chevydan04

I bought my 91 4runner, V6, Auto, 4*4 a little over a year ago. I haven't really cared too much about gas, but this thing is getting ridiculous.

I am averaging about 120 miles between fuel ups!!!

I have no CEL, No codes, and the truck sounds like it is running good

I have replaced spark plugs, wires, rotor, cap, and checked timing.

Any ideas on ways to get better gas mileage

I am averaging around 6-7 mpg around town and 12 on the highway

chevydan04

Also I have ran seafoam through it, replaced the O2 sensor

JSimmons

chevydan - I hate to be the bearer of bad news (as I once had a 3.0 V6 in a '95 4Runner) but the 3.0 gets horrible gas mileage. It is just an un-advertised feature or something. But, 120 miles per tank is alarmingly low even for the 3.0.

In all seriousness, I would check your injectors. Perhaps the cold start injector is continuously adding in fuel? Did you gap your plugs? I know you said everything seems to be in good order, however, perhaps you have a vacuum leak somewhere causing the engine to demand more fuel. Try the old spraying WD40 around your gaskets on the manifold to see if it affects the idle of the beast. That should let you know where the leak may exist.

Just throwing ideas out there if you haven't thought of them yet.

Good luck.

drmix

Yeah I would check the injectors or try replacing your fuel filter if it hasnt been done in a while

chevydan04

I appreciate the insight, and I would incourage more people to suggest ideas. I am going to run the a gambit of more stuff this weekend. My biggest problem is my wife hates the thing, so she just wants me to get a new vehicle, but I love my runner.

I am planning on removing my intake plenum to see how gunked up it is, and cleaning it out. also at that time I will be removing the air intake muffler, and doing the mod I have seen on the Tech articles.

I am also planning on putting a new timing belt on and taking it to a shop to have them time it for me.

I have new fuel filter sitting in my garage, I just need to replace it.

again thanks for the insight and as always more is appreciated.

I will keep you posted on what I do to the truck

JSimmons

Good luck.

Just an outside guess...but your rear brake drums aren't frozen/dragging are they?

Sansocal

Before you attempt to replace the fuel filter make sure you have a 13 mm flare wrench. Those fuel lines are on there good and a regular open end wrench will strip the brass.

sb5walker

x2 what JSimmons said - raise and check each wheel to make sure they all turn freely. Check timing. Check compression.

TNRabbit

Before you do anything, I'd replace the O2 sensor. When they are on the tail end of their life, your fuel mileage will drop at least 3-4 mpg. Start there-- then I would check if your Coolant Temp Sensor is bad or has a bad connection as it will run in cold engine mode & kill your fuel mileage, too.

chevydan04

Ok so I replaced the O2 Sensor a few weeks ago, helped a little.

Today I started removing my air intake manifold and found a bunch of crud in it, but it got real interested when I looked in the lower intake manifold. There is a ton of carbon build up.

I am in the middle of removing it and seem to be stuck. looking for better instructions than my haynes has to offer.

Anyone know of a tech article of removing the upper and lower intake manifold.

blake.nemitz

geez i get around 20, 300 miles per tank. i would clean out the plenum and manifold. the egr dirtys that stuff up. clogged cat? autos have worse milage by the way. i noticed better milage running premium gas with my timing advanced to 15* make it worth the extra cost of fuel. good luck also how many miles, and what size tires? bigger tired might count the miles slow like you drive 1.2 miles for 1 mile showing.

chevydan04

The truck has 196k on the Odometer. My Tires are 31 by 10.50. Actually I am in the process of removing the intake plenum now. I will take pics of the nastey crud and post them up soon.

I have an Auto tranny that was replaced this last summer, my input shaft seal blew out while I was towing my boat. I dropped the tranny and replaced the seal, it worked fine for about 40 miles then blew up the tranny pump, and the tranny was done after that.

But anyway 15 Degrees advanced is the way to go, and then I need to run premium?

chevydan04

Also how do you block the EGR system off, do I need to cut the long tube that goes into the upper intake plenum?

sb5walker

EGR actually improves gas mileage a bit. Doesn't engage at or near full throttle, so no effect on power. And lowers combustion temps, which is good for head gaskets, exhaust valves, and the quality of the air we breathe. (Nox - which EGR keeps down - is the worst, eye-burning component of smog.)

chevydan04

I don't understand how Hot exhaust being dumped into a intake plenum can cool combustion temps. Also it seems the EGR put all kinds of crap in the plenum to begin with which seems to have affected my gas mileage.

I don't understand how allready combusted crap can help my truck have better cobustion!!

Any insight from others?

Kiroshu

Are you sure that 17.2 gallons of gas in your tank is getting you 120 miles and thats it?

chevydan04

Yes I fill it up with about 16 gallons, and then I fill it up when the light comes on and it take about 16 gallons. Extremely frustrating.

chevydan04

My I reset the ODO on my GPS and it says I have gone 120 and so does the ODO on my truck.

Kiroshu

Yea if thats the case theres issue at hand.

How does it run?

Does it run kinda rough is nervously?

Check plug gap.

Tps out of adjustment?

Cold start injector stuck open?

Leaking fuel?

What is the timing set at? Should be set too *5.

Vacuum leak.

You said your going into the intake?

Clean it all out make sure you replace injector o-rings.

Check again for vacuum leaks make sure its all tight.

Exhaust leaks as well.

Dirty air filter?

4wd engaged?

Low tire pressure?

Carrying alot of weight around?

sb5walker

EGR doesn't make better combustion, just less combustion. Exhaust gas is inert - takes up space and doesn't burn. So there's less oxygen and fuel going into the cyls (when EGR is operating - at cruise). Counter-intuitive that it cools exhaust temps, but it does. That's why it keeps down Nox - Nox only forms at high temps. EGR essentially reduces the displacement of the motor when it is operating, but when you give it full or near full throttle, the EGR cuts off and you get the full displacement & power.

Less fuel/air going into the cyls saves fuel, and EGR also helps to keep the oxygen from combining with nitrogen - any oxy that does is not available to combine with gas vapor to make power.

If the motor is running right - clean, evenly-flowing injectors and a good O2 sensor, then there isn't much garbage from the EGR. Some, but not much. A lot more garbage comes from PCV than EGR. If the motor is running like garbage, tho, then you're right that EGR feeds the garbage back into the intake. But the best solution there is to fix the mixture problem.