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So, here goes-been battling with my mom's 2006 Chevy Trailblazer LS with a 4.2L Vortec engine for a while
Been dealing first with a bugger of a P0171 (Lean fuel trim Bank 1) code that has defied me and left me throwing wrenches in my garage
Right after we moved back here from Florida, the P0171 code made it's appearance. Starting with, I have smoked it numerous times, vacuum tested it-found a leak on the intake manifold gasket-replaced it along with the throttle body gasket to start with-turned off the CEL, and was able to smog it (live out here in Commiefornia).
About 8 months after smogging it, the CEL light came back on-same code P0171
Bought a code reader and have been slowly working my way up the food chain, testing the fuel pressure (found it was a bit low on spec) which resulted in replacing the fuel pump, which is in the fuel tank-got to do that job for the first time-ugh
Reset the PCM-2 days later the same code reappeared-P0171
Checked fuel pressure and vaccum with smoke and vaccum gauge-no dice-Did find one of the vaccum hoses was cracked-that got replaced. Reset the light, same day, it came back on-same code P0171
At this point, I did an pressure test using a scan tool on the injectors-they seem to be within spec too-now I'm shaking my head at this problem. I bought a OEM fuel injector cleaning tool and ran a bottle of Berrymans B12 through it-reset the code and test drove. Halfway through, the CEL came back on. Same code-P0171
It seems to be only coming on at idle and at stop signs.
Brought it home, ran another bottle of Berrymans through the system, now it shakes and misses bad, the CEL is flashing, and a new code has been set-P0300 (Random misfire multiple cylinders)
I'm lost now-any ideas? Thanks for the help!
 

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Ya gotta cure the P0300 first - and that's kinda tough when the ECM won't report which cylinder it is that's messing with ya.

The flashing SES is telling you that you're damaging the Cat if you keep it up.

California will NOT be understanding if you kill your cat. I know - I was a California Brake/Lamp/Smog Inspector-Installer-Adjuster for over 40 years.

You may have to resort to pulling each plug, inspecting them and making sure they are a (firstly) really good Iridium plug and (maybe) not a Chinese counterfeit.
Bosch Iridiums work for me - others say that only GM-Delco plugs work - meh....​

Stop tossing chemicals into it's belly and actually diagnose first and if you really want to do it, THEN toss in a liter of Chanel #5 if you like - but wait until you figger out the P030? code.

Suspects of the P0300 series codes:
1. Broken coil to plug spring or
2. cracked plastic coil body or
3. slipped and ruined silicon boot - etc, etc.,
4. Bent pin on COP primary connection
5. Fried coil
6. extra long plug gap puts excessive strain on dielectric properties of the coilpack
7. excessive plug gap puts excessive strain (amps-wise) on coil itself - zap!
8. gerbils like your wiring and are eating it - nightly

One oddball I had once (war story time) - it was a busted and slipped-down inner porcelain inside the plug - the part that surrounds the center electrode inside the plug.

It (the engine) was missing --- I KNEW IT (the plug) WAS MISSING --- but when I took it out, and held it up - it looked just fine: good gap, nice color, etc.

Then I was putting it back into the spark plug socket and I heard it slide down, masking the plug electrode gap!
FOUND IT!

That was one time when I should have expected zebras when I herd hoofbeats.

Normally - and I cannot say this enough - NEVER think zebras when you hear hoofbeats. It's usually just plain ol' horses!

And --- stop with the mechanic-in-a-can additives. They'll just mess you up.
 
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Yeah, that's why I shut it down when it started flashing-I read that the engine's pcm was shutting down injectors to protect the cat in the event of failure.
I'm a guy with limited fundage, and I thought maybe working with the Berryman would at least help, not hinder my progress-
Oh well, tomorrow is Veteran's Day-served 3 years in Navy as a Construction Mechanic in the Seabees-gonna raise a cold one to my bros in the Bees, then hit the garage and start pulling plugs and seeing what I can find-like you were talking about-it was on my mind tonight, since what I described with the P0300 started earlier tonight.
Thanks for your thoughts : )
 

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Been dealing first with a bugger of a P0171 (Lean fuel trim Bank 1) code that has defied me and left me throwing wrenches in my garage
How old is the O2 sensor? I diicked with a "lean" code on my K1500 on-and-off for two years. Everything tested good. One day I'd had enough, I slapped a new O2 sensor in, and my lean code has been fixed--and has stayed fixed for years and years.

Another likely suspect is a cracked exhaust manifold. Hatefully common, practically epidemic. GM had a bulletin and "secret warranty" on the manifolds. 'Course, they're cracked UNDER the heat shield where you can't see it. The Dorman replacement manifold "kit" includes everything you need except for new bolts to hold it to the cylinder head (available separately) and a new O2 sensor--you'd be nuts to install a manifold and not put in a new sensor at the same time. (The Dorman heat shield included in the kit is a piece of crap.)
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now it shakes and misses bad, the CEL is flashing, and a new code has been set-P0300 (Random misfire multiple cylinders)
As said, a FLASHING CEL is very bad news.

Are you dealing with a REAL P0300, or a PHONY P0300? Cheap scan tools report "generic" codes even when the computer is trying to give you a specific code. You may not have a "RANDOM" misfire at all. Could be a P0301--P0306, with the final number being the actual cylinder that's misfiring.
 
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Yeah, that's why I shut it down when it started flashing-I read that the engine's pcm was shutting down injectors to protect the cat in the event of failure.
I'm a guy with limited fundage, and I thought maybe working with the Berryman would at least help, not hinder my progress-
Oh well, tomorrow is Veteran's Day-served 3 years in Navy as a Construction Mechanic in the Seabees-gonna raise a cold one to my bros in the Bees, then hit the garage and start pulling plugs and seeing what I can find-like you were talking about-it was on my mind tonight, since what I described with the P0300 started earlier tonight.
Thanks for your thoughts : )
Where did you or who told you that the ECM shuts off injectors?

This is the first time I've heard that. Not that you're wrong .. I may have been in a cave for a while, that's all.
 
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How old is the O2 sensor? I diicked with a "lean" code on my K1500 on-and-off for two years. Everything tested good. One day I'd had enough, I slapped a new O2 sensor in, and my lean code has been fixed--and has stayed fixed for years and years.

Another likely suspect is a cracked exhaust manifold. Hatefully common, practically epidemic. GM had a bulletin and "secret warranty" on the manifolds. 'Course, they're cracked UNDER the heat shield where you can't see it. The Dorman replacement manifold "kit" includes everything you need except for new bolts to hold it to the cylinder head (available separately) and a new O2 sensor--you'd be nuts to install a manifold and not put in a new sensor at the same time. (The Dorman heat shield included in the kit is a piece of crap.)
View attachment 55967

View attachment 55968


As said, a FLASHING CEL is very bad news.

Are you dealing with a REAL P0300, or a PHONY P0300? Cheap scan tools report "generic" codes even when the computer is trying to give you a specific code. You may not have a "RANDOM" misfire at all. Could be a P0301--P0306, with the final number being the actual cylinder that's misfiring.
Good day-I did some digging and found that running the 2 bottles of cleaner through the injectors fouled the plugs-i knew that because I pulled them all and found black staining on all of them-no fuel smell, just some staining, and it's not oil either. I replaced the plugs and coil boots and cleared the P0300-now the shakes are gone, purrs smooth, runs idle cold at around 595 rpm-running at operating temperature shows around 1000-1100 rpm-just the P0171 code still makes its fugly appearance again.
I ran the code read through a Snap-On scan tool-one of the very good ones-and it didn't show a particular cylinder-and after I pulled the plugs I saw why.
I'm beginning to think it may be either the resistance on one or more injectors is just off enough to upset the short and long term fuel trims or the idle air control valve which is built into the throttle body is bad (the inside of the throat of the throttle body is clean-did that already) I can check the manifold for cracks like you suggested-I've been told that possible too the cat is bad but I did a temp check on the cat and the input and output temp is about even-so back to square one again : (
 

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Where did you or who told you that the ECM shuts off injectors?

This is the first time I've heard that. Not that you're wrong .. I may have been in a cave for a while, that's all.
Good day-I did some digging and found that running the 2 bottles of cleaner through the injectors fouled the plugs-i knew that because I pulled them all and found black staining on all of them-no fuel smell, just some staining, and it's not oil either. I replaced the plugs and coil boots and cleared the P0300-now the shakes are gone, purrs smooth, runs idle cold at around 595 rpm-running at operating temperature shows around 1000-1100 rpm-just the P0171 code still makes its fugly appearance again.
I ran the code read through a Snap-On scan tool-one of the very good ones-and it didn't show a particular cylinder-and after I pulled the plugs I saw why.
To answer your question, I went on both Mitchell Pro Demand and AllData for the diagnosis as far as the ECM shutting down the injectors-both say this is a protective measure by the PCM to prevent overheat and damage to the cat and/or internal engine damage to the valves and piston heads. May be right, may be wrong-but I'm being as careful as I can be on the internals.
I'm beginning to think it may be either the resistance on one or more injectors is just off enough to upset the short and long term fuel trims or the idle air control valve which is built into the throttle body is bad (the inside of the throat of the throttle body is clean-did that already-meaning the throttle body needs to be replaced) I've been told that possible too the cat is bad but I did a temp check on the cat and the input and output temp is about even-so back to square one again : (
 

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How old is the O2 sensor? I diicked with a "lean" code on my K1500 on-and-off for two years. Everything tested good. One day I'd had enough, I slapped a new O2 sensor in, and my lean code has been fixed--and has stayed fixed for years and years.

Another likely suspect is a cracked exhaust manifold. Hatefully common, practically epidemic. GM had a bulletin and "secret warranty" on the manifolds. 'Course, they're cracked UNDER the heat shield where you can't see it. The Dorman replacement manifold "kit" includes everything you need except for new bolts to hold it to the cylinder head (available separately) and a new O2 sensor--you'd be nuts to install a manifold and not put in a new sensor at the same time. (The Dorman heat shield included in the kit is a piece of crap.)
View attachment 55967

View attachment 55968


As said, a FLASHING CEL is very bad news.

Are you dealing with a REAL P0300, or a PHONY P0300? Cheap scan tools report "generic" codes even when the computer is trying to give you a specific code. You may not have a "RANDOM" misfire at all. Could be a P0301--P0306, with the final number being the actual cylinder that's misfiring.
Just that I forgot to answer your question-my bad
I replaced both up and downstream 02 sensors when I found the leaking intake manifold gasket just as a precaution-and the SnapOn tool shows both sensors work at spec both at idle and at freeway speed.
 

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I've been told that possible too the cat is bad but I did a temp check on the cat and the input and output temp is about even

Haven't refreshed my memory on this whole thread but this jumped out at me. The temps should NOT be even on a functioning catalytic converter. Unless it is still cold and has not fired off yet. Should exit a good deal hotter at the output side.

Also, did you say it is idling around 600 cold but 1100 warmed up?
 

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I was gonna say the same thing about the temperature in and out of the cat being wrong.

You beat me to it.

Good shooting.
 
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Haven't refreshed my memory on this whole thread but this jumped out at me. The temps should NOT be even on a functioning catalytic converter. Unless it is still cold and has not fired off yet. Should exit a good deal hotter at the output side.

Also, did you say it is idling around 600 cold but 1100 warmed up?
I used a temperature gun to check the inlet and outlet temps after the car had been running for a while-AllData had showed a few "Tech Tips" that had techs "suggesting" that if there is an issue with the substrate on the cat, that it could affect the o2 sensors enough not so much to throw a code for the o2 sensors, but enough to upset the short and long term fuel trims enough to set the P0171 code. An issue with the substrate would cause potentially the inlet temps to be hotter than outlet temps. When I checked this one, it was about even on the temps both inlet and outlet, but that was about 20 minutes after I had shut it down, so perhaps the numbers were not checked at the right time.
 

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Haven't refreshed my memory on this whole thread but this jumped out at me. The temps should NOT be even on a functioning catalytic converter. Unless it is still cold and has not fired off yet. Should exit a good deal hotter at the output side.

Also, did you say it is idling around 600 cold but 1100 warmed up?
595 rpm cold 1100 at operating temperature from the vehicle tach
 

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