Terrible gas mileage/Timing

[mem]

I have a 1999 4Runner limited 4x4. The check engine light has been on a little while but the vehicle has been running fine all except the fuel mileage has dropped. I had advance auto parts check the code which he said '"Left bank running rich/lean". After reading through the threads on this website most recommendations was that it was probably a dirty mass air flow sensor. This made sense because I had this problem before. I bought a Spectre cold air induction system and during installation the MAF sensor has to be transferred to the new intake pipe. I took this oppertunity to clean the MAF with CRC MAF cleaner. I also went ahead and replaced the spark plugs since the vehicle was almost at it's 30,000 mile interval. Once everthing was installed I reconnected the battery, let the engine idle for 10-15 minutes before I took it for a drive.:thumb3:The cold air kit makes the 4Runnner sound like my '77 Trans Am when the 4 Barrel kicks in. I topped off the fuel tank and after a few miles driving approx 15-20 miles The fuel gauge starts dropping. The Haynes service manual reads that one symptom for bad mileage could be "Ignition Timing". Could this be possible? When the accelerator is pressed to the floor the acceleration seems real sluggish, like something is holding it back. Since ths vehicle has no distributor , how do you adjust the timing?

 

[the great him]

you dont, unless you want to adjust it at the belt, but i wouldn't recommend that... how many miles on your rig? id replace wires too, fuel filter... maybe clean out the TB, run some seafoam through the intake and another can in the fuel tank, replace your o2 sensors...

 

[mem]

It's got 157,000 miles on it. Still has original wires and fuel filter. Probably O2 sensors as well. The thing runs great except under full acceleration. Never used seafoam, I heard it could damage?

 

[MAD 69]

I wouldn't use Sea foam, i heard more bad than good from that stuff. If the truck still has original wires and plugs you should change them and the fuel filter.

 

[the great him]

your o2 sensors are recommended to be changed every 90-100k miles, id replace them too, if you dont you run the risk of running too rich or too lean or a back and forth combo of the two and will end up burning out your new plugs and the cat... ive used sea foam products on all my vehicles (except the wifes car -its brand new) and never had any issues. both of the independent shops if worked at also used them with no undesirable affects, just read the instructions and youll be fine.

 

[mem]

OK guys here is what I have done so far:

1) Installed Spectre Cold Air Induction KIT...... :thumb3:

2) Replaced spark plugs with Toyota/Denso Plugs......:thumb3:

3) Replaced plug wires with NGK (Blue) Plug wires....:thumb3:

4) Replaced O2 sensors with NTK(NGK) O2 Sensors......:thumb3:

5) Cleaned MAF Sensor......:thumb3:

I took the Runner on a 13 mile drive, the fuel level gauge was reading half way between 3/4 and 1/2. After this 13 mile drive the gas gauge dropped down to the 1/2 mark!!! Am I actually getting less than 12 MPG?? What is going on?:redbrick: Any more suggestions?

 

[Nunyabiz]

You could try a "MotorVac" I have heard that has cured many bad MPG problems.
I have never used it myself so have no first hand knowledge.

Have heard anywhere from $150-$250 to have it done.

 

[02SE]

There was a TSB for '99-'00 4Runner fuel gauges. IIRC, it was TSB EL010. I'd look for a malfunctioning fuel gauge, rather then assuming your fuel economy is poor based on seemingly erratic gauge movement.

 

[the great him]

fill the truck up, and wright down your mileage. then drive it till the fuel light comes on, then full it up again, and look at/wright down your mileage again, then calculate it, im sure you will be getting a lot better than you think. what size tires are you running, and what psi are they at?