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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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