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Discussion Starter #1 (Edited)
Hey lads,

I have a 2001 Echo with about 185,000 miles on it. The car has been giving me intermittent P0171 codes and I have resolved to fix it. I purchased a BlueDriver scanner but the code hasn't come back since I bought the scanner. I do, however, observe a pretty steep LTFT of 19.5+ and cannot seem to figure out why this is happening.

So far, I have:
Cleaned the original MAF with MAF cleaner - no change.
Replaced the MAF with a Walker aftermarket MAF - no change, same LTFT value.
Replaced the intake manifold gasket - no change
Visually and physically inspected vacuum lines - no cracks were found.
Liberally sprayed carb cleaner around gasket mating surfaces and hose connection points - no change
Replaced the PCV - no change

The air filter is not dirty. The fuel pump was replaced about a year ago. The car has power and drives normally and gets about 33mpg in combined driving.

I have attached a screenshot of the bluedriver app showed my fuel trim levels.

I would be most appreciative of your help, thanks in advance!
 

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Maf reading looks about right, if no vacuum leaks then suspect lack of fuel.
Verify fuel pressure running/ shut engine off to check for pressure leak down.
If pressure/leak down test good then test individual injectors for flow.

Freeze frame for P0171?
 

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Discussion Starter #3
Can you suggest a tool and technique for measuring the fuel pressure? This vehicle doesn't have a schrader valve for easy access to the fuel rail as far as I know.
 

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Discussion Starter #4
I went out to the car today and began clamping off vacuum hoses hoping to coax the engine into revealing a vacuum leak somewhere. I did the following:

1.) Clamp off the vacuum line to the brake booster. I lost brake vacuum assist but otherwise no change in the LTFT during driving.
2.) Clamp off the breather line from the valve cover to the air duct that connects the MAF to the throttle body. No change in LTFT.
3.) Photo attached - Clamped off the vacuum line between throttle body and the vapor purge valve. This caused the LTFT to spike up to about 40+ and finally set the P0171 DTC. The freeze frame is as follows:

Make:Toyota Year:2001
Trouble Code P0171 triggered Freeze Frame.
Code Def: System Too Lean Bank 1
PID : Description : Value
04 : Calculated Engine Load Value : 20.4 %
05 : Engine Coolant Temperature : 187 °F
06 : Short Term Fuel Trim Bank 1 : 7.0 %
07 : Long Term Fuel Trim Bank 1 : 39.8 %
0C : Engine RPM : 697 rpm
0D : Vehicle Speed : 0 MPH
0F : Intake Air Temperature : 84 °F
 

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If Lt fuel trim is high positive at idle and decreases as rpm/load increases then chances are a vacuum leak causing the P0171.

Clamping off the purge vacuum control line may have opened the purge valve causing lean condition.

When you get a P0171 without intentionally causing it and it happens at idle/low RPM suspect vacuum leak.
If at higher RPM/loads then suspect maf/fuel..

Yes, no schrader so maybe better to have shop check running pressure/pressure drop/ injector fuel flow.
Otherwise auto parts store loan fuel test kit but need correct adapters.
 

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yes, that's the one responsible for checking up on mixture and creating fuel trims. It's a feedback loop, the sensor says rich so the computer goes lean, the sensor says lean so the computer goes rich, tiny bit back and forth. If the sensor is stuck lean then it'll keep adding fuel till it hits the 20% limit and sets a lean code.
 

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Discussion Starter #13 (Edited)
I replaced the upstream O2 sensor with a genuine Denso sensor and the spark plugs with NGK Iridium (OE spec) BKR5EIX model. I got the P0171 again after a short drive. Here is the freeze frame data.

Trouble Code P0171 triggered Freeze Frame.
Code Def: System Too Lean Bank 1
PID : Description : Value
04 : Calculated Engine Load Value : 16.5 %
05 : Engine Coolant Temperature : 194 °F
06 : Short Term Fuel Trim Bank 1 : 19.5 %
07 : Long Term Fuel Trim Bank 1 : 29.7 %
0C : Engine RPM : 712 rpm
0D : Vehicle Speed : 0 MPH
0F : Intake Air Temperature : 104 °F

I don't know if this is relevant but I occasionally observe spikes in the IAT value when observing the live data. Here is a screen shot of one of the spikes.
 

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Discussion Starter #14
I was out driving the car earlier and under load i would get a LTFT of 18 with the throttle pedal depressed. When I let off the throttle, the LTFT would shoot up to 28 while the car was decelerating. Does this mean anything to anyone?
 

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FT large vacuum leak at idle, decreasing with engine load probable vacuum leak.
Can't say if IAT spike causing lean condition.
If maf reading good at idle then keep looking for vacuum leak.
You mentioned replacing injector O rings?
 

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Discussion Starter #16
In preparation for doing the fuel injector o rings, I removed the valve cover. It was brittle and there was a slight crack in one section between the 3rd and 4th ignition coils, the section of gasket where the center most bolts screw the valve cover into the head. I will replace the valve cover gasket when I do the injector rings which are still in the mail.

If I can't get this thing fixed by those methods them I'm taking her to a pro.
 

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Discussion Starter #18 (Edited)
I took the fuel injectors off and ran carb cleaner through them while under pressure and activated with current from a battery. I then backflushed them the same way. All four injectors held pressure when they were not activated by the current and at the end of cleaning had a uniform wide "V" spray pattern than seemed effective at atomizing the carb cleaner. The lower plastic rings were a bit cracked and not very flexible. They didn't seem to be too terribly clogged or displaying a poor spray pattern before cleaning. I will be installing a new valve cover gasket, throttle body gasket, and new fuel injector rings this evening and will report back.
 

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Discussion Starter #19
I replaced the fuel injector o-rings, valve cover gasket, throttle body gasket, spark plugs, O2 sensor, MAF, and I still have a 19.5+ LTFT after resetting the computer. The good news is I'm not getting that astronomically high LTFT anymore (35%)

I have tried for the life of me to find a vacuum leak on this car. The gaskets I replaced were worn and hard and my STFT numbers are back to a normal level. I can't find any vacuum leaks in the hoses or pipes but some of them are fairly rigid from heat and time. The car is not setting a code but doesn't a LTFT that high mean it is running lean?

I don't mind using a bit more fuel if the engine is safe and it will pass emissions.

Should I replace the vacuum lines?
 

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19.5 is just under the 20% threshold for being too high for most cars, I would not be happy seeing 20% on either of my cars. You can use carb cleaner or propane gas (unlit torch without the torch tip) to help find the leak, look for O2 sensor voltage to go high when the extra fuel is taken into the engine. Are there any exhaust leaks? An exhaust leak can set an O2 sensor to read lean and push the trims high too.
 
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