Bad Drop In Gas Mileage!

[bassadict69]

I have always gotten about 14-14.5 mpg in my truck as long as I didn't tow my boat.

 

My last two tanks, I got between 12 & 12.5 mpg. What the hell?

 

Driving has been the same usual...no towing, same roads, same speeds, etc.

 

Plugs were changed about 2 months ago. Last weekend, I took the MAF sensor/screen out & sprayed it clean with MAF cleaner. It did not look dirty but I did it anyway since I had never done it.

 

Did I mess something up? I never touched anything inside the MAF other than with the spray.

 

What else do I need to check? This mileage sucks.

[jaybyrd]

Since it seems to coincide with the MAF cleaning perhaps try disconnecting the battery and letting the computer relearn everything, unless you removed the battery cable while doing the cleaning than it would have no impact. Did you change the plugs yourself? Were they gapped the same as the old ones and were they the same plugs? Seems either or both are related to the drop spark and air with fuel to combust. Too coincidental not to be related.... My 2 cents for what its worth.

[ken1mod]

O2 sensors can really affect mileage.

 

Ken

[Mighty HD]

same thing happened on my 07 classic.

 

I was running 14-15ish, once it warmed up outside my mileage is now between 8.5 and 10.5.

 

I'm pretty sure it has to do with the summer / winter blends of fuel.

[Nytemare]

did you replace the old wires when changing the plugs? You could have fractured a wire when pulling them off, now your missing on one cylinder.

[bassadict69]

Wires were not changed. I had a local small shop replace the plugs. It is a guy I use routinely & trust. We used AC Delco plugs which I understood as being pregapped. Were they not?

 

I will try the battery disconnect this weekend. Maybe that is all there is to it.

 

I will also check the wires...I guess first I need to make sure all the wires are properly on the plugs also.

[C & A s Dad]

James, you will see that most Techs will insist on changing the wires when they change the plugs. You will typically see physical damage to a wire or two but even if you cannot see the damage, they likely have some internally.

 

When you cleaned the MAF sensor. You did not actually remove the screen and sensor from the plasitc case did you? If you followed the directions and used the product sparingly, this should not have damaged anything. I know CRC's instructions say to let the MAF dry completely before plugging it back up.

 

Depending on your miles, I would consider the O2 sensors as previously mentioned.

 

Where the heck is Haughton, LA? I have been traveling most of rural LA for several years and cannot remember seeing Haughton.

[bassadict69]

James, you will see that most Techs will insist on changing the wires when they change the plugs. You will typically see physical damage to a wire or two but even if you cannot see the damage, they likely have some internally.

 

When you cleaned the MAF sensor. You did not actually remove the screen and sensor from the plasitc case did you? If you followed the directions and used the product sparingly, this should not have damaged anything. I know CRC's instructions say to let the MAF dry completely before plugging it back up. I did not remove it from the case. I just shot the spray through the screen & then also from the back side. I let it sit for about 10 minutes before putting it all back together.

 

Depending on your miles, I would consider the O2 sensors as previously mentioned. This has been mentioned several times. Where are they located? How do you change them?

 

Where the heck is Haughton, LA? I have been traveling most of rural LA for several years and cannot remember seeing Haughton. Haughton is East of Bossier City which is east of Shreveport in the N.W. corner of the state.

 

I appreciate all the suggestions & help on this!

 

 

[C & A s Dad]

You have 4 O2 sensors all in the exh pipes. They look very similar to a spark plug just a little larger. In some cases you cannot get to them with an open ended wrech so you have to have a special socket designed for them. It is a socket with a slot in the side to allow for the wire that is made on to the sensor. The socket is not very expensive but the sensors are. If you do change them, I would highly recommend NTK for your truck as the factory sensors in your truck are likely NTK. Bosch and Denso are also used as OE and would be fine as well. Just be sure you do not get some off brand universal style sensors. You want OE Form, Fit and Function.

 

Now I know where you are, between Minden and Bossier. We (CARQUEST) do not service that area of LA yet. I have traveled through there some but do not have much reason to go into the NW corner.

[bassadict69]

Yep, that is us...

 

I will keep the O2 sensors in mind, First I want to check everything else & make sure it isn't something simple...and CHEAP!

[bassadict69]

Filled up again today at lunch...205 miles & just over 16 gallons to fill back up...12.78mpg

 

I checked all the wires...they all seemed to be tight on the plugs & the other end of the wires were connected good also.

 

I plan to try to get the wires & replace them this weekend...

[HyperBuzzin]

You make no mention of a 'check engine' or 'service engine soon' light, but I'd have to guess the O2 sensors also.

[bassadict69]

You make no mention of a 'check engine' or 'service engine soon' light, but I'd have to guess the O2 sensors also.

 

I have gotten NO SES or check engine lights. With an O2 sensor problem, would my milage drop suddenly or over a period of time.

[VMax2007]

You make no mention of a 'check engine' or 'service engine soon' light, but I'd have to guess the O2 sensors also.

 

I have gotten NO SES or check engine lights. With an O2 sensor problem, would my milage drop suddenly or over a period of time.

 

 

Ever smell gas? Maybe you have a fuel leak?

[bassadict69]

I did think of that with the way these BFG AT's throw rocks. I climbed all over & under the truck & found nothing...not even an oil leak