KryptoKid

Hello all,

I am trying to think outside the box on how to fix this 3.4 Here is my original post from a good few years ago.

The symptoms:
3.4L currently has 140XXX miles and runs decently. It hesitates occasionally at start-up but seems to idle well and I can't really detect a miss on any of the cylinders. I do not have any CEL codes nor have I in quite some time. I do have Airbag, VSC, TRAC lights and no horn due to a clock spring I believe. I am currently averaging less than 200Miles to the tank. That is with 305/75's so probably a little over 200 with stock speedometer gear but not much. If I really run the tank down low I can get 220 miles out of a completely empty tank. I have been running the 305's for the last 6-7 years and the mileage has been slowly decreasing so I do not believe the tires effect to mileage is a factor. My driving style has not changed much if at all and I am driving mixed mileage of street and highway. When I drive long distance I can get up to about 250-270 to the tank on flat ground on a good day with a tail wind.

What I have done
-I have also always kept the tires maxed recommended PSI
-I rotate and balance the tires with every oil change every 3000 miles.
-I also get the alignment done at least yearly.
-I am running full synthetic oil and run injector cleaner every 4-8 tanks (depending how often I remember).
-I replaced Air filter, plugs and wires and PCV a few months ago with no resolve
-I can't find a single vacuum leak anywhere on the motor.

In 2007 I replaced Air fuel sensor and O2 sensor.
In late 2009 at around 100XXX miles I replaced the timing belt and water pump, fuel filter, Air fuel sensor and O2 sensor (Actually bought Bosche in 2007 then went back and re-bought Denso after counsel in my previous thread). I also cleaned the MAF sensor and throttle body.
In 2011 I replaced the entire charging system with a Delco HO alternator, Optima Yellowtop Battery and new 4GA grounds and power wires.

The evap, vacuum, fuel and exhaust systems are all bone stock.

My questions
I am curious if other things could cause Airbag, VSC, TRAC dash lights to go off that might have an effect on fuel consumption? Closed loop?

Anyone ever heard of MotorVac? Here is a link to a thread talking how well it works.

Other things I should be looking into? Coolant Temperature Sensor, IAC, Throttle Position Sensor, Catalytic converter, fuel pump or even injectors?

I am really at a boiling point and about to sell the toy out of frustration. I get better mileage in my CJ-7 on 35s with a 4.2L tractor motor than I get in my DD 4runner.

Any input is appreciated.

-Me-

habanero

Hesitates when you first start it and hit the gas but then fine the rest of the drive or...? You cleaned the MAF in '09 and not since? How's that look?

DRCOFFEE

What brand/type of spark plugs did you install? Any discolored fluids, trans, coolant, motor? Are the brakes releasing, possible drag on axles. Feel for excessive heat after driving. The odd startup would point me to the incorrect spark plug, first of all. possible clogged Cat. does it have good pulling power? You said it had no codes, right? Possibly a sensor. Or maybe a leaking fuel injector. Floods the cylinder after shutdown and cant fire up correctly. Could also explain the poor MPG.

http://www.toyota-4runner.org/proble...ghts-only.html

http://www.toyotanation.com/forum/74...ine-light.html

Heres a few threads that may get you in the right direction.

KryptoKid

Doesn't hesitate regularily, but normally it will only hesitate lightly and when it does hesitate badly it will only be for a few minutes. But this is not often, maybe once every 10 starts it will have a light studder. Although it always feels a bit weak in the petal, like its running rich.

Ill pull it next week when I have time and check it.

I can't remember which plugs, but while looking for receipts I found that I used a NGK (4412) TE66 Wire Set and replaced both exhaust sensors Denso 234-9002 and Denso 234-4261 Oxygen Sensor at the same time last year with the plugs.

Brake, tranny, coolant, oil and diffs look clean. Diffs and tranny were flushed/filled last year. Oil was chenged a few months ago.

I just replaced rotors and pads up front and they spin freely. Ill try to get it on a lift and check the rears soon.

Any recommendations or part numbers for the "Perfect plug"?

I think the cat is failing as well, but I am hesitant to replace it as it is fairly pricy and I worry about doing the MotorVac process after replacing the cat (rather do it to the old junk one). Also does anyone know of a good replacement CAT part #?

Definately no CEL, How to I troubleshoot?

really interested in how to troubleshoot this one. would the MotorVac help? or is this just a replace it type scenario?

Thanks these are helping me get the brain firing at least.

If you were to come up with a list of affordable parts that are cheaper/easier to replace than troubleshoot for this problem...Ideas?

habanero

Check the MAF. That's free, it's been 3 years, and you've covered a lot of throw-at-it parts already.

My 3.4 has NGK BKR5EKB-11 dual electrode
The owner's manual also states Nippondenso K16TR11

KryptoKid

Thanks for the heads up Habanero on the plugs, I'll go grab some and I will check/clean the MAF sensor next week. I remember last time i did it, the effect on mileage was not much. I was already down to about 240-270 a tank back in 2009-10 last time after I cleaned the sensor and gave it a good tune up. I also drove it across country from Seattle to Boston in 2010 and averaged 250 miles to the tank doing 70mph on the interstates.

The last couple of years I've been living in Boston and haven't hardly driven it so I didn't even try to fix the problem with mileage. I've been driving and working on my other rig a lot so as long as the runner started and got my wife to and from work a few miles from my house, I didn't care if she had to mash a little harder on the petal or pay a little more in gas. Lately she has been complaining about the mileage...

I guess what I am saying is that no matter what stage of tune up the truck is in, since 2009 the truck has been getting bad mileage so that leads me to believe that it is something I haven't touched that is going bad or faulting. For reference after I bought it in 2006 and put the lift and tires I would regularily get over 300 miles per tank and close to 350 per tank on the highway.

-Me-

habanero

I was thinking more your hesitation and it's one of those maintenance things that costs only a little time and some cleaner if the wire's dirty.
I'm interested in seeing if you find the culprit to your mileage loss, many of us are in your boat though in my case a lift, bigger heavier wider tires, a roof basket and lights and extra weight in mods are likely a large piece of it. I use fueleconomy.gov to keep track of mine so issues are easier to spot.

DRCOFFEE

Do you have any white smoke on startup from the exhaust. I remember reading about an early head gasket issue where the truck was rough until it blew out the coolant. Could also explain poor mpg. I'm probably wrong but something to keep in mind.

If you wanted to do a quick check, pull each plug and look into the cylinder. If it looks super clean, that would be the tell. It cleans out the carbon so it would usually clean inside.

KryptoKid

Swapped the plugs and the problem resolved. Looks like one of the plugs was a different part than the rest. Thank you all for the help.

habanero

Cool! Thanks for the update.