Back to bad MPG heat range causing it?
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djthumper
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gmcman
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- Dec 12, 2011
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Ok 10.6 MPG is unacceptable giving the parts replaced recently, what could be causing this horrible MPG?
gmcman
Member
- Dec 12, 2011
- 4,656
Ok 10.6 MPG is unacceptable giving the parts replaced recently, what could be causing this horrible MPG?
How did you calculate your MPG's?
Inputting odometer reading at every fuel up on Fuelly, I'm not even getting the 14MPG which is the norm
I am doing what the board stated....I am fueling up to full and letting it run down to empty and inputting on Fuelly based on odometer and gallons, I am not even checking my own miles anymore. I was right though about getting 11MPG, even fuelly agrees with me.
Plugs, fuel filter, both oxygen sensors, thermostat, front purge valve, replaced to free flowing air filter, cleaned throttle body, full synth oil change, transmission fluid change, and to get 10.7mpg? I feel like I am putting too much work and effort into the Trailblazer to get that MPG
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gmcman
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- Dec 12, 2011
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City/Hwy percentage?
I agree that's low, but it's so low it would point to a problem elsewhere.
Do you have a torque app/ bluetooth adapter?
You must check everything..
Did you get all the vacuum hoses reattached?
Does it feel like its lost power...are the plugs fully seated?
I don't know if it's possible to get the wrong O2 sensor in the wrong hole...but something to verify.
If it's the first tank after all the work, with a fresh PCM relalearn, I would wait another tank.
I agree that's low, but it's so low it would point to a problem elsewhere.
Do you have a torque app/ bluetooth adapter?
You must check everything..
Did you get all the vacuum hoses reattached?
Does it feel like its lost power...are the plugs fully seated?
I don't know if it's possible to get the wrong O2 sensor in the wrong hole...but something to verify.
If it's the first tank after all the work, with a fresh PCM relalearn, I would wait another tank.
I am doing all city driving and I expect to get at least get 14MPG
I haven't gotten the Torque tools yet, I was waiting to see how the MPG was after a while
All vacuum hoses are attached and look fine, I will be getting the Ac Delco gas cap tomorrow as the seal ring appeared to have cracks in it on my old one, after I checked it from a P0440 code that popped up again
No power loss and plugs are fully seated its running super smooth, better then when I first got it
Not possible as upstream and downstream have different plugs
gmcman
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- Dec 12, 2011
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What's your driving style, driving Miss Daisy or Talladega nights?
Fuel is going somewhere...
Leaking/evaporating
Heavy foot
Unmetered air
Weak engine/low cylinder pressure.
The torque app is very useful in watching knock retard, ignition timing, O2 sensor function, and fuel trims.
When you get Torque up and running we can narrow it down further.
Sorry if I missed this, but did you get an exhaust back pressure test done?
Fuel is going somewhere...
Leaking/evaporating
Heavy foot
Unmetered air
Weak engine/low cylinder pressure.
The torque app is very useful in watching knock retard, ignition timing, O2 sensor function, and fuel trims.
When you get Torque up and running we can narrow it down further.
Sorry if I missed this, but did you get an exhaust back pressure test done?
I feel the heaviness of the Trailblazer, I don't floor it. I have tested to see how the power is, and its there.
Had the exhaust back pressure done and it was fine, also I drove around with the manifold oxygen sensor out, just to double check and I didn't feel anymore power surges as I floored it. I don't know if I should trust the exhaust though, since its almost at 100k, could be bad and not throwing codes, feel like gutting the cat, since I live in city where is no emission laws.
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djthumper
Administrator
Mooseman
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He wants to know if you added a lift kit to bring the suspension higher than stock.
I can tell you that I gained 2 MPG with a new O2 sensor as I suspect that my old one was getting lazy. Reset the PCM and bam! 14MPG (EXT with 3.42 gears)
I can tell you that I gained 2 MPG with a new O2 sensor as I suspect that my old one was getting lazy. Reset the PCM and bam! 14MPG (EXT with 3.42 gears)
I was expecting a gain when I changed mine out too and nope.....
And that's a negative on the lift, I am no longer into lifted vehicles, best thing I ever did to my Trailblazer was to get rid of that ugly rake and front is stock still..
PS...Those rear springs are for sale if anyone wants a lift ha ha
Mooseman
Moderator
If you want a nice long read, this was the mother of all MPG loss hunting threads ever, all 12 pages.
Only getting 160 miles on 25gal tank
Only getting 160 miles on 25gal tank
gmcman
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- Dec 12, 2011
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I think he also had a little bit of a heavy foot as well.
Something else to check is the fuel pressure regulator. I replaced mine less than a year ago and it smoothed things out a little....something worth trying because you can't verify pressure after the regulator so it's not throwing money into the wind.
I researched this, it seems the smell of gas would be associated with the airbox area? I don't smell gas or seem to have leaks?
shovenose
Member
I think I averaged about 14 MPG in the Envoy with mostly city/traffic driving even with two-hour easy highway trips per tank. So, to expect 14MPG with all-city driving doesn't seem guaranteed. That's why I had no hesitations switching to a Suburban because city MPG won't be much worse. Try doing some easy highway driving at 65 (I lost MPG because I was hauling ass at ~75). 20MPG is doable on the highway at 65. Been there done that. But going too fast on the highway or in the city these things are still heavy, body-on-frame, somewhat brick-shaped SUVs. I'd look back at my Fuelly but I got annoyed and deleted it for my Envoy.
Here's the thing the last time I took it out for a 120 mile drive, I am pretty sure the MPG went way up. I don't drive with a heavy foot, like you said they are heavy, body on frame Suvs. Not expecting modern MPG, but at least 14mpg with all the parts replaced. Getting my new gas cap today, it would be funny if that got me up to 14mpg.
gmcman
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- Dec 12, 2011
- 4,656
I can get 20 MPG @60-65 MPH with a steady cruise on a flat surface, once I bump it up to 70 the game is up, 75-80 I'm looking at 15-17 MPG if I'm lucky and that's with 4:10's.
There are many factors that can contribute to a loss in MPG, you need a healthy engine though so without driving it, seeing it, it's hard to pin it down which is why we ask a bunch of questions and I appreciate your feedback.
I will always ask to check the vacuum, make sure your intake manifold bolts are tight, still doesn't rule out a gasket leak but it's a start. without seeing results from a torque app, there's always the chance of carbon knock in which you will likely not hear.
The fuel pressure regulator again is one of those things that can contribute to issues with fuel atomization and you won't know it's bad because you cannot verify pressure aft of the regulator. You aren't throwing money away if you change it and I would recommend changing it with about 150K on the clock. That's not a rule of thumb, just preventative maintenance. You could have puddling fuel and not know it, requiring more fuel to complete the burn as you wouldn't have fully atomized fuel to use.
You can do a load test by placing a board against the gas pedal and the seat, holding the RPM's to about 1500 and pull one coil pack at a time, noting the RPM drop...all cylinders should be pretty close, a weak cylinder would show less of a drop and would be obvious...not sure of the exact tolerance, maybe 10% but not sure....don't quote me.
What tires are you using? Low rolling resistance tires will get you a couple MPG's..this is not a fallacy.
There are many factors that can contribute to a loss in MPG, you need a healthy engine though so without driving it, seeing it, it's hard to pin it down which is why we ask a bunch of questions and I appreciate your feedback.
I will always ask to check the vacuum, make sure your intake manifold bolts are tight, still doesn't rule out a gasket leak but it's a start. without seeing results from a torque app, there's always the chance of carbon knock in which you will likely not hear.
The fuel pressure regulator again is one of those things that can contribute to issues with fuel atomization and you won't know it's bad because you cannot verify pressure aft of the regulator. You aren't throwing money away if you change it and I would recommend changing it with about 150K on the clock. That's not a rule of thumb, just preventative maintenance. You could have puddling fuel and not know it, requiring more fuel to complete the burn as you wouldn't have fully atomized fuel to use.
You can do a load test by placing a board against the gas pedal and the seat, holding the RPM's to about 1500 and pull one coil pack at a time, noting the RPM drop...all cylinders should be pretty close, a weak cylinder would show less of a drop and would be obvious...not sure of the exact tolerance, maybe 10% but not sure....don't quote me.
What tires are you using? Low rolling resistance tires will get you a couple MPG's..this is not a fallacy.
I'm at 98k miles, away from the 150k mark...unsure to change that out yet, I will put it on the list...
I am going to get the Elm327 Bluetooth box this week and get the Torque app, I think this might be the better route to go to share data with the group. Coil test would have to wait till the morning, we hit 111 today
As far as tires they are Dextro 245/75/16 and they weigh 33lbs and now since adding Bora Wheel spacers all around my weight per rim/tire is now around 56, mind you I was having MPG issues before the spacers...
I just bought some Dunlops 2 235/65/16 at 23lbs they should be with rim/tire at 46lbs a weight savings of 10lbs per tire, that should help with some MPG and also the steering feel
gmcman
Member
- Dec 12, 2011
- 4,656
It's not so much the weight of the tire, but the entire composition. ..ie, carcass, sidewall, tread design, etc. I lost 3 mpg's once to a set of Kumhos, I sold them with 50%tread to cut my losses, not agressive by any means.
What pressures are you running? I always keep mine at 35 psi cold, 33 or under I notice a loss in MPG's
What pressures are you running? I always keep mine at 35 psi cold, 33 or under I notice a loss in MPG's
http://www.tirerack.com/tires/tires.jsp?tireMake=Dunlop&tireModel=Signature+II+(T-Speed+Rated)&partnum=365TR6SIG2&vehicleSearch=false&fromCompare1=yes
I researched the Dunlops and I think they are good choice for doing a crossover tire as I want them to be. I took my tires over to discount tire and they checked the pressure on them and I cant remember what they changed them too. But my tires now, they need to be changed out due the age of them and inner wear. I am going to do the upper joints and upper arms before I put the Dunlops, those parts are bad.
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gmcman
Member
- Dec 12, 2011
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Check the sidewall of the tires, max pressure should be prob 44 psi...granted this is for increased loads but it's a good indicator you can run 35 all the time...most tires are this way.
I'm pretty sure you didn't lose 4 mpg over tire pressure, but low pressure will absolutely affect MPG's.
Get a good gauge, don't eyeball it, and in the morning if you're parked outside, check the pressure before the sun hits the side of the tire. Sunlight will increase pressure quickly as black is very absorbant of sun radiation.
Report back what the pressure is, if you're at about 28-29 psi, you can bet your mpg's will drop off a few compared to 35.
Low pressure will wear the inside of the tire. Yours could be the result of worn suspension.
Since this is a MPG thread, you do need to verify all these factors or its a lost cause.
I'm pretty sure you didn't lose 4 mpg over tire pressure, but low pressure will absolutely affect MPG's.
Get a good gauge, don't eyeball it, and in the morning if you're parked outside, check the pressure before the sun hits the side of the tire. Sunlight will increase pressure quickly as black is very absorbant of sun radiation.
Report back what the pressure is, if you're at about 28-29 psi, you can bet your mpg's will drop off a few compared to 35.
Low pressure will wear the inside of the tire. Yours could be the result of worn suspension.
Since this is a MPG thread, you do need to verify all these factors or its a lost cause.
I have shot upper ball joints and 1 bad bushing on the one of the upper arms, the board thinks the rest of the suspension is fine after I posted pics in the suspension section. So those 2 parts will be replaced next week and the vehicle aligned then the new tires put on. I will check tire pressure in the morning, its been 105 here. Thanks for the input
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Elm 327 is arriving tomorrow, what does the board recommend the settings to be for the Fusion app? I want to make sure all data is available to determine what's going on.
Mooseman
Moderator
Yes I have IOS so I bought the Fusion OBD app yesterday and was playing around with it, so many parameters with this app, which are the best to see what the fuel is doing? I did a dashboard of short and long term fuel % trim
Ok tires were checked this morning by Discount Tire and air added to them, they were within specs 35PSI
Ok here's the readings at idel and the O2 Sensor 1 was going up and down
Now with the rpm at around 1600rpm
My P0440 code
Other info
What do you guys think?
Ok here's the readings at idel and the O2 Sensor 1 was going up and down
Now with the rpm at around 1600rpm
My P0440 code
Other info
What do you guys think?
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So like others that have posted these Component ID fails on past posts, has anyone found a fix to them? I have checked all components and they seem fine...
Mooseman
Moderator
No clue what those components fail are but are likely related to your P0440.
Just looking at your fuel trims, they seem to be off a bit but, in the first set of pics, less than the 10% that usually means trouble. Negative trims means it's running rich and it's cutting that much on fuel to compensate.
In your second set of pics, your LTFT is off by over -10% (-11.72%) which means it's either getting too much fuel or not enough air. Could be cause by the evap system dumping too much fumes into the intake. Could also be caused by a dirty air filter.
If you want more info on fuel trims, this video explains it well despite the robotic voice.
I'd say track down and fix your P0440 before doing anything else.
Just looking at your fuel trims, they seem to be off a bit but, in the first set of pics, less than the 10% that usually means trouble. Negative trims means it's running rich and it's cutting that much on fuel to compensate.
In your second set of pics, your LTFT is off by over -10% (-11.72%) which means it's either getting too much fuel or not enough air. Could be cause by the evap system dumping too much fumes into the intake. Could also be caused by a dirty air filter.
If you want more info on fuel trims, this video explains it well despite the robotic voice.
I'd say track down and fix your P0440 before doing anything else.
I cleaned my K & N when I put on the oxygen sensors, cleaned the throttle and dumped some seafoam into the tank. I checked the K & N all tight and no major dirt on the filter, checked the FPR for any fuel leaks or leaks in general, nothing.
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Ill have to look at that video later on tonight, just got done changing front and rear diff oil, man that gear oil was so dirty. Going go for a test drive...
So I was missing around with the dashboard and added some more items, the first time around I think the readings where just going up and down and they have seemed to settle. I cleared the P0440 code, so lets see if it pops back up since I got a new gas cap...took these readings last night
1st
2nd set
So I was missing around with the dashboard and added some more items, the first time around I think the readings where just going up and down and they have seemed to settle. I cleared the P0440 code, so lets see if it pops back up since I got a new gas cap...took these readings last night
1st
2nd set
I am looking at my Diagnostic reports and I see that I am running rich and this means the following:
Leaky fuel injector Don't know how to test for that?
Excessive fuel pressure due to bad fuel pressure regulator or restricted fuel return line, Could be FBR is bad?
Extremely dirty air filter or restrictions in air intake system Nope Checked
Exhaust restrictions (clogged converter, crushed exhaust pipe or plugged muffler) Don't trust the converter even though it checked out, the thermostat issue was run like that for awhile, until I fixed, wonder if it burned the cat?
Bad O2 sensor (output shorted to voltage so it reads RICH all the time) Just replaced
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