Misfire help...

[Corrosive_23]

Hey what's up guys, long time I don't post.

So here I found myself, again, trying to get advice from all of you.

So like the tittle of the post says, I got a misfire in my GXP.

Let me get started.

About 3-4 weeks ago I did a tune-up. Plugs, filters, oil, you know that deal... and it ran beautiful.

2 - 3 weeks after the tune-up, one of the bolts that hold the rack & pinion came off (don't ask me how, because I got no idea how it came off) making my whole engine to move as I steer, braking a few things on its way.

Anyways... one thing that didn't broke but moved out of it's place was the tranny cooling line. This caused a huge oil leak from my tranny, but I didn't knew until a few days of driving.

During that week, was when I got the misfire.

When I knew what was happening, I put the line back on it's place, (took me for ever), and well no more leaks. I fixed the rack and pinion issue aswell, and all the other things.

I noticed that there was a build up of oil in the cat and 02 sensor. I was thinking the reason of my misfire was because of a bad 02 sensor and cat, but I didn't wanted to just guess and I took the car to Autozone to scan it.

The codes tha came up were P0420 and P0301/P0304 codes. I looked them up and it said that they are cat system efficiency bellow threshold and misfire in Cyl #1 & #4.
During my search, I came across a tread on cadillacinfo and said that the Autozone scanners can't tell you got a misfire on whatever cylinder, you need a tech 2 for that. (I need someone to tell me if this is true or not)

I would love to know if my 02 sensor is the cause of my misfire.
If not, what are the things I need to do to track down my misfire?

Thanks!

[CMNTMXR57]

You don't need a Tech2 to determine which cylinder is misfiring. It's in the code itself. P0301 = cylinder #1. P0304 = cylinder #4.

Well, tracking down a misfire, I would look at what you did during the tune-up. Bad plug(s), bad coil modules, bad terminals on the ignition feed, if the engine is moving as you say, that could be pulling on a harness causing bad connections at terminals and/or shorting it out somewhere. If it's not consistent, and cyclical, it might be on the fuel side too, which could also be the genesis of your P0420 code.

Search this forum on P0420. I've posted it about 227 times. This will give you everything you need to know about the code and how to fix it.

Edit: I went and looked it up. Post #10 I believe, in this thread, by yours truly

http://www.pontiacbonnevilleclub.com/fo ... 20#p131397

[Corrosive_23]

I already fixed the moving engine issue. I already fixed the things that broke or moved, but I'm going to check the harness.
I'll check for plugs, coils , aswell.


Thanks for the help and fast reply.

You should get paid, specially since you gotta repeat the same answer over and over lol.

[CMNTMXR57]

I'm just trying to think of obvious things based on what you posted.

There isn't a ton of slack in that main harness that comes over the back bank of the engine. So dependent on how much movement was going on, you don't know what stresses were put on the harness. This can also affect your HO2S's in the same manner (the P0420 code).

But misfires generally boil down to 2 things. 1) Fuel 2) Ignition.

What you would need a Tech2 for, would be diagnosing the fuel side of it, if you were to do an injector balance test to look for a bad injector.