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Back to bad MPG heat range causing it?

Discussion in 'Vortec 4.2L I-6' started by AzTruckGuy, Jul 11, 2016.

  1. AzTruckGuy

    AzTruckGuy Well-Known Member

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    Sorry to start another MPG thread but this ones a bit different.

    As the board knows I had a leaking gas tank that was replaced a about a month or so ago. After the tank was replaced I was getting decent MPG as 1/2 tank would last me about a week of driving around in my town. At the time the temps where in the upper 90s and low 100s. Well when the temps started to rise, it was time to replace the thermo stat, thermo sensor, front engine purge valve as I was getting a P0440 code before this.

    Everything was fine for a week, I was not experiencing the stalling as before and I think the gas MPG was decent. Well now that the temps are hovering 108 at times, I have noticed the past few days that my MPG sucks, the stalling seems to want to come back, but doesn't stall? The SES light has not come back on the dash, as I assume the thermostat and purge valve fixed the P0440 code.

    On 1/4 tank I only got about 30 miles as before it would go for at least 60+ miles.

    plugs, fuel filter, K & N air filter (no issues after installed), battery, purge valve, ignition switch, thermo stat, thermo sensor all changed within the last 500 miles.

    The only thing that has changed the heat range now....as before I had the AC on and still 1/2 tank would last a week...now not so much....what do you guys think is the issue?
     
  2. Mooseman

    Mooseman Moderator

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    How are your engine temps? I know mine doesn't seem to have as much power the hotter it gets. I think that's normal. Apart from the effects from the hot air, the A/C is working harder, the fan will pull more, using more power and gas, and so on.
     
    RTTBLT1 likes this.
  3. AzTruckGuy

    AzTruckGuy Well-Known Member

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    My temps are not even a notch to the right of 210 and the needle stays there. I have no power issues as the power is there, I just redid the brake booster check valve as well, which cleared up a delaying power issue I was having before
     
  4. nathaniel

    nathaniel Member

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    Not to just fling out a random link, but this page seems to give a pretty good laundry list of what to check (http://www.aa1car.com/library/poor_fuel_economy.htm). It feels like there should be a way to use the graph feature in Torque to troubleshoot this issue if one could figure out the right parameters to watch. On a personal note, please send some of those high temps up here to Western Oregon; getting a bit tired of high 60's/low 70's and rain...
     
    Mooseman and RTTBLT1 like this.
  5. littleblazer

    littleblazer Gold Supporter

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    Even with my thermal clutch locked decently when it's 90s I still get almost 14 on a tank. And I beat the daylights out of the truck and I always have like 700 lbs of gear in it too. Truck runs 206 top ac blows 40 and the fan sounds like a semi when you take off... it gets a lot doggier and I have to push it harder when it's hotter though so I could see the temp affecting it. But as its hotter it should pull less air and thus less fuel...
     
  6. Sparky

    Sparky Moderator

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    Start with some solid numbers.

    Fill the tank to full, reset the trip meter. No guestimating, go all the way until the pump clicks off. Do NOT top off the tank.

    Do your normal routine driving that you do.

    Fill up again until the pump clicks off. Again, no topping off the tank.

    Take the miles on your trip meter, divide that by how many gallons the pump reads you put in the tank. Report back :biggrin:

    Oh, and reset the trip meter again. I reset mine every time I fill up, and I hand calculate the mpg fairly regularly. If it drops significantly for a couple tanks with no change in driving habits then I start checking into why.
     
  7. littleblazer

    littleblazer Gold Supporter

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    Kinda like this? :biggrin: I don't reset the trip because work.

    2016-07-12 00.08.57.png
     
  8. gmcman

    gmcman Well-Known Member

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    Agreed, don't use the gauge to determine how much fuel you use.

    Also, need more info.

    What plugs did you use? Should be AC Delco 41-103

    Have you cleaned your MAF meter? I see you use a K&N, don't rule out the fact you may have oil on the thin MAF wires.

    Have you checked for a vacuum leak? Check the large hose under the resonator box.

    What is your fuel pressure? You also stated you have a new fuel filter, be sure you don't have the lines reversed......very easy to do. If I'm not mistaken, the output or the line with the Schrader valve goes in the middle port.

    Please report back after checking these. The best help we can give is only in conjunction with you checking what's been requested.

    Thanks.
     
    Redbeard likes this.
  9. Mooseman

    Mooseman Moderator

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    I just use http://www.fuelly.com/ to track my mileage. They even have an app.

    I know I gained a couple MPG by just replacing the O2 sensor. Maybe a backpressure check is also in order?
     
    smt 59 likes this.
  10. AzTruckGuy

    AzTruckGuy Well-Known Member

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    Japanese Ac Delco made parts used when it called for it.....

    Guys most of the parts were replaced before the tank was changed out, at the time I was chasing a stalling issue I was having and just stopped throwing money at parts that were recommended as I wanted the tank fixed and fuel pressure stabilized after the leak.

    Even with the thermostat failing and now I am unknown sure if the purge valve was bad, after the tank was replaced and repaired; the fuel was great as it was lasting for a week on 1/2 tank.

    Nothing has changed from my driving habits, since its so damn hot here I try not to drive out as much. The items that where changed out where the thermostat, thermostat sensor and purge valve. The SES light that I had before is gone now, and the Trailblazer was fine after a week of the repairs.

    What I have noticed and I think I may have had this issue before? Is the gas pressure supposed to be constant on the gauge? This seems like such a dumb question, because I would think that the gas gauge would not fluctuate as much as my Trailblazer does, but this morning taking it for a drive, the gas gauge was near the E while driving, when I got into my garage while idling the gas gauge went back to the spot on the photo

    IMG_1597.JPG

    Monday put in 2.782G of gas went to the 1/4 mark and at 18.4 miles today, it just feels like the gas is not lasting since I haven't even drive it that much in the past 3 days (Just noticed the temp gauge because of the angle of the pic, its not near the marker of getting hot, it stays at 210 constant, I always look at it since I repaired the thermostat)

    Another issue that I have is putting in gas, it seems the gas pump cuts out when I fill the TB with gas...it happens a couple of times and I have to rotate the gas pump to fill up, but it becomes annoying to fill up at times
     
    Last edited: Jul 13, 2016
  11. Sparky

    Sparky Moderator

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    Yes, the gauge can vary a bit (fuel slosh in the tank, hills, etc, mine would bounce some) It is not pressure, just level. Could be the sender is a bit cruddy though and causing more variance.

    Again though, fill to the top, reset trip meter (or write down odometer reading), drive, fill to the top again, divide miles driven by gallons used. Hard numbers is what's needed here.
     
  12. nathaniel

    nathaniel Member

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    I would highly recommend getting the Torque app to troubleshoot this issue. I was thinking about this problem yesterday when I drove my son to OSU for a conference, and set up a graph with the 02 sensors, fuel related sensors, etc. for the drive, and I was getting a decent amount of data. You could capture the data for your TB, and compare it with mine to see what the differences (if any) are.
     
    Last edited: Jul 13, 2016
  13. AzTruckGuy

    AzTruckGuy Well-Known Member

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    What else would I need besides the app to get readings from my Trailblazer?
     
  14. Mooseman

    Mooseman Moderator

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    A Bluetooth ELM327 OBD2 reader.
     
  15. nathaniel

    nathaniel Member

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    a bluetooth OBDII unit. I use a cheap panlong (https://www.amazon.com/Panlong-Bluetooth-Diagnostic-Scanner-Android/dp/B00PJPHEBO) but I don't know if I'd recommend it, becuase while it connects with my Nexus 6 phone, it doesn't seem to work with my Nexus 7 tablet (which was what I really wanted to use). The app is android only, so you need an android phone/tablet also.
     
  16. AzTruckGuy

    AzTruckGuy Well-Known Member

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    Ok lets talk about the PCM reset, because this is the only item that seems to have controlled the vehicle after a week. I have been reading up on the PCM and its not to the benefit of the Trailblazer after it has reset, as the reset is pretty much a generic reset. Is the PCM really that bad? It seems Chevy took a crude approach to manage its vehicles when it came to being computer controlled at the time?
     
  17. Mooseman

    Mooseman Moderator

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    PCM's are fine. "Normal" vehicles are not affected by a "reset" like the 4.2 is. That's because they built in an algorithm where it adjusts to the throttle body getting dirtier from the backwards PCV system it has. When it is reset, it thinks the TB is clean and is unable to adjust due to its dirty condition.

    That's the reason that you have to clean the TB when you disconnect the battery.
     
  18. Sparky

    Sparky Moderator

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    Well, it'll figure it out eventually, but it takes so little time to do that you may as well clean it while you're at it.
     
  19. Mooseman

    Mooseman Moderator

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    I'm not sure about that. The algorithm is time/mileage based so the TB will always be dirtier than what it "thinks" it is. The PCM will never catch up to the TB's actual dirtiness.
     
  20. AzTruckGuy

    AzTruckGuy Well-Known Member

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    So are you guys telling me to clean it again? I just cleaned the TB back in January, did it really get that dirty again?
     
  21. Mooseman

    Mooseman Moderator

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    Maybe. Worth a shot. And disconnect the battery or pull the PCM fuses for 30 minutes again so they are in sync.
     
  22. Sparky

    Sparky Moderator

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    I thought it just adjusted expected airflow to meet actual. They don't all gum up at the same rate as that can be based on a lot of things. Mine didn't gum up very quickly at all because I didn't get as much gunk through the PCV as others have (less blowby maybe?).
     
  23. nathaniel

    nathaniel Member

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    Are you conjecturing that another PCM reset would cause the excessive fuel consumption to cease until the underlying problem caused it to again command higher fuel usage? That would be an interesting and easy test to run.

    Also, I was thinking this issue is worthy of an ishikawa (fishbone) diagram to help track down the component causing the poor mpg's. I've used them at work to solve computer system bugs, and they definitely bring order to the process. A quick google search even returned an example using poor mileage. In this case each branch end would be a component that has the potential to cause the problem (cat, O2 sensor, etc.)

    fishbone1.jpg
    Wiki on the ishikawa diagram: https://en.wikipedia.org/wiki/Ishikawa_diagram
     
    Mooseman likes this.
  24. AzTruckGuy

    AzTruckGuy Well-Known Member

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    I may have solved the gas issue my K & N air filter system was loose at the filter and throttle body areas, I guess all that high reving loosened them up :bonk:Gas has seemed to stabilized now? I'll keep driving and checking MPG.

    Well as soon one thing gets fixed an old issue comes back, going into reverse the Trailblazer almost stalled out. Then in going forward it almost stalled also. But it didn't and after that it was fine. These stalling issues are driving me crazy, I thought the purge valve would fix this and it hasn't. So many parts could be causing this issue, but how do I narrow it down to the part that is causing it? Seems someone from Trailvoy had the same issue and they replaced the charcoal canister and that fixed it. But I don't want to start getting into the throwing money at parts game again.
     
  25. Sparky

    Sparky Moderator

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    My 02 would tend to sputter sometimes, I just would not touch the pedal for a second after shifting from reverse to drive or whatever and that seemed to avoid it mostly.
     
  26. shovenose

    shovenose Well-Known Member

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    Mine does this too.
     
  27. Mooseman

    Mooseman Moderator

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    Mine does that when I first hit the gas, like a stumble, but only the first time. If I let it idle a while, it will do it again.
     
  28. therealsethallen

    therealsethallen Well-Known Member

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    Mine does that as well. I've always kind of chalked it up to "platform oddness" but, I do just what the two prior guys do and it works.
     
  29. AzTruckGuy

    AzTruckGuy Well-Known Member

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    Love/Hate relationship with the Trailblazer...Took it out on a short 130 mile trip back and forth, didn't even use 1/4 of a tank, which means I should be getting very good MPG...The stalling issue is the hate among other known issues others experience as well... I'm in the middle of putting more money into the Trailblazer, I can see with a little more tweaking and money this would a very great SUV...but if putting more money and annoying issues such as the stall keep happening, its a waste of money
     
  30. gmcman

    gmcman Well-Known Member

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    From post #8

    Also, need more info.

    What plugs did you use? Should be AC Delco 41-103 (Confirmed)

    Have you cleaned your MAF meter? I see you use a K&N, don't rule out the fact you may have oil on the thin MAF wires.

    Have you checked for a vacuum leak? Check the large hose under the resonator box.

    What is your fuel pressure? You also stated you have a new fuel filter, be sure you don't have the lines reversed......very easy to do. If I'm not mistaken, the output or the line with the Schrader valve goes in the middle port.

    Please report back after checking these. The best help we can give is only in conjunction with you checking what's been requested.

    Also, what year is your vehicle to determine of you have a MAF or not.
    Thanks.
     
  31. AzTruckGuy

    AzTruckGuy Well-Known Member

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    TrailBlazer is a 2003 I6 so believe I am on the older "Speed Density" type engine control system?

    Fuel filter was put in correctly and yes when I changed it out I could see how they could get reversed.

    I have felt around for vacuum leaks when I got the P0440 code as I was looking to see if I had one, checked hoses and boxes, nothing.

    How would I check my fuel pressure?
     
  32. gmcman

    gmcman Well-Known Member

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    There is a schrader port on the output line of the fuel filter line. I have made a mess checking it, can't remember what adapter I used on my gauge to check it....I can check later.

    I would crawl up under the rear of the envoy and make sure your fuel filler neck isn't cracked or loose. Make sure the wire harness on the evap is fully seated.

    Make sure your vacuum hose on the throttle body is fully seated, as well as the large hose under the resonator box.
     
  33. nathaniel

    nathaniel Member

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    @MAY03LT has a pretty good youtube video on how to check fuel pressure if I recall correctly...
     
  34. AzTruckGuy

    AzTruckGuy Well-Known Member

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    Ok fuel pressure is with in range, mechanic buddy checked it out for me.

    So what does the board think of this MPG? Filled up to the 1/2 mark with 9.675 gallons, so for the first 1/4 mark went on short trip which got me 118 miles back and forth...the last 1/4 mark got me 43 miles around town.

    I at least expected 50 to 60 miles around town
     
  35. Sparky

    Sparky Moderator

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    Don't go by the fuel marks on the gauge. You can't get anywhere close to accurate numbers doing that.

    Fill it, TO FULL. Drive it. Fill it, again, to FULL. Divide miles driven by gallons used to fill.

    That is the ONLY way to get accurate MPG readings. Only partial filling won't tell you anything useful.

    Because of variances in tank shape, sender unit, heck even the level of the ground you're on, you can't assume the gauge is perfectly accurate. It isn't. No gas gauge is.
     
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  36. gmcman

    gmcman Well-Known Member

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    You cannot base anything off the gauge.

    You need to fill up until the handle stops automatically, go drive 1/2 tank or how ever much you choose, then fill back up. How ever much fuel you put back in is how much you used. Repeat that a few times and make notes.

    Drive easy, no jack rabbit starts, give it an honest run. You will drive yourself crazy basing this off the fuel gauge.
     
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  37. Mooseman

    Mooseman Moderator

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    And if you have trouble with the calculations, you can go to fuelly.com. They even have an app for that and will keep track foe you but you MUST fill it each time.
     
  38. AzTruckGuy

    AzTruckGuy Well-Known Member

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    Lets see what happens with Fuelly info inputted
     
  39. AzTruckGuy

    AzTruckGuy Well-Known Member

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    Ok guys since the Trailblazer is feeling smooth after the Oxygen sensors and oil change....I have looked more into the Elm 327 with Fusion(Torque) app for IOS....What benefits would this have for my vehicle now? Could I improve any issues that I may not be seeing or feeling at the moment? The app looks very cool and has a ton of data to it
     
  40. gmcman

    gmcman Well-Known Member

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    It's nice to view the o2 sensors and monitor intake air temp, knock retard, trans temp, fuel trims....heck, just about everything.
     

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