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View Full Version : Getting horrible gas mileage from a v6...



ThatChevyGuy
10-05-2009, 11:07 AM
I have a mountaineer with a 4.0 v6 and here lately its been getting 250 miles to the tank. I drive mostly highway miles back and forth to school. Im thinking it might be due to a clogged cat or something, i can smell rotten eggs when its sitting running and it smells like its running really rich. It has full intake and exhaust and is not throwing any codes. Im talking 12-14 mpg at best. Whats wrong? is it the cat? if so its about to get replaced with 3" pipe

whitedragon551
10-05-2009, 11:09 AM
Rotten eggs is the cat. Id also change spark plugs, wires, and fuel filter while your at it. Pretty cheap stuff and it goes a long way.

ThatChevyGuy
10-05-2009, 11:10 AM
I forgot to mention i just tuned it up, cleaned iac and maf, replaced fuel filter, cleaned air filter, ran some injector cleaner.

jco1385
10-05-2009, 11:14 AM
plugs, wires, coil packs. clogged cat, bad o2's... if you take out the cat, you'll need to get a tune or it will be worse. w/o the cat, your o2 will throw a code, and it will run really rich/lean ( i forget which :crap:)

whitedragon551
10-05-2009, 11:16 AM
plugs, wires, coil packs. clogged cat, bad o2's... if you take out the cat, you'll need to get a tune or it will be worse. w/o the cat, your o2 will throw a code, and it will run really rich/lean ( i forget which :crap:)

Unless he puts an O2 bung on the pipe and puts the O2 sensor back in. He could also do an O2 simulator which just plugs into the O2 sensor, but never goes back into the actual bung.

I would just change the cat and replace plugs and wires and call it good.

jco1385
10-05-2009, 11:18 AM
well the o2 would still get a bad read, which was my point. i run w/o cats and i have an SCT chip and tune.

ThatChevyGuy
10-05-2009, 11:26 AM
oh im gonna run without a cat, i already have headers

ARKANSAS RULES

REDNECK FO LYFE YA DEEG

jco1385
10-05-2009, 11:28 AM
no inspections ftmfw

Johnny Law.Lulz
10-05-2009, 11:34 AM
Here in Va we can get an inspection without a cat but we can get a ticket for it still.

Id rip the cat off, run some lucas through every fill up for a little bit, also check your trie pressure.

ThatChevyGuy
10-05-2009, 11:34 AM
im gonna replace 4 02 sensors after the shop does the cat delete, and do a dummy setup i guess if i have any problems. You'd think id be getting decent gas mileage with the mods, maybe its hurting.

ThatChevyGuy
10-05-2009, 11:34 AM
Here in Va we can get an inspection without a cat but we can get a ticket for it still.

Id rip the cat off, run some lucas through every fill up for a little bit, also check your trie pressure.

tire pressure is at 35.5 on brand new tires. Which lucas? i have about everyone. I just seafoamed it not too long ago

I think i might have an INTAKE GASKET LEAK (AAAAAHH)

jco1385
10-05-2009, 11:38 AM
cake job. *****. do the HG's while you're in there.

ThatChevyGuy
10-05-2009, 11:38 AM
well the o2 would still get a bad read, which was my point. i run w/o cats and i have an SCT chip and tune.

Where to get tune? I needs soon

Louisiana_CRX
10-05-2009, 11:40 AM
i usually got between 350-400 miles to the tank out of my 99 V6 4.0 ranger but everything was stock

jco1385
10-05-2009, 11:41 AM
well, i guess if you run a "dummy" o2, you might not need one. i'm guessing it's a sort of o2 simulator. i'm not too keen on them shits. i just dropped the $$$ on the chip for later tunage when i do more mods. i have the 3.8, and with tubular manifolds (basically headers), no cats, and dual flow 40's i still get 20-22mpg city/highway mixed driving. not too bad.

ThatChevyGuy
10-05-2009, 11:41 AM
i cant run true duals or i would (4.0 sohc loses too much bottom end)

Johnny Law.Lulz
10-05-2009, 11:44 AM
I meant the lucas injector cleaner. Get the little bottles. I put one in my 89 F-150 with every fill up and the ***** runs noticably better. Check your intake/filter and maybe find a way to get cooler air in there. My uncles gets around 18. Your doing worse than my 05 trailblazer and thats saying a lot considering what your in.

jco1385
10-05-2009, 11:52 AM
mine arent "true" duals either :crap:. y-pipes. i actually hate it.

ThatChevyGuy
10-05-2009, 05:15 PM
mine sounds better

I never saw the point of having dual mufflers with a y.

19psi
10-09-2009, 08:42 AM
actually, deleting the after cat 02 won't affect the engine at all. it's there [b]only[/] to tell the ecu if the cat is functioning properly. only the front 02's are used for feedback to adjust fuel trim.

I Like Waffle
10-09-2009, 11:39 AM
How big is your tank? My car is a 81 with same size v6, full exhaust and intake, cam, shaved heads and dif carb and i get 700 miles to a tank on the highway, about 15-20 mpg if im dogging it in town. (28 gal ftmfw)

I Like Waffle
10-09-2009, 11:43 AM
actually, deleting the after cat 02 won't affect the engine at all. it's there [b]only[/] to tell the ecu if the cat is functioning properly. only the front 02's are used for feedback to adjust fuel trim.

X2. I just unplugged mine after i removed the cat and mine runs fine, smells funny without cats but i assume thats normal. Runs like a champ though, even with the semi-electronic carb.