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Poor fuel mileage

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poor mpg
14K views 39 replies 9 participants last post by  BadDog38 
#1 ·
I have a 2017 Chevy Traverse. A while back my mass air flow sensor had went out. I didn't know it was the mass air flow sensor right away, it just lit up the check engine light and started not wanting to accelerate and seemed like the engine was choking. I started with the air filter, replaced that, then I went and had it plugged in to the reader and it came back my purge valve was no good, replaced that, still had the same issue, just kept getting worse. Went and plugged it back in again and results were bank 1 was running to rich. I wasn't really sure at that point so I started watching videos and stumbled across one that said it could be the Mass Air Flow Sensor, replaced that, and fixed the issue right away. Before this all happened I would average a out 17.3 mpg but during the time spent figuring out what was going on the mpg had dropped to around 5 or 6 mpg. After replacing the sensor it jumped back up to 12 mpg but never any more then that. Now, about 3 months later I'm getting 9 mpg. I've checked my air filter multiple times as well as the housing and intake tube, and replaced my spark plugs. What can I do to fix this issue. No check engine light is on and the rig seems to run just fine other then the mileage.
 
#2 ·
I started losing mpg on my Tahoe around 70k miles. Changed plugs first then the O2 sensors at 80k miles and got back 2-3 mpg with the O2 sensor change. That's a big deal on something that only gets 18-19 mpg then drops to 15 mpg. O2 sensors read fine on scan tool and did not set any codes either and it ran and towed like a champ. AC sensors only if you go that route. Hopefully you used a AC Delco MAF, aftermarket sensors are garbage.
From now on my fleet is getting it's plug and O2 sensor changes at 80k miles.
 
#3 ·
So you think I should change out the O2 sensors?? If so I start with the closest to the front of the car right?? Or do I just change them all at once?? Also no I didn't use AC Delco, I can't remember the brand off hand. Should I change it out again and put the AC Delco MAF in??
 
#4 ·
I'd put the AC MAF in first and see how it runs. Rock Auto is my go to for AC parts, box store junk only if I'm stuck for a temporary fix.
If your miles are up there then the O2 sensors next if mileage doesn't improve, the one's closest to the engine are the ones that control fuel mixtures. O2 sensors get ''lazy'' over time, how many times I've seen people post up pictures of sensors with it's end ''cage'' melted off and sensor was still not coding out.
 
#9 ·
at 100,000- I replaced all 4 of my O2 sensors.
I was NOT having any issues.
At 100K I did a bunch of maintenance. (plugs, oil, filters, struts, brakes, O2 sensors).
My Traverse continues to give great mileage.
Im about to hit 161,000.
This week with driving on the freeway- 55-60, this tankful is giving me 22-23 MPG DIC.
 
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#14 · (Edited)
speaking of lifetime guarantee....
At 161,000- I still have the factory rear brake pads. maybe 20-30% left. The wear indicator still not close to the rotor.
Early models came with Akebono brake pads. Really nice pads. Low dust.
I could get some auto part pads with lifetime warranty for $20-$30...
Since Im about to flush the brake lines (I last flushed 5 yrs ago).... I ordered Akebono rear brake pads. I figure theyll last another 160,000 miles.
$45 on rock auto, with tax and delivery- $55. dont want to mess with the cheapies.
The pads should be delivered today.
I also bought the AC DELCO brake fluid that helps quiet the brake pedal squeek.
I did this 5 yrs ago- and it did quiet the noise. Eventually it returned. The part # for the ACDELCO fluid has been updated. Pep Boys actually had it in store.
 
#19 ·
how about dragging brakes?
Coils... I personally would stay with OEM. the 09s had Bosch, my 2010 Denso. Delphis? I have no input on those.
Im at 164,000 and still on the factory coils.
Recently replaced the factory rear brakes with Akebono... but the factory stainless steel brackets had some buildup on them... so yours may not be allowing the brake pads to smoothly move back and forth easily.
You say youre going to replace the MAF sensor- but have you ever cleaned it?
In city I can get lows of 15-17 lately.
not much use of the AC.
About 1 month ago- I gassed up and hit the highway- headed towards San Diego.
Then I ran into an accident/backup that delayed me for a while.
But I had been going at an easy 55 till the backup.... this is the highest... then it went downhill from being stuck in traffic- stop and go.

Have you recently gassed up and hit the highway for a drive where youre in 6th gear... easily cruising along in the right lane? Engine purring along at 1500 rpms?
It would be interesting to see what your vehicle registers. Is your vehicle going into 5th and 6th?

 
#20 · (Edited)
how about dragging brakes?
Coils... I personally would stay with OEM. the 09s had Bosch, my 2010 Denso. Delphis? I have no input on those.
Im at 164,000 and still on the factory coils.
Recently replaced the factory rear brakes with Akebono... but the factory stainless steel brackets had some buildup on them... so yours may not be allowing the brake pads to smoothly move back and forth easily.
You say youre going to replace the MAF sensor- but have you ever cleaned it?
In city I can get lows of 15-17 lately.
not much use of the AC.
About 1 month ago- I gassed up and hit the highway- headed towards San Diego.
Then I ran into an accident/backup that delayed me for a while.
But I had been going at an easy 55 till the backup.... this is the highest... then it went downhill from being stuck in traffic- stop and go.

Have you recently gassed up and hit the highway for a drive where youre in 6th gear... easily cruising along in the right lane? Engine purring along at 1500 rpms?
It would be interesting to see what your vehicle registers. Is your vehicle going into 5th and 6th?

Brakes don't seem to be an issue as I just put new rotors and pads on her 9K miles ago and all the calipers checked out as well as cleaned and re-greased the slide pins. Used the AC Delco rotors all around and Akebono pads as well. Don't see any change in deceleration when letting off or pulling side to side and no excessive brake dust on any one wheel. I've cleaned the MAF and actually just cleaned it about 2K ago when I pulled the intake boot and cleaned the oil out as well. As to the fill-up and highway mileage, we just took a trip to Beaumont (about 2 hours away) from Houston for my nephews graduation last week and the best I could muster with 70-75 average speed and flat highway (no hills) with no traffic and easy acceleration (keeping RPMs down) was 18-18.5 for the whole trip. I used to be able to get 20-22 with no problem. Trans shifts fine and tires are brand new (properly inflated as well) - was getting same reduction in MPG with the older tires so that's not the difference here. Kind of stumped as there is no codes and car idles, starts and runs fine, just MPG has dropped? I figured MAF is a good start as it directly controls the Fuel Trims and for $50 is not a bad diagnostic tool and I don't feel bad for throwing parts at it as it can't hurt to have a new OEM MAF on a car with 125K Miles anyway. If MAF and Intake Gasket don't help, I'll throw some new coils at it and if nothing changes, I'm stopping there and just living with the slightly reduced MPG as the car is not worth throwing more and more parts at it without knowing for sure.
 
#22 ·
Yes - the PCV is functioning normally and I replaced and drilled out my PCV valve on the back VC last summer. I've also replaced the o-rings on the PCV tube that connects to the top of the intake and the PCV valve.
 
#23 ·
Okay guys, quick update, you're going to think I'm crazy but it looks like the culprit was the MAF sensor. I noticed today (before replacing the MAF) that when driving around the motor was idling higher than normal and was steady around 800 instead of the 600 stock idle. I didn't think anything of it really (other than I thought it was higher than normal) until I replaced the MAF as right off the bat it started idling smooth at 600 on the button without fluctuation and always returns there while stopped and also idling like at a light or in a parking lot. I also was able to drive about 30 miles(ish) and noticed the MPG's climbing rather rapidly on the DIC (just reset it yesterday at fill up). Time will tell if the MPG's go up over all and I'll see how it responds this week. Also, I noticed the shifting seems a bit smoother and it seems to shift at lower RPMs. I never had any MAF codes and the car actually didn't run poorly, but I'm shocked so far that the MAF seems to be the issue and maybe just getting weak or old (125K)? Also, YES - I did clean the MAF with proper MAF cleaner and let it dry a few hundred miles ago with no change.
 
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#24 ·
Glad to hear you got resolution! Sometimes sensors go bad and cleaning doesn't fix them, so I don't think you are crazy at all.
 
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#27 ·
Not sure when the idling a bit higher started as I honestly haven't paid much attention, but I definitely noticed the MPG's drop as I reset the DIC at every fill-up to keep track of it. My presumption is the shifting was also affected a bit and shifting a bit higher as well. It's still working and idling great with the new MAF and the MPG's are still climbing. Guess MAF's can get lazy without throwing a code just as O2's can as well, just strange to me.
 
#30 ·
MAF also measures intake air temp. as well as air flow. In the '80's they used to use a speed/density mapping system before going to the MAF / intake air temp method. Had a Z24 Cavalier with the speed density setup.
 
#31 ·
Yup - my 13' BMW X5M - is SD tuned as well as it doesn't use MAF's with the twin turbo setup. I didn't know our 3.6 used a IAT from the MAF as I'm used to separate IAT sensors as with my 95' TransAm.
 
#33 ·
Would be interesting to see what you find as I'd presume any leak in the gas cap would trigger an Evap code. Wouldn't think a small leak in the evap system would cause poor mileage, but I may be wrong. I've settled with 16-17mpg (mostly 15 if no highway to balance it out) average with our Traverse and 148K on the clock now. I've tried everything, injector cleaner, walnut blasted the intake valves, air filters, cleaned the intake, new MAF (OEM), etc... and my mileage is still just sub-par. I'm wondering if the DI injectors on these platforms get carbon'd up or weak over time causing poor mileage? Car runs like a champ, so tearing into the Fuel Injectors and lines (have to be replaced) is not worth the money unless I have a more serious problem or injector failure.
 
#34 ·
Just replaced the injectors last week hoping for better gas mileage. Like you, having replaced what you mentioned, 1 catalytic converter and all 4 O2 sensors... Only thing I can think of that hasn't been replaced are the actual spark plug wires and purge valve. I have a 2013 Traverse AWD with Odometer 162,355... City did improve day 1 after injector replacement. Was getting 11.x highway but today mpg went up to 13.4 city and creeped up to 20.2 after a total of 80 miles (with cataclean and premium gas). I don't get it. Maybe the computer needs to relearn fuel trims???
 
#35 ·
Did you do the injectors yourself? I've been thinking of taking mine out and using my ultrasonic cleaner (with some FI Concentrate) to clean the tips, but do our DI's have the teflon seals that you need to replace and a special tool to compress them before re-install? Some DI's need these, but not sure on this motor. Also, I'm sure you replaced the rail lines as I've seen they must be replaced when doing the injectors as they are one-time use? Any tips on this job are greatly appreciated.
 
#36 ·
I took it to my go to shop here in Elizabeth, NJ ADD Auto Body. They changed out the injectors with OEM parts. However I am not sure about if they replaced the rail also. I do know that the metal sleeve got temporarily stuck in the head (separated from the old injector) but they got it out and continued without issues.
 
#40 ·
Thats encouraging regarding the intake. Thank you. I would like to open it up if nothing more than to look at the valves to see what condition they are in. I have sprayed valve cleaners down the throttle body several times (watching for smoke out the back) but never getting the thick plumes i see on You Tube lol
 
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