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2.5L ('98-'01) Ok an engine question...


Cowboy Jim

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My little work truck Ranger that I have been building on....I took it out on a bit of a road trip today and clocked the mileage. The 2.5L motor has 322,000 on it, but still runs great. If I change the oil @ 90 days, its still yellow....IE its still tight. With a fresh transmission, 4.88s in the ass end running a 30" tire I am getting about 12 mpg. So here is my question....I dont really care about having a power house of a motor. I just want enough motor to get decent mileage, and 12mpg aint it. I had an RV cammed 350 small block with a 4bbl, headers and such in an S10 and it was getting almost 20mpg. That motor was basically idling that truck down the highway. So, do I go with a fresh 2.5L motor with a small chip, header and fresh air intake and hope? Or just put something with a bit more meat and taters in it? 1 key thing, I DO NOT WANT AN INTERFERENCE MOTOR. NO WAY!!!

Note: When I went to the larger tires, I figured in all of the math and to go back to OEM gearing would have put me at 4.53. I chose the 4.88 so I would have a bit more bottom end. Also tho, I do not have a tach in the truck and with the Yokohama GeoLander mud terrain tires, not a bloody chance in hell of hearing the motor when driving. So I might just be revving it a bit too much and not know it. I was planning to get a tach on it and then try again before I commit to building a motor/trans for this. What RPM range does that little 2.5L motor like to see @ cruise? 2800-3000rpm?

Would like to see 18-20mpg. I have an older 2.8 Chevy V6 here out of the old square body S10's. Its a Y block AKA a torque monster when given a small 4bbl and they do good on mileage. Could go that route if need be.
 
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RonD

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O2 sensors decide MPG and they last 100k miles or 12 years, they are THE ONLY sensors that wear out in miles or time, and will not set a code until MPG is in the toilet, so at 12mpg you are close to a code, but never let it go that far, lol

2000/2001 2.5l makes best torque/power at 3,000rpm

This is a good site for calculating what to expect from engine and drivetrain: https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

4.88 ratio
30" tires
3,000rpm engine
.75 4R44E OD ratio

Should be at 73mph at 3,000rpm

You really want to be about 400rpm lower than peak power for best MPG on the highway, so best MPG with that setup would be at 2,600rpm/63mph in OD

ASSUMING speedometer is correct

Not sure what original tire size was but not 30", lol
So your odometer will probably be minimum of 10% lower than actual miles travelled
If you were using odometer miles to get the 12mpg its wrong
 

Cowboy Jim

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O2 sensors decide MPG and they last 100k miles or 12 years, they are THE ONLY sensors that wear out in miles or time, and will not set a code until MPG is in the toilet, so at 12mpg you are close to a code, but never let it go that far, lol

2000/2001 2.5l makes best torque/power at 3,000rpm

This is a good site for calculating what to expect from engine and drivetrain: https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

4.88 ratio
30" tires
3,000rpm engine
.75 4R44E OD ratio

Should be at 73mph at 3,000rpm

You really want to be about 400rpm lower than peak power for best MPG on the highway, so best MPG with that setup would be at 2,600rpm/63mph in OD

ASSUMING speedometer is correct

Not sure what original tire size was but not 30", lol
So your odometer will probably be minimum of 10% lower than actual miles travelled
If you were using odometer miles to get the 12mpg its wrong
Thank you. You literally answered every question I had. The O2 sensor was last changed back when I took the stone wheels off and switched to rubber. Will def look into that. the little 2.5 has all the power I want or need, but at 12mpg, I should be toting the front tires off the highway in a wheelie down the highway at 60mph. Dont imagine it would be much of a surprise if I said that it wasent quite there would it. lol. On tghe speedo thing, I have a Garmin Traveler GPS rig in my truck and I use the speedo on it and also same for figuring the mileage. But with the re-gear, it came out the Speedo in the dash is 3mph off. lol. Pretty close!
 

RonD

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Problem is the rear axle gearing is not used in a 2000 Ranger for speed calculation
1998-2000 Rangers use the rear axle ABS sensor for speed, so strictly tire size mattered
It is just using rear axle rotation not the driveshaft
27" tire will have 776 rotations per mile
30" will have 695 rotations per mile

Older and newer Rangers did use drive shaft RPMs for speed, so rear axle ratio and tire sizes both would matter, and yes you could change rear axle ratio higherto off-set larger tire to keep speedometer close

So its odd its only 3mph off, in a 2000 Ranger
Should be at least 10% off, so when showing 50mph, actual speed would be 55mph

Anyway the 12mpg isn't right even with the taller stance and larger tires
2.5l automatics should be 18mpg around town, so maybe 16 with your setup
 

scotts90ranger

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There's something wrong... the lowest I've ever seen on my '97 2.3L ranger has been 19mpg even idling a lot and screwing around on the farm... it's easy as pie to get my '00 V8 explorer to 9mpg if you're going slow around the woods or running it hard but even that thing at 5k pounds averages 16mpg in mixed driving...

I would do a compression test or leak down test to see if everything is sealing right on the cylinders. The injectors could be going bad. I would invest the $13ish in one of those blue OBD II deals so you can run the Torque app and watch the fuel trims and other stuff...
 

Cowboy Jim

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There's something wrong... the lowest I've ever seen on my '97 2.3L ranger has been 19mpg even idling a lot and screwing around on the farm... it's easy as pie to get my '00 V8 explorer to 9mpg if you're going slow around the woods or running it hard but even that thing at 5k pounds averages 16mpg in mixed driving...

I would do a compression test or leak down test to see if everything is sealing right on the cylinders. The injectors could be going bad. I would invest the $13ish in one of those blue OBD II deals so you can run the Torque app and watch the fuel trims and other stuff...
Well on the cylinders, as I mentioned above, its tight. Injectors being worn is a possibility. I have a cheap scanner for getting codes and such but could you share a link for one you would suggest that would show what you speak of?
 

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Download the torque app and see if it works with the scanner you already have. Torque lite is free.
 

Cowboy Jim

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Download the torque app and see if it works with the scanner you already have. Torque lite is free.
The scanner I have is just a POS Autozone one from yrs ago. Also, this is primarily a farm truck....as in no cat converter. So on the 02 sensor placement, how far downstream in the exhaust should I weld up a bung and put one in?
 

RonD

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The scanner I have is just a POS Autozone one from yrs ago. Also, this is primarily a farm truck....as in no cat converter. So on the 02 sensor placement, how far downstream in the exhaust should I weld up a bung and put one in?
Without a Cat the downstream O2 can't work as designed
Google: downstream o2 sensor bypass

Never tried any of these "tricks" so can't say what to expect

The default for any engine computer is to run a richer mix, because its safer than a leaner mix which will cause engine damage
The downstream O2 plays a part in Long Term Fuel Trims

FYI
O2 sensor can only "see" Oxygen in the exhaust, and only after its heated above 600degF
The upstream O2 "tells" computer the oxygen level of the current air/fuel mix after it is burned in the engine
This gives the computer instant feedback if the air/fuel mix was too rich(low oxygen) or too lean(high oxygen)

Downstream O2 reads oxygen levels after the Cat converter(s)
Cat converter runs hot and uses unburned fuel and any remaining oxygen in the exhaust to burn up pollutants in the exhaust
So downstream O2 will show low oxygen levels

If downstream O2 is not showing low oxygen levels the computer will run the engine richer to try and "heat up" the Cat with extra unburned fuel

You can't just send the computer a fixed "low oxygen" signal because computer is constantly varying air/fuel mix to test upstream and downstream O2s to make sure they are responding as designed
 
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Fast Eddie

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O2 sensors decide MPG and they last 100k miles or 12 years, they are THE ONLY sensors that wear out in miles or time, and will not set a code until MPG is in the toilet, so at 12mpg you are close to a code, but never let it go that far, lol
This is the first I'm learning of this. Not that I don't believe you. I do. I'm at 97k. According to your above, I better plan on a change soon. My greatest fear here is not being able to get the old ones out due to rust and corrosion. Will a simple penetrating oil take care of it or am I introducing a fire hazard by doing that? TIA
 

RonD

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Penetrating oil residue should evaporate on warm up, wouldn't spray it on an already hot surface

Yes, O2 sensors are the ONLY feedback the computer has on its air/fuel mix calculations for fine tuning MPG
And they start to go Lean after 100k or 12 years so cost you money in wasted fuel
 

Cowboy Jim

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The more
Without a Cat the downstream O2 can't work as designed
Google: downstream o2 sensor bypass

Never tried any of these "tricks" so can't say what to expect

The default for any engine computer is to run a richer mix, because its safer than a leaner mix which will cause engine damage
The downstream O2 plays a part in Long Term Fuel Trims

FYI
O2 sensor can only "see" Oxygen in the exhaust, and only after its heated above 600degF
The upstream O2 "tells" computer the oxygen level of the current air/fuel mix after it is burned in the engine
This gives the computer instant feedback if the air/fuel mix was too rich(low oxygen) or too lean(high oxygen)

Downstream O2 reads oxygen levels after the Cat converter(s)
Cat converter runs hot and uses unburned fuel and any remaining oxygen in the exhaust to burn up pollutants in the exhaust
So downstream O2 will show low oxygen levels

If downstream O2 is not showing low oxygen levels the computer will run the engine richer to try and "heat up" the Cat with extra unburned fuel

You can't just send the computer a fixed "low oxygen" signal because computer is constantly varying air/fuel mix to test upstream and downstream O2s to make sure they are responding as designed
I am reading of this the more I am thinking about building that 2.8 Chevy V6 I got and stuffing that in it with a carburetor and all analog. This 2.5 has 2 of these 02 sensors I am seeing. 1 is directly in the exhaust manifold @ the engine and then the other is downstream of where the cat was.
 

RonD

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Yes, upstream O2 is closest to the engine, computer uses that to fine tune air/fuel mix for best MPG
MPG would start to go down after 100k miles or 12 years as this O2 ran out of chemicals

Downstream O2 is after the Cat(s) and is used to make sure Cat(s) are still working, if Cat(s) is failing, or missing, then computer has to run engine richer to try and "make the Cat work"


Engine size swap is never easy, lots of bits and pieces add up, lol

But a 2000 4cyl Ranger doesn't have the issue of PATS or speedometer
Really just need the new engine/trans and mounts, drive shaft conversion for GM
Fuel pressure regulator or fuel pump change for carb conversion
 
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ericbphoto

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Might have been 2 sensors upstream of the cat. One for left bank of cylinders and one for the right bank. Then one downstream after the cat.
 

RonD

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Its a 2.5l 4cyl Ranger, so just the one upstream and one downstream O2
 

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