You know when someone is a master in their trade when they make something complicated look easy, you are great at diagnosing problems which is often the most difficult part in auto repair.
A couple of notes here: You could have saved a lot of time doing the leak down test. You didn't need to take the valve cover off or put a dipstick in the spark plug hole. All you needed to do is connect your leak down tester and apply 10 psi. You then rotate the crank and when the needle starts to rise, you are on the compression stroke and both valves are closed. Continue turning until the needle stops rising and starts to fall. At this point, you just passed TDC. Turn it back the amount you turned it last and you're at TDC and ready to do the test. When you noticed the leaky cylinder, since you already had the VC off, you should have struck the intake valve with a plastic hammer as sometimes there could be some debris trapped between the valve seat and valve face preventing it from closing. In some cases, it could be some crap stuck in the valve guide. Striking it can sometimes free it up and bring the engine back into service.
@@darrellteague8629 You're not going to harm an engine by turning it a few degrees in the opposite direction. In fact this is unavoidable if you're replacing a timing belt.
I don’t usually comment on videos I see on RU-vid but you are great at what you do. You are very thorough and you explain everything so clearly. Just great work. Thank you.
Kit you are absolutely a genius at figuring out tough problems with engines! I took my 2007 Tundra to the dealership for P0420 and P0300 codes last week and they just coded it came up with the same codes and said I needed a new catalytic converter and a complete tune up for $5800! They did not test anything just scan for codes. I wish you were close to me (Georgia)! I have been fighting the P0420 and P0300 code going and coming for a year now and can't get it solved. Thanks for the videos!
I have replaced fuel pump, fuel filter, pressure regulator, plugs, wires, about to change injectors..after this vid i feel like this is exactly what's wrong...my engine has 300,000 miles..might as well change the chain too... I'll get another 300 out of it😁..im subbing out of gratitude and the fact that you did an amazing job
Thanks for a great video. Thanks for all that helpful information and knowledge you share. Great to know theres honest true technicians out there that can explain what they practice. It feels like been in tech school just by listening to you. 👍🏽thank you so much!
Just wow!! I'm now chasing that mysterious misfire of cylinder 7 on my 2000 chevy Suburban that has 317k miles. It doesn't run rough or anything. But the check engine light is keeping me from passing inspection in Missouri and I need my plates. This has helped a great deal. I was taking notes throughout the video and saved it to show to my mechanic. You are a GOD send my friend. Bless ya!
EXCELLENT! thorough diagnosis, crisp clear explanations. With single misfire showing on scanner, the first shop should have told the customer exactly that - a single cylinder misfire. A general tune-up (an 8 cylinder solution) is not correct solution for a one cylinder symptom.
Thanks for the thorough explanation of each part. My 2004 6.0L is doing the exact same. I finally got it to give me a code showing that it too was cylinder #6 on my truck. I did not replace all the parts only plugs and wires. I tested and cleaned all the other parts you mentioned including the MAP and MAF. Today I found a vacuum leak and that changed the rough idle to run a little better. Tomorrow I will try the pressure test and cylinder leak down test. Thank you for direction on my new route of testing. Here is hoping it is only the head and not the piston rings.
Thank you for giving us so many options to diagnose this code!!! I just had one pop up driving on my way home and I’m currently going through the diagnostic stage and trying not to throw money at it unti I have a definite answer and these bids help a lot!!!
I had the exact same issue with my 2000 Suburban 5.3 ls, code p0300, (random miss fire) after replacing many of those parts he mentioned (fuel regulator, spark plugs, wires, coils etc. etc. a friend mechanic recommended replacing the engine after diagnosing that the miss fire came from cylinder 5, low compression, so I took it upon myself 😁 and removed the head on drivers side and voila, the exhaust valve spring on cylinder 5 was broken (cracked) so it would stay open randomly, so I just replaced all of the valve springs, seated all the valves, new head gasket and it's been running perfectly for about 3 years now, I wish he could've had this video back then, his explanation is awesome
I have the same issue on my 09 silverado. I've watched 10 videos all saying the same thing with no success replacing sensors etc. But none of them discussed leak down test . I think you hit the nail on the head. I will know in the morning. Very informative
Very good information. Very patient with making your video very thorough. I appreciate you keep it up. There’s a lot of us out here to need people like you.
It actually turned out to be the timing chain and the thing the chain goes around. Was looking at 2500 fix at first but we paid 800 for the chain and the other thing lol idk what it’s called. But yeah.. 😊
I think its not my problem but I still enjoyed the video and watched to the end. You are like a doctor with cars! Good job and please keep up the good work! You are making the whole world a better place to upload these videos.
I really enjoyed watching your expertise in accurately diagnosing this issue. I came across this video after already subscribing to your channel a few weeks ago. I'm having a similar issue with the p0300 code but my engine is running fine. I wish you were closer or that I could take it somewhere to get properly diagnosed.
hcxchange Thanks for subscribing and welcome to our youtube community, you should take your car to a pro mechanic who can diagnose it properly!! Good Luck!!
Great video! I enjoyed watching this. My expertise is in 5SFE and 3SGTE Toyota engines, but I have had a LM7 5.3L engine since 2017 that I have been avoiding tearing down and replacing the heads on. Recently I got a P0300 code and I know that I am having valve seat issues. I have the stock Castech 706 heads which were notorious for developing a crack in the casting. I also am burning coolant. Time for me to man up, crack my knuckles, and tear this baby down. Thank you for such good information, and for giving me the inspiration to start pulling the heads.
Excellent video. I am fighting this exact same issue now. I pulled my engine after 225k miles due to one of the cylinder’s lifter making a crazy amount of noise. My 2011 features the DOD/AFM feature but not anymore after my rebuild. I didn’t do any piston or head work just cleaning and valve lapping. I will proceed next with your cylinder leak down test. I could use you here in South Carolina, lol. Thank You!
Awesome video!!! I have been chasing this same code in my 2004 sierra 2500HD. I did do the plugs, plug wires and coils which made a huge improvement but every now and then I still get the code. Definitely going to do more research before just replacing the injectors. Thank you so much for an excellent video!
@@budman201 unfortunately I got hit in the rear axle shortly after posting so I haven't done anything based in what I've learned from this video. If I figure anything out once I start working on it I will let you know.
You are a lifesaver! Thank you. I almost bought like 500 bucks worth of parts & do it myself 😅😅 I will have it checked. Thanks a million!! Blessings 😎😎
Dear sir,i have just found this video.i would like to compliment you,on the presentstion,it was do clear,precise,articulate,methodicsl.and analytiical.an absolutely brilliant video sir.this is exactly whats happening to my car.av just subbed,steve from the uk.keep up the great vids.
Excellent information! Helps me a lot! Ive probably misadjusted my rocker arms which is giving me the p0300 and rough idle after replacing my lifters. Dipstick was a great tip as well.
Thank for your thorough diagnosis of that vehicle. My supervisor has the same vehicle with the same failure code. Will consider your leak down test before he throws any other parts at it.
i have had the same problem for two years , i am so glad i watch your awsome video! i now know i will be doing a valve lash on my heads. btw my # 6 has the same high count of missfires. cheers
Amazing video, I have this code in my truck. I was about to start chasing down the problem myself. But I think I’m going to take it to my ASE certified mechanic and let him diagnose it the right way 😅
Hi mr k this is the first time l see some body show all this cyn miss fire and expand the all inf about leaking valves thakns mr k you are a master on mecanic god bless you you and you all family
Your car contains what seems like an endless array of sensors, one of which is the knock sensor. Although the knock sensor doesn’t get as much publicity as some of its counterparts, it does play a crucial role in keeping your car’s engine running right.
Your teaching is very useful , i have replaced all of things you said on 2005 avalanche. What is so helpful is you are speaking on a level of skill that doesn’t start with “This is a wrench”, it is used……..bla bla
I’m going through this with a 2017 Silverado except it’s cyl 3. I tried the leak down test but was inconclusive because when I put air in the cylinder the engine spun just enough to open the valves again. I know this because I marked the serp belt and alternator as a starting point. It’s crazy that these motors all have the misfire but I see so many things causing the same issue. Very good video. It’s been a little while since I’ve done this so I wanted to make sure I did it correctly. Thank you for this.
Great job, very well explained without a lot of wasted time on common preparation of test procedure. Your buddy is not going to like you making him look bad by throwing parts at this issue.Haha
Excellent diagnostic video. The other shop obviously did not have the proper equipment and skills to locate the problem and used the "shotgun" diagnostic procedure. The customer needs to find out if the other shop would prefer to issue a refund or spend some time in small claims court. With over 200,000 miles, the rod, main, and camshaft bearings as well as the timing chain, oil pump and all other internal parts have the same mileage. I would probably recommend a low mileage used engine or a rebuilt one if the rest of the vehicle is in good condition.
Best video so far I’ve seen about explain P0300. Other videos d add how how to check on a scanner and show the miss fire but never explain what the issue is. I think I have this same issue on my truck. I have a P0300 I changed the same plugs and wires. But that’s as far as I want to go. I don’t want to start changing everything.
Great video, very helpful. My 2005 Chevy Silverado 1500 5.3 threw a code PO303 on me at work a couple of nights back. The engine was running a little rough lately ( while in gear, idling with foot on the brake) so I pulled the ignition coil (I also smelled burning electrical components from under ) and it tested bad so I replaced it and the plug. I also changed the drivers side valve cover because I knew the fixed pcv orifice was likely plugged up. It was terrible. Cleared the codes with a scan tool and took a drive. Now the PO303 is gone but code PO300 Pending is now showing up. Engine light on, blinking etc. I'm a contractor and I own the truck..high mileage, 300,000 miles plus. Fix one problem, expose another one I guess. I didn't fire the parts cannon at it..just the number 3 ignition coil and spark plug which actually didn't look too bad. Anyway, hope I can figure this thing out. Oh, engine has low oil pressure as well which I confirmed with a manual tester, not just relied on oil pressure switch. Great channel Sir, new sub.
@@KITS_Auto_and_Truck_Repair My pleasure Sir, your channel is awesome! I have not as of yet..I have to go pick up another fuel/vacuum tester gauge from HF..probably pick up a noid set as well. I did not notice any noticeable vacuum loss but when I changed out the bank 1 side valve cover due to the fixed pcv orifice being clogged up, I disconnected brake booster for the install and then plugged it back in. Engine might be freaking out because it can breathe again. I wondered if that caused an issue. I ran another diagnostic today with my Autel Maxicheck scan tool which showed long term fuel trim bank 1 steady at 5.5 percent while the other trims fluctuated so I suspected a bad o2 sensor..not sure whether it would be sensor 1 or 2. My scanner does not support looking at all o2 sensors in real time data. I also think that cylinder 3 has a bad wire. I listened to all the plug wires through a mechanic stethoscope and #3 ticks like a spark tester lol. I know that's less than a pro approach but this PO300 pending code is perplexing . I'm not a certified real mechanic and my scan tool is limited.
@@kaylamarie8309 if you don't have some of these tests tools, you should have it diagnosed at a pro mechanic shop, so you can really find out the problem!!!
@@KITS_Auto_and_Truck_Repair Thank you once again for the kind reply Sir! Turns out I already had the fuel/vacuum gauge after all so I just went and picked up a noid kit at our local HF..never know when you might need that. I'm really trying to hard to learn all this stuff and you have to have equipment to really do that. After I changed cylinder 3 ignition coil I also bought a new plug for it just out of caution even though the plug that was in it seemed to indicate that it was operating properly and under the right heat condition. I kept the old plug. Coil for three tested bad so I knew it was an issue. Even with the new coil and spark plug, I tested them through the old spark plug wire and the spark in the tester seemed weak (dim and not firing well) to me so I put on a new set of wires before getting too involved with other directions. The spark in the tester was much brighter and more active and the engine ran great. I ran it a while under load and it still ran really good. I cleared the code with the scan tool which actually has more options upon closer inspection and I have been driving the truck for a couple of days with no problems and no further codes popping up. When I initially checked for the pending code po300 prior to clearing the codes , the scanner did not find it so I am assuming the problem is fixed. If it returns I will take it to a pro shop for a more in depth examination. Does that sound reasonable or should I take to to a mechanic anyway?
Just a suggestion . Would a relative compression test also point you to cylinder #6 . Then put an articulating bore scope with 2 cameras to look at the valves . If you see a piece missing , it could save removing the valve cover . The leak down test is positive proof . What I am thinking is that the other tests could possibly save you time if the result is obvious . Great diagnosis .
My point is if you suspect a problem and get a borescope in #6 and see a valve burnt , it may save you time . At that point , the customer has to make a decision . Lucky you could get the valve cover off and #6 plug out . And the leak down test is proof . Good Luck 👍 .
Let me bring Ppl up to date on a common problem with with GM / GMC with 4.8, 5.3, or 6.0 between 02 -06 if you only notice the P0300 code after reaching 65mph or more and especially after changing all of these parts out it is likely that the Crankshaft needs to be relearned. It’s definitely worth a try before changing out or rebuilding the motor. On the video the motor didn’t sound too bad to me while running. I got a 05 Yukon Denali with the 6.0 and it’s having the same P0300 code after changing out spark plugs, wires, mass air flow sensor, and all 8 ignition coils! No problem with fuel pressure or fuel injectors or Oxygen sensors! Im taking my truck to the shop on Tuesday for Crankshaft Relearn if anyone wants to know the outcome just ask l will reply
David Haynes Thanks for sharing that! the crank relearned was done before the truck was brought to me! it didn't fix the problem! Good luck with your truck!
Very nice video. Thanks. I've been helping my son with his 5.3 L engine. I did a relative compression test and a couple of the cylinders show a bit low on the trace compared to the rest. The truck runs good, and is not showing any misfires in scan data. I don't have a leak down tester, but I'm considering getting one. Question, if a leak down test showed a non-sealing valve, would it be an acceptable repair to just pull the head off and replace the valve and the spring components? Would I necessarily have to send the head to a machine shop to be resurfaced if there was no evidence of warpage with a straight edge? I also saw on eBay some used cylinder heads for this engine for around $200 for the complete heads. I'm wondering if that would be an acceptable route to take? My son doesn't have a lot of money to sink into this truck, so just trying to find the least expensive fix possible.
Timothy Horne Thanks! is the head on eBay new or used? it's always good to send the head to the machine shop to get it checked and cleaned if you plan on reusing it!
you are 1 awesome mechanic and very good teacher at that ! i am surprised that the compression test did not show a very low compression for cylinder 6 ! wow
WOW!! Outstanding video with sound mechanical reasoning and diagnostic's. Son has 08' Avalanche with very similar problem and shop in Texas is throwing parts at it. Told him to stop! Get it home and I'll come look at it. This video helps immensely in my thought processes and diagnostic plans. Well done my friend! Wished we had more True Automotive "Technicians" like you !!
@@mtsanchez27 Marcos...I could never definitively the culprit. His 2008 Chevy Avalanche still has some misfires on #5 and to lesser degree some on #7. I followed K Diagnostics logical approach. I scanned vehicle using my Bluedriver OBDII and checked Mode 6 data and many other parameters. I saw nothing that stood out. Next visual inspection of wires, connections, grounds. I replaced all plugs and wires with AC Delco along with air filter. Did spark check with spark tester set at 35Kv gap. Healthy spark. Did NOID light check of injectors and all were showing indications of electrical continuity. I checked MAF sensor, then removed and cleaned throttle body. I checked Fuel pressure at rail with Bluedriver backup. I did power balance. I ran vacuum check warmed up and truck pulls steady 19" Hg. Still nothing definite. I pulled valve covers and checked integrity of valve train, especially cylinders 1, 2, 4, and 7 since those are AFM cylinders. I did warm/dry compression check and all were around 185 psi! I did cylinder leak down test and all 8 cylinders had minimal leak and near identical numbers (Regulated 30 psi with leakage gage at 28 psi). Car idles great and for 156, 000 miles pulls strong. So I came back to OKC from Houston and told son drive it and keep me advised. A local Chevy dealer looked at it after all my work and told him he needed new engine due to suspect sticky valves!!! I asked the Service Manager to tell me with all the date I have (which I gave them), why they think it needs a new engine?! Nothing but crickets! Anyway, one item left untested was the actual injectors as to spray pattern etc. They appear original so I can only surmise that "maybe" that #5 fuel injector is erratic or dirty and maybe not spraying a nice atomized pattern? Good luck with your endeavors.
Marcos, I forgot! Early on when I did visual and got ready to check vacuum I pulled the PCV hose from drivers side valve cover...at the rear area. It has like a factory 45 degree angle hose fitting there about 2.5" long? It had a near 1" crack in it! I replaced the entire hose from that valve cover to the intake with new GM part number then did vacuum check. I suspect part of the issue was A/F ratio issue with intermittent leak from that hose. For grins I checked entire intake area and other common spots to see if there were any other vacuum leaks downstream of the MAF sensor and did not find any others.
Best explanation thanks. I have the same problem and did the same thing bought everything new. I have my misfires on 4. I will check the valves on 4. Super thanks very help full
Man this was an informative video. I am in the exact same position as this truck owner. Mechanic just threw new parts (exact same) for this mystery P0300 code. They just gave up but I ended up with the bill for all the parts which they claimed the L99 engine needed but didn’t. I am praying its not an exhaust or intake valve. But i had new o2 sensors b1s1, 8 spark plugs, 8 spark wires, 2 coils, 3 injectors, but P0300 remains 😤 I wish you were near NYC!
I’m going through this right now. Heading to Harbor Freight right now to get one. Cyl 5 and 6 constantly misfiring. Replaced damn near everything because we are planning on keeping the truck and just rebuilt the engine but still couldn’t get past this. I suspect this is my problem but heading out to get the tester. Thank you so much. You are a great teacher.
Yeah. It turned out to be several problem. Rocker arm was loose on cyl 6. I also used an aftermarket crankshaft sensor that would fail when it got hot. Put the original ac delco back in and the problem went away without having to do the crankshaft relearn process.
Bro! This is ridiculous! Nobody is going to comment on how cool this brother is? I want to know where you are from? Thank you my brother! I wish you lived near me. God bless you!
GREAT FREAKING VIDEO AND INFORMATION!!! I BEEN STUCK WITH MY LQ4! I DID A DIY CYLINDER HEADS AND CAMSHAFT SWAP BECAUSE THEY NEEDED TO BE REPLACED AND WHILE DOING THAT I ALSO CHANGED OTHER PARTS JUST BECAUSE WHY NOT! SO I PUT THE ENGINE BACK I BELIEVED DAMN NEAR PERFECT WITH THE HELP OF A HOW TO REBUILD LS SERIES ENGINE BOOK OFCOURSE A LITTLE BIT OF RU-vid AND EVERYTHING WAS ON TO THE T WITH THE TORQUE SPECS AND EVERYTHING! THE ENGINE LOOKS BEAUTIFUL AND WELL PUT BUT FOR SOME STRANGE REASON IT STILL MISFIRED!?!?! I WAS HEARTBROKEN! BUT NOW WITH THE HELP OF THIS MANS KNOWLEDGE AND VERY GOOD AND DETAILED EXPLANATION ( BECAUSE FOR SOME STRANGE REASON SOME PEOPLE ON THIS RU-vid CANT EXPLAIN THE EASIEST EXPLANATION!) IM ALMOST POSITIVE IM GOING TO FIND THE PROBLEM WITH MY BEAUTIFUL TRUCK NOW! THANK YOU SIR FOR YOUR KNOWLEDGE AND TIME U TOOK TO MAKE THIS VIDEO FOR SOME STRANGE REASON WHEN I SAW IT I KNEW THIS VIDEO WAS IT! AND I WATCHED AND LISTENED TO EVERY SECOND OF IT AND USUALLY I DONT HAVE THE PATIENCE BUT LIKE I SAID I JUST KNEW THIS VIDEO WAS IT AND SURE ENOUGH! THANKS AGAIN SIR!
Very Cool, You Explained it Very Very Well. I have a PO308 and have checked and exchanged ignition coils , test Wires, Plugs, Compression at min, but did not do a Leak down test. This Video Should Help me determine what problem is. I have tho 487k miles on motor and Did a Valve and grind years ago at under 200k miles. I know I should get a motor at junk yard with hopefully low miles of 80 to 100k. Thank You, You Explained well that I can try following your Class Advice Tutorial. I'm not a Mechanic but I have years of Machinist Exp... Thanks, Gracias.
Thank you, this is awesome. I have been chasing a P0300 on my own 4.8 2006 truck for months as well, I "inherited" the truck from my brother who could not afford the transmission work, but was also chasing the P0300, and had completed a tune-up and fuel-pressure test before the transmission died. And yes, a year later after taking ownership and replacing the transmission, I did go to the parts-store and change out all the coil packs (which actually did cure a "blinking check-light" misfire and an indicated P0304, after which i replaced the other 7 coils to be thorough) but i still, after that, had the P0300 left. So, I have just finished compression-testing and next i am going to check vacuum leaks and repeat my brother's fuel-pressure tests (trying to go in order of easiness) -- I did NOT know how a leak-down test worked, or to check spring-condition. I will follow your plan and check those things after checking scanner counts again (not sure if my el-cheapo scanner has PIDs for each cylinder's misfire count but will see) and finding candidates -- kind of sad, that you did not get to complete a timing test. I sort of hoped that a timing-light test against moving belt would still work, i guess that is dreaming? do you have another video showing the timing test? FIVE STARS MY FRIEND.
This same thing P0300 Drove me crazy for a year. In the end it was because when I changed the plugs I googled the gap which was wrong but I didn't know it because GM issued a bulletin with the correct gap after my initial search. 1 year later and 7 coil packs later I decided to pull the plugs again I googled the correct gap which was the real gap. Problem solved
good man i am having a p0304 in my 5.3 same thing tear down and fix or replace but no one could tell me for sure did the replace part thing to thanks for pin pointing the fix again good man thanks bill
