91bluetoyota

i have a 91 toyota pickup king cab v6 (4x4) and i dont do much more then 12-13 mpg on highway with only 235 75 15r tires...truck is pretty well stock accept for a magna flow exaust out back....is this normal???

MudHippy

Don't be too offended by this, but have you checked the psi in your tires lately?

How 'bout the last time it had a tune up? Air filter change? Spark plugs? Fuel filter?

You know? K.I.S.S.?

JDS1992

No. check PSI I have the same size tires you do. PSI is supposed to be 35..Then pull a spark plug and if there is alot of corrosion, probably need a new set..mise as well buy ignition wires to if the plugs are bad. Is your check engine light on? because a bad O2 sensor. Specially the MAF sensor can reduce your gas mileage by 40%. I recommend NGK G Power Plugs, and NGK Ignition Wires, you get what you pay for with those. They're Platinums so you dont have to gap them. Your MPGs should vary from 15-18 if your truck is tuned up..and has no issues. I drive about 95% city, and I get 15-16 MPGs, 18-19 on the Highway. Its a 3/8th Spark Plug Socket Puller is what you need to pull one. I recommend pulling one from both sides, Ik its a PITA. because I replaced mine about 1200 miles ago, with Ignition Wires. It definatly improved my MPGs by 1-2 Miles. And it wasnt to hard. it took me an hour to pull them and then another hour to replace them, which was to long.

JDS1992

Also. It depends on how you drive. If you want more MPGs start out slow, and shift around 2700-3000. IF you stomp the gas everytime your bound to get bad MPGs.

thook

K.I.S.S.? What's that all about, Mudhippy? Knights In Satan's Service?.... (from the days of yor when KISS was accused of being Satan worshippers.)

Anyway, enough diversionary tactics.......

I second what the Mudhipster says. An old O2 sensor alone will cause bad mileage like that. As well as loss of power, etc.

Oh....and, SEARCH! Highly covered topic.

Tally ho!

MudHippy

Keep
It
Simple
Stupid!
http://en.wikipedia.org/wiki/KISS_principle

Thank you Kelly Johnson!

Basically, start with the easy stuff moving progressively toward the more complicated, IF NEED BE!

thook

And, TYVM, Mudhippy, for that enlightening bit of candid yet appropriate sarcasm. Once again, I agree....

camo31_10.50

Hey there JDS1992.....you do realize that a 3/8's socket is just a bit bigger than a 1/4" right??????




he means 5/8's!!

theres a number of things it could be..

if your check engine light is on, get the codes off the computer and we can help you decipher them!

if no light..plugs, wires, cap, rotor.....hell have you done an oil change? lmao

TNRabbit

1. If your O2 sensor has never been replaced, I GUARANTEE you will get better mileage by doing so.
2. Check for vacuum leaks; there are MILES of vacuum hose on these models, & the age catches up to them. Use an UNLIT MAPP or propane gas torch & run it around the hoses while it's running--it will idle up slightly anywhere you have a leak. I'd also check the intake rubber hoses for any leaks.
3. If you have "corrosion" on the spark plugs, it's time to change!

DJ99

^+1. What he said. O2's can fail without telling you so.

91bluetoyota

My tire pressure is about 28 psi ...when i bought the truck the engine line indicated my o2 sensor wasnt working so i bought a new one from toyota and i have new spark plugs and wire set from ngk and also new rotor... this truck is also an auto-matic . i have heard that if my fuel pump is weak and old the truck will suck alot more gas?

thook

If the fuel pump is weak you will have less fuel pressure. Less fuel pressure means your engine will technically be running lean before O2 sensor adjustments are made to compensate. When the O2 senses this lean a/f mix, it will cause the ECU to inject more fuel than normal to keep it from being lean. So, yeah.....it'll suck more gas.

28psi will be a big contributing factor. You should run atleast 35-40psi.....a little more in the rear than up front if you haul weight on a regular basis. I run 40-45 on my wife's heavy ars 4rnr. But, before you go replacing the fuel pump, you might try and get your hands on a fuel pressure tester. Thing is, though, dirty injectors will cause basically the same symptom as low pressure from a weak pump. As will a weak or failing fuel pressure regulator. So, test that pressure. If it's normal, the pump is most likely fine for now. And, so will be the regulator. The injectors then become a possibly. One experiment I ran on my wife's 4rnr, in lieu of actually inspecting the injectors, was to disconnect the O2 and run the vehicle through a couple of tanks of gas and then compare the mileage. It had gone up from what it was averaging. Without going into a lot of technical detail, this told me the engine was running lean because, without the O2, the ECU could no longer monitor the exhaust and therefore adjust the a/f ratio accordingly. So, it continued to run lean eventually leading to spark knock and timing retardation by the knock sensor. The injectors have over 200k on all but one. Pintle injectors seem to go about 100k + miles or so before they need servicing. I'll be rebuilding them sometime in the next couple of months.

TNRabbit

Then that leaves vacuum leak.

Fuel pump either works or doesn't. As long as it's able to supply @ 45 psi to the fuel injection, it's golden.

Edit: just saw Matthew's post above; again, as long as the pump is able to supply the psi, you shouldn't have a problem.. I'd be MUCH more inclined to believe dirty injectors are causing your problem than the fuel pump. HOWEVER, I still think it's LIKELY (& cheap to check) you have vacuum leak(s).

thook

Yeah, then there's the possibility of a vacuum leak...lol!