1999 Lexus ES300 P0171 trouble

Alex Technician San Diego, California Posted   Latest   Edited  
Question
Driveability
1999 Lexus ES300 3.0L (1MZ-FE) 4-spd (A541E)
P0171 - System Too Lean Bank 1
System Too Lean Bank 1

I have here a 1999 Lexus ES300 with codes P0171, and P0420. I needed some pointers or if someone has encountered similar codes or symptoms with this vehicle. So far I was able to repair two vacuum leaks one being @ the brake booster hose, and the other at the intake/induction hose boot revealed by a smoke machine test. Got a new Denso A/F Ratio sensor, and my supervisor bought a used Catalytic converter, you know how that goes anyway still the same issue. 

Got freeze frame data: 

  • Calculated Load Value - 42.75%
  • Engine Coolant Temperature - 159.8 F
  • Engine RPM - 2,512 RPM 
  • Fuel System 1 Status - CL 
  • Short Term Fuel Trim Bank 2 - 0% 
  • Vehicle Speed Sensor - 44.12 MPH 
  • Fuel System 2 Status - CL 
  • Intake air temperature - 77 F*
  • Long Term Fuel Trim Bank 1 - 39.84%
  • Long Term Fuel Trim Bank 2 - 42.97%
  • Short Term Fuel Trim Bank 1 - 0%.

Any suggestions? If I come to any conclusion I will re-post my results, and findings here.

- Alex

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Guan Diagnostician
Sacramento, California
Guan
   

i have seen a few with injecto seals leaking but that’ll show in a smoke test which you’ve done already What’s the upstream read when WOT? Maybe fuel pump? bad MAF? if you have other drivability codes along with a P0420. Should always nail down the other first

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Alex Technician
San Diego, California
Alex
 

I don't remember off the top of my head but I have the data saved and it was @ around 3.3V @ Idle with very little change.

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Daryll Diagnostician
Seymour, Tennessee
Daryll
 

Have you checked the maf elements for buildup?

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Alex Technician
San Diego, California
Alex
 

I have tested the MAF but have not done a visual inspection of the MAF Sensor element itself.

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Albin Diagnostician
Leavenworth, Washington
Albin
 

Since fuel trim is an active pid, then use your scan tool to gather the needed information, and let the scan tool direct you to the problem. Select RPM, throttle blade position, load, MAF, oxygen sensor voltage for all sensors & long & short term trims, now take it for a drive going from idle through a WOT shift point, then cruise. With that information, you will have your direction

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Alex Technician
San Diego, California
Alex
 

Ok I will capture, and record that data thank you.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff
 

Since your Freeze Frame data showed us the LTFT is very high at cruise, as opposed to at idle, I believe you have an actual fuel delivery problem, not a vacuum leak. However, you could also have bad MAF. To help narrow it down; Check the fuel pressure under full load. Also, do a VE test by recording your scan tool and using one of the available online tools. Add those results when you post the

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Alex Technician
San Diego, California
Alex
 

Ok will do thank you, I will post the calculations, and screenshots of the data captured.

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Robert Owner/Technician
Scunthorpe, United Kingdom
Robert
 

Hi Alex, I had an issue a couple of years back with a GS300 here in the UK, turned out there is a manufacturer issue with the fix being a pair of modified lambdas and a replacement ECU with a software update, I'm unsure why the fitted ECU couldn't have had the SW loaded but I just followed the manufacturer TSB and it sorted mine. I have the TSB but it will not let me upload them - says the file

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Alex Technician
San Diego, California
Alex
 

I see, I have looked up some TSB's but didn't find anything in particular for this problem. I'd like to see that TSB that would be helpful I will email you, thank you.

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Michael Owner/Technician
Montague, New Jersey
Michael
 

Check the air intake tube for cracks. Ck the PCV valve. Make sure it is the correct one and not aftermarket. The karman vortex MAF on these rarely fail and are very expensive. Ck the a/c idle up and the hoses. Has anyone had the intake plenum off? If so the center bolts and nuts MUST be tightened first before the bracket bolts, otherwise you will have a vacuum leak.

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Alex Technician
San Diego, California
Alex
 

Ok I see. Yes I have done a smoke test, and it did already uncover a torn intake boot.

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Alex Technician
San Diego, California
Alex
   

Here is some of the data I have gathered. Mr. Moore, and Mr. Welsh I have gathered those pieces as advised, and here's what I got. To me its looking like a MAF Sensor problem, but the throttle position looks a little odd as well since i do have the pedal all the way to WOT, anyway I have yet to continue. Back at it tomorrow!

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Guan Diagnostician
Sacramento, California
Guan
   

Can those graphics be zoomed in a little? Kinda hard to see. Also, old cars like that computer is really slow. i’d pick fewer pids for better and faster sample rates.

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Alex Technician
San Diego, California
Alex
 

Yes here they are, these first 6 pictures are @ Idle.

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Alex Technician
San Diego, California
Alex
   

And these are @ WOT

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Chad Technician
Winter park, Florida
Chad
 

Wot shows very lean. Idle shows rich. Gotta check fuel pressure With a gauge At idle and wot. Make sure there are no blockages in the intake track, like someone leaving a rag in the air box. Im gonna guess maf

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Alejandro Technician
San Diego, California
Alejandro
 

Ok, will do.

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Albin Diagnostician
Leavenworth, Washington
Albin
   

Alex, I have read over all the replies, and the data you have posted. Please be patient with me, since I'm old and lazy. I have spent many years with a scan tool, and have found ways to get it to tell me what the problem is. Most times I will use a Snap on scan tool for this kind of work, since it does a great job of both capturing data, and displaying it in a format that is easy to

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Alejandro Technician
San Diego, California
Alejandro
 

Ok, thank you again Mr. Moore, and no problem. The way you explained it to me the first time helped. I took your pointers, and got to working on the car, and found my clues, hints, and data pieced it altogether, and got a confirmed fix. I have a Launch scan tool but the Matco tools version. I plan to invest on a OTC Evolve Scan tool but I would first like to purchase a pico. The shop I work at

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Daryll Diagnostician
Seymour, Tennessee
Daryll
 

After reading your info, I would recommend doing a TPS sweep test with a scope/graphing multimeter because that pid isn’t reading right. Could have a scan tool data issue as well. Also the MAF barely hitting 40 g/s at WOT is a problem. But here’s my question: did you record this while driving the vehicle? Or did you do this in a stall? Vehicle needs to be under max load while accelerating, an

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Alejandro Technician
San Diego, California
Alejandro
 

Yes, I did this while driving the vehicle. The vehicle drives fine, its does not have a stall condition.

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Alejandro Technician
San Diego, California
Alejandro
   

Here are the final results for a confirmed fix for P0171 on this 1999 Lexus ES300 thank you for everyone's input. As for the P0420 it also needed the Cat at the very rear of both banks, along with the O2 sensor just to cover my butt, but anyway here is the data for both the vehicle @ Idle, and WOT with the MAF Sensor replaced, and also the results of the VE Calculation with the data entered. I

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Chad Technician
Winter park, Florida
Chad
 

That is a dirty maf! Good job bro. Great community

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Alejandro Technician
San Diego, California
Alejandro
 

Indeed it is! Thank you, great community indeed everyone had amazing input into this problem. Happy New years!

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