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Power Train Gas Mileage Musings


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HI All,

I have a 94 Pathfinder XE and a 95 Pathfinder XE.

The 94 used to get @ 16 mpg and had no issues that I can recall....but it rusted badly and is now a parts donor vehicle.

The 95 is my daily driver but ..... it gets about 12 mpg. (This is all highway miles BTW).

My musings are thus. Comparing the two pathfinders and how they drove, it seems like....the 95 has more drag.

When I let off the gas pedal, it decelerates almost as if applying brakes, but not quite. Still, the body kind of hunkers down as it will when you apply brakes and momentum pushes on the suspension.

I am pretty sure the 4wd isn't engaged as I forgot to disengage it one time and over 50 mph, it made a definite noise. It doesn't do that in this circumstance.

Also, at a given highway speed, the 95 runs at a couple hundred higher rpms than did the 94. I.E. the 94 would do about 67 at 2500 rpm's, the 95 will do about 62.

Also, the torque required to accelerate seems to be higher and unless I pay good attention and try to manipulate the power, it won't upshift until about 3000 rpm. If I let off the gas a bit, I can get it to do so earlier but, of course, I lose some acceleration.

Perhaps I have transmission issues? It does shift hard sometimes, and at others @ 50 mph, it may seem to hunt up and down between 4th and 5th but these are rare instances.

I have serviced the transmission and checked the fluid but no adverse indications there.

 

Anyone care to chime in? I would really like to keep it, But at 12 mpg, it's a good candidate for replacement.

 

Thanks

 

Oh, I also posted some months earlier, that when it starts out cold (less than 70 degrees outside) in the morning, it will drive as if in limp mode. If I drive it @ 100 yards, shut off the ignition, and start it again, it drives normally (as described above) and the transmission light flashes the code for no faults. Related? I never got any good answers to that post, but maybe it has a bearing on this one.

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Also, I might suspect cleaning out or bypassing the in-radiator ATF cooler may help (per previous posts about cold temp issues), making sure that the same tires, same oil, same plugs, same wires and a good MAF cleaning might make enough of a difference collectively. Gapping the plugs all the same (to 0.001") and confirming that you don't have an injector stuck open will also help. The only other thing might be a dieing oxygen sensor but that's all I can think of that would actually affect fuel mileage. New plugs and wires?? New cap and rotor?? I'm just throwing those out there since you didn't mention changing them recently.

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Thanks all. I appreciate the tips and I've considered them before. The usual fuel consumption service items do need to be done, but the apparent drag and rapid deceleration when I let off the gas are what got me thinking along other lines. Unless there was a stock gearing change between 94 and 95, I'd assume they were the same. Tires are identical and weight almost identical. Besides we're talking about a 25% difference in fuel mileage.

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That's what I'm thinking, you need to take the wheels off and service the brakes. Do all 4 corners. And repack the front bearings at the same time.

 

Mine gets 16-17mpg even with 33's so definitely something wrong there.

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Wouldn't the brakes have eventually worn and the effect lessened? I've had the vehicle for over 4 years now. Up to now I just figured the poor performance was due to the abuse of the previous owner (I've been improving things as I've been able over the years). Which gear oil? Differential or transfer case? Or both? The front bearings had been repacked last summer.

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I'm not totally familiar with the jatco auto, but most other 4 speeds will coast in high gear. A one way clutch will freewheel when the drive train is being pushed by the wheels.

 

It sounds like it's engine braking, which is usually done by engaging a band or clutch, usually triggered by a drop into low.

 

I'd start with the brakes though. Especially the drums. Most people struggle with them, and I've seen them put together wrong multiple times. My bet is that they're dragging, which is probably making the transmission feel weird when the torque converter tires to lock up.

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