2001 Toyota Avalon P0174 (Did also include P0171)

Alright, this is my own vehicle here. So before yesterday I had both P0171 and P0174. I run my LTFT's, with Load, and MASS air flow rate. My LTFT's are around 0% at idle, freeze frame is telling me it keeps happened around 40% load. I look at the graphs with Load and LTFT's and the long term fuel trims max out at load with anything above 35% load. It drives great, like cruising, but whenever i need to push it on the highway alittle bit I can tell it seems to be a litttle lackluster. But it would be really hard to tell for anyone else to see this...but I drive the car 72 miles on way on a highway to work, driving 70mph for 1 hour straight I can really get dial in with whatever I am driving.

My first thought was well, maybe I have a fuel pressure or volume problem. So I go to my FSM, I was only able to T into the Bank 2 FR. I probed the fuel pump and got 46 psi. Spec is 50-44. I turn the car on and its the same fuel pressure. I revved the engine, and I would noticed whenever I really yank that throttle body hardy it would drop about 2psi. Shut the car off, and it dropped to 42 psi, and stayed around there for about a good while. It didn't hit the minimum 21psi up until the 8 hour mark. I thought about hooking up the FP gauge again and bleeding the fuel out in a bucket and measuring how much is dumped in 5 seconds. But I have no spec on what the fuel pump is rated for. So i cant really check volume, and again, this is a problem I have at load, I would probably be spinning my wheels.

for the Avalon, there is no return line. and the regulator is inside the fuel tank attached to the fuel module. I think this has been a challenge for me to pin point because this is only occuring under load. So no matter what I keep checking at "idle" really doesnt do me any good because most of my research online is giving me values for whenever the car is at idle.

This car was new to me 1k miles ago it has 200k miles on it, I had misfire codes before all this. those are long gone. It was the OCV's both changed with OEM units, I have OEM plugs in and the coil packs are good. fresh oil change. new PVC, I dont have a vacuum leak, even more so nothing on the PID's tell me i have a vacuum leak.

I am at a loss here. help me. lol please help

Be sure your O2's can respond to full RICH/LEAN conditions and you've no exhaust leaks before any pre-cat O2's.

Sounds like its time for a Propane run!!!!!

Get can of propane, and put a long length of rubber hose on it and set it in the intak stream, go for a drive under the code setting criteria, bring the scan tool, when the trims go lean turn on the propane into the breather. Trims improve??? You got a fuel volume issue.

You can also test the 02's @WOT, if you have a lack of fuel they will be pegged lean.

A good rule of thumb is a minimum of 0.5 GPM of fuel flow or 1.9 liters per minute.

Paul P. wrote:

Be sure your O2's can respond to full RICH/LEAN conditions and you've no exhaust leaks before any pre-cat O2's.

Sounds like its time for a Propane run!!!!!

Get can of propane, and put a long length of rubber hose on it and set it in the intak stream, go for a drive under the code setting criteria, bring the scan tool, when the trims go lean turn on the propane into the breather. Trims improve??? You got a fuel volume issue.

You can also test the 02's @WOT, if you have a lack of fuel they will be pegged lean.

A good rule of thumb is a minimum of 0.5 GPM of fuel flow or 1.9 liters per minute.

Never thought about the propane trick....Ill double check the o2's respond properly. Need to look at the snappy throttle reponses for this wideband O2s.

And for wideband O2's a lean condition is high voltage. I have screenshots on my phone where it was running around 4 volts I just couldnt remember what I was doing at the time. there was one instance where the voltage when up to 5 ish really sharply, stayed there for a bit, then dropped back to 4ish volts. And both widebands were doing that, not just one bank.

Alright so did some tests during lunch. After warming up, at idle its around 3.8-4v. Then I wanted to test if the O2's can respond to LEAN/RICH. I popped off the air filter box, fed it some propane at idle, I watched the voltage go down to around 3-3.2V.

Not going to lie doing these test on my phone is really annoying. I am thinking about buying a bi directional scanner with a tablet so i can see my graphs and metrics better.

So after feeding it propane, the O2 did start cutting the fuel out.I put the propane away. Now, at idle, I pulled a vacuum hose and the voltage went to about 5v. My downstream o2 read around 0 volts when I pulled that vacuum line.

Now when driving and then decelerating my O2's went down to 3.5v on both banks and then downstream went to around 0.1v.

now i know sensor 1 on both banks are widebands, but for the downstream O2 doesnt high voltage signify rich and low voltage mean lean?

STIMECE wrote:

now i know sensor 1 on both banks are widebands, but for the downstream O2 doesnt high voltage signify rich and low voltage mean lean?

Correct. The fact that both the downstream sensors and the upstream sensors agree about a lean condition is a good sign.

I'd suggest a WOT run from a stop through first and second gear if possible. Select the engine speed, Load, IAT, MAF g/s and both upstream air/fuel sensor PIDs only. Record the run and see what your highest readings were. Low airflow numbers would suggest an incorrect air flow measurement, resulting in a lack of fuel delivery.

Okay new pump, regulator, fuel module filter and external filter what a difference. The car drives as should now.

I still have pending lean codes, I've been looking at STFT AND LTFT my LTFTs are still high whenever I am driving around but my STFT go between -2-3% to positive 2to3%.

I suppose even after clearing the memory on the Toyota the LTFT numbers are still retained? I did try and drive a constant 65 mph and it seemed to start lowering them from 35 to 30%.

I guess this is a fix that has to take time to fix itself?

I ordered a Topdon Phoenix 2 Lite today

Okay so I have a Topdon Phoenix Lite 2 now, I replaced the fuel system and its been running great, I now have the fuel delivery I know the car needs when driving highway speeds.

But now, I still have the same codes. I just did my 70 mile commute to work, and freeze frame data says it happened at 267 second of engine operation, the STFT were around 0.8% but the LTFT's were at 41% ish.

Will look at my data streams closer when I get back home, I have graphed the values of both the ST and LT, and the ST are always really low, like around 0 to +/- 5%, and my LT's are always just off in never-ever land. I always understood the LTFT to be an averaged out STFT, so I am confused as to how my ST's can be so low and my LT's are still high and do not come down at all.

did you try smoke test or leak test in exhaust

So for starters, after going through this diagnosis, my initial understanding of fuel trims was wrong. I do not even know how to explain how the LTFT and STFT work together but they do....The STFT will adjust the LTFT but its not an average.

Initially I thought:
LTFT = STFT averaged over time, ie if the STFT is low, and the LTFT is high then then LTFT should equal to the STFT after it learns.

Now I see it as:

The LTFT is a macro, and STFT is micro. The STFT makes adjustments to whatever the LTFT is.

Total Fuel Trim = (+/- LTFT) + (+/- STFT).

So after realizing that I went back and looked at my fuel trims and it pointed to a dirty MAF. Now I still had low FP issues which is also solved buttt...I guess in my infinite wisdom I didnt really clean the MAF well, I pulled it out again and saw dirt, so i went HAM on it, squeaky clean, threw it back in and viola, started seeing negative short term fuel trims.

This was a very enlightening experience. Nothing ventured nothing gained. Now I have a really good grasp on FT's now. I give credit to Mr. Scanner on this one....bought a book to show support.

The main factors in rechecking my work....LTFT's increased as RPM and load increased, widebands running lean, downstream lean, fuel delivery was already factored out. at idle i was still lean around 5-10% but nothing crazy, more load, and more rpm the LTFT went up.

Before cleaning:


After cleaning

This car hates me. Now I have s P0325 code for a knock sensor on bank 1.

Will have to try and test resistance of sensor before pulling the intake assembly off to get it. Maybe I have knock. But I'm doubtful.