02 Ford Ranger - MPG City 11 / Hwy 20

[carmstrong227]

Trying to figure out why my city mileage is so much lower than my hwy mileage on my 02 Ford Ranger - V6 4.0 - 4x4, which has just under 170,000 miles on it. The best I have gotten in the city is 11.3, and hwy 20.6. Thats pretty good for hwy, but my city mileage is horrible. What I have done thus far to try to improve my mileage.

-BG Fuel/Air Induction
-K&N Air Filter
-New plugs (Olds ones didn't looked too bad)
-New Fuel Filter (Filter was a dirty, will change again next oil change)
-New PCV Valve and hose assembly (Hose was torn)
-All 4 catalytic converters removed (They were clogged, and causing 10lbs of back pressure). Hwy mileage improved from about 18 to 20, city mpg did not.
-Muffler was removed (Busted/rattling baffle)
-2 resignators were added (To provide some back pressure, and to quiet exhaust)
-MAF Sensor cleaned
-Installed new shocks (The old one's had 165,000 miles on them)

Normal maintenance is performed regularly: Oil changes, tire pressure, etc. Engine runs very nicely/smoothly. No stutters, misfires, weird noises of any kind.

When I let off of the brake, the trucks idle pulls the truck pretty fast, without me pressing the gas pedal, which indicates no/minimal friction within the breaking mechanism and drive train. Idling RPM ranges from 550-850

I've talked with a local mechanic, and he is at a loss. He mentioned that is may be stuck in 4 wheel drive, but I tested that as well when the roads were wet. Gased it, and only the rear wheels were spinning.

Additionally, I drive like my grandpa! He's 73, so yeah, very slow! I've even practiced Hypermilling, which resulted in the 11.3 mpg, from a previous best of 10.8.

I believe the only thing I haven't done is change the spark plug wires, ignition coil, and maybe get a new ECM programmed from fuel efficiency...

If anyone has any suggestions as to what may be causing this gap between city and hwy mpg, I would greatly appreciate them! Thanks in advance.

 

[Frank The Tank]

Maybe you aren't letting the higher gears open up ie: driving too slow.

My full size gets 11 city 17 hwy. If her legs don't stretch she gets thirsty.

 

[carmstrong227]

Thanks for the quick reply Frank. That very well could be the issue.

Its about 4 miles to work, which about 3.5 of it I am able to get up to 45-50 mph. Once I reach that speed, the rpm's drop down to about 1500 - 1800. But of course I hope not to hit one of the 3 red lights.

Then again, doesn't city mileage calculations include low speeds, and multiple stop and goes?

 

[martin]

Accelerating the mass back up to speed is what kills city mileage, the harder you accelerate the worse it gets. the five hundred pounds of tools etc in the back don't help either.

 

[Ozwynn]

if you just removed them you need to put your cats back. that engine is designed to run with them. the rear oxygen sensor knows they are not there and it will cause an out of tolerance code and make the engine run rich.

 

[adsm08]

If your cats were clogged you are probably running rich or never getting it fully up to temp.

You need to get some good cats back in place, like BDAB said (and for the reasons he provided). Next, get on the google and look up "italian tune up". Then do that once or twice a month.

 

[Andy D]

I am a firm believer in Italian tune ups. Your short commute is about the worst thing there is for an engine. Chances are if you put the sooted up cats back on and got them hot , they would clean out. Get the engine warm , take the vacuum line off of the fuel pressure regulator Use the richness to start cooking the soot off the ceramic matrix of the cat. Drive for 10 minutes at 70 mph. Stop, re-attach vacuum to FPR and drive at 60 - 70 in a lower gear, 3rd or 4th, for an hour or so . A bad coolant temp sensor is a possible root cause.

 

[buckshotmudder]

A bad coolant temp sensor is a possible root cause.

^^^I would check this first ^^^. With the help I got from reading TRS, I fixed my poor fuel mileage by replacing that sensor. My advice is put the cats back on.

 

[carmstrong227]

Thank you for all of the suggestions!

I will most definitely check for a bad coolant temp sensor, and perform the italian tune ups.

It sounds like everyone is in agreeance that the cats being taking off are causing it to run rich. But...I saw mpg improvement when I took them off. When I had them on there, I was getting 11 city and about 18 hwy. After taking off, 11 city, 20 hwy. The engine light did come on about 3 weeks after I took them off. Got autozone to run a scan, and it was the o2 sensor. After the engine light appeared, I am still seeing 11 and 20.

Would someone mind elaborating on how reintalling, or getting new cats, would be beneficial...when taking them off increased mpg... Would just like to know how, and if putting on cats will actually improve mpg, before spending $500+. Thanks in advance!

 

[det107]

Its about 4 miles to work, which about 3.5 of it I am able to get up to 45-50 mph.

You could easily save $$ on gas by commuting to work on a bicycle. Nuff said-

 

[adsm08]

No, I don't think that lack of cats is causing it to run rich. I think running rich is what clogged the cats, but you have dealt with the most immediate cause of that (the tune up).

It also sounds like you just don't get it out and fully up to temp often enough.

The exhaust flow is dependent on a certain amount of flow space in the system though. Removing the cats by punching them out hurts the system's ability to scavenge itself and that makes the engine work harder to push the exhaust pulses along.

The same effect can be had by putting smaller pipes in there.

 

[carmstrong227]

How correct you are! I'd say 95% of the mileage I've put on the truck (since I've had it) is all city mileage.

And by the engine working harder to push the exhaust out, the RPM would run higher, correct?

 

[adsm08]

No, you won't see it spin any faster, but it will dump more fuel, especially at low speeds.

I have this same issue since I drive about 8.5 miles to work every day, half of it is through stop lights in town.

 

[carmstrong227]

Ah, I see. But my city mpg didn't budge when the cats were removed. So I don't think it is dumping anymore fuel than it already was.

 

[adsm08]

Might not be, but if you removed a restriction but didn't restore the system to it's proper configuration you may not have helped anything, just traded one problem for another that will hurt you in the most noticeable spot.