The never ending lean code - Page 2 - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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  #11  
Old 03-19-2017, 08:44 PM
Olejbrown Olejbrown is offline
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2006 Chevy TrailBlazer LT
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Well I played with it my bank 1 O2 voltage never got above .8 and that was being pretty aggressive with the pedal. I put in a new fuel pump today (that's a real treat) and I am hitting new heights at .9 and a regular .8 so it is safe to say I do have better fuel delivery now one odd thing or it may not be odd is I did get a hell of a lot of lean codes after I initially put the new pump in I figured this might be because of air in the lines or the amount of time it might take that giant filter to saturate. After 45 minutes to an hour of driving though the codes stopped coming and my 02 voltage started rising when I gave the engine more throttle.
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  #12  
Old 03-19-2017, 09:41 PM
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If the pump has been replaced and you cleared the codes, you shouldn't get any lean codes, if the pump was the cause of it running lean. The fuel system is bled very quickly, no air will be in it by the time you get it out of the driveway.

As far as highs & lows, the O2 voltage does not regularly hit the extremes of its range.


How does it drive now? Does it have good power at WOT? What voltage do you have at WOT?

What are the short term fuel trims while cruising?
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  #13  
Old 05-11-2017, 10:40 PM
Olejbrown Olejbrown is offline
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Alright I had to take a step back from this since I'm buying a house but I have made some observations that should help, so the fuel pressure did get stronger when I replaced the fuel pump. However that was a issue and not the issue, so the CEL only comes on when the vehicle is at idle, never when the vehicle is at speed. The short term fuel trim is at roughly 12.3 or so bouncing when at normal first start idle, when the RPM are at 3000 St fuel trim drops to zero. AFTER the engine is warm St fuel trim is steady at idle or at 3000. I thought this sounded like a intake leak but I have had no luck hosing it with carb cleaner to detect it and I haven't built a fogger yet. The other thing I noticed and this may be common in idle but the IAT seems to be 20 to 30 degrees hotter than ambient air but the sensor is correct if I check it before the engine is running. I have read that a plugged cat could cause this but I would think there would be other symptoms.
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  #14  
Old 05-12-2017, 01:27 AM
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It does look like your st/ft is pointing to an intake leak. Hose, gasket, cracked manifold. I have no experience with the 4.2 intake.

Finding a leak by spraying a liquid only works on a typical V cylinder layout. An inline engine can have possible leaks underneath where you cannot see. A smoke machine can reveal the location. You may be lucky and find it, or maybe somebody can chime in with a common leak you can check on.

As far as a cat being clogged, causing a lean code, it would not have much power above about 2500 RPM, you could not go WOT.
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  #15  
Old 05-12-2017, 06:15 AM
Olejbrown Olejbrown is offline
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The riddle would be what's a vacuum leak when it's cold but normal when it warms up. So the higher IAT is normal, now keep in mind I have only checked it at idle so going down the road with forced fresh air in the engine bay it might be more normal?
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  #16  
Old 05-12-2017, 12:02 PM
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Quote:
Originally Posted by Olejbrown View Post
The riddle would be what's a vacuum leak when it's cold but normal when it warms up.
Again, no experience with a 4.2 intake.

What I have seen on 2 vehicles, both Fords, a V6 & a V8, plastic manifolds.
I suspected the manifold was warped after replacing the intake gaskets alone and it improved for a while but returned a couple of months later. A new intake, Dorman, solved the problem.

EDIT: I'll mention that the V8 one was a friend who's truck only had the lean codes in the winter when the temperatures were most extreme. The codes would happen during warm up. I'm assuming that the intake was warped at its worst when the temp was lowest and leaked during warmup causing the lean code. He didn't have issues in the summer.
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  #17  
Old 05-12-2017, 01:22 PM
Olejbrown Olejbrown is offline
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So I hosed the back 3 cylinders around the intake with starting fluid and watched short term fuel trim drop from about 26 to 14 or 15 and rise back up, I never heard an increase in RPM, though I do notice a subtle drop as St trim goes down and it begins to draw up.
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  #18  
Old 05-12-2017, 01:54 PM
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Without a smoke machine, I'd pull the intake and have a close look.

Dorman has intakes for this, includes gaskets.
http://www.dormanproducts.com/p-48544-615-567.aspx?year=2006&make=GMC&model=Envoy&parttype=I ntake%2520Manifold&origin=YMM

On eBay you can buy a new intake for $115
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  #19  
Old 05-13-2017, 08:51 AM
Olejbrown Olejbrown is offline
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So my intake was slowly migrating from my engine about half the bolts were loose St fuel trim is now stable and flashing 1.6 -1.6
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  #20  
Old 05-13-2017, 12:05 PM
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Well that's good news!
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