Misfiring, high s1 o2 circuit voltage, bad ECU? Ideas?
 

I have a 03 6mt G35. The problems started with bank 1 and 2 sensor 2 (post cat) o2 circuit low voltage. After some probing, it looked like one sensor was bad and the other had a bad connector. Bypassed the bad connector and replaced the other sensor, cleared the codes, those codes never came back up. Fast forward 30 miles, now I've got a code for bank 1 and 2 sensor 1 (primary) o2 circuit high voltage. It's exceeding 1.3V when I blip the throttle. It seems to do this intermittently. This car has factory narrowband sensors, so it should only see between .1 and .9V. This implies either a short from the heater circuit, or a bad ECU.

Initially I only had a intermittent misfire at idle. After driving in today's rain, it misfires even while driving. It seems to have low power too.

Any ideas?

Before while trying to diagnose the misfire, I thought that it was running rich. I cleaned the PCV, MAF, air filter, and replaced the plugs. After replacing the plugs it initially seemed to rev more smoothly. This was a couple days ago, now it seems reluctant to rev and misfire throughout the rpm range.

B2S2 voltage is now pegged at 2.54V until I drive for a bit.

Finding a random misfire is a huge task. The FSM lists 19 tests to do but I am not convinced all of them are usefull if the misfire isn't occurring constantly.
I've just started on this myself and don't read anything in your post yet that I can recognize something to help you.
Other than this. I can't tell how knowledgeable you are on this yet. If you are watching live data on a handheld scanner or laptop program be sure to pay attention to other things besides your O2 readings. You need to pay attention to all of your Fuel Trim readings to get a better idea of what is going on. There are several articles out on the web to teach you about fuel trim readings. Any one of them should be helpful.
Also I found this article very useful after I had given up on trying to follow the FSM flow chart on diagnostics and began looking for other peoples advice on misfires in general. http://www.searchautoparts.com/motor...sfire-concerns
Using this article you get to hopefully figure out if your problem is fuel or spark related and focus on one. It saved me a lot of time and worry.

On top of normal misfire problems you do seem to have a sensor issue but not sure what it is. What O2 codes are you getting? Also getting P0300 for Random misfire??
I thought my sensors were fine except O2B1S1 always reads about half of what O2B2S1 reads and cannot figure out why. My O2B2S1 can read up to 1.27 on a blip I just noticed the other day, when I had figured that all this time the last few weeks I would have guessed the B1 was reading too lean. I was surprised to see it above 1 like you are with yours. Now I am not so sure about them being OK if I have in fact fixed my misfire problem. Waiting on a coil pack in the mail to complete all of my repairs first. Was going to post a question on O2 readings myself. Maybe we will end up helping each other :dunno:

I had almost the identical situation you describe with my 2003 Performance model 350z.

After experiencing the power loss problem, I replaced my camshaft position sensors. All was good for about 30 days when the problem returned. The code was a faulty O2 sensor, but elected to clear the codes and wait for a reoccurrence. The problem came back after a couple of days, but this time the code was a faulty crankshaft sensor. I replaced both sensors and the fix has held for 18 months now.

I’m beginning to believe that at 80K you should simply replace all of these sensors. They are not expensive and a complete set-replacement avoids piecemeal fixes and additional costs.

--Spike

^Spike,

Did you use OEM sensors or aftermarket

OEM

You live in Illinois, so chances are you store the car during the winter. That means a possibility of mice, and mice can chew wiring. I'd be checking the wiring first.
What makes you think it could be the ecu?

^^ Renegade mice determined to damage your car might (but this is unusual) chew on wires, and either cut through (rarely to never) or compromise the ground (more common, but still rare). The engine shrouding in the Z discourages a “mouse-attack.”

The problem won’t be what avuswill (the OP) describes, but rather a problem with starting the car or a battery drain.

--Spike

It's too bad you think you know everything, because the shroud actually encourages them to move in. I should've taken a picture of the "valley of mice" when I changed my knock sensor and sensor sub harness 2 years ago. The little bastards had quite a setup in there.
As for the possible symptoms you describe, I'd say that just about anything can happen when mice chew wiring. These can systems are simple, but the way they function makes them very difficult to diagnose. One rusty ground, corroded connector, or partially chewed wire can make life a living hell on any car with a canbus system.

My point is a mouse attack is one of the least likely causes for this problem.

That's fine, and I apologize.

My point was to check the wiring. Always start with the easiest, most obvious things then go from there. A lot of problems are staring right at you if you take the time and think it through.

I saw styrafoam & found a nest under the passenger carpet. My car has lost all power after 3k rpms. Haven't found the prob but found the nest at only 20k miles