Jetts4u2

OK, I posted in other po300 threads, but this is new info.. Everyone said check wires and connections, Harness is "good" and dialectric greased connections and ECU.
I am getting random PO300 misfire cel's, car will stumble, misfire, won't accelerate, then clear up and run perfect. Car is an 05 with 69k miles, I don't drive it much and have work truck.
When it 1st happened, I scanned codes, got the 300, then 02's, knock sensors, but never a single cylinder misfire. I replaced 02's, knock sensors, then coil packs, wires and plugs. Was thinking water in fuel, ran it down to 1/8th tank and added heat, no better, filled it up with 93 non- ethanol. Took it to my buddy's shop, he put his scan tool on it. He could see rich 02 sensor on bank 1, and 1,3,5 and would start misfiring as ECU pulled pulse width out trying to lean out bank. Buddy said, injector 7 is stuck or leaking. I changed out injector last week, fixed it, ran great around the block and short cruise. Week later, Took it for our car club cruise today, didn't make it out of town before it started doing same thing again. Drove it on cruise, hoping to drive the devil out of the car. Topped it off with 93 at Sam's, cheaper 93 there. Did cruise, messed up more when not warmed up and slow, drove home fine after warming up, 40 miles total. Got home, had check engine, scanned codes, had 7, 2 PO300 random misfire, PO132 02 sensor high voltage bank 1, and PO327 knock sensor low voltage bank 1, , PO1133- inssufficiant number of switching cycles HO2S 1. I'm leaning towards ECU glitch or injectors are old and need service. Any help is appreciated.
I can get a replacement ECU, or have mine checked, checked is better as my tuner buddy moved away. Or injector service, just because of low use. Car has been doing this for 6 months, I have other hot rods, so it sat as I trouble shoot it.

Purple92

Could be a number of things.

I would start by trying to look at fuel pressure - see if fuel pressure is good during misfire time. the pump could be intermittently slowing down, or the regulator could be screwed up...

Sending injectors out for cleaning & flow testing may be a good idea - but anther thing to look at is the possibility of an intake leak. If that was happening - it would impact idle more than higher RPM, higher load conditions. Still though - may be a good idea to hook up a vacuum gauge and check.

C5 Diag

NOT a good idea to use dielectric grease on low voltage circuits especially the ECU if that’s where you put it…dielectric grease is an insulator…you have a “sensor high voltage” on bank 1 so that should be looked at..the bank 1 O2 may be reporting a “false rich” condition which will decrease injector pulse width or pull fuel…car will stumble and misfire…did you see if your long term fuel trims are negative on bank 1 ??…have your friend hook up his scan tool and see if the O2 sensor is stuck high…with key on you should see 450 Mv which is a bias voltage…if still high while running shut the car off and disconnect the O2 sensor and see if you see 450 Mv…if still high you will have to check the wiring !!…you are seeing the P0133 because the ECU is not seeing the O2 switch between 200-800 Mv while running.

Jetts4u2

Good info. I switched out injectors. Got scan tool on it, and b1 never dropped below .4v, while bank 2 goes to .02 v. replaced 02 again and same issue. Checked to see all cylinders firing with timing light and new plugs, all good. Got PO1133 Ho2s inuficient switch, PO132 HO2s High voltage S!, PO172 Fuel Trim system rich. B1S2 showing dead lean on scan tool. No idea why, swapped everything, High voltage shouldn't be bad wires to ECU, ECU may be bad. Help! LOL..Bank 2 S1 and s2 fine. I disabled the secondary O2's due to small inneficient cats, so they don't show CEL's, but saw them today, have new ones, haven't installed them.

C5 Diag

Ok, so you’re saying bank 1 upstream is “stuck” at 400 Mv (.4 volts) and bank 2 upstream is “stuck” at .02 which is basically ground ??…when the engine is running spray some starter fluid or Brake Kleen into the PCV at the intake manifold…see if the O2 sensors go full rich (900 or more Mv)…if they do not respond the O2 sensors or wiring is bad…to tell if it’s wiring disconnect both O2 sensor connectors and see if the scan tool reads 450mv…if it does the wiring is good and the sensors are bad…you can also check wiring by waiting till the engine is cold and now remove the O2 heater fuse at the underhood fuse box…turn the key on and see if you see that 450mv bias voltage…I just went through this on my own car a few weeks ago and it was a bad sensor…my upstream was stuck at 100 Mv but when I looked at my downstream it was reading 900mv because the PCM thought the engine was running lean and was adding fuel…my exhaust smelled and my injector pulse width was more than doubled !!..I replaced with a Delphi sensor which didn’t work on my car..I then replaced with 2 Bosch sensors (3 new sensors in total)and they didn’t work..,WTH ??…went to Autozone and I replaced with a Denso sensor…that brand worked !!..if you see your upstream read low the downstream should read the same…you CAN’T have a lean upstream and a normal downstream…any questions PM me your number and I can walk you through this…I did a YouTube video on this but I have to edit it !!..you FIRST must determine if the O2 will respond to a rich or lean condition by spraying in brake kleen or pulling a vacuum hose to see if you have a REAL rich or lean condition or a “lying” O2 sensor.

Jetts4u2

C5Diag.. the bank 2 goes .8 to .02 all the time, it is fine.B1 goes .8 to .4, but no lower, B1S2 goes flat lean. Replaced 02 and injectors on bank 1, same thing, runs perfect some times. Will try cleaner and see if it changes. Watched some youtube and they say 02 and injectors. Car has 69.726 miles, guess it doen't want to turn 70. That is 3rd O2 I have put in it.

C5 Diag

Best if we just say 200-800 mv and not tenths of a volt because that is what the scan tool is reading...it wouldn't be .02 anyway...so then bank 2 is OK...if bank 1 goes from 400-800mv the O2 is reading a rich signal...anything above 450 is considered rich so the PCM will be pulling fuel so are your fuel trims negative on that bank ??...if the ECM is pulling fuel your downstreams will be reading lean...my bad O2 was the opposite...upstream lean and downstream rich...your bank 2 is rich so pull the brake booster or PCV and the O2 sensor SHOULD go lean like 100mv or lower ...if it stays above 450mv the sensor is bad or wiring (you did have a P0132) or like I said disconnect the sensor and see if your scan tool now reads 450...if it does NOT and stays high you have a wiring issue !!...once you determine that indeed the sensor is bad a new O2 should work...in my case it took 3 new sensors...what kind of O2 sensor did you use ??...if the car is actually running rich that must be diagnosed accurately...yes, it can be injectors that are flowing too much fuel and should be checked even though you replaced the injectors…I don’t trust new parts these days !!...you will need to do an injector balance test...also your bank 1 cat “may” be starting to get clogged...you will see a rich O2 signal and negative fuel trims with that...just too bad you didn't live so far away...would be an interesting diagnosis !!

Jetts4u2

My scan tool shows it at .8 and .02, yes milivolts, but I see that. Downstream is showing dead lean on graph. Will work on it again Friday. thanks for the help. Throwing parts at it hasn't changed anything, it does run better when it runs good, but beyond that symptom hasn't changed. probably is wiring or ecu issue. I don't like changing the 02, i have long tubes and is a pain to zip tie the wire to keep it off the header, and the car is looowww.

C5 Diag

Well the first thing on Friday is to check for a wiring issue on that 450mv bias voltage when the sensor is cold . Now on the 05's the O2 heater circuit is grounded at the ECM so we don't want the O2 heater circuit to be energized when you energize the ignition system...I'm not 100% sure if the car has to be running for the heater circuit to work but anyway just pull the "O2 SEN" fuse #6 and now look at the O2 sensors with your scan tool...they should all read close to 450mv...if it doesn't you have a wiring issue and the high and low signal wires will have to be checked !!

Jetts4u2

Took car to buddy that worked at the dealership. He disabled O2s and found that the passenger side injectors were dead lean. He swapped sides, still lean. Swapped out the injectors and all the codes cleared and the car runs stronger than ever, no idea why. I still get the knock sensor code sometimes. But, now the idle jumps all over the place and after a spririted run it was idling at 2500. I cleaned the MAF and throttle body, thinking it may be sticking. Better but not perfect. With the engine off, the butterfly isn't closing all the way and I can push it both directions. Is that correct or maybe an internal spring broke in the throttle body. Thanks for any imput.

bradford.howell

Hey! Just ran into a similar scenario on a Ranger i was rebuilding. Originally got a P0304 for the misfire in cylinder 4. Went ahead and did a diag by swapping the injector from #4 to #1 and that did move the code to P0301. Went ahead and swapped the injectors and after a few drives it threw your dreaded P0300. Went through replacing the PCV valve, cam sensor, valve and intake gaskets (worn to ****) along with a new fuel pump and filter. I was getting the feeling there was an air fuel ratio problem with sputtering when shifting into second and third with some tinted smoke out the exhaust. After clearing all codes and running a few times a day i couldnt get any more codes to populate and i was stumped. Long story short, it was the bank 1 02 sensor in front of the cats that wasnt reading and was throwqng everything off.

Start with the cheapest, easiest replacement first and work down the the more difficult. Would be a good idea to compression test your cylinders as well so you have a solid starting point as well as fuel pressure so you can identify if either of those are issues.

Hope it works out man!

bradford.howell

In addition to my previous reply, have you swapped out your IAC Idle Air Control Valve? Not sure if that would be enough to pull open your butterfly though. If it failed in the open position it can cause rich air fuel ratio during idle as well as having a higher idle RPM.

C5 Diag

No IAC in the C6.

bradford.howell

Well ****...

Jetts4u2

My 05 vette was down for a year for po300. Then flashing Check engine light, bank 1 o2 sensor. Changed EVERYTHING, plugs, coils wires, knock sensors and injectors on bank 1, no issues with bank 2 in codes.. Still would cut power and turn off cylinders on bank 1, could see on tool it reduced pulse width on bank 1. Took to tech buddy that worked at Chevy. He checked it, disabled o2s. Found bank 2 lean, he swapped injectors to 1, lean followed injectors. Replaced injectors, all codes went away and car runs really good, still needs retuned, high idle. My take away is, ethanol gas absorbs water, low mile cars the ethanol rusts the inners of the injectors. Replace injectors. My 05 has 70k miles, I bought it 9 years ago with 42k miles.

Jetts4u2

Thank you for all your input. Was odd. Now idle hangs, odd. Sat at CVS, idle at 1000, 2 minutes in dropped to 500 and ran right, Thinking TPS, but it doesn' have one?

Jetts4u2

I drove it last night, idle jumping up, put my tow under pedal and pulled it back and it came back down to idle., throttle is sticking, trying to see if I can remove, clean and lube, or just replace, can't find anything on here. No code for pedal, but plenty for sale.

C6VetteLover

What brand O2 sensors are you using? Delphi or Delco are the only thing I'd use in a GM. Never the Bosch that the parts stores sell. 5 years as a GM at an auto parts chain store and a year in an import dealerships parts department I've seen many people who use the cheap junk sold by the auto parts stores come in with issues. For anything electronic always try to use OEM or whatever manufacturer made the OE part (for example Hitachi makes a lot of early 2000s GM MAF sensors)

C5 Diag

When I had a bad upstream O2 on my 2001 6 months ago I bought a Delphi from Rock Auto (AC Delco were not available at the time) and it didn’t work so I sent it back…went to NAPA and got a Bosch…still no good…got a replacement figuring it may just be a bad from stock part…that one no good !!…went to Autozone and picked up a Denso…worked fine !!