Looking for suggestions on Gas Mileage

[cormel]

I have a 93 v6 4runner with 238000KMs. I have changes the plugs, plugs, D cap, fuel filter, o2 sensor and I am getting pretty bad gas mileage (like 8 Miles per Gallon). It has stock 31' tires with 4.56 gears in the rear. The timing was done not too long ago alot with the head gasket and new radiator. The truck seems to run good it starts right up, doesn't seem to hesitate with accelerating. I am looking for suggestions as to what people think it could be before I decide to bring it to a mechanic. I haven't checked to compression in the cylinders. I saw in a previous post one guy had a similar problem and he had some burnt exhaust valves. I just bought this truck and I am already thinking it might have been a bad investment if I can't get the fuel mileage straighten out. Also I have not been driving the truck hard at all.

I know these trucks are somewhat hard on gas (like 13-17MPG) but my mileage is way off and something is wrong. Looking for all and any ideas, thanks.

 

[obex26]

I am guessing you also changed the air filter as well. If you had the timing done is it possible that they advanced it causing it to run richer that could consume more fuel. Also if your idle is abouve 1K rpm not a plus either. Just a side not for preventative have the tranny and torque converter flushed out with new fluid not just recyled. also do the diffs. I can not remember if those have the performance power button like my taco did. if that is engaged it changes the shift points and also will affect your fuel milage.

 

[cormel]

Thanks for the reply. The air filter is new as well. I have started to change out all the fluids, had a leak in the rear pinion seal so I changes that and the gear oil, put in synthetic. I guess I may have to buy a compression tester and see how the compression is. If the compression is bad could that possibly mean a bad exhaust valve or will that only tell me if I have a bad piston or HG?

 

[cormel]

One other thing I forgot to mention. The other day when I checked my spark plugs #5 (the middle plug on the driver side) had so black build up on it. The others all looked fine (grey dust like) Would that tell me somethign is not right?

 

[cormel]

I just did a compression check 140-150 accross all the cylinders, any other suggestions. I was thinking bad exhaust valves but compression is good

 

[77'911]

Here's what I checked....

-ohm out O2 sensor to see if it meets factory spec
-set base idle (this really improved mpg!)
-check wheel bearing condition and torque spec
-check state of tune(ie plugs, filters, etc.)
-set timing, check condition and placement of the timing belt as well. If its off, this can make a big difference.
-check fuel pressure(rest pressure as well as running).
-tire pressures(I tend to run them high, manufacture spec instead of toyota).
-check to see if any of the calipers, pads, or shoes have issues.
This is what I checked on our 1990 4runner(V6,auto, awd). Its also worth considering that you might have winter additives in your petrol that will greatly reduce mpg. Ours went down alot this winter, then in the summer it goes way up again.

 

[cormel]

I checked the barings, all look and seem to be in order. I will ohm out the o2 sensor to see if there is a problem there. Also the bas idle should be around 750-850 shouldn't it? If so mine is.

 

[77'911]

Idle speed for 3VZ-E , V6 toyota engine is 800 rpm. I set mine a tade lower at 700-750, with no stalling or stumbling issues at all. If the wheel bearing grease is getting old, bearing is over torqued, or its starting to wear out, these can all effect mpg is a big way. I recently cleaned , repacked the front wheel bearings(replaced wheel seals) on our 4runner and found the bearings exceedingly loose. Clearly the last tech who had worked on the truck had not followed the factory torque setting procedure. As an fyi, it really tightened up the front end.

 

[jbyrdman]

I have a 91, and get between 12 and 15 mpg, on highway after adjusting for tire size