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Nissan Frontier Gas Mileage in tank! HELP

Hi all

Ihave posted this in the forums before, but I have new information on my issue and would like the opinion of the smart people here.

Last November I had a fuel line service done on my 2005 Nissan Frontier. prior to the service I was getting 16 mpg in the city, and 21 on the hwy. Post service I am getting 11mpg city and 16 hwy. This has obviously ticked me off (thank you big oil for 3.20 a gallon), so I am trying to get to the bottom of why this has happened.

Last week I went in for my scheduled maintenance on my truck and had them put the meter on the Mass Air Flow Sensor and found that it was off by quite a bit. The normal for it at 1dle would read 1.3 with the top range of 5 and it was at 4.8 at 2500 rpms it should be close to 4 to the max of 12, and at 2400 rpms it was reading 11.9. These reading are not out of scope, but the mechanic tells me that they are way high for what they should be. He suggested a new sensor, but at 270 bucks I passed at the time, maybe the local salvage yard can get me one cheaper.

The Question is, that sensor being high, I wonder if that is causing the wrong air flow, air temp or the vehicle to run rich like that, therefore causing the loss of mileage. Any thoughts?

Any help on this would be great, and if someone can find the silver bullet to solve it there is a box of good dominican cigars in it for them since my local garage tells me to just suck it up…


That can cause the engine to run rich. It’s a variable in the equation the computer uses to adjust the injector pulsewidths to the engine demand. If the ECU thinks there is more air flow than there really is, it could provide more fuel than you really need.

What I can’t understand is how this could have been a result of the servicing. The MAF sensor is in the air intake and should be unaffected by any fuel line service. The fuel doesn’t even get spraying in until the air gets to the intake ports, way, way beyond the MAF sensor.

Is there information missing here? What caused you to suspect the MAF sensor? Can you tell us more about the “fuel line servicing”?

You can have someone else check the MAF. In fact I would guess that you also have an error code stored in the computer indicating a MAF issue. I would not bother with a junk yard MAF.

BTW you don’t have a K&N Air filter do you???

HI thanks for the help, I checked the MAF when I pulled the air filter and it was half covered in carbon from the service. The service was insterted into a vaccum line, I am not sure what happens from there. I thought the MAF just as a hunch, guess, total out in left field wild arse guess…

Oh, man. I’d be inclined to try cleaning the carbon off the MAF sensor to start.

Man, the fuel doesn’t go anywhere near that area. The air passing by the MAF sensor doesn’t even go through the fuel lines, just blows by the outsides of the injectors picking up fuel spray as it passes and heads past the valves into the cylinders. That becomes your fuel mix. Any “fuel line service” that is injected into a vacuum line won’t go through the fuel lines or the injectors. I’m wondering of the shop injected what should have been injector cleaner into the airstream and it combusted, blowing carbon back onto the MAF sensor.

I’m getting a real uneasy feeling about this one. Anyone else out there have any input? Fellas?

This was for a fuel line induction service? I had it done at wallyworld, and it was gumout material. My garage does something similar, but for a lot of money. they put the cleaner in the vacuum line and it is to clean the valves etc…So you think that some compressed air like from my cpu cleaning kit could clean it out?

Any further thought on why this may have happened?

Question? Is this air flow sensor a hot wire design or a moveable flap design? If you got crud on the hot wires that could not be cleared by the shut off burn off cycle, the sensor should be giving excessively low readings and the computer should be cutting the injector pulse width. If this sensor is a moving flap type, the potentiometer in the meter may be faulty which would drive the computer crazy as it selects the wrong injector pulse memory cells. It would be likely be enriching during startup, acceleration, full power, and other open loop driving conditions.

Keep us updated on the outcome of this.

Sorry, no further thoughts. I still don’t understand why this would have happened. I keep getting the sense that we’re missing a puzzle piece. However, since you know the MAF sensor is providing too high a reading, you might try cleaning it or changing it and see if that helps. I’m not into “shotgun” maintenance, but I am into changing known bad parts before continuing down the diagnosis path.

I don’t really know what you mean by the above statements, sorry computer geek here, but it appears that there are wires or coils inside the sensor. I was wondering if hitting the wires with some air that I use to clean my cpu, if that would be ok. I am willin to try anything at this point.