Crappy gas mileage... out of ideas
02-22-2018, 09:55 PM
#1
Junior Member
Thread Starter
Crappy gas mileage... out of ideas
I religiously check my gas mileage at every fill up, and today's number has me confused and a little pissed.
I was getting 13-14mpg pretty consistently, and figured I'd do a tuneup, with new plugs (Motorcraft SP-546), and new coils (MSD Street Fire coils). No change in gas mileage over the past month or so... which was very disappointing.
After filling up the tank today, I did the math... twice just to make sure I didn't make an error. I got 12.3mpg. WTF???
I'm fresh out of options on what to do at this point. Anyone have any ideas what could be wrong? Engine runs strong and idles smooth. No cam phaser issues, no exhaust leaks, no codes. I'm using either 89 or 92 octane with no apparent change or improvement with either octane rating.
I was getting 13-14mpg pretty consistently, and figured I'd do a tuneup, with new plugs (Motorcraft SP-546), and new coils (MSD Street Fire coils). No change in gas mileage over the past month or so... which was very disappointing.
After filling up the tank today, I did the math... twice just to make sure I didn't make an error. I got 12.3mpg. WTF???
I'm fresh out of options on what to do at this point. Anyone have any ideas what could be wrong? Engine runs strong and idles smooth. No cam phaser issues, no exhaust leaks, no codes. I'm using either 89 or 92 octane with no apparent change or improvement with either octane rating.
Last edited by NChoy; 02-22-2018 at 09:58 PM.
02-23-2018, 03:42 AM
#2
05 5.4l 3v s.crew lariat
how much load are you carrying
It makes a big difference . I carry a lot but shes a working truck . I empty her out now and then and she gets real frisky.
02-23-2018, 07:01 AM
#3
Moderator
Winter blend gas?
02-23-2018, 08:05 AM
#4
crappy gas mileage???? I get 11.8 I don't see an issue its a heavy brick with a huge engine. Its going to be crappy. All kinds of things come into account driving style, roads, inclines, tire pressure, tire wear, gas, air density. crap its everything. I wouldn't worry about it drive it till the wheels fall off. If you are really worried about gas milage get a Prius as a daily.
02-23-2018, 08:18 AM
#5
Mark
iTrader: (1)
Clean the throttle body and Maf with proper cleaners.. change fuel filter..disconnect battery during this maintenance and re-connect when done.. do re-learn procedures...this will re-set fuel trim levels. You are wasting your money on anything above 87 oct. unless you have a tune.
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digitaltrucker (02-24-2018)
02-23-2018, 08:34 AM
#6
LightningRod
Like @redfishtd asked, "how much load are you carrying"? With those integrated USB chargers, aux input for iPod/iPhone you got on there, you probably downloaded too much music and data! 
"LOL". But I wouldn't go as far as @jaiello suggests!
SERIOUSLY. I agree with @jaiello, 12.3mpg is really not bad - especially being down 1 to 1.7mpg from norm. All the varying conditions as ratio of city/hwy or driving conditions (speed/temp/head wind) or route (hilly/level) can very easily make that difference.
You did not mention miles or other engine health. My 2004 5.4l Lariat is 2WD, stock lift- wheels-tires etc, and it will not beat that much (.5mpg) on average. And I have seen it below 12.3 with 25%-30% increase in city driving.
@techrep is 'RIGHT' again! I would just add that 92 octane fuel does not contain more energy than 89 octane, or 87-88 for that matter. No more BTU in it. That rating is an inverse rating of ignition point (pressure/temperature) and how 'fast' it burns. Higher octane = higher presure/temperature before it ignites, then it burns slower. That would make one think it is not as 'potent'. But your PCM monitors engine 'labor knock' constantly in a closed loop fashion exactly like O2 sensors -v- injector pulse width, or cam retard position -v- PCM requested retard. If the PCM detects pre-ignition, it will decrease ignition timing AND adjust cam retard to stop the pre-ignition as determined from the 'Knock Sensors'. The NET result of this _can_ be a small but measurable improvement in milage (just not enough % difference to justify the difference in fuel cost).
The reason I mention all this ^^^^ malarky. I had a 'very' noisy A/C compressor on my truck - Never connected the two, but had noticed Knock Sensor voltage on Bank 1 consistently ran very much higher than bank 2. When I changed the A/C compressor - I noticed it came down to normal / even with Bank2. I was VERY SURPRISED the Knock Sensor could sense vibration coming from a bad bearing in front of the engine.
After replacing the A/C compressor, I noticed a difference in power responsiveness ---- and "I THINK" (though we can convince ourselves of mis-truths sometimes) I noticed an improvement in mileage. I definitely CAN see ignition timing is VERY sensitive to Knock Sensor voltage by monitoring live data on them both. You might analyze that as a possibility. Increasing timing and adjusting retard both have an impact on performance, power, efficiency - and mileage. So try to keep the engine as quiet as possible and free of vibrations. Just a thought.
"LOL". But I wouldn't go as far as @jaiello suggests!SERIOUSLY. I agree with @jaiello, 12.3mpg is really not bad - especially being down 1 to 1.7mpg from norm. All the varying conditions as ratio of city/hwy or driving conditions (speed/temp/head wind) or route (hilly/level) can very easily make that difference.
You did not mention miles or other engine health. My 2004 5.4l Lariat is 2WD, stock lift- wheels-tires etc, and it will not beat that much (.5mpg) on average. And I have seen it below 12.3 with 25%-30% increase in city driving.
@techrep is 'RIGHT' again! I would just add that 92 octane fuel does not contain more energy than 89 octane, or 87-88 for that matter. No more BTU in it. That rating is an inverse rating of ignition point (pressure/temperature) and how 'fast' it burns. Higher octane = higher presure/temperature before it ignites, then it burns slower. That would make one think it is not as 'potent'. But your PCM monitors engine 'labor knock' constantly in a closed loop fashion exactly like O2 sensors -v- injector pulse width, or cam retard position -v- PCM requested retard. If the PCM detects pre-ignition, it will decrease ignition timing AND adjust cam retard to stop the pre-ignition as determined from the 'Knock Sensors'. The NET result of this _can_ be a small but measurable improvement in milage (just not enough % difference to justify the difference in fuel cost).
The reason I mention all this ^^^^ malarky. I had a 'very' noisy A/C compressor on my truck - Never connected the two, but had noticed Knock Sensor voltage on Bank 1 consistently ran very much higher than bank 2. When I changed the A/C compressor - I noticed it came down to normal / even with Bank2. I was VERY SURPRISED the Knock Sensor could sense vibration coming from a bad bearing in front of the engine.
After replacing the A/C compressor, I noticed a difference in power responsiveness ---- and "I THINK" (though we can convince ourselves of mis-truths sometimes) I noticed an improvement in mileage. I definitely CAN see ignition timing is VERY sensitive to Knock Sensor voltage by monitoring live data on them both. You might analyze that as a possibility. Increasing timing and adjusting retard both have an impact on performance, power, efficiency - and mileage. So try to keep the engine as quiet as possible and free of vibrations. Just a thought.
Last edited by F150Torqued; 02-23-2018 at 08:38 AM.
02-23-2018, 08:50 AM
#7
Fuel filter ever been changed
Edit: just saw that techrep mentioned this
Edit: just saw that techrep mentioned this
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02-23-2018, 08:55 AM
#8
Super Duper Senior Member
02-23-2018, 10:25 AM
#9
Renaissance Honky
That kind of mileage drop can be as simple as filling up at a different pump with a different nozzle and/or different grade where the car is parked. If it keeps up at the same pump across three or more tanks, then you have a problem.
02-23-2018, 10:49 AM
#10
