ktuck

Just a general note to everyone in reference to purchasing O2 sensors from Rockauto. I have used RA many times and basically well pleased. However, this recent purchase of what was advertised on their site as GM Genuine Parts made by AC/Delco turned out not to be correct. When I opened the box to look at the sensors, staring at me on the upper housing of the sensor was the word DENSO! No wonder they were only 46 bucks. If you go to this part and click on their "info" icon, their description further indicates this is a Delco made part. I'm sorry, but this is false advertising, and in my case will cost me more time and trouble. I have already re-ordered the sensors from a different provider and had to pay for faster shipping because this is holding up the works for on this Silverado. The real kicker was that Rockauto will not pay for my return shipping of a couple sensors they misled me about. So, basically that means I paid for shipping the wrong sensors to me and now I get to pay to return those same wrong sensors! Okay, there's my rant for the day, but just be forewarned.

Thank you for your suggestions and the very comprehensive diagnostic aids as well. That is what I have been looking for, circuit testing procedures and factory parameters of sensors and devices associated with the ECM. I had run a compression check a few weeks ago, the results were not as I had hoped as all were on the low side, but at least they were similar throughout ranging from 120-135. I thought a very clean engine with just 114K would have higher compression numbers, but I don't believe they are low enough to cause a misfire. Also, my compression gauge is very old, (around 50 yrs!) and possibly not too accurate anymore. It has mostly been laying in a drawer in my toolbox forever. The injectors have been replaced twice so 2 and 5 have already had new injectors yet they continue to misfire. I have detected no evidence of fuel in the crankcase at any time in recent weeks. Looking at some of the circuit testing, I noticed that I have one sensor (MAP) that is reporting out of range. It is 9.2psi at idle and spec is 2.7-6psi. I don't know how big a deal this is or not. I have tested for vacuum leaks and found none (but wouldn't a vacuum leak cause positive trims anyway?). What I do know is that the misfires occur immediately upon cold start...the engine does not have to warm up for the misfiring to be felt and show up on the scanner. So, open or closed loop, doesn't matter. Newdude recommended I get rid of the denso O2 sensor I replaced recently and go with a GM OEM sensor. I plan to do that when I return to Ky tomorrow. Also there are two modifications I have done to the truck in the two years I've owned it, both about a year and a half ago. One was a cat-back Borla dual exhaust system. The other was adding a S & B CAI system. I'm guessing the Borla exhaust isn't causing me this problem, but perhaps the CAI is. Also, a few weeks ago, I messed up and incorrectly cleaned my MAF sensor. I used CRC brakleen which I now know is a big time no-no. Thankfully, I saved my original air filter box and induction system, so I am going to remove the CAI and put it all back as it came originally along with a new MAF sensor. After this, if the problem remains unaffected, I'm not sure what to do. Possibly go ahead and pull the heads and look for problems internally? Any other ideas would be appreciated, thanks.

You make some logical and valid points, I think, especially about the amount of fuel in the cylinders. The spark plugs reflect a lean condition and the extremely high negative fuel trims give reason to see where the fuel amount has been cut drastically. I'm wondering if some sensor(s) are fooling the ECM into thinking there is too much fuel when there really isn't. There are two cylinders missing consistently but others are missing too, just to a much lesser extent. I was curious about the overall misfires so I separated the historical misfires by banks. Bank 2 has 6992 and bank 1 has 5752, so each bank has a similar share of misfires. Individually #2 has 6859, #5 has 4188, and #7 has 948. The rest of them range from as few as 14 to around 400. One shop I had diagnosing the issue said collapsed lifters were the likely cause. Interestingly, the total misfires from the AFM cylinders is 1479, while the total misfires from the non-AFM cylinders are 11,265. I don't believe collapsed lifters are the problem. But there could still be a problem with the valves as you mentioned. I think I can rule out intake gaskets as I've had the intake off twice and the gaskets on cylinders 2 and 5 were perfect. And if I had boogered up the gaskets, how likely would it be I would mess up the exact same cylinders each time...I'm not that skilled!

I agree. I'm now about 2 months into this diagnosis and continue to come up empty. And its not just me, I've had to an independent speciality shop and to a GM technician. So far, it has defied all logical conclusions and I don't even want to think about the money I've thrown at this.

I'll try that even though O2 sensor scan data reflects fairly steady alternating of lean and rich readings. That was the upstream sensor on bank 2. If it was to make a major improvement in fuel trims on that bank, good chance I'll need to do the same for bank 1 upstream sensor as well since the LTFT is nearly negative 20 on that side. I won't be back home until the 4th of May, so it will be a few days before I can do that. I'm way overdue some good news on this truck, I'll let you all know what, if anything changes.

I have heard that the denso was a worthy option to the OEM O2 sensor, but maybe not you think? Sometimes the info put out on youtube and other videos isn't completely accurate. For instance, there is a guy with video to test MAF sensors that claims that if the engine doesn't die when you unplug the MAF, it is faulty. I know that not to be accurate at all. It was on a Saturday when I replaced the O2 sensor and a denso at autozone was the best I could get at the time without having to order an OEM. Since the negative trim numbers are so out of range on both banks, and each bank has a cylinder misfiring steadily, do you think it a good idea to just break down and replace both sides O2 sensors, at least the upstreams?

A couple of typo corrections, that should have read "denso" sensor, not dense. And I meant to say "have your ear in the engine bay".

Sorry to just getting back to this, I'm going to be out of town for a week or two, sadly my wife's oldest brother passed away and will be with the family for a bit. Actually, I think it will be good for me to take a break from the Silverado and get away from this for awhile and clear my head a little. Thank you for your thoughts and all the info you provided. Yes, I most certainly looked at the valves and intake ports quite closely. There was some crustyness on the backsides, but not an alarming buildup by any means. I do detect a slight ticking sound, but you have to have your engine in the engine bay to hear it. From within the cab, it isn't detectable. I have spun the engine over with the valve covers removed and all the rocker arms move as normal. As far as the oxygen sensors, they are all original except bank 2 upstream sensor which was replaced a couple months ago with a dense sensor. I can't remember the code that led to its replacement, but that code has not come back since. The intake gaskets were replaced and each time I exercised great care not to dislodge any during manifold reinstall. One new code has set since this second injector replacement, and that is a P050D, rough idle cold start.

Well, my theory did not play out as I had hoped. After replacing the injectors (again), there was no change to the misfires, numbers 2 and 5 still misfiring regularly and number 7 misses occasionally as well. Upon removing the manifold and fuel lines, I did not notice anything incorrectly done from the first injector replacement. I tested all 8 injector wires in each harness and each read the same. No leaks around the hi pressure pump or any of the lines. The only thing of concern I saw was most of the injector tips had brown deposit stains on them...not a bunch of buildup, but a very thin layer of crust. The truck has been driven less than 200 miles since the first injector replacement. that seems like a very short time for that amount of buildup. Oddly, with the high negative fuel trim numbers, the porcelain tips of all the spark plugs appear more lean than rich. So, the consolation prize is that I guess I have effectively eliminated the injectors from the equation. However, P0300 and P219A remain along with the CEL. I feel like I've simply become a parts changer now and chasing after new theories each time. I was ASE mechanic in the 70s, 80s and 90s, but so much has changed since then and I've been away from the automotive scene for a while. OBD2 was new when I hung up my wrenches professionally. The amount of money I've thrown at this problem has grown to a ridiculous level. If I had known what was coming, I would have cut my losses and wholesaled the truck right off. Now I'm invested so deep in it, I feel I have to see it thru and besides, I still owe 11K on it and that complicates things even more. The only thing I know to do, is go back to the data. My autel scanner shows high LTFT negative trim numbers on each bank, but bank 2 the highest at -33%. Bank 1 is running around -14%. This is the only data showing up which is out of normal range and actually by a good bit. It seems logical to me that if I find and correct the fuel trim numbers, I will be solving the running problem and CEL. That has proven easier said than done. None of the suggested common causes for high negative trim numbers have proven to be the problem. Most have been either eliminated or replaced with no difference, The only exception is the MAF which I have tested and it shows normal function. I've got to be missing something and for the life of me, I don't know what. My latest "theory" is that possibly the misfiring itself is what is causing the high negative LTFT. The two worse misfiring cylinders are 2 and 5. Cyl 2 is clearly misfiring worse than 5 and is on bank 2 which has worse LTFT numbers. Cyl 5 on back 1 which has about half the negative LTFT number bank 2 has. But that may not hold water either as cylinder 7 is misfiring at times and when you add the total misfires of 5 and 7, they are slightly more than cyl 2. Trying to make sense of this, any ideas would be appreciated, thanks.

If the rain can hold off, I'm going to replace the injectors today. I may not finish until tomorrow, I'm an old man now and work much slower! Pulling that intake with a engine that is set back so far, is a real challenge for me. Afterwards I'll post how everything turned out. Meanwhile, fingers crossed.

Wow, that is good information to know, thanks newdude. That kinda makes me more inclined now to go ahead and redo the injectors, although the injectors I put in have the same GM part # as the original ones I took out. That is why I bought them, I assumed they were an exact match. Apparently, they have been upgraded since 2017. At this point, it would be worth it to purchase all new injectors with the current part # you listed and see what happens. Another reason I suspect injectors as the culprit is that when I floor it, it pulls fine with no hint of misfire. That makes me think the injectors, for whatever reason, are getting adequate fuel spray at higher speeds/load and at idle and light throttle driving not so much. Thanks again for enlightening me on those new part numbers.

I am trying to figure out this problem I'm having methodically and accurately, and I must say, it has challenged my skillset greatly! To briefly restate, my primary issue is a constant misfire on cylinders 2 and 5, with an occasional misfire on #7 to a much lesser extent. All other cylinders firing off like clockwork. Two permanent codes persist, P0300 and P219A. The concerning data I am getting from my scanner is the very high negative long term fuel trims and questionable fuel pressure readings. I have read about various causes of high negative trim and they point to things like MAF, O2 sensors, leaky injectors, high fuel pressure and not enough air. I am inclined to focus on the two misfiring cylinders and consider causes that would isolate those two cylinders. For instance, if the MAF was defective, would it isolate just two cylinders and all others fire just fine? I don't think so. Same thing with high fuel pressure, or O2 sensors. Cylinders 2 and 5 are on opposite banks, if it were to be because of inaccurate O2 data, then there would have to be an O2 sensor on each bank that is bad in the same way...not too likely it seems to me. With that line of thinking, if that makes any sense at all, I feel like I should focus on an injector problem which most certainly could isolate one or more cylinders. It was about a month ago, I installed a new set of OEM injectors. As best as I recall, I have intermittent misfires prior to that, but not the consistent misfire on the two cylinders I have now. As many have said, there is no assurance that a new part couldn't be bad right out of the box. Also, and perhaps more likely, I may have done something during the installation of the injectors that brought this about even though I felt like I took great care and diligence when doing so. This is one time where I would not be too mad at myself if I find out I boogered up the job somehow, because at least then I would be able to finally put this problem behind me! Does this approach to the diagnosis at this point sound logically to all of you? I certainly welcome any other ideas I haven't considered yet.

This is what my scanner is reporting to be my low side fuel pressure as I understand it. It is supposed run around 50 psi or so? I'm not real sure on that and haven't found the accurate spec for it yet. However, my scanner reads as low as 25 to as high as 63 psi. I don't think that is normal, is it? Also, my scanner gives a readout for commanded fuel rail pressure of 580psi at idle and 580 at 2K. On the high fuel pressure side, my fuel rail pressure is running between 480-603 at idle and 574-602 at 2K. So, is it safe to assume that in reference to the commanded fuel rail pressure readings, mine are within range pretty much? The low side of course may be another story and I do not know if that wide range of variation is normal due to engine load, temperature or other sensor inputs.

My GM tech is telling me negative LTFT indicates a rich mixture, but he has been wrong about a couple other things I found out. Also, the spark plugs do not indicate a rich mixture, but more towards lean. The porcelains are very light tan, almost still white. He thinks my o2 sensors are being "fooled" into reporting a rich mixture and as a result the ECM is pulling back fuel...hmmm, does this make any sense?

I found my receipt for the injectors, the GM number on them is 12668390. Since I think I have eliminated plugs, wires and coils by substitution, it may be worth going back in and switching some of the injectors around to see if that moves the misfire problem away from #2 or 5. I'm quite aware of the chance of getting a defective new part. I also am concerned with the wide variance in fuel pressure...could that be playing a part in this?

I used OEM injectors. They have GM part #, I don't remember what it was. I did replace all 8. It seemed to make sense to do so after going all that trouble.

Thanks for the suggestions, Buck. No, I haven't researched the wiring to the coils, perhaps that could be the issue. Does that involve a check of reference voltage and ground continuity? I hear talk about checking the various ground points on the engine or frame...maybe that could be a factor? I haven't heard of the gas pedal deal, what's the issue with that? Thanks again.

I have a 2017 Silverado 1500 LT with a 5.3L with 114.000 miles that I bought from the original owner two years ago. I am sorry for the length of this post as I have tried to give the briefest but comprehensive analysis possible. I began noticing random misfires on occasions about 6 months ago but they have became more frequent and now are not intermittent anymore but constant. I currently have a steady CEL and codes P0300 and P219A. It shows up on light to moderate acceleration. I took it to a GM tech who suggested decarbonizing the engine. It made no difference at all, so he then suggested replacing the injectors. I did that myself to save a couple bucks and used GM injectors. In the last 6 months I have had two new sets of AC plugs in it and all the plug wires. I had a coil pack failure on cyl #1 so I replaced it and the misfire there went away. Erratic misfires began to start up again so I replaced all the other coil packs as well but the problem remained. The GM tech now thinks I have a collapsed lifter issue. I pulled both valve covers and inspected rockers, lifters and valve springs...no problems found. The inside of the engine looks pristine. There are no wobbly rockers and when spinning the engine over, all 16 valves appear to be opening consistent to all the others. Does not appear to have any wiped lobes or bent push rods. The original owner changed oil religiously at 3K intervals and I have followed that pattern myself. I drained the oil pan and looked for any traces of metal in the oil and found absolutely nothing. The oil is still very clean and clear and easy to see if contaminated. My scanner shows cylinders 2 and 5 as the chronic misfires I have switched plugs, wires and coil packs from good firing cylinders to see if the misfire will move to those cylinders but the misfires stay with 2 and 5. Since both are non-AFM cylinders, it kinda counters the GM techs theory of lifter problem, especially since visual inspection revealed nothing. Another data concern are the fuel trims. Bank 1 LTFT is around -15% and Bank 2 LTFT is around -28% which indicates a rich condition. I am puzzled that with the high negative LTFT, all the plugs are light colored almost white and certainly don't show a rich condition. Are the O2 sensors somehow being fooled? Their numbers look normal. The high fuel pressure is running around 480-600. The low fuel pressure jumps around while driving, I see it go as low as 25 and as high as 63...it never really holds steady very long, is that normal or possibly a sign of a fuel delivery issue? One more thing I'll throw out there, when it is missing and bucking on light load acceleration, if I kick it down and floor it, it takes off without any hesitation and runs strong and smooth. That seems kind of odd to me considering the multiple misfires. What am I overlooking here? I welcome any thoughts or ideas about this chronic misfire condition.