97 Lexus ES 300 runs lean on bank 1

Mathew Technician California Posted   Latest  
Resolved
Driveability
1997 Lexus ES300 3.0L (1MZ-FE) 4-spd (A541E) — JT8BF22G6V5013227
P0171 — System Too Lean Bank 1
Lacks Power Under Load

Car came in with codes p0171 and p0441 evap purge fault. found purge valve stuck open at all times. Replace purge valve clear codes and test dive noticed severe lack of power under heavy load. scan tool o2 data showed bank 1 #1 and bank 1 #2 o2 sensors lean 0 volts bank 2 #1 reads .9 volts. Perform VE test came out 85% should be good for breathing faults. power brake engine until it bogs out and o2 runs lean add carb cleaner to intake engine power comes up and o2 sensor reads rich. there is one reading for injector pulse on scan data when problem happens read 11ms . check each injector with Modis edge lab scope bank 2 normal bank reads 11ms bank 1 reads 16ms, looks like computer is trying to richin it up. also did fuel pressure test at fuel filter and fuel rail 50 psi under load and steady. I thought had to be bad fuel injectors, replace all injectors same problem. customer said thats the problem he has been having and had it at the dealer last month they replaced fuel pump and filter, Mass air flow sensor, and pcm they got a used one when it did the same thing they put original back in. I did verify that cam timing is on and that the exhaust is not restricted and that alternator is not putting ac voltage out. running out of ideas any help appreciated. One more thing when I did fuel pressure test on the fuel rail it was on bank 2 side, looks like the fuel damper inplace of a traditional vacuum regulator looks new could they come in different sizes cuting fuel flow to bank 1 ?

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Glenn Owner/Technician
Texas
Glenn
 

Hello Mathew, The way All Data reads, this is not a bank specific code, but your bank 1 is staying fixed at 0 according to what you are seeing? Both banks should be switching. Both bank 1 sensors stay steady at 0 would indicate they are not reading in my opinion. Have you run the flow chart for the code? Apparently, everyone else has been throwing parts at this thing. I am surprised a dealer…

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Kevin Diagnostician
New Zealand
Kevin
 

Hi still sounds like one of the cats is blocked ,are they up in the manofolds you have one side too. Lean and one side too rich.0.9 is maxed out rich you could try driving with both precat o2 sensors removed to see if power improves. swap precat o2 senors over to confirm operation.

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Cody Diagnostician
Illinois
Cody
 

seen a case study like this where one bank cat was partially restricted pushing more air from intake into free flowing cat. bank that is rich is likely partially restricted. id second pulling precat O2 sensors and test drive to confirm if power returns.

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Glenn Owner/Technician
Texas
Glenn
 

Hi Cody, You bring up a good point, I recall a case study as well. I think it was a Chevy 5.3 0r 5.7. It turned out to be one side was restricted. I think it was a You Tube done by South Main or Scanner Danner, it was a few years ago. At the time I thought it was not possible, but it was.

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Ted Owner
Texas
Ted
   

What do fuel trims look like? Exhaust back pressure at 2500rpms?

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Cameron Technician
Ontario
Cameron
 

i think if this were me I'd be drilling a hole in the exhaust ahead and after the cat and measuring diff between pressures. Anything more than 1 psi is a restriction. I had a cat yesterday (single cat) that the owner said was ‘fine’ as it was only 2 years old. Turned out to be partially plugged and that was the problem. I use 3/16" brake line so I can attach a pressure gauge. Easy to weld up if…

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Stephen Technician
Tennessee
Stephen
 

How about using an in-cylinder transducer to check exhaust back pressure? And a temp gun to check temperature of each exhaust port? Having this B1/B2 disparity really leans on a breathing problem. Then there’s the old O2 sensors plugged in reverse thing to wonder about.

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Matthew Diagnostician
Kentucky
Matthew
   

Is there any way you can provide some scan data showing tps, overlaid with fuel trims and maf, map and rpm this would aid in assisting you

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Mathew Technician
California
Mathew Update
 

Let me add more info sorry first time posting system is 1 catalytic converter o2 sensor each bank one after the cat. exhaust back pressure 1 psi on snap test 2500 rpm. at idle fuel trims 0 to 5 both banks ¼ load same fuel trim both banks o2 switching normal. at above ½ load bank 2 fuel 0 to 3 and o2 sensor switching normal intill full load then goes to .9v normal, bank 1 ½ load fuel trim 12 to…

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Ted Owner
Texas
Ted
 

Your back pressure test isn't representative of the engine exhaust dynamics when your problem is occurring. Brake torque load test or actually road test in same situation where you have been duplicating the issue and see what you back pressure is. I've had vehicles that it may take 3 miles at 60mph to duplicate a restricted exhaust situation.

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Matthew Diagnostician
Kentucky
Matthew
 

hey bud If your exhaust pressure seems good then i would be focusing on the possibility of the timing being off on the bank 2. It looks like there is a breathing issue however it might be good practice to ensure your moving a lot of air through the engine when performing the back pressure test. However it seems reproduceable at idle and when you add fuel it appears it doesn't bog. This according…

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Richard Technician
Virginia
Richard
   

Your description sounds like you are getting less available volume to bank 1. I would disassemble the piping to the rails. Pay attention to the fit of the damper. The fuel flows through the pipe into the banjo and exits through a second pipe , then into the bank 2 rail. I believe the bank 1 rail gets the fuel through the damper or possibly the gaskets. I think some of those aluminum gaskets had…

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Mathew Technician
California
Mathew Resolution
 

sorry to say this one didn't get resolved customer came in yesterday saying they made a deal on a new car and needed to trade it in. thanks for all the help. I didn't get a chance to check the fuel rail as Richard recommended.

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John Mechanic
Massachusetts
John
 

O2 sensors or air fuel ratio two different sensors they dont read the same

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