Tired of Replacing Parts- ISO a real fix

Gary Service Advisor Columbus, Ohio Posted   Latest   Edited   Bounty  
Bounty
Driveability
2005 Toyota Corolla CE 1.8L (1ZZ-FE) 4-spd
P0171 - System Too Lean Bank 1

My tech has been banging his head against this car for weeks, and the only solution he can come up with is throwing more parts at it. He has already replaced BOTH O2 sensors, the mass air flow sensor, spark plugs, and the air filter. I can't keep asking the owner to pay for things that aren't fixing the issues. What else can I have my tech look at?

EDIT/UPDATE:

Test that were done: 

-Long term fuel trims were 7% at idle and went to around 21% under load

-Tech said mass air flow was around 2g/s at idle. Aftermarket and OEM sensor made no change

-Smoke test showed no leaks and flow gauge was near 0

Thanks everyone for helping me out. This is a newer tech just building his diagnostic process. We're focusing him on training and this was a great learning experience for him. Please understand this tech is NEWER and was looking for a direction, not a silver bullet. Thanks to all that helped us. 

FOLLOW UP:

-Tech put about 30 miles on the car, no check engine light

-Fuel trims never go over 5%

-Car has plenty of power. I'm calling this a fix. Thanks again. 

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Chris Diagnostician
Bryans Road, Maryland
Chris Default
   

What all has been tested? Any history on the car? Does it run ok ? The more info you can give us the better. Have you tried to smoke the intake with the throttle body caped off. The intake gaskets are pretty common to leak. You could also try to spray some brake cleaner around the intake and see if it affects the fuel trims.

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Gary Service Advisor
Columbus, Ohio
Gary Default
 

-The car runs fine at idle. -The tech sprayed the intake manifold (no change) -I will have him smoke the intake

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Luis Technician
Lake Forest, California
Luis Default
 

smoke intake manifold, check for leaks, spray propane and see if o2 responds, injector balance test, possible an injector issue, what are fuel trims at idle and off idle? What is mass air flow reporting at idle with no loads? are new parts denso or original from dealer?

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Paul Owner/Technician
West Collingswood, New Jersey
Paul Default
 

You must leaking intake manifold gasket. Smoke test when cold.

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Eric Owner/Technician
Edgerton, Wisconsin
Eric Default
   

Please post all tests performed along with the results of those tests. That will allow us to help you. If all you want are silver bullets I would suggest replacing the engine, complete fuel system, the air inlet system from the air cleaner to and including the intake manifold and the exhaust system from and including the exhaust manifold to the tail pipe. :-)

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Tanner Instructor
Wellford, South Carolina
Tanner Default
 

At idle look at fuel trims, slowly bring engine rpm up to around 3000 and see if fuel trims start to go back towards zero. If they do then suspect a vacuum or intake leak. If they don’t then you likely do not have an intake leak. have your technician drive the vehicle and do a wide Open throttle pull and record the entire Data capture when he does it. Record engine rpm, maf and iat. Then after…

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Gary Service Advisor
Columbus, Ohio
Gary Default
 

I'll have him do your test next

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
   

For direction we need to know what the fuel trim trends are. We need to know what the fuel trims are reading at idle, 2500 RPM, city cruising speeds and on the highway. Not just STFT but all trims or the TOTAL fuel trim. This will give direction. Example. Idle trims near normal would not have me focused on an induction leak as a starting point. Edited to request Freeze Frame Data. Let's get a…

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Bill Owner/Technician
Jackson, Michigan
Bill Default
 

Intake gaskets are very common - Smoke test with cold engine (spraying with brake clean Not acceptable method...) There are also 2 related TSB 's for your fault code Can you supply some useful data? fuel trim numbers, MAF, O2 readings front and Rear

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John Technician
Morgantown, West Virginia
John Default
 

Check the intake boot going from air cleaner housing to throttle body, make sure the resonator and what not is there and intact. I’ve ran into a few issues where the resonator was deleted and the hole capped off causing a similar condition. If everything looks good there. Bring the engine off idle to about 2k and see if the fuel trims start to go back to normal. Post any pictures of engine data…

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Pj Technician
Pleasant Hills, Pennsylvania
Pj Default
 

You have received many good answers. My suggestion is to check the flow of all 4 fuel injectors. Its an extremely common problem with these that I see at my dealership regularly. It may sound crazy that all 4 are bad. But I see it about once a month. I use an injector pulse tool and a fuel gauge to see how much each injector drops. They'll all drop evenly, because theyre all probably bad. But…

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Jeff Diagnostician
Cathedral City, California
Jeff Default
 

I agree with everyone else , more test data would be helpful , Volumetric Efficiency test is important and so is knowing when it is lean . That being said I had a 02 corolla come to me with all the same parts you have installed hanging off of it and it still set lean codes. To make a short story shorter I did an injector pressure drop test and found 2 injectors with 4lbs difference in drop, it…

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Florin Technician
Niagara Falls, Ontario
Florin Default
 

Hi Gary, it might not be relevant but I had recently a similar issue with VW Beetle, after replacing almost everything we found leaks with the smoke machine at, we still had this lean condition code. That is when we realized that the most basic fuel pressure test was not performed during the diagnostic. After performing the fuel pressure test while running we found that fuel pressure was at…

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Gary Service Advisor
Columbus, Ohio
Gary Default
 

The tech checked the fuel pressure and it was good at idle. When he drove it, the pressure dropped dramatically! He will replace the pump and recheck. I will get back to you with the results. Thanks!!

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
 

A restricted filter can behave that way. It may flow enough at idle but not under load.

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Florin Technician
Niagara Falls, Ontario
Florin Resolution
 

That is right Jim and I would recommend starting with the filter as we did too prior to replacing the pump

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Gary Service Advisor
Columbus, Ohio
Gary Default
 

Replaced the fuel pump (this car doesn't have a separate fuel filter) and the pressure stayed steady. FUEL TRIMS ARE BACK TO NORMAL! Will Drive the car to confirm fix, but this looks like it's good. Thanks!

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Florin Technician
Niagara Falls, Ontario
Florin Default
 

Looks like that was your problem, but just to make 100% sure, drive for a little longer and maybe a few ignition cycles and if code doesn't return you are rocking.

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
 

My initial reply, asking for how trims were tending with load as well as freeze frame was intended to help target the testing. I hope this has actually been a good learning experience for you and your tech. Use data and operational strategy where you can to know when and WHY to preform a test. This zeros in faster on the cause. There is a great QTG (Quick Training Guide) Toyota has on…

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Gary Service Advisor
Columbus, Ohio
Gary Update
 

Update: -The Tech smoked the intake and found no leaks. -The Fuel trims were 7% at idle and got higher as he drove it. -There was a denso mass airflow sensor from Worldpac and then swapped that out for an OEM sensor

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Michael Technical Support Specialist
Concord, California
Michael Default
   

If your lean condition is worsening as he is driving the vehicle, this is most likely pointing to a fueling issue. As others have mentioned, fuel injectors are not an uncommon issue on this engine. Assuming you have tested the fuel pressure and it is within specs, I would remove all 4 injectors and test them off-car.

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Mike Diagnostician
Toronto, Ontario
Mike Default
 

Without much info and just merely spitballing here - I seem to recall many moons ago that a colleague of mine who worked for Toyota replaced a brake vacuum booster for a system too lean fault......just a thought if all else fails Mike

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Bob Owner/Technician
East Longmeadow, Massachusetts
Bob Default
 

Gary, I think You need to have your tech take a step back for a minute and then perform some testing and analysis first. You need to look at fuel trims and other data to see how the engine runs under various conditions. This kind of testing will give you the proper direction and dictate what pinpoint tests need to be performed. More time needs to be spent with the scanner before replacing any…

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Rudy Technician
Montebello, California
Rudy Default
 

Check the fuel quality. Had a Saturn with excessive ethanol that drove me nuts for a few days some years ago. Also check fuel volume/pressure. Flat rate test is to drive the vehicle at WOT for as long as possible and graph the rear O2 sensor. Should be pegged at .8v or higher and never drop out until you let off of the gas.

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Michael Owner/Technician
Montague, New Jersey
Michael Default
   

First off, where did you get the parts? If you ordered oxygen sensors and the MAF from the auto parts store, what brand? Do you have the originals? As has been noted intake gasket leaks are somewhat common but bad MAF's are even more common. However, do not overlook the vacuum lines. I have personally had zero luck with anything except OEM parts on Toyota especially electronics. Throwing parts…

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

I feel your pain. Why not let the vehicle tell YOU what is the problem. Go here and read the post diag​.​net/msg/m61bqk58h6… , then capture the information that is needed. Post the information up that the vehicle spits out. Now, post that information here, so it can be discussed. The vehicle has the answer to your problem, All you need to do is ask the correct questions.

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Daryll Diagnostician
Seymour, Tennessee
Daryll Default
 

When does freeze frame say the fault set? Idle? Light cruise? Heavy throttle? Cold? Hot? What is fuel pressure? Does fuel pressure maintain while under load during accel?

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Daniel Owner
Long Beach, California
Daniel Default
 

I have fix this issue with injectors they get restricted very common on toyotas ba e him look at the fuel trims most of tbe times long term will be high at high rpm but preaty sure thats ur problem if u have no leaks or a bad maf

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Keith Diagnostician
Staten Island, New York
Keith Default
 

The answer you are looking for is simple. I've tested many of these injectors and a good one will drop 12psi under a pulse test using an otc tester . 10 psi is where we commonly hit that p0171 point. I probably diagnose this on average of 20 times a year.

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Tanner Instructor
Wellford, South Carolina
Tanner Default
 

What was the fix?

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Luis Technician
Lake Forest, California
Luis Default
   

It seems like the fuel pump, and Florin that was rewarded suggested the fuel pump and filter

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Thomas Technician
Manassas Park, Virginia
Thomas Default
 

Gary I was going to add this but before i did i had to read all the replies first. Looks like your tech figured it out. I highly suggest your young tech read some of these articles and watch the video of Fuel trim on Automotive Test Solutions website. automotivetestsolutions​.​com/escan-training…

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