Okay car runs like crap(shutter, jerking , surging) at part or half throttle, idles like it's gonna die and produces a heavy fuel smell in exhaust, runs like new wide open. Only does this for about 20 min of driving then smooths out and runs decent at all throttle positions. I think I have a bad O2 sensor causing these problems. Any thoughts. Check engine light flashes when missing.

 

For starters - year, model, engine, trans and any modification to the vehicle you are asking about?

Have you scanned it for codes? You should get P0300, but there may be others. If you use a scanner with GM enhanced parameters, you can pull up the misfire count by individual cylinder, which may lead you to the problem cylinder(s).

 

Didn't realize my signature doesn't appear on the mobile version. 96 z28 t56 long tubes, off-road y pipe, mad z28 tune, 52 mm throttle body, throttle body bypass, stock otherwise. P0300 and p0307. All cylinders on the left bank counting misfires. Also got a code for b1s2 not switching. That's why I figured it was an O2.

 

Yesterday I unplugged one fuel injector at a time on the left bank and it made no difference( the idle didn't change) when the car was running like garbage, does this mean the whole banks not firing? today however the vehicle runs fine. I really don't think it has anything to do with ambient temp or humidity but those have changed slightly in the past couple of days. does this sound like a bad O2? if not, what.

 

Did you have P0140 - insufficient signal activity, bank 1/sensor 2? I don't see a "not switching" code for that sensor in Shoebox's code list, specifically for the LT1:

http://shbox.com/1/Dtcs.htm

Since that's an after-cat sensor, it shouldn't affect the way the engine runs.

Was the misfire count on cylinder 7 higher than the other cylinders on the left bank?

 

Slightly higher. But after rescanning today no counts on any cylinders. And yes the code I got was inactivity. I toyed with the idea of a head gasket but no coolant loss and temp stays normal. I'm really leaning towards something electrical it seems to be worse on wet days. Weird huh. Why cylinder seven?

 

Okay it rained last night and the car runs like crap again. Definitely something getting wet.

 

With the engine idling, in the dark, mist the wires/coil/opti LIGHTLY with water. Look for arcing.

Pull the plug wires and coil wire and check the terminal ends in the Opti and in the coil for corrosion.

Pull the two Opti short harness connectors, and look for corrosion or damaged pins.

 

Thanks I'll give it a shot and see what I come up with. Thanks for your help. Earlier you asked about cylinder seven, what's the correlation?

 

#7 may be misfiring due to arcing, the unburned air blows into the exhaust, the O2 sensor reads "lean", PCM starts adding fuel to the bank making it run too rich, and now all cylinders can misfire.

 

First to clear up some things from my original post, I stated that I had a code for an oxygen sensor and called it b1 s2 however that was a mistake because I only have the single O2 on each header collector so the a accurate term should have been b1s1. And as previously stated it was bad. I did replace that sensor and the car does drive a lot better. I also checked for arching and saw non so I'm guessing it's doing just that arching when wet and the faulty O2 just worsened things. I'll update when wet and let you know a long term outcome. Thanks again.