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2007 chevy trailblazer_ls
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5 Posts
Discussion Starter #1
Hello all. First time poster here, located in Ontario. I am no auto mechanic, but I am somewhat familiar with electrical & mechanical.

I have come seeking help on a 2007 TrailBlazer LS 4.2L 4x4. 135000km.
It is showing code P0171 (Lean Bank 1). Long Term Fuel Trim running 10%-28%. Also showed a P0300 once (multiple misfire). Fuel usage is very high. Idling around 900 rpm.

The IAT & MAP seem ok based on readings taken from a cold start. The MAF appears to read properly, but I am not entirely certain where it should read. The upstream O2 sensor also seemed ok, but after scratching my head I changed it, to no avail.
I dumped 1 bottle of good injector cleaner into the tank.
I have a 22" vacuum on the intake, and 60psi fuel pressure at the rail. I cleaned the throttle body following the directions on this site.

Now I'm stumped. :confused:
Sometimes I think I hear a a vacuum leak on the drivers side, but I have checked and isolated the crankcase vent hose and the brake booster and hose.

Should I be considering the intake manifold gasket? The manifold itself?
Any help would be greatly appreciated.

TR23
 

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Moderator
2003 chevy trailblazer_lt
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57 Posts
Po171 means your engine is running too lean. A vacuum leak or a leaking intake manifold are likely causes of this. If you think you hear a vacuum leak you can hook up a smoke machine to your main vacuum line and see if any smoke leaks out of any of your vacuum lines. Another good test is to spray carb cleaner on all of your vacuum lines and see if the idle changes. If the idle changes then you've found your vacuum leak wherever you sprayed, also do this to the intake manifold because if you spray carb cleaner to the intake manifold and the idle changes then your intake manifold gaskets are leaking and need replaced. Hope this helps.
 

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2003 chevy trailblazer_lt
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57 Posts
Its best to spray the carb cleaner when your engine is cold just fyi, the later model trailblazers 07 and up do have a lot of problems with intake manifold gaskets leaking so it is a common problem
 

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2007 chevy trailblazer_ls
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5 Posts
Discussion Starter #5
OK, thats good info, thank you. How hard is an intake manifold gasket to take on? I'm well equipped with mechanical tools, but very few specific automotive tools. I understand gasket from compressors and mechanical systems, but this would be my first gasket job on any engine type work. Is it typically baked on from heat and needs painstakingly removed - or do they typically peel off?
 

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2007 chevy trailblazer_ls
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5 Posts
Discussion Starter #6
So I tore the intake manifold off. Found signs of a loose bolt. Bolt head oil covered, area around bolt clearly oil stained once manifold off, manifold gasket itself much more oily than other two. So I'm hoping I've found it, and that I can get it back together now!
 

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2007 chevy trailblazer_ls
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Discussion Starter #7
All back together, and fixed! Works as good as new now. Thanks for the input and help along the way.
 

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chevy trailblazer_ls
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Thanks to advice from this site...

Had p0171 code. Advice from members on this site to check torque on intake manifold bolts saved me a ton of time diagnosing. Most of the bolts ony eife's '06 TB were below the 10 N m spec. The bolt farthest near the firewall was so loose U was able to wiggle by finger...I say by finger because there is no way anything more than a skinny finger will fit to check. After 1/2 hour with a variety of socket extensions, u-joints, and a small mirror, all bolts torqued to proper and P0171 code gone. Thank you again to all who provided this advice. Advise i can give is take the PCM out of the way to allow better access to the bolts.:thx
 
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