Fuel milage

[Duck Commander]

COURTESY TO (PoconoPAFJ) FJ FORUM;:021:

READ AND TRY, IF HELPFUL DROP A WORD OF THANKS HERE.:015:

I’m posting this information here to make sure everyone has a chance to review my findings. Since fuel mileage has been a concern for nearly every FJ owner out there modified or not. All of us have read, heard and experienced the horror stories surrounding this subject.

My problem started approximately 12 months ago. With 4 trips to Toyota and more frustration then you can ever imagine. Even to the point I no longer wanted to drive or own a FJ. Not to mention the time and costs associated with this ordeal.

In early November 2009 I began to notice a potential fuel mileage and drivability problem. I spent the next 4 weeks tracking fuel consumption which yielded on average 220 miles per tank. Prior to this for nearly 2 years I regularly averaged 300 miles per tank. And so everyone knows, it didn’t matter if I used premium or regular. So I scheduled an appointment with Toyota.

I delivered my truck and waited while they checked everything out. Four hours later the service manager told me nothing was wrong with my truck. No codes in the computer and no mechanical problems they could find. Here’s the bill and off I went.

Two weeks later I returned again complaining about fuel mileage. Fresh off of a 190 mile tank I told Toyota it’s just not feasible to drive a truck in this condition. So I requested the service manger go for a drive in my truck. I took him on a 20 mile trip up hill which burned a ¼ tank of fuel. He agreed the truck had a problem and offered to keep the truck. Five days later Toyota called and told me nothing was wrong.

Over the next 4 weeks I tracked my mileage with fuel receipts and spread sheets. I returned to Toyota with my documentation and requested they perform another check. I spent the next 1.5 hours discussing the problem with them. Only to be told bring it in when the check engine light comes on. I even coined the new phrase “I can’t even pass a prius“. They didn’t think it was funny in light of problems they were knee deep in. But it was true, on one given day a prius actually pulled away from me, I just couldn’t keep up.

At this point I decided to start my own trouble shooting. There were only two events which could have spawned a problem, the back to school run and new iridium spark plugs. So I focused on the spark plugs and pulled them. Every plug was black and wet not a good sign. The original plugs were perfect when removed at 45k dry and ashed. I bought a new set of oem NGK’s with the feeling of success. With no change in fuel mileage I pulled the plugs for review and found black and wet.

I stopped by Toyota to discuss my findings. I was told they were expecting me back and opened a ticket with Toyota corporate after my last visit. Toyotas regional engineer would investigate the problem personally. A week later the engineer was working on my truck. Six hours later I’m informed no problem found. The engineer and I took the truck for a ride with Toyota’s PC scan gauge attached. I explained the vehicle was sluggish, lacked power, poor shifting and no throttle response. After the drive his response was I don’t feel it. They had another 2007 on the lot, so he suggested we take that one for a ride. I drove the vehicle off the lot and to my surprise it had the same problem. Even the odometer reading was within 2K of mine. (I’m convinced this vehicle was traded in because of fuel mileage problems.) The engineer suggested one last ditch effort wiping the computer memory. Well after a test drive it appeared the drivability problem was somewhat restored.

After another 3 weeks of fuel mileage review I was now averaging 250 miles per tank. Still not back to normal but better then it was. At this point I figured I’m on my own and started isolating the symptoms I knew.

No check engine light or codes stored.
Plugs black and wet no matter oem or iridium’s. (Reinstalled the iridium’s since they are a better plug)
Poor throttle response. (Acceleration was poor and breaking traction almost impossible)
Lack of power. (Truck felt like I was dragging an anchor all the time)
Transmission down shifting and searching way too often. Any push of the throttle caused a down shift. Basically no throttle dynamic range in any given gear. (Where you can accelerate by pushing the throttle without down shifts)
Interior cabin exhaust note changed. (Exhaust was much louder than normal)

So on to the trouble shooting phase.
Based on conventional wisdom everyone would say cat converter. With O2 sensors fore and aft it would produce a trouble code.
Next thought was possible plugged muffler. Chip monks and field mice are abundant around here. Maybe one made a new home. Good possibility since there’s no sensor monitoring exhaust pressure. Would also explain louder exhaust note. Since I was in the market for a performance cat back system anyway, it was replaced. Did not fix the problem.

More research and investigation I was lead to possible transmission issue. Since many complained about black transmission fluid at about the same mileage could be a problem. So I replaced all 16 quarts with no fix. By the way at 45K the fluid was pure black. So replacing the fluid was a good thing (cherry red). 100K service interval don’t you believe it.

With no more tricks up my sleeve I spent the next couple months reading and researching. I visited every Toyota forum and website out there. When it came to fuel issues most people’s complaints started in the 40 to 50K. When you quantify the complaints they averaged a 30% loss. Nearly the same results I’m experiencing. I now began focusing my search on every post by those people looking for a pattern. I found another common complaint from more than 50% of the individuals. Each one posted at least one complaint about difficulty defrosting ice from the windshield during snow storms. I then recalled cursing the FJ during one bad snow storm last winter. The windshield kept icing up in stop and go traffic, but not at highway speeds. I now had a new focus engine temperature.

I went out and purchased the best OBD scanner available (needed one anyway). From the information that was available the engine operating temp was 180. I started monitoring the coolant temperature for the next 4 weeks. I found a wide swing in temperature 160 to 184. I also found when the engine was started and just idled in the drive way it never got above 168. On the highway it stayed a solid 184. But in stop and go traffic it never exceeded 168. Throughout this process I kept checking the heater temp and noticed the slight changes. Then on one 90 degree day I drove to long island and my fuel mileage was back to normal. Low and behold the temperature returned colder my mileage got worse again.

With the learned information I decided to replace my thermostat. Well it’s now 35 degrees and my fuel mileage is back to normal averaging 300 plus per tank. Engine temperature is a solid 181 degrees plus or minus 4 degrees under all circumstances. Heater temperature will literally burn your hand. After removal I tested the thermostat and found it was weak. Once open it didn’t have the ability to maintain coolant temp. It would basically stay wide open all the way down to 150 degrees. Additional back up was this problem would not throw a code since the engine thinks it’s in warm-up mode. Therefore it burns much more fuel than required. However, since the engine is to cold the fuel ends up getting burned in the cats. Cat temp then rises as well as exhaust tone. This problem may also contribute to the people with premature cat failures. And the final confirmation check of the iridium spark plugs. You guessed it no more black and wet, just like new dry and ashed.

With the fix in hand it was time to visit Toyota to discuss my displeasure with them. Toyota did allude to a possible known issue with thermostats, but would not confirm their statement. Therefore I suggest anyone who is experiencing poor fuel mileage replace their thermostat. The cost is 60 dollars, 1 gallon of pink antifreeze and an hour of work. You could possibly regain the new truck mileage you’ve been missing since 40 thousand miles. By the way if you look up the recommended replacement term for thermostats its 2 years with a coolant flush.

[Al Marshoudi]

It is good thread Shafiq ..

Thanks dude ..

[Wasif Ahmed]

It is good thread Shafiq ..

Thanks dude ..

LOL>..what do you care .....you sold your FJ

[birrdog]

Great bit of detective work DC, there must be a lot of FJ owners out there who do not have the time or knowledge to do what you did

[Duck Commander]

Great bit of detective work DC, there must be a lot of FJ owners out there who do not have the time or knowledge to do what you did

Birrdog thanks for your remarks but I didn't did this work it is another guy in US who suffered a lot and did this research in one year. On the top you can see his name.

[Al Marshoudi]

LOL>..what do you care .....you sold your FJ

Wasif, it is universal problem but FJ was involved (as usual) :S