Jump to content

Search the Community

Showing results for tags 'misfire'.

  • Search By Tags

    Type tags separated by commas.
  • Search By Author

Content Type


  • GM-Trucks.com Original News & Product Reviews
    • General Motors Product and Industry News
    • The GM-Trucks.com Garage - Vehicle Testing & Product Reviews
    • The Newsroom Archive
    • The Garage Archive
  • Battery Electric Vehicles - 2022-2026 Ultium Platform
    • 2022-2024 GMC HUMMER EV Pickup & SUV
    • 2024 Silverado EV & Sierra EV
  • Fullsize Truck & SUV - 2019-2023 T1XX Platform
    • 2019-2023 Silverado & Sierra
    • 2020-2024 Silverado HD & Sierra HD
    • 2021-2023 Tahoe, Suburban, Yukon, Yukon XL & Escalade
  • Fullsize Truck & SUV - 2014-2019 K2XX Platform
    • 2014 - 2019 Silverado & Sierra
    • 2015-2020 Suburban/Tahoe & Yukon/Yukon Denali
    • 2015-2019 Silverado HD & Sierra HD
  • Fullsize Truck & SUV - 1999-2006 GMT800 & 2007-2013 GMT900 Platforms
    • 1999-2013 Silverado & Sierra 1500
    • 2000-2014 Silverado & Sierra HD
  • Chevy Colorado & GMC Canyon
    • NEW 2023 Colorado & Canyon
    • 2015-2022 Colorado & Canyon
    • 2005-2012 Chevy Colorado & GMC Canyon
  • Classic Chevrolet / GMC Pickup Trucks
    • 1988-1999 Chevrolet & GMC C/K GMT400 Platform
    • 1973-1987 Chevrolet & GMC Square Body / Rounded Line Pickups
    • 1967-1972 Chevrolet & GMC Glamour / Action Line Pickups
    • 1960-1966 Chevrolet C/K/Apache & GMC 1000-3000 Pickups
    • 1982-2005 Chevrolet S-10/Blazer & GMC S15/Sonoma/Jimmy
    • 1969-1994 Chevrolet K5 Blazer & GMC Fullsize Jimmy
  • Marketplace
    • For Sale/Wanted
    • Member & Vendor Rating Forum
    • Member Product Reviews
  • The Lounge
    • Off-Topic
    • Future Vehicle Speculation & Spy Shots
    • Automotive Industry & Market Discussion
    • New Member Introductions
    • Meetups, Events, & Gatherings
    • GM-Trucks.com Comment Box
  • Hobbies & Lifestyle
    • Photography
    • Major League Sports, Outdoor Recreation, Firearms, Hunting, OHRV
    • Racing, Strip, & Track
    • Trailers, Hitches, & Towing
    • Garage & Home, Snow Plowing, Landscaping, & Lawn Care
    • Technology, Devices, & Gaming
    • Vehicle Buying, Financing, Incentives, & GM Card
    • Vehicle Builds
  • Technical & Advanced
    • Vehicle Appearance, Care, & Maintenance
    • Ask the GM Technician
    • Performance Engine Tuning
    • Transmission, Suspension, Transfer Case, & Axles
    • Wheels, Tires, & TPMS
    • Audio, Electronics, OnStar, MyLink, Intellilink & SiriusXM
    • How-To
  • Commercial Vehicles
    • 1980-2009 Chevrolet Kodiak and GMC Topkick
    • 1996-2018 Chevrolet Express & GMC Savana
    • 2019-2021 Chevrolet Silverado 4500HD/5500HD/6500HD
  • Black Truck Club's Topics
  • Texas Owner's Group's Topics
  • California Owner's Group's Topics
  • New England Owner's Group's Topics
  • Midwest Owner's Group's Topics
  • South Carolina Silverado Owners's Topics
  • Canadian Owners Club's Topics
  • SCUBA divers of GM-Trucks's Scuba Talk
  • Red Truck Club's Topics
  • Idaho Sierra & Silverado Owners Club's Idaho
  • Colorado Trucks's Exhaust Setups
  • Colorado Trucks's Pics of trucks
  • SEO Paint's seo color ordered
  • NorthSky Blue Club's NorthSky Blue Metallic
  • NorthSky Blue Club's Pics
  • diesel 3.0's Topics


  • Events
  • Birthdays
  • Texas Owner's Group's Events
  • California Owner's Group's Events
  • Midwest Owner's Group's Events
  • Red Truck Club's Events


  • Articles
  • News
  • Reviews
    • Project Sierra
  • Resources


There are no results to display.

There are no results to display.

Find results in...

Find results that contain...

Date Created

  • Start


Last Updated

  • Start


Filter by number of...


  • Start




Website URL









  1. I have a 2014 Silverado LTZ, with a 5.3L engine. There is approximately 145,000 miles on the engine. I have a misfire on the #3 cylinder. I have replaced the induction coil on the #3 cylinder, but I still have a misfire on this cylinder. My mechanic says that the lobe on the camshaft is worn and the camshaft needs to be replaced. I would think that if the lobe on the camshaft is bad then other lobes would also be bad, a defective camshaft. Has anyone else had this problem? Does anyone have any suggestions as to what might be causing the misfire. Thank you in advance for any advise the you can provide. Julian.
  2. Okay guys I bought this truck from a dealership in September. It was used and I got a 30 Day warranty. After the 30 day period, this is what’s happening. I got in my truck and noticed a rough idle. My truck would shake and out of no where the check engine light starts flashing and my traction control light comes on. I took it to my buddies and we got a P0308 Misfire Detected Cylinder 8. So I did some research.. I also had a code which was P219B. Air/fuel mixture ratio. I changed the spark plugs.. didn’t work. I moved coil packs.. the misfire didn’t move. So we watched Live data on the scanner and injector 7 was acting up. So we replaced all the injectors on that side and this truck is still missing.. I’ve ran seafoam through it and cleaned the throttle body and MAS. My buddy things I have a valve issue or something wrong with the cylinder… there is no AFM deleted or anything of that sort. The truck has worked flawlessly until now. 135,000 miles on it. The rocker arms all looked great. please someone give me something to try. I just want my truck fixed lol. posting a link below of what it’s doing…
  3. driving a 97 k2500 camper special, 4l80e with 454 vortec couple days ago I got in my truck after work and noticed it would stumble when hot, 100C no problem but a little bit warmer and i would have issues. always under load during acceleration. got home and idled in drive and it felt like an obvious misfire, RPM would drop to about 500. pop it in neutral or park and no misfire or stumbling, its been confusing me since in the mornings when i pull it out the garage it has no problems all the way to work (5 minutes highway and 5 minutes city) but end of the day and evening- same issue bought the truck with 268km now has 276, oil change every 5000k. did fuel pump (48psi at idle now) FPR, distributor cap and rotor, plug wires and plugs, ran seafoam through the intake and in the fuel tank. ive heard of distributor gears going south but id assume then i would have the issue when cold too. runs like a top at any temp below 100C, no engine light, plugged the scanner in anyways and no codes whatsoever. any help is appreciated, looked through forums for a couple days now but nothing exactly like what I'm experiencing. kevin,
  4. Hey guys and gals, Long time creeper, first time poster. I currently have a 2011 silverado 1500, with 163,622 miles on it. It's a 5.3 vortec engine. It smokes from the exhaust a light blue exhaust that's mixed with a grey/white exhaust. It stops smoking after roughly 10 seconds of running. Haven't noticed it while driving. It also doesn't smoke every start-up. It rough idles when in park. I replaced the plugs and wires a couple weeks ago, and I started misfiring on cylinder 8 after the change, before the change it was cylinder 5. The only codes it's thrown is for the misfiring. I also pulled plug 8 after the codes to check it and found oil on it. I did a combustion gas leak test and the liquid stayed the same color (blue). I'm starting to lose my mind. Any thoughts, suggestions to try? Also, as of now....I've noticed no loss in power at the moment.
  5. Hi. I bought a new 2021 AT4 March 5. 20 miles on it. Drove home from the dealer (4 miles) and the next time I turned it on, CEL and OnStar diagnostics emails me to take it to the service department. They say they reset MAP sensor and send me on my way. Later that day, same thing happens. I take it back in, they say MAP sensory needs replacing. They had it almost 2 weeks waiting on the part. After they replaced it, everything went fine for about 1200 miles and then I get blinking CEL for about 30 seconds then it stops. Next day, blinking CEL for a minute or so, and then it turns solid. I took it back to the dealer and they say the only code pulled was P0300 misfire. They have no idea what’s causing it, and quite frankly I’m pretty fed up at this point. They’ve had my new truck longer than I have in the month I’ve owned it. Has anyone had something similar happen?
  6. First time posting but have searched the forums for years and have always found what I needed. Well this time I'm stumped, so I have a 1994 gmc k1500 pickup with a rebuilt 350 tbi bored .030 out with a stage 2 cam and long tube headers. (About 4000 miles on engine.) new distributor, plugs, wires, vss, So here's what's going on, the speedometer jumps around super erratically but when I turn the heater on it seems to change how much the speedo jumps around. If its on high it jumps around the least. Low or off its just bouncing off 85mph like bouncing to the point I can hear it slamming into whatever stops the needle from going any further. When I turn the turn signal on left it makes the radio light dim with each flash. The odometer turns constantly when while sitting in park. I have replaced the vss at the very end of the trans where the rear drive shift meets. I was drive the other day and the truck just didn't want to move seemed like it was just constantly back firing or misfiring. I have been trying to check all the engine grounds but not sure what all needs to be grounded. Any info/advice would be greatly appreciated.
  7. Hey all, so I have a 17 Silverado 5.3. 33000km was driving around yesterday. Truck was at operating temp and trans temp was at 76 so all was good. it was driving fine, then I got home. And backed into my driveway. Parked emptied groceries yadda yadda. 5 minutes later realized I had to pull in. Got in, and did just that. Then 5 minutes later had to run to corner store. This is when the truck started rough and check engine light started blinking and it was like I had no power. ( and when I say rough, it was god awful. Like bucking and lurching) Turned around a parked it. 2 hours later drove it 40km and not an issue. Next morning drive to and from work (7km each way) no issue. some say it can be the anti theft , or dirty injectors or worse clips or plugs. Trucks only got 33k help?!
  8. So I am at a loss here. I have had an issue with my 2012 Silverado 1500 LT where cylinder 1 eats spark plugs for whatever reason. No big deal I just keep a spare and swap them when I need. That’s happened 3 times since I’ve owned it. The other day I am on the highway running probably 75 when it started running rough, tapping and the check light started flashing. The tapping was like a pen on a desk not a knock. I pulled right off and checked the oil and no. 1 plug. Oil was a lil low and I swapped the plug but the problem persisted. I drove it another 15 miles doing 55 and the light changed to solid and the misfires and tapping went away. I still have a light on solid reading the codes p0300, p0466, and p0300. I am inclined to change plugs and wires along with an oil change. I still have oil life left and is full synthetic and I did plugs and wires a few years ago. Has anyone had similar experiences?
  9. I have a 2020 gmc sierra sle 5.3, I bought it may 13th. Starting at about 800 miles check engine light would flash for a minute or two and then go off, this occured every 300 miles until I got in one day around 1500 or 1600. Check engine light stayed on. Called the dealership and took it in was throwing misfire codes, the diagnosed it as fuel pump module reset the codes and ordered the part and sent me on my way. Come back in and had it replaced when the part arrived, well now fast forward to a tank and a half later and now the check engine light is on for the evap system/gas cap, and fuel pressure at 2200 miles. Right at a week from the time it come out of the shop. I've been extremely happy with the truck but I can't believe I'm going to have to find time to get it in the shop to be looked at and fixed again. I'm at wits end already. Anyone else having these issues?
  10. Hi there, new to the forum. Looking for information if someone already deal with this problems. 2014 Silverado 5.3 I changed spark plugs, cables, all the injectors. And after that the truck worked well for 2 days after that I started getting code for misfire cilynder 4, the stabilitrack light, engine power reduce, I know I need to remove the valve cover and check for lifters, but I just want to know if someone already deal with this and what was the fix for this. I like the truck but it just sucks to many issues with this engines. Thanks.
  11. 2007 Silverado 5.3 V8 with AFM with 180,000 miles Truck had lifter ticking sound and white smoke upon every start up which would go away after a few minutes, no check engine light Replacement list : - headgasket - valve gaskets - upgraded drivers side valve cover - valve stem seals - intake manifold gasket - exhaust manifold gasket - 8 new afm lifters - 8 new non-afm lifters - head gasket bolts - engine coolant temperature sensor - spark plugs - spark plug wires - fuel injectors - water pump - thermostat - cam sensor - crank sensor After completion of engine reassembly no longer had white smoke upon start up and no ticking sound but flashing check engine light code p0300. Code p0300 was for cylinder #1, #4, & #7 Moved coil packs between cylinder #1 and #2 to see if coil packs was bad but no change. Set engine at TDC before installing the rocker arms. All bolts have been properly torque and no parts have been left unplugged or uninstall. Any possible advice would be helpful
  12. I've got a 2014 GMC Sierra L83 single cab... I recently decided its time I start getting some performance out of my truck. I installed: L86 Thottle body and intake manifold 1 7/8 header + full 3 inch exhaust (magnaflow muffler) Stage 2 GPI cam kit + DOD Delete Transmission Oil cooler I had the car dyno tuned and everything went perfect. We later had a few trial runs on the street and hit issues with sort of a misfire at specific rpms and gears... 2nd gear at 4,200ish rpm it would have a slight nudge and again at 5,200ish another drop and kick. It would happen almost all the time. We thought it would be the spark plug cables, went and got MSD plug cables added those, tried again, same thing! Spark plugs are new, fuel injectors are serviced with zero issues... the car ran perfectly before we did all of this... The tuner now tried raising the oil pressure in the transmission thinking its a gear slippage due to the oil pressure. Tried again, same thing!! We've ruled out alot of the problems, now theyre saying that its the disc thats slipping in the transmission which would make sense but I want to get ideas as I'm spending money trying to fix the issues that we're not a 100% sure about. Can you guys let me know if anyone went through anything remotely similar or if you have any views on the matter. Many thanks!!!!
  13. I had a rough idle ans I noticed my tahoe losing power ans engine started missing. Code acanner said random misfire. Changed plugs, wires, and crankshaft sensor. It started ran finw for about 30 seconds- 1 minute maybe, then it just died instantly. Hasnt started since.
  14. I just put a new 6.0 long block in my 2002 chevy Silverado and it won't start. All new sensors, plugs and wires. When I go to start it it back fires through the intake. Plugs are soaked in fuel as well. I've checked to make sure nothing is unplugged....any suggestions?
  15. So i have a misfire...i change my cap, rotor, plugs, ignition coil, ignition control module, i even replaced my lower intake manifold gasket and timed my distributor. Then after all that i still had a misfire. What more could it be...a timing chain!?
  16. I need some help I’m not a mechanic totally but I have been going to school for it and my 03 Silverado 5.3 is misfiring and I don’t know what the problem could be I replaced the spark plugs coils and all the cylinders are getting spark and I had a compression test and the the cylinders have near perfect compression so I don’t think it’d be that. I even replaced the ecu/pcm in it and nothing changed it’s a hard idle and had no power can’t even make it a block really it also dies when I hit the brakes after going anywhere over 5 mph.
  17. I have a 1993 GMC Sierra C1500 v6 4.3L with an automatic transmission and i have tried replacing the distributor cap, router button, spark-plugs and the module that sits under the distributor cap but nothing works it just rolls tries to kick and if it does start it dies instantly. also when trying to start it smoke rolls out of the throttle body I have no clue how to fix this
  18. Fixed! See page 2 update. Rebuilt Trans! 2014 Sierra 1500 5.3 120k miles Hey all, I searched and read some of the transmission threads but it wasn't helpful so hoping someone can guide me or had the same issue.. Truck has been running great no issues, one morning i go to work as usual and half way into the commute i get this skipping/shudder when under load. I let off it goes away. RPM is steady at idle and its not doing it or is not noticeable in cruise. No codes. Does it in Manual, all gears and all speeds. Only when i get on the gas. Power is less, it feels like a slipping trans but also feels like a misfire. Plugs are assumed to be originals so tonight im replacing all to see if it fixes it, if not: they needed to be done anyways so no harm done. Trans has been flushed at 95k at GM dealer. My next option is another flush. Any ideas?
  19. Currently in the process of trouble shooting a p0304 code. Ruled out a bad coil pack by hooking an ohm meter to it and also swapping cylinder 2 & 4 to see if the the Mis fire would follow. Replaced spark plugs, plug wires, and put a can of sea-foam in the intake. Not hearing any abnormal sounds coming from the engine while running. Just a steady misfire on 4. I’m thinking it is a bad injector. Anyone else experience something similar, and to also see if anyone yet has tackled changing the injectors on the new models. Thank you
  20. Hey guys, first post on here and I've got something that stumped me 100%. I have a 2005 silverado 1500 flex vin code Z. It Idles rough it has terrible acceleration, wide open throttle it takes off like nothing is wrong. It misses on 7 every time, misses on 2 every other time, every other cylinder misses here and there. No misses when in park and rpms are kept about 2500. CEL flashes most the time when accelerating (except WOT) otherwise the light is on solid. It has 220k on it and I have replaced alot of parts. New parts All 4 02 sensors OEM Plugs OEM wires OEM Fuel pump OEM Throttle body cleaned 3 stage fuel system cleaner BG Brand Air filter believe it or not OEM again New transfer case (unrelated issue) I have covers the base of the intake with brake cleaner multiple time, no signs of leaks. I've had the smoke machine hooked up 3 to 5 times and again no signs of leaks. At this point what is the best route to take? Remove intake manifold so it's easier to get to and replace the main grounds behind the heads and replace gasket at the same time? Replace the pcm? Replace throttle body maybe? Any other suggestions or recommendations would be greatly appreciated.
  21. Looking for help/instructions on replacing fuel injector/s for a 2017 5.3L Silverado. Truck has 80K miles on it and a #5 misfire. Dealer ran a diagnostics and said the injector needs to be replaced. I found a couple pictures on the forum of the fuel injectors but very little information on steps to replace them. The only videos I could find online were for older models with a different injector diagram. Talking to the dealer they quoted me $770 to replace a single injector, gaskets and piping associated with the job. 4 hours or labor and $240 in parts. Are there any good instructions or videos out there on replacing fuel injectors on a 2017 Silverado? I've never done a job like this but consider myself mechanically include, is this an easy enough job or should I leave this to the dealer to do? I know they say if your replacing a single injector you might as well replace all 4 on one bank but is that really necessary, $110 a piece and if the other 3 are fine why replace them? The dealer said the piping and gaskets must be replaced even for a single injector replacement job. Is this all necessary? I've never had another vehicle with injector problems so this will be a first. Parts quoted- 12687650 (1) injector 12626354 (8) gaskets 12677002 (1) pipe 12677004 (1) pipe Any help, links to instruction/diagrams or videos would be awesome! I enjoy working on these projects rather than paying someone else to do the work since you learn something every time. I also want it done right. Thanks all in advance!
  22. I recently bought a used 2016 Sierra Denali 5.3L 4x4 in March with 48k miles. Truck has been great until yesterday (now 52k miles) when I ease into the gas it shudders and shakes like crazy until i punch it. The tach is bouncing up and down and it doesn't matter if it's in v8 or v4. It almost feels like it's a misfire but it's weird that it only does it when I'm easing into the throttle or going uphill. The truck has the 8 speed transmission. Has anyone else ran into something like this and would the manufacturer warranty cover the fix for this?
  23. Good Evening, Gents. I hope all is well. Let’s get started with a little introduction of myself. My name is Cody and I’m new to this forum. I’m a long-time active member of other forums with previous vehicles. A year and a half ago I traded in my 2001 Z06 for an 07 Silverado. Extended cab, Flex Fuel 5.3 with 78,000 miles. 1 owner and a VERY well maintained vehicle. The truck has done me very well and is extremely dependable (duh; Chevy and the 5.3). About 4 months ago I started having a random misfire issue when traveling between work and home (~300 miles each way on the weekend). I had a minor misfire/hesitation and a check engine light. It wasn’t flashing, so I drove into the next town and had it checked. It was a p0352 and p0300 code. I got to my trailer where I work and changed the plugs and coil pack that it was indicating was the issue. It cleared up for a bit and then the p0352 returned. I swapped the coil pack with a different cylinder, along with the spark plug wire as well, and the CEL return. Same code. I’m sort of at a stump for what it could be as some people have said ground issues, wiring issues, etc. I’ve always been mechanically savvy and have maintenanced my own vehicles and have repaired/modified them. I’m really just seeing if anyone has had a similar issue and what their outcome was. The truck has a very intermittent miss. Sometimes it drives and runs great, then out of the blue with stumble and fall on its face. It’s very inconsistent. Any insight would be awesome. Thank you so much.
  24. So I had a few after market parts installed on my 2015 Silverado: Flowmaster 40 series, Volant cai and finally some Gibson performance headers (heat wrapped and all). I didn't have any issues until the headers were installed. Shortly after leaving the shop my truck isn't shifting correctly and my engine light is on. I figured over heating was the culprit and that I should let it cool down before taking it back out for some fun. Hours later the problem is persistent and my truck is down shifting at too high of rpms causing it to jerk and stall for a second. I also feel like there's some power loss. I plugged in my Diablo inTune i2 and it showed the error code being a 3rd cylinder misfire and rough idle. I checked all of the spark plugs, the wires and all the bolts but I can't see an issue with any of them; all the plugs tested good and all the bolts are secured. Does anyone have any insight as to what the problem could be?
  25. (I posted this on another board, if you've seen it there and replied then disregard. ) Hey folks, I’m new here. I’ve been reading post for a while, my vehicle before the 2010 Tahoe I now have was an ’03 Tahoe. I’m looking for input on a problem I can’t wrap my mind around. A quick bit of info about me, I’m one of those older guys from the days of points and condensers and manually setting your timing (1970’s era) etc. I never built ‘hot rods’ so I never got deep into the technical side of things, but I have rebuilt 3 or 4 engines over the years and usually do all my own repairs. I’m not into engine modifications, pretty much an OEM spec kind of guy. I do commercial low voltage electronic systems for a living, so I have no problem with automotive electrical, and have a decent understanding of module control of inputs and outputs. I’m not a pro at this by any means, but I’m also not a newbe. No doubt you can get over my head if you happen to be a pro and have some input, but hopefully you won’t have to candy coat it too much. So back in November, I traded my ’03 Tahoe in for a 2010 LT Z71 Tahoe with a 5.3 and 120,000 miles. I plugged in my cheap code reader and there were no codes and all the monitors were ready, and it ran fine, so, no need to fix what’s not broken. I wasn’t real pleased with the mileage, it averaged a little better than 13.5 mpg, but figured I’d work on that as time went on. I did put new plugs and plug wires in the first month. Back in April it started idling rough, but didn’t throw any codes. Knowing it’s 8 years old with over 120,000 miles, and not knowing the history, I don’t have a problem replacing parts so I’ll know what I have, especially anything that will help gas mileage. I replaced the throttle body and position sensor (along with the accelerator pedal w/position senor), and once the idle speed settled down it was still rough, and threw a P0305 code (cylinder 5 misfire). I’ve been fighting that code ever since. I have a scan tool, I can see the misfire counter add up on cylinder 5, and it seems to be only at an idle. I moved plugs, plug wires, coils and injectors to other cylinders, but the misfire at idle stays on cylinder 5. I researched the hell out of Active Fuel Management, which I have, and I know all the lifter issues and problems they can have, but AFM is on cylinders 1, 4, 6 and 7, and my misfire is on cylinder 5. It’s not consuming oil like the ones with the AFM lifter problem. I’ve replaced the Mass Air Flow sensor, MAP sensor, water temp sensor was replaced when I changed the water pump back in February (shaft bearing was starting to squalk), I changed the oil pressure sensor (and the VLOM screen underneath it) just to be sure the oil pressure reading I was seeing was accurate. I changed the vapor canister purge valve and vapor canister vent valve (problem with gas pump handle disengaging while filling the tank), I changed both the crank and cam position sensors (and did the crank position relearn), still have the misfire. I’ve checked compression with all the plugs out, over 180 pounds on every cylinder, including cylinder 5. I checked vacuum (inserting a ‘T’ at the brake booster vacuum connection) 19 inches at idle, goes to 17 inches if the AC is on. I have a noticeable loss in power, most of the time it feels like I’m towing a pontoon boat. My gas milage is down around 12 mpg or less. I noticed on my scan tool the long term fuel trim on bank 2 was running about +12 at idle, but would go down to about +1 while driving, while not the same bank as cylinder, assumed I had a vacuum leak on bank 2. I also noticed O2 sensor Bank 1 Sensor 2 constantly stayed around 810 mV regardless of what the others were doing. Thinking the O2 sensors may be the original ones I went ahead and changed them. I suspected that if they were getting old and slow and sending bad info to the ECM, that when it was open loop (with a vacuum leak) and then going closed loop and seeing bogus info from the O2 sensors and making fuel adjustments for that that it was constantly changing fuel mixture as it bounced in and out of open and closed loop mode, which I thought may be why it was so sluggish. I decided to change the intake gaskets, went with Felpro. While I had the intake off I went ahead and changed the fuel injectors. The long term fuel trim is back down low again so apparently I did have some vacuum leaks. And now I feel better about the fuel injectors actually delivering what the ECM thinks they are delivering. But, still have the misfire on cylinder 5 and recurring P0305 within two drive cycles. I can pull the injector electrical connector off cylinder 5 while idling and it really doesn’t change the idle speed. At that point I was suspecting maybe the ECM is stuttering on the pulses to the cylinder 5 injector. I put a noid light on the injector connector for cylinder 5 and at an idle (when the scan tool is steadily counting misfires on cylinder 5) I’m seeing a nice steady light pulse not missing a beat. I put a spark indicator on the spark plug, same thing, steady light pulse, not missing a beat. Now, off with the valve cover. Cranking the engine over I can see both valves on cylinder 5 open and close as they should. I put #5 at TDC and removed the rocker arms, no visible damage, no cracks, no wear. Pulled the push rods, not plugged, you can clearly see light thru them and their walls just like looking through a new straw. Both valve springs look fine, neither is broken, both seem to be keeping the valve closed tightly. That didn’t satisfy me, so (after reinstalling the rockers) I hung the coil pack with some string, reconnected the harness and plugs and started the motor to watch the rockers in action. Neither valve missed a beat, both opening and closing the same amount as the other valves by just watching them (I’m sure there’s probably a scientific way to measure that, but with the naked eye they appear to be working just fine) Both pushrods are pushing out oil on top of the rock arm, not tapping any louder than the other, so I’m thinking the lifters are. I got my stethoscope and listened to the fastening nut on all 8 rocker arms. I will say this. On seven of the eight rocker arms you can hear that whirring sound of the engine and a slight tapping sound as the valve operates, but the exhaust valve of cylinder 5 was a little louder and sounded kind of rattley in between taps. Not extremely louder than the others with the stethoscope, but enough to notice it was not as smooth and quite as the others. BUT, still opening and closing the valve and pumping oil. And with the naked ear, it’s no louder than any of the others. I found a TSB (#11-06-04-007B) about changing the throttle position sensor that said for Tahoes from ’08-’10 if you put a new throttle position sensor that you MUST reflash the ECM with he latest software, but from ’11 up the reflash was not required. Mine is a 10 and I have changed the throttle body/throttle position sensor as and assembly, so I put the old one back on for now just to be sure that’s not causing an issue. So I’m at a loss. I’ve used all ACDelco parts (except for the Felpro intake gaskets) I’ve eliminated every external thing I can think of that could cause a misfire, I have compression, vacuum, fuel pressure running 58-60 psi key on and engine off, and stays around 58 psi at idle, no vacuum leaks. The one and only thing I’ve found wrong with cylinder 5 is a little extra noise on the exhaust rocker are when listening with a stethoscope. I may be wrong, but I can’t believe THAT is enough to cause a constant misfire since the valve is opening and closing as expected. The only thing I haven’t changed is the knock sensors. Starting in ’07, they moved them from underneath the intake to down on each side of the of the lower block. Easy to get to now, and ironically the one on the left side is about where the #5 cylinder is. The scan tool shows no knock on any cylinder. I really don’t thing a bad knock sensor would cause a cylinder specific misfire, but they are less than $8 each at Rockauto, so I ordered a couple of them. On a side note, I’ve also ran some Seafoam in the oil for about 200 miles thinking if the problem was a lifter it would loosen up. I haven’t tried Marvel Mystery Oil yet. If you have any input that would help I would appreciate it. I’ve seen posts about misfires on discussion boards, but most of the time there is no follow up post if they fixed the problem. If I find a solution I will absolutely post what I did to resolve it. Thanks for reading if you got this far, sorry it’s so long.
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.