P0171 on 01 Echo with 19.5+ LTFT from 2 MAFs - Toyota Nation Forum : Toyota Car and Truck Forums

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post #1 of 44 Old 02-26-2017, 09:47 PM Thread Starter
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P0171 on 01 Echo with 19.5+ LTFT from 2 MAFs

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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File Type: png IMG_4329.PNG.png (130.2 KB, 19 views)

Last edited by priceprice; 02-26-2017 at 09:52 PM.
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post #2 of 44 Old 02-27-2017, 10:16 AM
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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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post #3 of 44 Old 02-27-2017, 12:47 PM Thread Starter
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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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post #4 of 44 Old 02-27-2017, 04:21 PM Thread Starter
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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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post #5 of 44 Old 02-27-2017, 08:06 PM
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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.

Last edited by cj1; 03-01-2017 at 09:08 PM.
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post #6 of 44 Old 02-27-2017, 09:09 PM Thread Starter
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It happens at idle and under load. I am ordering fuel injector o-rings and will see how that helps.
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post #7 of 44 Old 02-27-2017, 09:45 PM
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Lets us know if fuel trim comes down to normal.
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post #8 of 44 Old 02-27-2017, 09:45 PM
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It could be a bad O2 sensor that's skewed to a false lean. Introduce some propane to the air intake while idling to see how the O2 responds, it should go rich, then make a vacuum leak to push it lean. After about 100k miles O2 sensors get weak and can do bad stuff like this.
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post #9 of 44 Old 02-27-2017, 09:56 PM Thread Starter
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By going rich, do you mean that the short term fuel trim should go negative?
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post #10 of 44 Old 02-27-2017, 10:17 PM
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I mean the O2 sensor voltage should be over 450mv
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post #11 of 44 Old 02-27-2017, 10:59 PM Thread Starter
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The pre cat sensor I assume?
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post #12 of 44 Old 02-27-2017, 11:25 PM
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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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post #13 of 44 Old 03-01-2017, 03:44 PM Thread Starter
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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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Last edited by priceprice; 03-01-2017 at 03:48 PM.
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post #14 of 44 Old 03-01-2017, 06:08 PM Thread Starter
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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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post #15 of 44 Old 03-01-2017, 09:11 PM
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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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