Question about Chevrolet Avalanche

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Does anyone out there have a good understanding of fuel trims and how to diagnose using them.

I have a 2005 chevy avalanche 5.3l The plugs are good, the wires are good. Has new Map sensor, Maf sensor, Air filter, Fuel pump, and throttle body. My fuel trims are like this. STFT B1 -0.8 to -3.9 LTFT B1 11.7 STFT B2 -3.9 to 1.6 LTFT B2 4.7 to 5.5 all of these numbers have a short term spike that jumps way down to -93.8 bouncing around. My O2 sensors read B1S1 STFT 34.4 B1S2 STFT 99.2 These readings were taken at idle only. Still unfamiliar with using my scan tool but...I'm slowly catching on. A little. I realize this kind of points to a vacuum leak but. I don't believe it is. The truck runs fine. It is only under hard acceleration do I experience problems. Other than that it drives and idles good. I did hear something about idle air control giving this sort of symptom but..I can't find that on this vehicle. I forgot to mention that there are no codes present also that I have changed the purge valve as well. Just so it is known. All those things I replaced had issues. I had to take care of them first.

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Posted on Jan 23, 2019

Testimonial: "Thanks Carl. I did know of scanner danner and I did know that a vacuum leak on the intake would give those kind of readings but...Mine aren't that high and I have no codes and have tried setting a code by repeatedly doing what it does when it does it but it just won't set a code. I'll try the water thing as well as use the scan tool. As for the guy who said you just don't replace things and hope for the best. Everything I replaced had issues except for the map sensor but its gasket was very worn."

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  • Carl Rock
    Carl Rock Jan 23, 2019

    That it runs ok and the one extreme reading(s) may imply bad data. Might be a good idea to try a different (better) odb interface tool.

  • rodger
    rodger Jan 24, 2019

    Well I don't know. It is a innova 3160g and it gets updated all the time.

  • rodger
    rodger Jan 24, 2019

    It does run good. Only if the tires spin the engine winds for a couple of seconds after letting off the pedal. Or if I stomp on it from a stop it bogs right down as though it floods or not enough gas then gradually picks up. Two other things it does but those are my major concern.

  • Carl Rock
    Carl Rock Jan 24, 2019

    Ok so not likely the scanner, but I still believe a 90 fuel trim is bad data, just no easy way to prove/disprove. Have you re-seated ECM/PCM cables yet? And always look out for corroded ground connects.

    Its been my experience rough acceleration is MAF sense. And sure, wouldn't it be great not to guess, but shop rates over $100/hr... amateures can afford to misdiagnose and replace a few good sensors. I just consider it cost of learning and still $100/1000s ahead.

  • rodger
    rodger Jan 25, 2019

    Like I mentioned. It idles good and runs good. Only last night I was going through some things on my scan tool and came up with two things. A P090C Which has something to do with clutch 'B'actuator control circuit low. Also P0900 clutch actuator circuit open. I have more. But I only started looking into it. These two caught my attention. Having to do with an injector circuit malfunction. I don't know where to start on that one.

  • rodger
    rodger Jan 28, 2019

    This spike I mentioned is seen on a lot of things on live data. I also came up with 20 different codes which are not the usual DTC's Like P08 type of codes and U type of codes. The P09 codes I mentioned have to do with the encoder motor. But my four wheel drive does work. So I am thinking I have a power to ground somewhere. Where to start.

  • Carl Rock
    Carl Rock Jan 28, 2019

    I assume the codes are recent. I believe the root problem is a poor ground which would explain bad data, and other transient issues.

    I don't believe its a power to ground short as I would expect blown fuses or fuseable link fryed.

    No idea which ground point may be the culprit as there are several and model/yr dependent.

    The major ground is likely a #6 or larger wire from the battery to engine block. You'll need to follow it from the battery to the block. Even if block end looks ok, get a wrench on it and try to tighten as it may be loose. There maybe another smaller gauge wire(s) at the same point of the block... make sure not corroded inside terminal.

    At the battery end there's likely a smaller gauge wire in with the larger ground wire. Make sure it is not corroded... a good strong pull, if it breaks off it needed replaced. This smaller wire generally leads to a chassis grounding point, sometimes underneath the battery but check if easy access from wheel well else you may have to remove battery. If its under the battery it will be highly suspect.

    You might search online for the ECM and PCM ground points for your vehicle so you can locate and trace back to battery ground. These are critical for error free comm between control modules.

    As you look around the engine compartment you'll notice several chassis grounds, check as you find


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Cud b mass air flow sensor. A data stream run w factory scannr the most accurate..partstore readers just toys. Dont go to a dealr. Library has chilton shop manuals

Posted on Jan 28, 2019

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  • 141 Answers

If it had all those issues I expect high mileage. Check the cat. Converter.

Posted on Jan 24, 2019

Testimonial: "If there was something going on with the catalyst do you think it would give fuel trim readings like it does? On one bank?"

6 Suggested Answers

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SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi there,
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Posted on Jan 02, 2017

SOURCE: 2003 GMC Sierra Has recently developed

You never replace anything, on a Wishing,Hoping,Pushing,Poking,diagnostic approach

You learn the vehicles Systems,Test,then Replace,if you have a failed component.

Work on the Misfire Issues.
Then you lean O2 Codes will go away.

Not a the plugs.

Think lean---Vacuum leaks,EGR Valve leak,EVAP System leaks,anything with a hose that lets air into the intake system.
Exhaust System leaks,near sensors

Posted on Nov 24, 2010

  • 11896 Answers

SOURCE: 2001 toyota celica vaccum leak, po171 keeps comingon

problem is most likely your purge canister itself.

Posted on Apr 15, 2009

  • 4 Answers

SOURCE: 89 Corsica: no power, hesitates in drive, idles

Check your fuel pressure, and or injectors. You may have too much fuel getting into the engine causing it to burn rich and overheat the converters.

Posted on Apr 26, 2009

  • 117 Answers

SOURCE: 2000 bmw 323i P0173 & P0170 trouble codes

Hello There

These are very common codes on BMW's which can also be false codes, try clearing the codes and run the test again they may not come up again.
With regards to the sound which you thought was a vacum leak there a breather pipe which runs under the plastic engine cover near the injectors which always gets a tear init which will need replacing.

Hope this helps, please don't forget to rate me.

Posted on May 20, 2009

  • 407 Answers

SOURCE: My 93 chevy 1500 4.3 is pouring to much fuel, I

were the injectors replace? 4.3l engines are know for messed up distributors

Posted on Oct 15, 2009

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