Good Afternoon!

Need some guidance or suggestions. Just purchased a 1999 coupe. 83k miles 6 speed manual. Has headers, intake and cat back exhaust. Drove it from Texas all the way back to AZ. Car ran nice for the most part till the end where it developed a code P0306, Misfire Cylinder 6. So I purchased a new coil and installed, same issue but made it home. It runs ok but still same issue. Where I need some help is where to look but let me put down what I have done so far is this

1) Swap coils from Cyl 6 to Cyl 4
2) swap spartkplugs and wires from Cyc 6 to Cyl 4
3) Swapped injectors from Cyl 6 to cyl 4
4) checked for vacuum leaks-Nothing
5) Pulled valve cover and inspected valve spring. - Visual ok

I did this in hope to see the issue move but it hasn't. I looked at the Bank 1 and Bank 2 O2 sensors and noticed that bank 1 is at .446v while bank 2 is at 1.2v. I am not sure if this is a cause or a symptom of the above issue but I can see in bending codes that the bank 2 will toss a code eventual. . I am hoping that you guys could have a few more ideas for me to look at or review.

Thanks in advance for any advice!
Bryan

 

Welcome to the Forum…from the Phoenix area ??…sorry to hear about your misfire…a faulty O2 can cause a misfire but it will normally cause all cylinders on that bank to misfire…another thing is it may not be #6…the crank sensor is the PCM’s “misfire monitor” so it’s not always correct and it can be the cylinder before or after #6 in the firing order or #6’s companion cylinder…you can try using an infrared thermometer on the #6 header tube to see if it reads much cooler than the other 3 or doing a cylinder drop test…pull the #6 plug wire off the coil and see if you notice an RPM drop (if RPM drops that cylinder is contributing) and if you do have spark on 6…it’s hard to hear on a V8 but you can try. You will need a 12 volt test light to check for injector power and that the PCM is grounding the ground side of the injector.Now you tried swapping PARTS but did you electrically check that the injector and coil pack wiring is good ??…let us know if you need some electrical help with this…so do your upstream O2 switch from 200-800mv’s ??…so is bank 2 stuck at 1.2 volts and not switching…if it is stuck at 1.2 volts (rich signal) the PCM will be “pulling” fuel so you will now have a lean misfire….to see if it’s a bad O2 remove the O2 connector and see if the O2 now reads 450mv’s…if you see 450 the O2 sensor is bad…if still stuck at 1.2 you have a wiring issue…to check for a mechanical issue a quick check is to do a “cranking cadence” check…push the gas pedal to the floor (clear flood crank) and keep it there while starting the engine…it will only crank so listen if the engine cranks over with a steady cadence.

 

Thanks! To start, Surprise AZ. Little north of Phoenix . So will do the following things you have suggested. For the electrical piece, on the ground side of the injector, Little advise on that and how to test a coil would be great. I can take a guess but would rather make sure I am doing it correctly.

Thanks again for all of this!

Bryan

 

For the power side of the injector that would be the pink wire…with key ON see if you have battery voltage there. To check that the PCM is providing a ground hook up your 12 volt test light to battery POSITIVE…what the injector still unplugged place the tip of the test light on the other wire which should be yellow with a black stripe…with the engine running if you have control the test light will flash…better to see when it’s a little dark out…the coil packs have 4 wires…a 12 volt power (pink) with key ON and it’s ground (black) and the other 2 are a 4 volt control wire (light blue/white) which is a digital square wave and not 4 volts as seen with a voltmeter and it’s ground (brown) wire…to check those grounds check with test light connected to battery positive..I did a video a while back on checking the coils which is below…I basically covered checking the control wire.

 

Fantastic! Will check this tomorrow and will let you know but this is great stuff and thanks for taking the time to respond!

 

No problem !!...if you get stuck shoot me a PM with your number...first thing is to correctly identify the misfiring cylinder and go from there...I've been using an advanced technique the last few years with a pressure transducer and a labscope in the tailpipe...a misfire will create a vacuum in that cylinder and the pressure transducer will pick that up...if you've ever heard about the "dollar bill trick" hold a dollar bill or a piece of paper up to the tailpipe...when a cylinder is misfiring the bill or paper will get sucked back towards the tailpipe...the colored chart below the waveform lets me know what cylinder is on the exhaust stroke...easy to do and keeps one from going down that "rabbit hole".

 

I picked up a misfire on track last year. After swapping coils, plugs and plug wires, the miss was still there so I removed the valve cover to find a rocker arm had come loose. Guess which one!

 

Well that would do it! I did pull the valve cover to inspect the springs to see if there was anything visually wrong or if the rockers are loose. They looked fine and nothing crazy. I am going to try what Rob suggested on the coil and injector test and figured I would test the one prior and post firing order for them to see if they had any issues. Will let you guys know but I really do appreciate the help and advice. My '72 Cutlass is a lot less complicated. :-)

 

If that bank 2 O2 is "stuck" at 1.2 volts I'd address that issue first...I had my bank 1 "stuck" at 0.1 volts (100mv's) a while back so the PCM was over fueling that bank...garage stunk and since my O2 sensor was reading 450mv unplugged I changed the O2 and everything was fine after that...at times I had misfires on all that banks cylinders.

 

So to start, thanks all for the great info! One, learned a lot and 2 fixed that little bugger. It turned out to be the O2 sensor. I guess I was just surprised that it didnt toss that code nor did any other cylinder register a misfire. 2 things, really 3 things, sealed the deal. 1) the reading that was stuck high and never seeing it move. 2nd, read the temps at the headers and the whole 2nd bank read 200+ degrees cooler then the 1st bank and last but not least, all your guidance and info in the issue/ . I know now how to test a coil and fuel injector. I 100% mean this but thanks!

Bryan

 

Glad you got it fixed !!…the most important thing is you learned something….and you’ll learn that you never diagnose based on a trouble code…others may have just replaced plugs, coil packs,plug wires and injectors and still have the same problem…gather all the data and look at the evidence for a diagnosis !!