Hi, so I recently bought a 2006 Trailblazer 5.3 4wd with 176000 miles on it. I get it to my house and it is throwing a P0301 code (cylinder 1 misfire). Okay, no problem. Changed the spark plug, no result. Swapped the spark plug wires, no result. Swapped the coil pack. No result. Changed the fuel injector, no result. I'm so confused on what I could be! It does have the AFM (DOD) system so I swapped the valve cover to the upgraded design but that didnt do anything either. Now, I'm looking at the real time data and I have misfires on 1, 2, 3, 4, 5, 7, and 8. Although 1 and 8 are by far the worst, 2 is concerning, and 3, 4, 5, and 7 are running one misfire for every thousand misfires on 1. I am pretty sure compression is good but I have no idea if the torque app can actually give an accurate reading for that nor what it should be. Has anyone run into this? I mean this is getting ridiculous and is starting to make me feel like I really got screwed by buying this truck. Everything but the engine is in great condition though. This is really urgent as I need the truck to be in good running order ASAP!
URGENT- Misfire help needed
- Thread starter Smartin11
- Start date
Welcome to GMT Nation... Albeit, presently with your understandably stressful circumstances...
With so many Cylinders Mis-Firing ... consider that the possibility of ALL 8 Spark Plugs AND ALL 8 Coil On Plugs and even ALL 8 EFIs going "T*ts Up" at the same time are simply Astronomical Odds. Therefore... I am suspicious of your FUEL PUMP not being able to deliver enough FUEL to 'Feed The Beast".
With that in mind...AND by following the Diagnostic Suggestions in the link below... I'd concentrate my efforts on Testing for Low Fuel Pressure due to a Failing Fuel Pump or a Seriously Clogged Fuel Filter from Too many Bad Loads of Gasoline/Water at a Local Gas Station notorious for having "Bad Fuel". Your Torque App will NOT be able to Read or Measure the Compression Levels in the Engine
easyautodiagnostics.com
The Important thing is that you need to THINK CLEARLY and Do Not Panic!
Download a FREE GM OEM Digital Service Manual from @Mooseman 's Link Below and Follow those Diagnostic Troubleshooting Charts!
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With so many Cylinders Mis-Firing ... consider that the possibility of ALL 8 Spark Plugs AND ALL 8 Coil On Plugs and even ALL 8 EFIs going "T*ts Up" at the same time are simply Astronomical Odds. Therefore... I am suspicious of your FUEL PUMP not being able to deliver enough FUEL to 'Feed The Beast".
With that in mind...AND by following the Diagnostic Suggestions in the link below... I'd concentrate my efforts on Testing for Low Fuel Pressure due to a Failing Fuel Pump or a Seriously Clogged Fuel Filter from Too many Bad Loads of Gasoline/Water at a Local Gas Station notorious for having "Bad Fuel". Your Torque App will NOT be able to Read or Measure the Compression Levels in the Engine
How To Troubleshoot A Misfire (GM 4.8L, 5.3L, 6.0L)
GM 4.8L, 5.3L, 6.0L Index of Articles
The Important thing is that you need to THINK CLEARLY and Do Not Panic!
Download a FREE GM OEM Digital Service Manual from @Mooseman 's Link Below and Follow those Diagnostic Troubleshooting Charts!
Need service manuals? Get them here!
********* Please note that the FireFox browser has issues with the password handling and that these downloads are not under HTTPS, flagging them as security risks. Chrome and Edge work fine once you allow the download. ********* ATSG 4L60E Manual 4L60E Rebuild Manual 2005 GMC Envoy XUV...
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I downloaded the manual, thanks for that resource! I just have a hard time believing it is the fuel pump because my idle is sitting right at 500 RPMs and the engine hasn't stalled on me. It runs rough and shakes and once sitting for around 4-5min drops into more of a light clunking. The other thing is should mention is that cylinder 6 hasn't had one recorded misfire on the computer with every other cylinder having at least some (pictures attached). Cylinder 1 has over 18k and cylinder 8 has over 3k. This really has me baffled. Also isnt the fuel filter inside of the gas tank on the 2006 (2005?) And up trailblazers? I thought I read that somewhere. Would you still say it's the fuel system?
Attachments
Yes... The Fuel Filter is nested inside of the Fuel Tank on Later Model Trailblazers-Envoys-Raniers... another brilliant effort on the part of "Stealerships" to take control away from GM Vehicle Owners and place an undue burden for the necessity of overly complex repairs.
Alternatively, the presence of a Vacuum Leak along either Bank of the Intake Manifold Gaskets or judging from the Misfires occurring with your Engine as being "Equal Opportunity Offenders" on BOTH sides of the Block... any Vacuum Leak from a Loose or Cracked Hose or Line allowing 'unmetered... uncontrolled air' to invade the otherwise Stoichiometric contained control of 14.7:1 A/F Ratios... would thereby Lean Out the Fuel Air Mixture. After that... Checking for a Sketchy Upstream Oxygen Sensor would be the another place to look.
EVERYTHING about a MAF Controlled A/F System centers around controlling the Air Intake and Flow... and ANYTHING that by-passes that control mechanism makes the A/F Ratio FUBAR. If you have not as yet obtained some CRC MAF Spray Solvent... please do so... and Spray down that MAF/IAT Sensor.. While you're at it... Put in a Brand New Quality Air Filter as well.
Alternatively, the presence of a Vacuum Leak along either Bank of the Intake Manifold Gaskets or judging from the Misfires occurring with your Engine as being "Equal Opportunity Offenders" on BOTH sides of the Block... any Vacuum Leak from a Loose or Cracked Hose or Line allowing 'unmetered... uncontrolled air' to invade the otherwise Stoichiometric contained control of 14.7:1 A/F Ratios... would thereby Lean Out the Fuel Air Mixture. After that... Checking for a Sketchy Upstream Oxygen Sensor would be the another place to look.
EVERYTHING about a MAF Controlled A/F System centers around controlling the Air Intake and Flow... and ANYTHING that by-passes that control mechanism makes the A/F Ratio FUBAR. If you have not as yet obtained some CRC MAF Spray Solvent... please do so... and Spray down that MAF/IAT Sensor.. While you're at it... Put in a Brand New Quality Air Filter as well.
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The Fuel Pressure Regulator if present with a Dual Fuel Line System may be the one last thing that if present and failing may ALSO cause a condition of Lower Fuel Pressure if it is NOT functioning properly. Usually in these kinds of systems... One Line delivers Fuel to the Fuel Rail while maintaining control via with the Fuel Pressure Regulator fitted with a Small Vacuum Line...while the OTHER Fuel Line acts to Return unused Fuel right back inside of the Fuel Tank.
The Later Model Trucks and SUVs utilize a "Return-less" Single Line Fuel System that not only has the Fuel Filter hidden inside of the Fuel Tank with the Fuel Pump... but is fitted with a "Check Valve" that allows any excess Fuel to by-pass entering the Single Fuel Line under pressure and then dumping that excess, unused Fuel Right Back inside of the Fuel Tank. You will have to Check your New GM OEM Digital Service Manual to know Which Type of Fuel System is on your Vehicle.
The attached Video will explain How The Fuel Pressure Regulator WORKS and its implications during investigations of Poor Engine Performance Due to Fuel Delivery Problem Diagnostics:
Here is an "On The Vehicle" investigation of a Failing Fuel Pressure Regulator:
The Later Model Trucks and SUVs utilize a "Return-less" Single Line Fuel System that not only has the Fuel Filter hidden inside of the Fuel Tank with the Fuel Pump... but is fitted with a "Check Valve" that allows any excess Fuel to by-pass entering the Single Fuel Line under pressure and then dumping that excess, unused Fuel Right Back inside of the Fuel Tank. You will have to Check your New GM OEM Digital Service Manual to know Which Type of Fuel System is on your Vehicle.
The attached Video will explain How The Fuel Pressure Regulator WORKS and its implications during investigations of Poor Engine Performance Due to Fuel Delivery Problem Diagnostics:
Here is an "On The Vehicle" investigation of a Failing Fuel Pressure Regulator:
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Maverick6587
Member
I'm going to have to completely agree with MRRSM on the vacuum leak. That happened to me. It presented as a random misfire P0300. I could NOT figure out why the cylinders were misfiring so randomly, pretty much like yours are.
I couldn't find any leaks in any of the hoses but, I did tighten down the intake manifold bolts and that completely solved the problem. Some of them were so loose, that they were barely touching the intake manifold. After finding that out I replaced the intake manifold gasket.
I couldn't find any leaks in any of the hoses but, I did tighten down the intake manifold bolts and that completely solved the problem. Some of them were so loose, that they were barely touching the intake manifold. After finding that out I replaced the intake manifold gasket.
Okay. Thanks to all of you for your help. I'm taking it to the mechanic this morning so he can test it for vacuum leaks and fuel pressure. Something is going wrong somewhere and I'll get to the bottom of it!
Maverick6587
Member
I would try tightening those intake manifold bolts before you pay a mechanic to test for anything. Most of them are easy to get to and they're 10mm bolts.
The two near the firewall are kind of hard to get to though but, if all of the other ones are tight, I wouldn't worry about those last 2-3 bolts. I think there are 11-12 bolts total.
Attached, is a picture of the intake manifold. You can see the bolts at the bottom of the manifold.
The two near the firewall are kind of hard to get to though but, if all of the other ones are tight, I wouldn't worry about those last 2-3 bolts. I think there are 11-12 bolts total.
Attached, is a picture of the intake manifold. You can see the bolts at the bottom of the manifold.
Attachments
xavierny25
Member
According to my reading the OP has a 5.3 and its a completely different intake from the 4.2.
Maverick6587
Member
Ha! look at me paying attention. Thanks for letting me
.
Is there a cover that goes over the intake manifold on the 5.3? Looks like the fuel rails are in the way as well.
I'm going to have to jump ship on directions for the 5.3 intake manifold. I'm not sure how easy or hard that job would be.
There is but, like you said, everything is in the way. I'm just gonna take it to the mechanic for a diagnosis and then Ill be able to do the repair myself. That is, if it doesnt require a new engine block or rebuild or something big along those lines
If you can get a definitive answer from your Mechanic for a Flat Rate Fee... Remember this... You're One of US now... A Member of GMT Nation, Brother... and More Help will emerge from other Members with experience in performing most Tasks, should these occasions arise. :>)
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Update! Was able to borrow a compression tester from my grandpa and got around to actually swapping all 8 of the spark plugs. Now I have no misfires on cylinders 3-7. Cylinder 1 still has a consistent misfire and its compression read 25 (the rest of the cylinders read 125). What could be the cause of this? Cylinders 2 and 8 have good compression but misfire at idle (not under throttle). What could cause this?
What I'm Hoping for here is that your "Grandpa"...(and more than most of us... I can use this term in the pejorative sense since I AM One) may have a Sketchy Compression Tester. Before I would conclude that the NEXT things I describe as 'Bad Possibilities' turn out to be REAL.. I'd spend $20.00 at Harbor Freight and Buy a New Compression Tester Kit if I were you and then focus Testing Cylinder #1 all over again... as follows:
(1) Pull the COP Wire and Remove the Spark Plug on the #1 Cylinder.
(2) Install the Metric Spark Plug sized Compression Hose and install the Gauge afterwards.
(3) Pull the Fuel Pump Relay.
(4) Turn the Engine Over for 10-15 Seconds with a Minimum (5) Minute Break in Between.
(5) Observe the Compression Gauge. You should see 160-180 PSI within 15% variation for All (8).
(6) Record the Pressure on #1 Cylinder and any other you perform Repeat Compression Tests.
(7) Repeat (2)-(6) on this List ....but THIS time... inject 2-3 Drops of Motor Oil into the #1 Cylinder.
(8) DO NOT SQUIRT IN TON OF OIL... Or You WILL Risk Hydro-Locking the Engine!
With a prior Recorded Compression Test of the #1 Cylinder at only 25 PSI... Think about it... That is Hardly 10 PSI Greater than Ambient Air Pressure at Sea Level of 14.7 PSI. If this turns out to be an accurate reading... that additional 10 PSI could just be getting generated from the Excess Compression Ring Blow-By from the other (7) Cylinders when the Starter Turns the Engine Over and ends up pushing that slightly pressurized atmosphere from the bottom of the Crankcase upwards and past the Possibly FUBARed Piston & Rings in the #1 Cylinder.
I am ever the Optimist... So let's hope this is just a case of a slight problem with your Compression Test Procedures and a second look at the situation may improve these prospects. Here are the Other Bad Things that can make this situation of having Extremely Low Compression occur:
(A) Broken Valve Stem in the Engine Head at the #1 Cylinder ...either the Intake or Exhaust.
(B) Cracked or Fractured Compression Rings.
(C) Shattered Piston.
(D) A Hole in the Piston Head caused if a Broken Valve Descended into the Cylinder at any RPM.
(E) Cracked Cylinder Wall from Over-heating or from FOD (Foreign Object Damage).
You should consider performing these Dry/Wet Compression Tests (in THAT order) again...and THIS time... write down precisely Which Cylinders By Number Have What Compression Readings ...doing ALL DRY Tests First... followed by ALL WET TESTS second. RECORD EVERY SINGLE READING.
I'm really hoping that something went wrong with your "G-Pa's" CT Gear...or that the Compression Hose was Old, Damaged or simply was NOT screwed in tight enough (BUT NOT OVERLY TIGHT) and it just had a Bad Seal, allowing the Compression Stroke atmosphere to leak out of the #1 Cylinder.
You MUST be thoughtful and systematic when performing any Automotive Testing... especially when using any 'specious' equipment that you may be unfamiliar with. Check on Youtube and watch a few Videos on "How to Perform a Dry-Wet Compression Test" especially on the GM 4.8L,5.3L, or 6L Engines.
If your Engine has NOT received Good Treatment and Maintenance for its entire life... the Lower Average Compression is indicative of Badly Worn Rings that no amount of "fixes" with different Motor Oils and Engine Lubrication Treatments can repair.
However... if you are able to prove that there was an error when first Testing The Compression on the #1 Cylinder ... De-Carbonizing the Pistons and Compression Rings and Cylinder Valve Seats may help to improve the overall compression level within the engine and allow it to Start and Run with Modest Power. At this point... You should Perform a Complete Regimen of Compression Testing all over again and hope for a small miracle that 'a minor mistake' was made during the First Attempt.
(1) Pull the COP Wire and Remove the Spark Plug on the #1 Cylinder.
(2) Install the Metric Spark Plug sized Compression Hose and install the Gauge afterwards.
(3) Pull the Fuel Pump Relay.
(4) Turn the Engine Over for 10-15 Seconds with a Minimum (5) Minute Break in Between.
(5) Observe the Compression Gauge. You should see 160-180 PSI within 15% variation for All (8).
(6) Record the Pressure on #1 Cylinder and any other you perform Repeat Compression Tests.
(7) Repeat (2)-(6) on this List ....but THIS time... inject 2-3 Drops of Motor Oil into the #1 Cylinder.
(8) DO NOT SQUIRT IN TON OF OIL... Or You WILL Risk Hydro-Locking the Engine!
With a prior Recorded Compression Test of the #1 Cylinder at only 25 PSI... Think about it... That is Hardly 10 PSI Greater than Ambient Air Pressure at Sea Level of 14.7 PSI. If this turns out to be an accurate reading... that additional 10 PSI could just be getting generated from the Excess Compression Ring Blow-By from the other (7) Cylinders when the Starter Turns the Engine Over and ends up pushing that slightly pressurized atmosphere from the bottom of the Crankcase upwards and past the Possibly FUBARed Piston & Rings in the #1 Cylinder.
I am ever the Optimist... So let's hope this is just a case of a slight problem with your Compression Test Procedures and a second look at the situation may improve these prospects. Here are the Other Bad Things that can make this situation of having Extremely Low Compression occur:
(A) Broken Valve Stem in the Engine Head at the #1 Cylinder ...either the Intake or Exhaust.
(B) Cracked or Fractured Compression Rings.
(C) Shattered Piston.
(D) A Hole in the Piston Head caused if a Broken Valve Descended into the Cylinder at any RPM.
(E) Cracked Cylinder Wall from Over-heating or from FOD (Foreign Object Damage).
You should consider performing these Dry/Wet Compression Tests (in THAT order) again...and THIS time... write down precisely Which Cylinders By Number Have What Compression Readings ...doing ALL DRY Tests First... followed by ALL WET TESTS second. RECORD EVERY SINGLE READING.
I'm really hoping that something went wrong with your "G-Pa's" CT Gear...or that the Compression Hose was Old, Damaged or simply was NOT screwed in tight enough (BUT NOT OVERLY TIGHT) and it just had a Bad Seal, allowing the Compression Stroke atmosphere to leak out of the #1 Cylinder.
You MUST be thoughtful and systematic when performing any Automotive Testing... especially when using any 'specious' equipment that you may be unfamiliar with. Check on Youtube and watch a few Videos on "How to Perform a Dry-Wet Compression Test" especially on the GM 4.8L,5.3L, or 6L Engines.
If your Engine has NOT received Good Treatment and Maintenance for its entire life... the Lower Average Compression is indicative of Badly Worn Rings that no amount of "fixes" with different Motor Oils and Engine Lubrication Treatments can repair.
However... if you are able to prove that there was an error when first Testing The Compression on the #1 Cylinder ... De-Carbonizing the Pistons and Compression Rings and Cylinder Valve Seats may help to improve the overall compression level within the engine and allow it to Start and Run with Modest Power. At this point... You should Perform a Complete Regimen of Compression Testing all over again and hope for a small miracle that 'a minor mistake' was made during the First Attempt.
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