MPG.. OUCH!

[Voymom]

I just filled mine at a 1/4 tank and it took 16 gallons

That sounds about right for me as well. I know I have the issue where the pump stops and I have to wiggle it around to keep it going. I can't remember the name for the part in the truck that causes it, but maybe that's causing him not to completely fill up? I know from 1/4 tank to full I am looking to pay close to $75.00 at almost $3.50 a gallon and with Silver or mid-grade. I know it has cost me upwards of $85.00 for a completely full tank of gas with only 20 miles left on the DIC fuel gauge(miles left per fuel amount).

Just wait lol they are calling for close to if not over $5.00 a gallon this summer!! I'm thinking of buying a camel

Wanted to add- I do believe I have a 22 gallon fuel tank as well.

 

[jham]

Where did it say he put in 11the gallons

ohhh my bad I thought the 10.99mpg said gallons

 

[Gump2773]

Just wait lol they are calling for close to if not over $5.00 a gallon this summer!! I'm thinking of buying a camel

Can we carpool?

 

[gmcman]

My bet is on the plugs. Like others have stated, use ONLY A/C Delco plugs and change them with the motor cold. Use a torque wrench to tighten the coil bolts or just very slightly more than snug if you cannot get one.

Forgot to mention, coil bolt torque is 89 inch-pounds, only about 7 foot-pounds.

 

[Matt]

My bet is on the plugs. Like others have stated, use ONLY A/C Delco plugs and change them with the motor cold. Use a torque wrench to tighten the coil bolts or just very slightly more than snug if you cannot get one.

Forgot to mention, coil bolt torque is 89 inch-pounds, only about 7 foot-pounds.

I'll take your bet. I'll say thermostat.

 

[gmcman]

Not a legal move but I'm gonna raise you a temp sensor.


Not really fair since you should replace both.

 

[Gump2773]

sitting at the shop now having plugs coil thermo air filter and throttle body done. my mechanic said I should easily get 15 city and 21 highway. I guess only time will tell. wish me luck!

 

[gmcman]

Hope so....worst case any other MPG ssues will surely be narrowed down.

Just ensure the temp gauge reads almost straight up afterwards.

Are you changing the temp sensor as well? Since its adjacent to the stat.

 

[MedicatedMike]

Cant guarantee the therm will improve the MPG DRAMITICALY, but I have the exact same thing, well did. The engine never ever once reached 210 (always 2 clicks left of 210 or less) and our MPG is 12.5 with granny driving, and mostly highway! Just got the therm swapped yesterday and it now runs right on 210!! :wootwoot:

*Make sure to test the new one in a pot of water with a cooking therm first! These are a PITA to change! It should open at 190F or just over. I risked not changing the temp sensor bc I was certain it was therm, and I have no fan right now so its much easier for me to get back in there right now, than what it is for most. I too recommend doing both at once though.

Will keep you guys updated on MPG change.

 

[Chickenhawk]

Well, the most important clue from you (and others who may search upon this thread from time to time) is the temp needle.

There is no debate or question - if your temp needle is a couple of ticks to the left, you NEED to change your thermostat and/or your coolant temp sensor. (Might as well do both anyway.)

If the truck runs cold (or thinks it is running cold) it will pump an insane amount of fuel out the exhaust.

This is also why you NEED to get your truck checked for exhaust backpressure. The cat converter is very sensitive, and if the truck was run for a month or two with a bad thermostat (or a minute or two with a serious misfire) then the cat will be getting plugged.

For some reason, we give this advice a lot and people ignore it, listen to their cousin/brother-in-law/shadetree mechanic and don't do this SIMPLE and often FREE test. They will take out your front O2 sensor and screw in an exhaust backpressure gauge. They will take readings at idle and at 2500 RPM. Pressure should be near 0 at idle and less than 4 PSI at 2500 RPM.

I bought my own exhaust backpressure gauge and it will become invaluable as these vehicles age. The cats run on a VERY narrow ratio these days, and the slightest deviation will impact both performance and mileage. (Well, plus we own two Trailblazers in the family too so these simple tools will pay for themselves.)

 

[gmcman]

I don't want to be labeled a temp needle cop ....but I would like to clear something up. I know I make mistakes so if i'm wrong please let me know.

There are alot of threads on the temp needle and it's proper position at normal operating temp. When you are looking at the needle in the driving position it should be straight up, or appear to be. Lean over and look directly at the needle and it shows a tick to the left, this is the position for normal temp. Again, 195 is normal and 210 is straight up, if normal was 210 then it would be straight up when looking directly at it. I just don't want anyone to have to get in and change their stat if nothing is wrong with it. I also agree that are variations in builds and needle placement when the vehicle was built so placement is not exact.

Chickenhawk I also agree that a couple ticks to the left can indicate a problem.

 

[TB2k4]

Chickenhawk I also agree that a couple ticks to the left can indicate a problem.

My stat was slightly left of center. swapped it out, and the shop said an O2 sensor was corroded or misreading, replaced that too. they told me i should get better fuel economy. mow i run at 210. Went from 13.5 combined to 15.1 CITY (daily routine changed) which is better than the sticker 14, never gotten to really test the fuel economy for highway yet.

 

[Chickenhawk]

Yes, there are variations in needle position, especially if the gauge steppers have ever been changed, but gmcman, if that was my vehicle, I would be monitoring my temps with a scan gauge. The thermostat should begin opening around 195, and temps should stay above that point in most conditions, so unless your needle is out a bit more than normal, yours looks more like it is running at 185 to 190.

The gauge is neither linear nor accurate, and GM makes sure it fudges the readouts to not concern drivers, but I tend to get very nervous any time I see one drifting even one tick to the left. The implications on mileage and cat converter life scare me too much for my own good.

 

[gmcman]

I have changed the speedo stepper which entailed pulling all the dials, however I made absoultely certain they went back in the same position, I was overly anal about it. I have driven with a scan tool and the stat opens at 195 and drifts towards 200 and settles right back down at 195..on occasions it falls to about 190 when the fresh coolant is introduced into the block and then right back to 195 and stays there.

The needle is actually just right of center of the first tick to the left. I understand what you're saying but if the stat opens at 195, and the gauge is reading the sensor at 195....why should it read 210? That's a 15 degree difference.

 

[Sparky]

Cuz the gauge aint accurate that's why

I fully expect to replace my stat this summer. Mine has never been above that first tick below 210 since I got it, but mpg has been fine. But a few times it has dropped below almost to 2 ticks below 210, and mpg on a couple tanks has been a little lower than normal. It isn't consistently lower, so I think it is just starting to warn me. That's OK, the thing has 155k miles on it so I'm not going to complain too much. At least, not until I start taking it apart and get frustrated at the engineers who designed the darn thing!

 

[03envoy]

My temp gauge is never at 210. That means my t stat is bad? I know its winter but I don't believe towing my two sleds at 65 for 200miles would still be under 210. I also got about 10.5 MPG's.

 

[UMEXT]

I went from a Tahoe to a Mercury Mariner(first Ford ever) to save on gas.Under 50k and two transmission jobs later I'm back to a real truck,apparently that enormus 16' ski boat of mine was to much for that "soccer mom's Suv" .
I'm getting 16mpg around town and will glady pay it now.When I think of the $$ that I wasted on that POS, repairs,sales taxes,etc. I could have bought an SS,run Hi-test,drove with the E-brake on and still been money ahead...Mike.

Of course, it could be worse. You could, for example, have a current Mustang GT, and have your "5.0" (what the hell was wrong with "302"?) shred itself at 200 miles. (That is not a typo.)

The current 6.7 diesel is also a prize, though those wait till 20K miles before they disintegrate. The people who had the 6.0 were much luckier, they just change EGR coolers and radiators like most people change their underwear.

My 1994 Lumina Z34 was the biggest piece of crap I've ever driven, and I'd still rather have it back than ever own a Ford.

 

[UMEXT]

My stat was slightly left of center. swapped it out, and the shop said an O2 sensor was corroded or misreading, replaced that too. they told me i should get better fuel economy. mow i run at 210. Went from 13.5 combined to 15.1 CITY (daily routine changed) which is better than the sticker 14, never gotten to really test the fuel economy for highway yet.

My T-stat died the night I bought the truck, and the gauge was consistently around 165. Since changing the T-stat and the coolant temp sensor, I'm always at 210 or slightly under. My mileage has not improved one bit--still at 16 combined (on a typical commuting day, I drive about 28 miles city and 40 highway). My lead foot was forever cured by my Grand Prix, may she rest in peace--not only was I running 93 in 2008, but she also had a DIC, which was always set to either average MPG or range.

 

[christo829]

My temp gauge is never at 210. That means my t stat is bad? I know its winter but I don't believe towing my two sleds at 65 for 200miles would still be under 210. I also got about 10.5 MPG's.

How far off 210 is it? More than a needle width or two under 210, and most likely the t-stat is weak.

Also, how is the gauge behaving? If it's fluctuating, the problem could be the ECT instead. If it's low and
steady, it's almost always the t-stat opening too early or never really closing, and not allowing the engine
to get to proper operating temperature.

Good Luck-

Chris

 

[MedicatedMike]

03Envoy---Deff replace your therm when you can. I was the exact same. Ours ran 2 ticks left of 210 and I too thoght it was normal especially with winter time in Michigan, but the 10.5 mpg was buggin me bad and I noticed a rich smell from exhaust.

Changed therm and it runs straight up on 210 at all times now, and mpg went up emmiedietly but only to 13mpg. i noticed the exhaust doesnt start coming out of tailpipe for like 30 secs after starting and it should be at least 14-15 mpg, so im pretty sure our cat conv needs replaced from it running that way too long (previous owner didnt know either).

So replace it asap in hopes to save you even more on a cat conv and mpg!

 

[MichEnvoyGuy]

For those with really bad mpg's and have tried the basics already (tune up, t-stat, tire air pressure, et al):

Consider replacing your bank 1, sensor 1 O2 sensor. If you have over 100,000 miles they tend to get lazy. If they are lazy, your PCM will not be adjusting to the proper air mixture and dollars to donuts you'll be running overly rich.

Check your TB gasket. Mine was flat as a pancake and hardened. Suckin' extra air into the mix will make the engine run lean. Lean mixture = PCM richening it out. A whole $3 at Advance Auto Parts for a new gasket!

Check your intake manifold bolts. Ive read of them loosening over time, just like the exhaust manifold bolts (see below). Heck, when I removed my intake manifold a few weeks ago, 2 bolts were finger loose!

Check your exhaust manifold bolts/manifold. If the manifold is cracked or your manifold bolts are loose, the air leaking IN to the exhaust stream will skew the O2 sensor readings to be lean. Lean= PCM richening the mix. The bolts sometimes loosen over time, like the intake manifold bolts do, too.

Im going off of my own personal experience. I was getting awful mpg's for the last 6 months or so, and found the above with my truck and my mpg's are back to the EPA rating 15/20

 

[03envoy]

03Envoy---Deff replace your therm when you can. I was the exact same. Ours ran 2 ticks left of 210 and I too thoght it was normal especially with winter time in Michigan, but the 10.5 mpg was buggin me bad and I noticed a rich smell from exhaust.

Changed therm and it runs straight up on 210 at all times now, and mpg went up emmiedietly but only to 13mpg. i noticed the exhaust doesnt start coming out of tailpipe for like 30 secs after starting and it should be at least 14-15 mpg, so im pretty sure our cat conv needs replaced from it running that way too long (previous owner didnt know either).

So replace it asap in hopes to save you even more on a cat conv and mpg!

Yep, I will need to replace it. How big of a job is it? And I will hopefully be replacing the cat too.

It's consistent and doesn't fluctuate.

 

[03envoy]

Just found out the owner before me changed it???

 

[DJones]

I got 24.5 MPGs on the highway today. 30 miles and accumalative incline of approximately 130 ft.

 

[Regulator]

I am getting about 11 this will be a fun trip

Sent from my SCH-I510 using Tapatalk

 

[deekster_caddy]

sitting at the shop now having plugs coil thermo air filter and throttle body done. my mechanic said I should easily get 15 city and 21 highway. I guess only time will tell. wish me luck!

So how's it going? Any improvement? Those are some great suggestions by MichEnvoyGuy to try next.

 

[MedicatedMike]

03 Envoy, do you have access to a scan tool? It would be the best way to know exactly when your therm is opening but just bc the last guy replaced it, sadly doesnt mean much. Unless it was in the last few months AND HE TESTED IT IN A PAN OF WATER FIRST. That is the only way I wouldnt be swapping that out first and foremost. Honestly I suspect you have a secondary problem along with it like bad cat conv or o2 sensor just from it sounding extremely similar with what Im dealing with.

I swapped therm and mpg went up by over 2mpg but i expected atleast 4, so Im working on figuring out what else mine needs with me being almost certain its cat conv or o2 sensor (or both).

I recommend swapping your therm more than anything, but a scan tool would provide the ease of mine that you wouldnt do it for nothing.

If you do change it, TEST IT IN WATER FIRST ON STOVE! Should open between 190-200. If it opens before 190, do not install it, take it back and get different brand.

 

[Gump2773]

Well unfortunately Im really not seeing much of a difference. 12 mpg city. Heres is what has been done.

TB Cleaned
New Air Filter
New Plugs
O2 Sensor checked out. OK
Temp Sensor changed
Thermo Changed. Reads half a tick left of 210 (not even half. was almost 2 ticks left before changed.)
Fresh oil change (max life)

I paid $550 for all that to be done so Im gonna have to wait a bit for anything else.

Like I say, Im no mechanic so I dont think I could do Michenvoys suggestions myself.

 

[MichEnvoyGuy]

Like I say, Im no mechanic so I dont think I could do Michenvoys suggestions myself.

And before anybody assumes their O2 sensor is bad or anything else I mentioned, I have to let you know that I did use my EQUUS 3130 handheld.. it cost me about $179 5 years ago and its worth every penny. It reads live data from most of the sensors that have helped me diagnose and troubleshoot along the way. The prices have comedown a ton and you can get a used one for mega cheap. I really recommend some type of OBD2 scanner that reads live data if you are going to own a T360. lol.

I made a thread a few weeks ago about my fuel trims. My long term fuel trim was +13.1 which means the PCM is adding fuel and pulsing the injectors longer to richen the mixture, as the feedback system was reporting a lean mix.

Well, I started poking around. Yes, my exhaust manifold was making noise again I knew it was loose. I tightened it down real good. 4 or 5 bolts were really, really loose. This will let fresh air get sucked into the exhaust and skew the O2 sensor as a lean mixture. Once I tightened the bolts, my long term fuel trims started decreasing. Now I was down to +10! Still very high but at least it went down.

Next I decided that I was going to check my throttle body. Hey, its easier to get at then the intake manifold bolts why not start with the easy stuff right?

My lower 2 bolts on the throttle body were barely threaded in - my fault. Im sure when I had everything apart I forgot to tighten them in the excitement of getting everything back together after replacing my cam actuator. I took the throttle body off and cleaned it, disconnected battery, etc... noticed that my throttle body gasket was FLAT and looked crimped in a few spots. I went to Advance Auto and got a new gasket for $3 or so. Replaced that, tightened the throttle body down, and ran the truck. Drove the truck for a day or two, and my fuel trims are now at -3 which is within specs and a heckuva lot better than having a fuel trim in the positives, especially the double digit positives!!

 

[Gump2773]

I made a thread a few weeks ago about my fuel trims.

Forgive my ignorance. "Fuel Trims" Is this something the live data tracks?

 

[MichEnvoyGuy]

Forgive my ignorance. "Fuel Trims" Is this something the live data tracks?

Yeah. And they are semi-important! They can be very helpful in tracking down a mpg or driveability problem.

Good read here

 

[MedicatedMike]

Great explanation MichiganEnvoyGuy! I have been looking into getting a scan tool but was not familiar with fuel trims either and yes that would be extremely handy in pinpointing. I too have a TB running way too rich.

 

[03envoy]

03 Envoy, do you have access to a scan tool? It would be the best way to know exactly when your therm is opening but just bc the last guy replaced it, sadly doesnt mean much. Unless it was in the last few months AND HE TESTED IT IN A PAN OF WATER FIRST. That is the only way I wouldnt be swapping that out first and foremost. Honestly I suspect you have a secondary problem along with it like bad cat conv or o2 sensor just from it sounding extremely similar with what Im dealing with.

I swapped therm and mpg went up by over 2mpg but i expected atleast 4, so Im working on figuring out what else mine needs with me being almost certain its cat conv or o2 sensor (or both).

I recommend swapping your therm more than anything, but a scan tool would provide the ease of mine that you wouldnt do it for nothing.

If you do change it, TEST IT IN WATER FIRST ON STOVE! Should open between 190-200. If it opens before 190, do not install it, take it back and get different brand.

Yea, I am going to check the t stat (to see how far its off from 210) this week to see where its at, I beleive I may have a bad 02 sensor but, I am not sure yet. I have an advanceautoparts store right down the street that has a scan tool. Will that work? I may have them check for pending codes. The cat I am not excited about doing it, Because isnt it a B*tch to get off? Rusted bolts and whatnot. But, I would like to get a Magnaflow High flow cat...

 

[MichEnvoyGuy]

Just wanted to update... I drove the 'Voy up north this weekend to our cabin in Lewiston, Mich. I used to get 20.5mpg on the highway on trips up there, I go up about a dozen times a year. For the past year at least I dropped to 17mpg on the trips

After all of the work I did I expected some kind of mpg increase this trip to the cabin but wasnt sure of what.

Unfortunately, on the way up Friday night winds were very strong out of the W/NW 15-30mph. Not good for my mpg's as that was the direction I was traveling. The winds were pushing the truck all over the road, was very frustrating. Got 17.8mpg average.

On the way home today, winds behind us 5-10mph. MUCH better. For the longest time I was driving 60-65mph and averaging 21.5mpg. Once I merged onto I-75, I stuck the cruise at 74mph and I ended up averaging 19.6mpg. There was 270 miles on my trip ODO for this tank.

Im sure if I was more conservative with my driving style I would've easily gotten the EPA highway rating of 20mpg. But after having suck-ass mpg's for the last 8-12 months, Ill gladly take 19.6mpg!!

 

[Gump2773]

small update... at half a tank today i was sitting at 129 trip miles. just got home from dinner now sitting at 151 trip miles with 1/4 tank left. I want to kick something.

 

[MedicatedMike]

lol, I feel you.

When we bought truck it was getting 10.5

Took off clutch fan - 11.3

Changed Therm - 12.5 instantly (slowly climbed to 13.0 over next 5 days)

Cleaned TB with deep creep and Seafoam in gas tank - Over last several days has creeped its way up to 13.3!

I know for a fact that the truck was run for a while with a bad therm before we bought it, so I dont know how the cat could be in great shape on top of the odd dent/weld job I noticed on the cat conv. while under there last. Like someone had messed with it before or it was damaged when it was recked few years back by previous owner, so I feel its deff worth investing in a new cat and o2 sensor next.

 

[Gump2773]

Going to fill up in a bit here. Gas light just went on 4 miles ago. Needle is just left of E. got 210 miles on the trip. If I had to guess its looking like 12.8 mpg. Last time I filled up at this position I put 16.3 gallons in. Im wondering if maybe some seafoam gas treatment would be a good idea? Also Im looking to try and find a muffler shop that can test and tell me if my cat is bad hopefully for free.

 

[MichEnvoyGuy]

Since my PCM4Less tune, replacing my O2 sensor and air filter (and a whole bunch of other work that Im not sure made any difference or not but my CPAS went bad and I replaced that too), Im DEFINITELY getting better MPG's now. I got 310 miles out of this last tank and when I filled up it wasnt even empty. It took just over 16 gallons. My DIC said I was averaging 19.7mpg but I think it was closer to 19.3mpg or so. That was 90% highway. Now after I filled up Im averaging 17.7mpg according to my DIC so its slightly lower in real life. Im probably getting 17mpg or so. Not bad for all city driving.

Im going to say having my PCM tuned has helped. And if thats the case, the tune should pay for itself in due time! :wootwoot:

 

[MedicatedMike]

So excited to hopefully change the cat and o2 sensor tomorrow, on top of changing oil to 25k AMSoil Sig Series, that I can hardly sleep. :wootwoot:

Sprayed the o2 sensor with PB blaster and will do again in morning. Planning to buy the special 7/8 open slot socket (as I call them) locally before getting started and I read that a breaker bar and doing it while manifold is hot will likely also be required.

Im saving my Tuned PCM for last so I will know exactly how much it helps.

Thanks again to ROCKAUTO for super fast ship on my new magnaflow cat and o2 sensor. Ordered Monday at lunch and got Wednesday at lunch. Had tons of packing material too for an exhaust pipe which is rare. A+ all around!

And 03Envoy, I will let you know how big of a PITA the cat pipe is to remove.

 

[suburbs]

I got 24.5 MPGs on the highway today. 30 miles and accumalative incline of approximately 130 ft.

From my front door to Denver: 26.3 MPG.
From Denver to my front door: 12.3 MPG.

Cruise control at 70 until I got into the city. 60 miles and 6k in vertical change at the highest.

Better than my little brother in town borrowing the Tblazer, 10 MPG average. Think he might have a little issue with right foot patience.