GMC with Misfire

Greg Technician University Place, Washington Posted   Latest  
Unsolved
Driveability
2008 GMC Sierra 1500 WT 4.8L (C) 4-spd (4L60-E)
P0300 — Random/Multiple Cylinder Misfire Detected
P2272 — O2 Sensor Signal Biased/Stuck Lean Bank 2 Sensor 2
P2270 — O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 2

have this Sierra here with an random misfire code and lean on both banks (downstream O2) codes. Misfire data showing #1 is only cyl. misfiring. Have swapped coils plugs and injectors removed valve cover and watched rocker arms move apparently as much as other cylinders. Can unplug the #1 coil at idle and off idle with no change. Bank 2 upstream and downstream O2 sensors are showing lean at idle and cruise but can add fuel to get them to go up to 900mv. Don’t have a pressure transducer only did running compression which looked the same as #3 cyl. Spark plug on #1 was noticeably darker than other cylinders. When you unplug coil on bank 1 (#3,5,7) bank 2 O2 sensors will go rich. Have checked for vacuum leaks numerous times. Have confirmed everything is plugged in to its correct bank the O2 sensors coils injectors which would be almost impossible to swap but check anyway. Any input would be much appreciated. Thank you. 

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Troy Owner/Technician
Longbranch, Washington
Troy Default
 

I would think that maybe you have plugged fuel injectors have found that a few times with returnless fuel systems sometimes you can pull the injectors and see the rust or crud in them the problem i see is why would unplugging bank one coils cause bank 2 to go rich

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Greg Curriculum Developer
Tacoma, Washington
Greg Default
 

Thanks next time you post something I’ll 1/2 ass read it and send you message.

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Troy Owner/Technician
Longbranch, Washington
Troy Default
 

dont worry I wont

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Robert Owner/Technician
Washington, New Jersey
Robert Default
 

How many miles on this truck. I would check the fuel pump. A currant ramp of the pump can tell you a lot. I would also check Pressure and volume. I just had two fuel pumps that had PSI in spec but would just flow enough fuel to keep them running. I use the Mitty vac FST tester.

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Greg Curriculum Developer
Tacoma, Washington
Greg Default
 

Ok thanks.

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Eric Owner/Technician
Edgerton, Wisconsin
Eric Default
   

Stop throwing guesses and parts at this truck, sit down and think this job through. Why are you focusing on a misfire on cylinder #1 when the computer isn't? You have three codes, two of which are for basically the same problem. The left and right mixture codes tell you the computer is seeing a lean condition that it doesn't like. The random misfire code is telling you the computer is seeing…

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Stuart Mobile Technician
Blue Island, Illinois
Stuart Default
 

You mentioned that the one plug seemed darker then the others​.​Was it carbon or oil​.​If it was carbon you probably would have a rich condition because not burning the all the fuel​.​But you have a lean condition so you might have a leaky valve​.​Just a thought.

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

Here is a link to save you some time. diag​.​net/msg/m61bqk58h6…

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Samuel Technician
Somers Point, New Jersey
Samuel Default
 

Known goods are gold....Step 1, hook up your equipment, Step 2. Identify if the waveform is good or bad...we could look at the patterns all day, but if we don't know the difference between good and bad, there is no point! Thank you for dropping in the link!

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Paul Mechanic
Harvey, Illinois
Paul Default
 

GM does not set specific cylinder misfire codes, so I assume that's why he is looking at live misfire.

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Eric Owner/Technician
Edgerton, Wisconsin
Eric Default
   

What are the codes, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308 I keep seeing stored by the PCM in these GM trucks for then? Not only does GM set cylinder specific misfire codes but they store freeze frame data for them. GM also shows real time and history misfire counts in the data stream and has done so for decades.

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Paul Mechanic
Harvey, Illinois
Paul Default
 

Not stating the pcm won't, but I assumed regardless of your scanner, you were using the gm side​.​It's been my experience even with the tech 2,gm never I.d. cylinder specific misfire. Generic obd2 will. There fact that you listed p0300 and not p0301 caused my assumption.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Paul: I'm confused by what I think that you are saying. Perhaps. I am misunderstanding you. Are you saying that GM doesn't support this? youtube​.​com/watch?v=u-7ftG… Or this? Guido

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Guido, I think the confusion came about because Eric was expecting a specific cylinder DTC (P0301) before he would look for a misfire, and there was a "P0300 Engine Misfire Detected" stored. This is to be expected as GM wants you to look at the Misfire Data to determine the specific cylinder(s) misfiring.

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Greg Curriculum Developer
Tacoma, Washington
Greg Default
 

Ok thanks

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

Here is it Friday morning, and you still have a broke car. Please step back from the car and rethink this problem. The PCM is telling you a lot of stuff, waving red flags at you and they seem to be ignored. Yes, I know, playing with the diag toys is fun, but playing with the toys will not make you any money if not used properly. This would be a good chance to hook up your scanner and do a…

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Greg, A few questions/observations - Cylinder 1 misfire is this at an idle, cruise, acceleration? All the time, as in a dead miss? P2270 and P2272 are different than P0171 and P0174. Have the HO2S's been replaced? Is the wiring intact and routed correctly for the HO2S? What's fuel pressure? Have you checked for ethanol, E85? What are the actual fuel trims at idle and cruise, ST/LT? Is it…

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hik Greg: In …e you think the people responding are being mean, they are not. ECMs work under a set of ground rules. Codes have enable criteria. When you look that up, it'll tell you what it takes to make the ECM bitch and, in many …es, any default strategies. Just as importantly, it'll tell you what has to be good in order to flag that code. Don't get me wrong, you can have a faulty…

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Greg Technician
University Place, Washington
Greg Default
 

Thanks Anthony. I don’t think people are being mean. I have been doing this long enough (25 years) and I’ll never know everything. I send a reply to Phillip if you want to read it. It is looking like a mechanical issue. Customer has a Carshield warranty and doesn’t want to spend any of his money So I only got an hour to check it.

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Eric Owner/Technician
Edgerton, Wisconsin
Eric Default
 

Please explain the mechanical issue.

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Phillip Diagnostician
Anchorage, Alaska
Phillip Default
 

Ignore the random misfire for right now and focus on why the vehicle is is saying the O2 sensors are stuck lean. What are your fuel trims for both banks? Roughly what is O2 sensor data at idle and cruise? Start with that and get back to us.

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Greg Technician
University Place, Washington
Greg Default
   

One thing I overlooked is that when the bank 2 O2 sensors go lean it is going into open loop. Start truck let run can see the fuel trims going up when bank 2 gets to around +9% then goes open loop and both sensors go lean on bank 2. Unplugged MAF sensor bank 2 LT FT stays around +5%. The miss on #1 is constant. O2 sensors look normal except for the turbulence on bank 1 O2 sensor from misfire but…

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Eric Owner/Technician
Edgerton, Wisconsin
Eric Default
 

If it takes twice as many rotations to get to 175 psi as the other cylinders then the compression of cylinder #1 is not 175 psi. I love it when techs leave important information out of the original post and combines important data into an incorrect inference and presents it as actual test results. Perform a compression test by disabling fuel and removing the spark plugs, I do all, but one at…

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Stuart Mobile Technician
Blue Island, Illinois
Stuart Default
 

I agree with you on both issues you have mentioned.I have seen techs do some terrible diagnosing techniques like the compression test as you described.I even worked with techs that still pulled the battery cable off to test the alternator​.​You expect to get a full description from them also?And some of the responses,you just wonder sometimes. By the way last weeks game between the…

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Greg Technician
University Place, Washington
Greg Default
 

The good news is I don’t live in Illinois or Wisconsin.

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Stuart Mobile Technician
Blue Island, Illinois
Stuart Default
 

Yes but Washington has the most aged hippies that have offsprings that are very smart but lack any common sense​.​Driving in Washington State,where the passing lane is on the right​.​That is not the rules,just how they drive there.

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Greg Curriculum Developer
Tacoma, Washington
Greg Default
 

actually much of them don’t even go on the freeway. And don’t even have a desire to figure out how to drive a manual transmission. You’ve been here before then.

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Greg Curriculum Developer
Tacoma, Washington
Greg Default
 

Ok thanks. Nothing you said helped.

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Scott Owner
Moreno Valley, California
Scott Default
 

"It's usually easier to predict the winner once the game is over." John Madden or maybe it was Yogi Berra. All I can say is I'm not going after a "fuel trim" problem based on P2270 and P2272, (when those DTC's are not lean codes) if the engine has a constant miss. A cylinder that misfires under all conditions should be easy to figure out what is going on. Spark tester, ST125, good, next up…

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Stuart Mobile Technician
Blue Island, Illinois
Stuart Default
 

Scott,I like your way of thinking.I have one question for you since you are from California​.​Do they still produce California vehicles?I mean since California has stricter emmisions standards over cars built for Federal guidelines.I don't recall working on a California emmisions equipted vehicle other than pre-obdII.I was just wondering if they still build strickly for California…

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Stuart, Yes they do. Here's an example for a 2018 - But seeing as you mentioned it, I don't see a lot of vehicles from Illinois here, and for that I'm grateful. I don't know how you guys work on that stuff with all the rust. :-)

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Stuart Mobile Technician
Blue Island, Illinois
Stuart Default
 

LOL only in California.I can make a living if I opened a shop just to replace brake and fuel lines except that the population that have that need are too cheap(not poor) too cheap to profit from it.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
   

Hi Stuart: When I conduct training, I mention the VECI label or the vehicle module ID on the scan tool. If it displays "50 state", I'll ask if it is a CA vehicle. Most people say no. They forget that CA is a state. I remind them of that. Separate calibration standards are getting fewer and fewer though there are still some. The game plan was to eliminate it totally. You may've heard that there…

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Stuart Mobile Technician
Blue Island, Illinois
Stuart Default
 

I alway understood that 50 states or Federal,you could legally drive it in all 50 states but could not title them in California unless it follows California emmissions standards​.​Then again with so many vehicles manufactures overseas they are most likely manufactured with the stricter standards so they can be sold in California.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Stuart: Yes but it is not only CA that they can't be titled in. As I mentioned, almost every Northeast state has the CA requirements. Which is why your assumption about building to CA standards makes sense. But there was that election that I mentioned. There is currently an attempt to change things. It'll probably take a couple of years in court for things to shake out. OEMs don't want to go…

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Eric Owner/Technician
Edgerton, Wisconsin
Eric Default
 

Hi Scott, A big frustration on these websites for me is the way information is presented. I think techs learn this from the customer who is either afraid that more information means more cost or they don't understand enough about what they are working on to present the proper information. The story changes as the post ages. In this case he states compression is the same but it takes more…

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Eric: I agree with your first sentence. (I'm not going to touch your last paragraph.) You may be overlooking something in the rest though. In my job, I interact with people of varying ability. I usually do this in person, at least initially. I also notice what you describe in the first sentence. My conclusion, in many …es, is that the thought in the head doesn't make it to the lips (or…

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Eric Owner/Technician
Edgerton, Wisconsin
Eric Default
 

Guido, When extracting information from customers at the front counter if I feel I'm not getting the answers I should be I change direction, several times if needed, and ask questions that come from different areas. Sometimes it is a matter of talking to the main driver of the vehicle instead of the person dropping it off. It is a feeling that comes with experience and even then it can be hard…

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Scott Owner
Moreno Valley, California
Scott Default
   

Hi Eric, I agree with a lot of what you said and this has been a source of frustration for me over the years. In your response to my 'fish post' you described (paraphrasing here) how we're setting people up for failure by not allowing them to fail. I agree with your thinking. We're doing a major disservice trying to get everyone to 'feel good' all the time. Not trying to get this thread down…

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Eric Owner/Technician
Edgerton, Wisconsin
Eric Default
 

We are getting way off topic here, but oh well, I learned a long time ago, very few people think like I do. It doesn't bother me any more, I just try my best to adapt to the person I working with. Communication is a two way street, you have to ask the right questions to get the right answers. If you're not getting the right answers, you're probably not asking the right questions. ;-) Ha, ask…

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Eric, What is different with your example of plumbers, electricians, and HVAC companies then us? I know of a few things, but at least in California there is a minimum requirement for licensing in their chosen field of expertise. You might have a plumber come out to fix a leak - um, while you're here can you take a look at why my lights don't work over there? The correct response from them…

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Eric Owner/Technician
Edgerton, Wisconsin
Eric Default
   

A plumber, HVAC, or electrician has an obvious separation or limit to their job, or used to. Now with computer controlled water heaters and electric exhaust venting things are starting to overlap. How are we to know where to stop? Where do we place the line we no longer cross? Model? Year? Make? System? I only program body computers? A long time ago I stopped working on Mercedes and BMW's…

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Paul Mechanic
Harvey, Illinois
Paul Default
 

Has someone replaced rear O2s recently? Brand/quality matters. What are the failure records reporting rpm range/load codes are setting? Is the exhaust tight? What are the fuel trims while rear O2s are reporting lean? Sorry more questions then answers, but need more data.

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Scott Owner
Moreno Valley, California
Scott Default
 

"have this Sierra here with an random misfire code and "lean" on both banks (downstream O2) codes." I heard a story yesterday on the radio. The professor teaching medical students was emphasizing using your senses for diagnosing patients. He had a jar of urine which he opened up. He gazed intently at the urine, held it up to his nose, and then dipped his finger into it - and then tasted it…

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Greg Technician
University Place, Washington
Greg Default
 

So you don’t know either

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Scott Owner
Moreno Valley, California
Scott Default
   

Um, not sure what that has to do with the price of tea in China, but... Sometimes the truth is painful, but this can be taken two different ways. As a learning experience, or to just get pissed. Which one is helpful? Your post IMO should be used as a what not to do. Lest you think I'm walking on water I can give you many examples of what I've done and where I've messed up. Would that make you…

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Greg Curriculum Developer
Tacoma, Washington
Greg Default
 

Scott you nailed it! We are all still learning. Looking and feeling what the car does is 90% of diag. I’m new to this website so I’ll be learning I Have a hard time determining sarcasm and actual help. If I don’t know or can’t be any help than I say nothing. Or if I don’t read all the info including comments then I say nothing.

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Scott Owner/Technician
Troy, Missouri
Scott Default
 

Have you tried a relative compression test? I do them all the time from the driver's seat. Reset fuel trims to zero, then disconnect your 02s. Now you are not dealing with a potentially false fuel delivery. Now diagnose the misfire, then let us know.

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