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  1. #11
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
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    493

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    Hope the drive went well. Like you, I don't know what a properly tuned and well running engine graphs should look like but the engine timing sure looks to be all over the place. Do you have or do you know of anyone with a similar truck that you could use to compare? Where did you get the interface and software and do you find it easy to use?
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  2. #12

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    Test drive with the new MAF didn't go well.
    Here is what I did. In the off chance that the K&N air filter oil was fouling the MAF, I went a got a Purolator air filter and drove with the new MAF and the STFT was high(range from 0 to 39) and the truck felt bogged down. Unplugged the MAF and the fuel trim was not as high, but still high(range from 0 to 23) and the truck ran a little better, but still bogged down. Then, as a sanity check, I swapped in the K&N filter and kept the MAF unplugged. The truck ran well and the STFT was close to +-10.


    So, with the MAF unplugged, the air filter appear to make a huge difference in the STFT. The K&N filter is supposed to be a higher flow filter. It is 4+ years old and last oiled about 2-3 years ago. It does not appear to be dirty. My guess is that the K&N filter flowing better than the “stock” Purolator filter.


    I was not sure about the fuel pressure after my test. I was reading 50-57PSI (I typoed and said 67 in a previous port). From reading around the web, it seems that the pressure should be higher, like 60-66psi. Does this sound right? I'm not sure where to find the “real” spec.

  3. #13

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    The scanner is a Elm5 I got it off Amanzon with the OBDWhiz software for $28


    http://www.amazon.com/ElmScan-Compac...r+with+obdwhiz



    The Elm scanners are pretty standard and you can buy better software that helps in diagnosis. It just depends on how much you want to spend. I'm cheap, but so far, the OBDWhiz has been really helpful.

  4. #14
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
    Posts
    493

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    Fuel pressure for the V6 is 60-66psi, 48-54 for flex fuel and 55-62 for all others, this is with the key on and engine off. These figures are from a Haynes manual. I recall your pressure was a bit low but came up when you hit the throttle, maybe just not enough pressure at idle and start up. Do you hear the pump come on for a few seconds when you turn on the ignition but not start the engine?

  5. #15

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    You are correct. I also checked my Haynes manual and saw that the spec is 60 to 66psi. Today I disassembled the upper intake, took the regulator out, and went back to Autozone where I bought it 7 months ago. While they were looking up the part number I noticed that their computer screen showed the an operating pressure of 50psi for this regulator...which is exactly what I was getting. Thus, the Autozone computer has the wrong part number cross referenced for a fuel pressure regulator for a 2000 Chevy Silverado 4.3l v6. We looked back to a 1998 and its a different part number with an operating pressure of 65psi. I had them swap pressure regulators. So far, the truck runs good, Short Term Fuel Trim within range and O2 values look good.
    I did a lot of work on the truck in the last two weeks tracking the problem down. Much of that work and various parts just simply needed to be done after 190k miles. However, It really sucks that they sold me the wrong part!

  6. #16
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
    Posts
    493

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    Very fortunate that you noticed that!! WOW, it looked like fuel issue to me at first but can always be something else and with the work you had already done it was off to other things. Really glad it is running ok now. Now is the time to take some base line readings and keep them for future reference.

  7. #17

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    Thats a great idea. I'm gonna do a full cold to warm drive, tracking all the parameters as a baseline. The software has a data logging feature to a text file. Then I can graph things in a spreadsheet. Really, for $28, you can't beat the insight this give into the operation of the vehicle.


    Thanks for the help!

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