P0171 on 01 Echo with 19.5+ LTFT from 2 MAFs - Page 4 - Toyota Nation Forum : Toyota Car and Truck Forums
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post #46 of 69 Old 03-23-2017, 06:17 AM Thread Starter
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Originally Posted by oobuck View Post
What kind of scanner are you using

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I'm using a BlueDriver scanner with the iPhone app
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post #47 of 69 Old 03-23-2017, 03:42 PM
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I'm using a BlueDriver scanner with the iPhone app
Would that tell me why my speedometer and fuel gauge don't wotk

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post #48 of 69 Old 03-23-2017, 08:56 PM Thread Starter
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No, it would not.

Ok. So EFF THIS CAR. I pulled the entire exhaust and replaced the gaskets. No change in LTFT. Still at 19.5+

The fuel pump swap didn't do anything. I'm back to 19.5+ LTFT.

WHAT THE EFF?!?!?!

What could possibly still be wrong with this damn thing?
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post #49 of 69 Old 03-23-2017, 09:08 PM
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any gaskets down stream of the O2 sensors won't matter for LTFT.

Maybe you've got a bonked ECM? I had that once in a Chevy truck, it would NOT control fuel trims at all. Trims were always zero and it was running like crap, new ECM and it was fine. Something had gone wrong with the ROM inside it I guess.
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post #50 of 69 Old 03-23-2017, 09:33 PM Thread Starter
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These cars don't have chip keys.... do they have to have the ECM reprogrammed to work?
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post #51 of 69 Old 03-23-2017, 09:35 PM
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I don't think so, but I'm not confident it's a bad ECM, it seems to be responding when you add propane to push the trims around. Maybe go for a drive with some propane added to the air intake via a tube and see if that does in fact push trims toward zero or even toward negative. That would confirm the PCM is working properly.
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post #52 of 69 Old 03-27-2017, 04:16 PM Thread Starter
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Ok lads, so I'm pretty sure my catalytic converter was clogged because I had a noise that sounded like one of those silly cold air intakes the tuners put on their car, hesitation, and the fact that I rain it with 35+ LTFT for 200 miles and the car has 190,000 miles on it.

So, I gutted the cat. I reinstalled the exhaust system and reset the computer. I allowed the car to come up to operating temperature and go into closed loop. The change in LTFT was almost instant. I took it for a 20 mile drive and let it idle, drove in normal stop and go traffic, and got on an interstate to go fast and to accelerate quickly.

The change in throttle response and MAF flow was noticeable. I have attached a screen shot of my trims and MAF readings after I gutted the cat.

I plan on replacing the cat after researching prices and finding a good brand. I don't mind paying for quality to get this thing fixed once and for all.

Can anyone explain how a plugged exhaust system would have such an effect on fuel trims?
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post #53 of 69 Old 03-27-2017, 07:22 PM
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That's weird but I guess if it's not passing exhaust it wouldn't be able to empty and refill the cylinders with the proper mix of air and fuel, exhaust could have been partially displacing the fresh charge and making it a lean mix, like if the EGR valve was stuck open.
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post #54 of 69 Old 04-21-2017, 10:07 PM
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lean code

I had that problem. It turned out to be a vacum hose running off the MAF, the end cracks causing an air leak. If you find cracks cut them off and see if that helps. If it does buy a new one from the dealer. good hunting!
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post #55 of 69 Old 04-22-2017, 09:20 AM
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Ye gods! U guys have the patience of a saint....


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post #56 of 69 Old 11-01-2018, 12:57 PM Thread Starter
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Update after a year and a half: still stuck with 19.5 LTFT and have no idea why

Edited to add: replaced catalytic converter to pass state emissions test. No codes.

Last edited by priceprice; 04-06-2019 at 03:08 PM.
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post #57 of 69 Old 11-04-2018, 08:08 PM
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Try some Chevron Techron Injector cleaner. My P0171 code disappeared after that single action (200k miles). Worth a try seems like you have done EVERYTHING else.
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post #58 of 69 Old 11-28-2018, 11:51 PM
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Anyone fix this? Samething with my mothers 2000 corolla. Her STFT is at about 12.5 and her LTFT at 19.5 steady. The car idles smooth at about 850-900 RPM. And throws the P0171.
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post #59 of 69 Old 12-24-2018, 03:49 PM
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Anyone fix this?
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post #60 of 69 Old 04-06-2019, 03:06 PM Thread Starter
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Updated: still have persistent 19.5 LTFT. No vacuum leaks detected with smoke machine. New-remanufactured injectors didn’t help. Car runs fine. Sometimes shudders when stopped and in gear (auto). No codes.
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