Only getting 160 miles on 25gal tank

littleblazer

Member
Jul 6, 2014
9,265
But if I drive it like I stole it in the city and get close to 13, I'd imagine it shouldn't be that bad... just saying.
 
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
City vs highway does kill MPG. At stop lights, you are basically getting 0 MPG, same as idling. And in a traffic dense city like NYC, it's a no win situation.
 
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pcharm129

Original poster
Member
Aug 15, 2012
191
gmcman said:
Also, I believe you told me that you have a heavy foot. If that's the case, jack rabbit starts will surely kill mileage.
Driving like Im balancing wine glasses I get 14 to 16 in the city.
Yup... But no matter how heavy my foot is, i shouldnt be burning more gas than a Hummer... And since this last refill, at least half of my driving WAS/IS hwy...
 

Gerbil21

Member
May 28, 2014
839
pcharm129 said:
Yup... But no matter how heavy my foot is, i shouldnt be burning more gas than a Hummer...
Not true, ask me how I know [emoji17], I'm in the single digits too, getting 8mpg with not that heavy throttle. but get the best of 10mpg with a Lightfoot and smart driving, *not driving ms.daisy kind-of driving* I don't think I can ever drive that slow[emoji3] and remember it's smiles per gallon not miles per gallon lol
 

pcharm129

Original poster
Member
Aug 15, 2012
191
Gerbil21 said:
Not true, ask me how I know [emoji17], I'm in the single digits too, getting 8mpg with not that heavy throttle. but get the best of 10mpg with a Lightfoot and smart driving, *not driving ms.daisy kind-of driving* I don't think I can ever drive that slow[emoji3] and remember it's smiles per gallon not miles per gallon lol
Ohhh its True. You're just in the same leaky ship as i am! Welcome to the Titanic! Lol!
 

Gerbil21

Member
May 28, 2014
839
pcharm129 said:
Ohhh its True. You're just in the same leaky ship as i am! Welcome to the Titanic! Lol!
Except this titanic doesn't sink since it runs out of gas before anything happens lol
 
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pcharm129

Original poster
Member
Aug 15, 2012
191
I was just thinking. The sensor on the air intake, i think the MAF sensor, could it go bad without the PCM throwing a code?
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
06+ has the MAF. If you're talking about the one in the back of the intake tube next to the resonator, that's the intake air temp sensor.
 
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Gerbil21

Member
May 28, 2014
839
pcharm129 said:
I was just thinking. The sensor on the air intake, i think the MAF sensor, could it go bad without the PCM throwing a code?
It could get dirty and react slow like a o2 but still be in the pcms threshold of OK while actually hurting performance, you could always clean it with the correct maf cleaner or contact cleaner aka electronic cleaner.
 
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Gerbil21

Member
May 28, 2014
839
So everyone can be up to date can you make a list of your truck specs "miles, year, rear end ratio tire size, etc..." and work done
 

pcharm129

Original poster
Member
Aug 15, 2012
191
Gerbil21 said:
So everyone can be up to date can you make a list of your truck specs "miles, year, rear end ratio tire size, etc..." and work done
Its got 148,718 miles on it. Everything else is in my profile.
 

Gerbil21

Member
May 28, 2014
839
pcharm129 said:
Its got 148,718 miles on it. Everything else is in my profile.
Can't see on tapatalk, I'll look later
 

littleblazer

Member
Jul 6, 2014
9,265
Gerbil21 said:
Can't see on tapatalk, I'll look later
He's got 3.43s and his tire size is about the stock 29.5 iirc.
 
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DAlastDON

Member
Apr 6, 2014
5,550
Kentucky
Whoa. About 1.5 gallons to go 8 miles. At that rate of consumption your distance per 25 gallons of fuel is only 128 miles.
 

gmcman

Member
Dec 12, 2011
4,656
Sorry if I didn't look back through the posts, but have you had a compression test done? Dry then wet?
 

pcharm129

Original poster
Member
Aug 15, 2012
191
gmcman said:
Sorry if I didn't look back through the posts, but have you had a compression test done? Dry then wet?
Yeah. Dry, not wet. Compression is awsome. I believe 185 to 190...
 

gmcman

Member
Dec 12, 2011
4,656
I don't know if internally the sensors are different but they are different part numbers just make sure you get the upstream in the correct location. may even be a different harness I can't remember but just something to consider
 

pcharm129

Original poster
Member
Aug 15, 2012
191
gmcman said:
I don't know if internally the sensors are different but they are different part numbers just make sure you get the upstream in the correct location. may even be a different harness I can't remember but just something to consider
No worries. Yes they do have different connectors. But i changed the last ones so im familiar. However, I DID try to change the downstream sensor WITHOUT jacking the truck up...BIGGGG mistake. Took me 4ever! Small work space... But its done. Now lets see if anything changes.
 

pcharm129

Original poster
Member
Aug 15, 2012
191
This is the old down stream sensor...20151002_192531.jpg

The old up stream sensor fell and disappeared somewhere onto the engine under compartment and i couldn't find it so i dont know what it looks like. I've driven since then so it may have fallen out somewhere. But if i find it i'll let the thread know if it looks like this one...
 

gmcman

Member
Dec 12, 2011
4,656
Do you have a catalytic converter? If so, has it been gutted? Just curious....that's a real sooty looking sensor especially being downstream. Maybe it's normal but I don't remember mine looking like that.
 

pcharm129

Original poster
Member
Aug 15, 2012
191
gmcman said:
Do you have a catalytic converter? If so, has it been gutted? Just curious....that's a real sooty looking sensor especially being downstream. Maybe it's normal but I don't remember mine looking like that.
Yes. No its not gutted.
 

BlazingTrails

Member
Apr 27, 2014
19,409
pcharm129 said:
Hello gentleman. I'm having a seriously confusing and costly problem with my truck, and NOBODY seems to be able to figure out what's going on. I have a 25gal tank and for some unexplainable reason i'm only getting 160 miles on it. Basically 6mpg! AND i don't have any codes! I have a pcm4less tune and i removed the resonator. Got a straight pipe from the muffler. My exhaust drips water and my mechanic is no help. It also stalls from time to time. I've addressed everything i can think of except a faulty pcm. Which i will address soon because i have another one i bought from pcm4less some time ago. I don't think anyone knows these trucks better than you guys on this forum. If you can help me solve this mystery i would GREATLY appreciate it...Thanks
Has this been covered yet?

http://gmtnation.com/forums/topic/14297-rebuild-your-ignition-switch-intermediate-trailblazer-9490/
 

Daniel644

Member
Feb 27, 2015
573
pcharm129 said:
Update time... Went to see littleblazer today.

Filled up before leaving, drove 46 miles, topped off on arrival. Burned 4.6 gallons (AC off). Littleblazer calculated about 9.8mpg (hwy).

Littleblazer checked the vacuum pressure and said its good. Checked the manifold and tightened a loose bolt. No other issues were noticeable. We are now both suspecting PCM or Injector issues...

I drove 40 miles on the return trip and topped off again. Burned 3.127 gallons. I calculated 12.8mpg (no AC, about 85% hwy). Improvement, but still far from good.

Around 2000 RPM @ 75MPH...

Confirmed. RPM jumped a few hundred when done at 75MPH...

@littleblazer...Thanx for the help homie! I really appreciate you taking the time out to look at the truck...

And thank you EVERYBODY here on this thread trying to help me thru this headache...!!!
I know this is a while back in the thread, but I've got to say with that short a trip combined with using different pumps to refill, you can't trust those numbers, you would have been better off to fill up, drive there and back and refill at the SAME EXACT pump, I drive about 160-180 (till the needle is around the half mark on the gauge) before I refill and at the same station if I fill up at pump #1 and drive (my typical 160-180) then refill at pump #2 (backside of pump #1) I get around 13.8 MPG then if I reverse that and after filling up at pump #2 then refueling on pump #1 I get 15.8 MPG but if I stick to pump 1 or 2 for several refills I get 14.8 MPG (the average of the alternating fill ups) everytime, so even spread across 160-180 miles of driving the variations between how full each of those pumps gets the tank before the pump cuts off can cause a multi MPG difference in calculations, so I could guess how much that throws off things on short drives like that.
 

Mounce

Member
Mar 29, 2014
13,667
Tuscaloosa, AL
Daniel644 said:
I know this is a while back in the thread, but I've got to say with that short a trip combined with using different pumps to refill, you can't trust those numbers, you would have been better off to fill up, drive there and back and refill at the SAME EXACT pump, I drive about 160-180 (till the needle is around the half mark on the gauge) before I refill and at the same station if I fill up at pump #1 and drive (my typical 160-180) then refill at pump #2 (backside of pump #1) I get around 13.8 MPG then if I reverse that and after filling up at pump #2 then refueling on pump #1 I get 15.8 MPG but if I stick to pump 1 or 2 for several refills I get 14.8 MPG (the average of the alternating fill ups) everytime, so even spread across 160-180 miles of driving the variations between how full each of those pumps gets the tank before the pump cuts off can cause a multi MPG difference in calculations, so I could guess how much that throws off things on short drives like that.
You realize that pump 1 and 2 at the same station (and as far as that matters 3 through 8 or however many are there) are both fed by the same tank of gas going through the same filter for each grade right? Nothing fancy there, it's not the gas in your case bud.
 

Daniel644

Member
Feb 27, 2015
573
Mounce said:
You realize that pump 1 and 2 at the same station (and as far as that matters 3 through 8 or however many are there) are both fed by the same tank of gas going through the same filter for each grade right? Nothing fancy there, it's not the gas in your case bud.
I think you misunderstood what I was try to say, I was NOT implying it being anything about the fuel itself, I know it's all the same gas regardless the pump, it was about the auto shut-off of the individual pumps or as we call it around here the point "when the pump clicks off" being more sensitive on one pump vs the other pump resulting in about a half to 3/4 a gallon difference (in my case) in the fuel level in the gas tank after a fill up from one pump to the other (being the cause of my different MPG averages) and that at such a short drive as his 40 mile trip that that discrepancy from one pump to the other could significantly effect his MPG reading.

my overall point being for ACCURATE measuring you need to remove as many variables as possible and the pump "cut-off" is a variable based on my experience.
 

littleblazer

Member
Jul 6, 2014
9,265
I haven't used the same pump the last 10 times I've filled up. My milage only changes by 10 miles between fill ups and my mpgs are all within .1. If one station has an issue then I can see that but that's also spread between 3 different gas stations. I understand what you're getting at though.

Edit: last 5 times I've filled up. Just looked at my log.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Pumps that inaccurate would cause some serious lawsuits.
 

littleblazer

Member
Jul 6, 2014
9,265
Just so you know I'm not messing around. The only vehicle I've had an issue with the shut off is the sierra. The fill line is a mile long and is only a half inch with little pitch. So it false trips on most pumps about 5 gallons in.

uploadfromtaptalk1444236579573.png
It's miles, mpg, price.
 

gmcman

Member
Dec 12, 2011
4,656
I really don't think you can accurately calculate your MPG's from a 30 mile trip or by adding 4 gallons, too many variables.

I don't know how you are achieving 8 MPG with a healthy engine and not using a heavy foot or towing the ark...that's crazy....lol. :crazy:

Something is way off here, I so wish I could take it for a drive, at least feel if it's down on power or something. I have a few thoughts but fill up a 5 gallon gas can and keep it with you and drive it until it runs out of gas....without getting my hands dirty there isn't much else I can suggest at the moment., but I will give you a list of things to go over tomorrow after work. Your rear O2 sensor is pretty sooty for it's location so where on earth is all this fuel going if you don't have a burned up cat or a code by now?

With good compression, good vacuum, no dragging brakes, no codes.....8MPG is way off kilter.

Don't worry about the fuel gauge for now, drive it until it runs out of gas, note the mileage when the fuel light comes on and when it starts to sputter. I don't like suggesting this but don't be on the interstate during rush hour, :thumbsup: That's what I would try anyway.

Have you taken it to the fuel light since all this happened?

Don't let it idle for excessive periods, ie warmup. I don't know you're driving style but just throwing this out..don't drive with an on/off, jerky gas pedal foot, keep it steady, set the cruise if possible on the highway and just drive it real easy.
 

Daniel644

Member
Feb 27, 2015
573
ddgm said:
If any pump meter readout differs by 1/2 to 3/4 actual gallon dispensed versus another pump, that station owner had better pack his belonging for a vacation at the government's expense. That's why you see those stickers on the pump certifying the accuracy.

littleblazer said:
I haven't used the same pump the last 10 times I've filled up. My milage only changes by 10 miles between fill ups and my mpgs are all within .1. If one station has an issue then I can see that but that's also spread between 3 different gas stations. I understand what you're getting at though.

Edit: last 5 times I've filled up. Just looked at my log.

HARDTRAILZ said:
Pumps that inaccurate would cause some serious lawsuits.
I'm not saying one pump is SAYING it pumping more then it is, they ARE ACCURATE (recently certified by the testing agency responsible for testing them), as exampled by the AVERAGE mileage between the 2 pumps being within 0.1 MPG of my tank averages when I use the SAME pump repeatedly, there is NO question to the ACCURACY of the pumps, what I'm saying is one pump physically puts more fuel into the tank BEFORE the pump clicks off and that because of the different levels of fuel in the tank as a result of the different "click" points is what causes the variation and why it's important to use the same pump repeatedly for accurate results.

to be clear, if I always use pump 2 for refilling I will be within the normal variation plus or minus 0.1MPG from my longtime average of 14.8, and the same if I always use pump 1, it's when I switch from one pump to the other that I see the variation, this indicates one pump (pump 1) puts physically more fuel into the gas tank before it shuts off then pump 2 does, the pumps are still accurate to how much fuel they dispense, one just gets more fuel in the tank before it shuts off.
 

littleblazer

Member
Jul 6, 2014
9,265
I dunno. I normally tell the guys to not round it up since when they do it it normally over flows out the fill neck. Each truck is different but I've never really noticed a difference in the click when I was working. (See attached image. It stabilizes as it goes down because the routes became more consistent on tanks.) The outliers are highway trips. All I'm trying to say is topping off before you leave then refilling when you get there should give you a pretty accurate measure of fuel used even if let's say it was a gallon more or less then it should've been when you refueled. At nearly all highway that is still terribly low though.

By the way, my recent trips, 180 miles highway and about 40 miles in town yield that 15.5 mpg measurement. You gave my truck the disease man! [emoji6] Nah I'm only kidding. But it's pretty bad since I'm making my trip at 72 mph with cruise control on where as just this spring I made the same trip and got about 22 mpg... I blame the fuel pump. The truck hasn't been the same since I replaced that.
uploadfromtaptalk1444254320089.png
 

Daniel644

Member
Feb 27, 2015
573
littleblazer said:
I dunno. I normally tell the guys to not round it up since when they do it it normally over flows out the fill neck. Each truck is different but I've never really noticed a difference in the click when I was working. (See attached image. It stabilizes as it goes down because the routes became more consistent on tanks.) The outliers are highway trips. All I'm trying to say is topping off before you leave then refilling when you get there should give you a pretty accurate measure of fuel used even if let's say it was a gallon more or less then it should've been when you refueled. At nearly all highway that is still terribly low though.

By the way, my recent trips, 180 miles highway and about 40 miles in town yield that 15.5 mpg measurement. You gave my truck the disease man! [emoji6] Nah I'm only kidding. But it's pretty bad since I'm making my trip at 72 mph with cruise control on where as just this spring I made the same trip and got about 22 mpg... I blame the fuel pump. The truck hasn't been the same since I replaced that.
attachicon.gif
Screenshot_2015-10-07-17-35-36.png
I never "round up", when it clicks it clicks, rounding up removes the control point of knowing your refilling the tank to the same level. thats why it's important to use the same pump since the level of fuel in the tank before it clicks might be different from one pump to the other.
 

littleblazer

Member
Jul 6, 2014
9,265
Daniel644 said:
I never "round up", when it clicks it clicks, rounding up removes the control point of knowing your refilling the tank to the same level. thats why it's important to use the same pump since the level of fuel in the tank before it clicks might be different from one pump to the other.
Using works card I had to. It was prefered to be round.

Enter rant: But yes I understand. Under lab conditions the click method is accurate within probably 10% but if it were to be perfect, miles would need to be logged by GPS and fuel weighed when entered. Canister weighed after driving cycle would then give the absolute best results. Really going on a test track where the road surface is the same all the way around would eliminate driving factors too. But all of that is unnecessary to this. End rant.

To do it right it should be the same pump and only till it clicks. Or like was mentioned earlier. Run it out of gas, then record the milage. Add the 5 gallons which is exactly measured and drive until that runs out. Record the milage and compute. That should be almost exact. And really bad for the fuel pump...
 
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
I know of one pump at a particular gas station clicks off before being completely full. When it's full, my gauge is pegged past the F but at that particular pump and maybe the odd one, it clicks off right on the F. So there could be a slight variable of the pump sensitivity.

My V8 Saab normally gets around 14 MPG combined +/- 0.5, DoD disabled.
 

gmcman

Member
Dec 12, 2011
4,656
what I'm suggesting is to fill it up, then run it out of gas and use the 5 gallon gas can to get you back to a gas station or home.

A healthy Trailblazer does not get 8 miles to the gallon, where is the other half of the fuel going?
 

gmcman

Member
Dec 12, 2011
4,656
I was able to meet up with pcharm this week during work, he made a trip over to my location as I passed through Jersey. I wish I could have spent more time with his TB but there was a delay on my end costing me an hour.

The engine seems healthy, I did hear a light tap but it was a deep sounding tap but not a knock under the valve cover. At first I thought it was the timing chain contacting the front plastic cover but couldn't pinpoint the location, could possibly be what I heard...when the RPM's were raised to 1500 or pretty much above idle the noise completely went away...so this part is not fully diagnosed.

The cat's temp was about 350 deg in and roughly 475 out, vacuum was just under 20 inches and I only saw one or 2 very minor fluctuations, nothing other than the TB controlling idle but I would rule out any intake valves not seating.

So we hit the highway and I had my torque app loaded and once we settled at 60 MPH, I noticed I had to slightly increase pedal pressure to hold 60, a little more than mine but it was noticeable. This is what I had at right around 60, flat ground, steady speed.

Screenshot_2015-10-09-01-15-27.jpg

Granted calculated load can be sensitive, 95 is very high for a steady 60 mph cruise so the engine is just working too hard to maintain a steady speed, also only 7 to 8 inches of vacuum is quite low so that's a huge factor also.

I asked if he had 4WD and he said yes, (sorry I wasn't aware of the selector location on the TB so I didn't see it). Not to the fault of the OP, as he was not 100% clear on the 4WD operation but it was in A4WD. This will engage the front disconnect and add drag to the driveline.

This was my screenshot after I put it in 2HI

Screenshot_2015-10-09-01-17-10.jpg

Another screenshot showing that the fuel trims seem good as well as the O2 operation.

Screenshot_2015-10-09-01-15-47.jpg

On my envoy I have about 45-50% on the load at 60 but it's also a SWB and I have LRR tires. Now we are onto something as this will likely impact the mileage positively. The other thing that may have an impact is the aftermarket wheels and tires. I don't know for certain as of yet but with my couple years working with tires, generally the heavier 20" rims with non LRR tires will negatively impact mileage. This may not be the case here, but it's a safe assumption that they could cost the OP 1 to 2 MPG, but that's not confirmed.

Now also we have the HWY speeds at cruise as a factor, these platforms will drink fuel when we venture above 70-75 MPH. I know for a fact if I go from a decent 20 MPG at 55-60 MPH, i will certainly fall to about 17 MPG at around 80...maybe slightly less.

So for now, we have the OP using 2HI and hopefully we will get an improvement over the next few tanks.

Again, it was cool to meet up, wish we weren't so pressed for time but I appreciate him and the significant other in taking the time to meet.
 
Last edited:

littleblazer

Member
Jul 6, 2014
9,265
On the pedal pressure, I've noticed I need to use a bit more on the highway in the envoy and load is a tad higher according to torque as well. But the envoy has 3.43s vs 3.73s in my tb. And the envoy gets 24-25 on the highway at 75. Not saying that was it but iirc there are 3.43s in that truck.

Good report though. That is something I missed, the selector... I was able to snug up a couple of loose bolts on the manifold back in july. There were about 3 that were loose. And I remember the tap that you are referring to but I think I decided it was just piston slap as it almost completely went away after a little while. It didn't sound like something to worry about. Hopefully that nets 2-3 mpg and then it should be about right. Members getting together and helping other members and everything. It is a good thing. [emoji106]
 

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