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Strange Things Lately..

GasHog369

By GasHog369
in Ask A GM Technician

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GasHog369 Senior Enthusiast

GasHog369

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Some strange things lately in my truck going on... I'll try to keep this short and to point. :D

 

For the last year or so my truck has always got 13.7 mpg.. one day i was really punching it trying to get to work and it dropped it 13.6 Right after that its been at 13.7 average mpg and dosent move.

 

For the past 2 weeks once in a while during a cold start up it sometimes will hesitate and then jump up in rpms and idle normal.. if i shut it off and restart, it starts fine.. only happens sometimes after cold start.. At first i was thinking fuel problem like pump or filter...

 

About a week and half ago i filled up with gas and ran my usual choice of lucas fuel treatment. Havent noticed much of any change. except that my gas gauge dint go down much at all since last fill up even after my good amt of driving to work...

 

Heres where the weird part comes in.. bare with me :eek:

 

Today im driving to a side job after work that im in stop and go traffic trying to get there and pushing it a little harder that usual. Get to the house and back in and i notice my average mpg is counting down 9.1 , 9.0, 8.9, 8.8, im like WTF! Remember it dosent move from 13.7! So i turn it off. Turn it back on 8.7, 8.6, 8.5.... So now im pissed, have to work and think about what repair bill is up next.

 

Time to leave the job, I start it up and it keeps dropping , At this point i cant believe it and had to take a video (uploading now..)

It dropped all the way to 6.0! I started driving and it started going up.. Climbing to 7.......8......9.......10.... etc mpg... If i would give it some gas to start moving it , it would drop a tenth of a mpg, and if i let it roll it would go up... Almost as if it was acting like instant fuel economy like on the new trucks... Not Average like what it is..

 

So i got closer to home and got on thruway to average my speed of 60mph and it topped out at 15.8 mpg! Then i got off there and kept it steady at 45-50 and it topped at 16.2 mpg~! :lol: So now i am grinning from ear to ear! By the time i got home, back in my drive way up a steep incline to my parking pad it settled down to 15.8 mpg..

 

So the question is, was there possibly something in the fuel filter , etc, that was restricting mpg and the lucas cleaned it out ? In turn did the comoputer reset itself seeying i had more gas in tank than usual and went down to 6.0 to reset to go back up to my average now?

 

I am bafflled on this and am hoping it is just fixed itself and i am now averaging awesome mileage! :lol: Well awesome for the track record of this pig 5.3.. :lol:

 

Thankyou for reading

 

Thoughts/ opinions?

jro909 Senior Enthusiast

jro909

Posted
Posted

i don't think you have a serviceable fuel filter...it may be a fluke in your pcm...one time i ran a bottle of gm fuel system cleaner and it made my fuel guage bounce for about a minute then back to normal..i would get it scanned, if anything the fuel treatment may be causeing weird conditions in the pcm

GasHog369 Senior Enthusiast

GasHog369

Posted
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Posted

Ive added this all the time in the past tho.. idk... i'll keep an eye on it tomorrow on my way to work. Hopefully it will be ok and not mess up on my drive in...

GasHog369 Senior Enthusiast

GasHog369

Posted
  • Author
Posted

Drove today and averaged 15-16mpg in light to medium traffic.. averaged 14.0-14.5 in heavy stop and go for an hour traffic on way home...

 

Put $40 in gas in just in case gauge is messing with me and it really has less, lol.

 

But i definitely see a increase in mpg according to how much gas i have left according to the gauge. I think the computer was just stuck on 13.7

 

 

Its weird cause some days if i drove like a gramma it stayed 13.7, and other days i put it in tow haul / crazy tune mode (thanx to wait 4 me performance tunes) and drove the shit outta it and it stayed 13.7!

 

I think its back to normal now.. hopefully but ill keep an eye on it. thanx for advice

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