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Since I purchased my 99 with 83k miles on the odometer I have yet to see a decent city fuel economy... At about 104k miles I decided to run multiple doses of fuel additives through the tank so that I could change plugs at 105k... So one time I dumped about 12oz, possibly even more, of LUCAS ULC to nearly empty tank and drove about 4 mile to fuel up, which at the time it caused multiple misfires as I arrived to fuel... Misfires slowly went away and then came back then went away again... As 105k got closer I was still experiencing misfires every now and then, sometimes to a point where engine almost shut down... I then decided to seafoam, which didn't help so I did it again and still misfired. Then a third seafoam still not clear... Added full can of seafoam to tank...slowly the misfiring went away but fuel economy is still horrible...
Odometer is currently at 106,450 and I have gone through 4 -5 seafoam cans, about 10 Berryman B12 cans into fuel tank, 3-4 cans of gumout complete system cleaner(similar to seafoam), 4 bottles of Chevron Techron, 4 bottles of gumout regane, about half gallon of LUCAS ULC, MMO and most recent fuel up I went with RISLONE complete fuel treatment... Forgot the occasional standard stp fuel injector cleaner in between... So I have completely overdosed this RX for the last 2,500 miles in the hopes to get better fuel economy but have not succeded with all the concoction mixes I threw at it...
So I at least hope that my fuel tank is super clean and pump/filter also clean and well lubed... Spent enough money on all the additives chasing this ghost and dealing with gremlins that followed so now I need to find out what exactly is still causing this horrible gas guzzle. BTW, I still have not changed the plugs as I would like to make sure it is not the injectors or fuel pump/filter first as I don't know if they would cause the new plugs to go bad.
The most recent code has been p0171 so I just clear it and it stays away for a few weeks then it does come back... I have cleaned the maf sensor several times with crc but still did not help... Guessing it may just need to be replaced...
Dash should read 100/mpg when I let off gas but when I am driving gently I get 60-70 mpg when I let off, if I drive hard for a few hard runs I can get it to read 100mpg but don't want to keep beating it to get that reading...
Sorry for this long story but trying to get any help in finding what is actually causing this... I don't put too many miles on it but would still like to see a tankful last longer.
Last edited by 6.0PSD; 10-19-16 at 03:19 PM.
Reason: Odometer mileage stated was off by 10k miles throughout post...
Only code I get is 0171... I clear it and it stays off for some time but eventually comes back... It's been over a week with it off but economy still sucks
P0171 lean on bank 1. Double check your hose from your intake box to the throttle body for any cracks or tears and that connections are snug. Also check for loose or cracked vacuum hoses off the intake manifold. Any unmetered air can result in fuel dumping. If all looks good, consider replacing the bank 1 A/F sensor.
When cruising on a flat straight road with almost no head winds, what rpms do you see?
Salim
I haven't been on the highway as of lately but if I recall I would be at about 2,500 doing 65mph, this is an approximate number but will try to get it out on the highway tomorrow and confirm.
P0171 lean on bank 1. Double check your hose from your intake box to the throttle body for any cracks or tears and that connections are snug. Also check for loose or cracked vacuum hoses off the intake manifold. Any unmetered air can result in fuel dumping. If all looks good, consider replacing the bank 1 A/F sensor.
By A/F sensor do you mean the O2 sensor upstream pre-cat at bank 1? Wouldn't other codes pop up if that sensor went bad?
I've only been getting P0171 for the last couple hundred of miles but did get both 0171 and 0300 codes come up together about 300 miles ago, the 0300 has not come back but figured it may be needed in trying to narrow down what needs priority
By A/F sensor do you mean the O2 sensor upstream pre-cat at bank 1? Wouldn't other codes pop up if that sensor went bad?
I've only been getting P0171 for the last couple hundred of miles but did get both 0171 and 0300 codes come up together about 300 miles ago, the 0300 has not come back but figured it may be needed in trying to narrow down what needs priority
Originally Posted by 6.0PSD
I'll start checking out those hoses hopefully tomorrow... Thanks for the info.
If they need replacing would fuel hose be ok to use?
Use rubber or silicone hoses for vacuum.
Yes, the pre-cat oxygen sensor on bank 1. It's sometimes a crap shoot if other codes show up. Often they are other codes based on the same sensor.
It might be time to buy a bluetooth or wifi OBD2 device to use with engine link app on your phone to monitor your engine in real time while you are driving. When I bought our 99 RX last June, i was getting poor mpg. What I found was the thermostat was failing and opening fully at 160* keeping the engine in choke mode. After replacing the t-stat and continuing to monitor the coolant temps, I found the ECT sensor was faulty too. It was erroneously giving low readings. Those two items helped me go from 15 mpg to 22 mpg. You may think of changing the vvt valves as well since they control valve timing. But to be honest with you, dumping gallons of fuel additive into the engine is a waste of money. You need to know what your engine is seeing and right now you are blind. The device will cost you $20 and the engine link app is a punishing $6. Or you can just start throwing parts at it. O2 sensor is $100. MAF sensor $90, etc.
It might be time to buy a bluetooth or wifi OBD2 device to use with engine link app on your phone to monitor your engine in real time while you are driving. When I bought our 99 RX last June, i was getting poor mpg. What I found was the thermostat was failing and opening fully at 160* keeping the engine in choke mode. After replacing the t-stat and continuing to monitor the coolant temps, I found the ECT sensor was faulty too. It was erroneously giving low readings. Those two items helped me go from 15 mpg to 22 mpg. You may think of changing the vvt valves as well since they control valve timing. But to be honest with you, dumping gallons of fuel additive into the engine is a waste of money. You need to know what your engine is seeing and right now you are blind. The device will cost you $20 and the engine link app is a punishing $6. Or you can just start throwing parts at it. O2 sensor is $100. MAF sensor $90, etc.
It is a Bluetooth scanner that I have been using to clear my codes... I don't really know what readings to look for... I have TORQUE app to connect to Bluetooth scanner...
Any specific reading that I should check?
I replaced the battery today and it will be the third new battery in the last 4 years so not only do I have a guzzler but have a batteryaholic as well... Lost receipts for the other two batteries but they would have still been under warranty... Going to save this receipt in the glove box this time.
Took a quick highway run to 60 mpg and rpms sat about 2,400 as I let off throttle...
BTW, both ocv valves have been changed... Bank1 about 10k miles ago and Bank2 about 4k miles ago... Both purchased through local Toyota dealer, both brand new in toyota sealed box. I also pulled both ocv screens about 1k miles ago and cleaned thoroughly, they were not bad though... New Toyota pcv valve and grommet as well.
I am experiencing an oil leak and am pretty sure it is the rear valve cover so I already have a gasket set to throw at it including the the tube seals... It will then get the new plugs in there.. Just hoping it is not the cam seal.
You should see the coolant temperature at 180 consistently. Mine was running in the low 160s. You can also monitor your O2 sensors. I dont have the torque app so I dont know what its capable of. Check you transmission temps while you are there. Shouldnt be above 180-200. Ideally 170*.
I Also gained a few mpg by replacing all four brake calipers. They were seized and not releasing properly causing drag. There are so many possible causes that you just have keep searching google for alternate possibilities.
09-26-16, 04:44 PM
Chasing a fuel consuming ghost
