Montero Sport mileage issue

Hello guest and welcome:

It certainly sounds like you've done all the preventive maintenanceand repairs correctly. As long as everything is functioning properly I can only offer two possibilities.

First these computerized contraptions require time to reset themselves up, I'm not sure about the latest generation but the initial generation of computerized engine management controls was set to average over a 28 day cycle, or at least that's how I remember it. I'm sure the battery cable was removed for more than 15 minutes doing the repairs so that is one possibility.

The other is outside temperature and driving time, I noticed this quite by accident with my 2006 Dodge ram, while I was playing around one morning with nothing better to do on an empty freeway I decided to do a instantaneous mileage check with the onboard indicator, the mileage was lower than normal ,at first I attribute it to inaccuracies in the onboard mileage indicator, to my amazement the mileage returned to its normal readings rather abruptly.

I finally realized that this change occurred when the engine reached full operating temperature. During warm-up the engine operates in what is referred to as an open loop state, which means it's running on pre-mapped mixture and timing settings.

Generally the system switches to the closed loop setting once the engine is fully warmed up (I'm sure some systems have some intermediate adjustments), which then uses the feedback from your various engine monitoring sensors to adjust the engine for best fuel economy and emissions.

The last part of this I've pulled off a website, I did a quick check on to make sure I wasn't going to come down with foot in mouth disease, and the engine management systems hadn't changed significantly from the ones I was familiar with.

Two things mentioned on this site were that winterize gasoline has a lower energy content, and that also the vehicle is actually diverting energy to heat the interior, along with some other overhead parasitic costs that come with cold air. I am somewhat unsure of the latter statement, having a significant effect on fuel economy but I suppose it is possible with a high fuel economy vehicle, personally I've never seen that affect, and my avatar loves cold air.

So I am making the assumption that a significant temperature change has occurred since your previous fuel economy readings, this would be especially significant if you're driving relatively short distances, however this is all speculation. I'm including the link I referred to, it may be of interest to you.

http://midlandshybrid.com/the-news/111-winterizing-your-vehicle-warm-up

Hello YWROADRUNNER

Thank you for taiking time to answer my questions.

No problem , I hope some of the information helps. Hopefully you will consider becoming a member of the site, there's always room for a mechanical engineers.

are you sure your timing marks are on the money?that could cause a slight loss in power and fuel economy that most people would not feel.all so which sensor did you replace there are 4 sensors on that car the most important are the front sensors after a 100k or so it's a good idea to change them they are the most important parts that the computer looks at to change injector pulse with and fuel trim if you only change 1 it could affect the readings by working to good.Always use OEM O2 sensors.Did you change you plugs wires and fuel filter?Get back to where you were with fuel mileage then try other things like indexing spark plugs,premium fuel gets you more millage also tire air pressure jack it up 2-4 psi you wont notice any extra tire wear with only 2-4 psi over what it says on the door

Thank you for your comments mr.wrenches

I am not sure about the timing belt marks, I have done it at PepBoys. I do not feel any change in power, only gas mileage. I have ONLY two sensors on my Mitsubishi one before and one after cat, I changed ONLY the one before cat (check engine line code indicated a failure of the O2 sensor before cat). I changed the spark plugs (OEM), wires and fuel filter 4-5 months before, making a huge difference in power not much in gas mileage.

according to my All Data that car with a 3.0 has 3 sensors I was wrong before and may be wrong again.usually all data is on the money if you did not change it yourself to a look at the back of the exhaust manifolds the sensors should be easy to see if they are there. good luck with it that is an easy timing belt to screw up I have done it myself.you can only be wrong 100% of the time