It isn't a wire if it's an on and off kind of issue. Try the o2 sensor.

Just a warning, Chasing a missfire is about the worst thing in the world. No shops will figure it out, or they will say it is fixed but it isn't. Have fun.

 

Could somebody please explain to me why an O2 sensor would cause an Injector Circuit Open Cylinder 3 code? After I reset the codes the only ones that came back were the Injector Circuit and the Misfire codes, the Evap code did not come back. It just doesn't make sense to me.

 

I wouldn't rule out wiring as a cause for misfire. Harnesses routed close to underhood components or fenderwell/firewalls can do funny things after being submitted to heat, vibration and flex. Loose or dirty connections can create all kinds of gremlins, too. I'm not saying my suggestion is the definitive answer, but I've seen more than one intermittent misfire problem caused by broken wire strands (hidden under the insulator) and dirty/corroded connectors.

If the injector circuit is malfunctioning (P0203) and not firing #3 every time it would create a misfire (P0303). Unburned fuel from the misfire will be in the exhaust stream. The cat can't process it quick enough so its efficiency drops below threshold (P0420). The way to prove this would be to check the fault data in the PCM and see what code was triggered when. IMO P0203 is the clue you need to follow in order to solve this mystery. But that's just my opinion...and you know what they say about those... Good luck & let us know if/when/how you get it fixed.

 

I think the circuit is the issue as well. But, I traced the wires and didn't see any fraying or anything. There is a connection underneath some sort of sleeve that connects all of the injector grounds to what looks like a common ground but I don't know if I should take that sleeve off to look at it or not.

I did find that the ECM is not secured down to anything and I live in Hawaii and take it on many bumpy roads. However, if it was that I would think it would happen all of a sudden when I went over a bump and not the way it did.

 

Oh, one other question, I am reading that some injectors need a certain amount of pressure before they will fire. Is it possible I am losing compression on cylinder 3 and that's why it won't fire?? I want to rule out any mechanical issues. I really appreciate all the help!

 

If you found no breaks in the wiring and all connections are clean and tight then I would have a shop/dealer hook up a Tech II scanner to the vehicle and let them take it for a spin. They can get some real time data on what all the systems are doing when the misfire occurs.

 

I was afraid of that. Thanks so much for the help. I'll update the thread once I get some more feedback.

 

03SSLE gave some good info. Nice explanations.

This is a bit of a tough one. Being intermittent is a pain too.

Here's a silly one to try before going to a shop (but I'm not holding my breath). Get a can of starting fluid, with the car idling, mist it around the injectors and vac lines. See if the idle changes, if so, you may have a vac leak (if you do, I'd suspect around cylinder #3, like an injector that's not properly seated).

It's a long shot. I'm not holding my breath because of code P0203. I agree with 03SSLE, that is more then likely your big clue, the rest are domino effect results. I'd say swap the injector, but re-reading that was one of your first steps.

 

Here's what I've done.

I was trying to pass a car and at about 4,000 rpm the car wouldn't shift into the next gear, the motor started to shutter, misfiring. I then put a MaxiScaner on it and got a P0141 code, which is a 02 sensor hearter circuit Bank 1 Sensor 2, and a P0303 Cylinder 3 Misfire detection. Spoke to my cusin, who's a engine machanic for GM and he thought it was just plugs and wires. So I replaced them all. Still have the problem. While changing the plugs and wires I accident broke a couple of vacum line as it was -18 C. I replaced those and still have the issue. I spoke to the service agents at my cusins work and had them do a Vin search on the vechile to see if there was any recalls on that car. There was one that said the catalytic converter sometimes can have issue with a brick in it falling out of place and blocking the fist compartment. I went to the muffler shop and had them take a look but they think it's fine. My cusin doesn't thing that the O2 censor in the exhaust would be a problem but I'm not sure as while I was driving out west for work I experienced shifting problems when trying to pass cars but it was not missing at all just reving out and not wanting to shift gears and I got pretty good milage about 675 Km out of tank. So I'm stuck too, not sure what to do now.

Ok today I switched the coils around to see if the problem moved to a different cyclinder. It didn't still have the same issue. My cusin thinks maybe it's the injector in that cyclinder. Hopefully he'll have time this weekend to swap those and see if that's the problem. I'll keep you guys updated.

Have you taken yours into the shop and have a Tech II diagnostic done?

 

HI,

For those of you that are having similiar problems.

Had the cadilitic converter change and that fixed the problem. No more miss cyclinder codes, pulls like a freight train. wOOt.

Cost for the fix. 291.00 CA.