, and the stock metal heat shields on the plug wires and did all of this after 2&3 lol. Eventually I swapped the wires on that pack and the issue followed the wire. Fixed!

Yours may not be the wire but you should be able to narrow where the problem is coming from.


If you rearrange your coil packs that will tell you a lot. If the misfire follows then it's the pack. And if it doesn't then odds are it's between the air, fuel, an fire for that cylinder and not a component that's prior to the coil pack. Reasoning is it started after a fuel additive.

 

A plugged cat will cause a random cylinder misfire. I have had the code come up on several cars with a plugged cat.

 

I said it will not cause a miss, random miss fire is a lack of response from the motor the computer assumes it is a miss. As the pressure in the exhaust builds the cylinders get less and less Oxygen and Fuel and some point the computer registers the drop in power as a miss. You can hold your foot to the floor on a car with a plugged cat and it will feel more like you are climbing a steep hill then a miss. Of course this is a stress test for all the other systems in the engine so you may find a week spot, but you are just finding a weak spots that are all ready there they are not cause by the plugged cat. So a plugged cat can not cause a coil to go bad but it can cause you to feel a failing coil you did not feel before.

Over time a semi plugged cat can contaminate the O2's which would cause a rich condition, which can cause a plug to foul which would cause a miss. This normally takes awhile to happen. But the OP said he just did the plugs and saw no issue.

 

Im putting the new wires in today ill see if it changes anything.