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Higlander is running lean on bank 1 (P0171)


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gausse
Novice

Jul 29, 2016, 11:18 PM

Post #1 of 16 (1246 views)
Higlander is running lean on bank 1 (P0171) Sign In

I have a 2002 Toyota Highlander V6 with 250k miles. It runs decent when cold but when it warms up it runs very poorly, missing and bogging down on acceleration. It generates P0171 error (lean bank 1) and cylinder misfire errors (P300,P301,P302,P305). I replaced plugs and coils a year or so ago, recently replaced bank 1 O2 sensor and main cat converter and cleaned MAF. From what I gather P0171 can mean vacuum leaks, Mass Air Flow (MAF) sensor, bad PCV, fuel system problems.

Trying to narrow it down and have these questions:

1. If the car runs fine when cold, can fuel system issues be ruled out?
2. Would a bad MAF cause errors on both banks, rather than just bank 1?
3. The rear O2 sensor (after cat converter) is dead, what if anything would that effect?

The intake plenum was removed twice to do the plugs and coils. I am wondering if that gasket may have been damaged. Could a bad plenum gasket cause a vacuum leak and error only on bank 1 though?


(This post was edited by gausse on Jul 30, 2016, 12:16 PM)


Hammer Time
Ultimate Carjunky / Moderator
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Jul 30, 2016, 6:16 AM

Post #2 of 16 (1231 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

Have you tested for a plugged Cat?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



kev2
Veteran
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Jul 30, 2016, 11:19 AM

Post #3 of 16 (1219 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

Do you have a scanner, vacuum gauge, fuel pressure gauge? Also sensors should come from TOYOTA. What are ALL the codes you have as you mention post cat is dead?


1. If the car runs fine when cold, can fuel system issues be ruled out? CHECK fuel pressure. use a gauge and let us know.

2. Would a bad MAF cause errors on both banks, rather than just bank 1? No MAF code then Using a scanner look at data - no oiled air filter !!

3. The rear O2 sensor (after cat converter) is dead, what if anything would that effect? What does "dead" mean here? Use ONLY Toyota sensors.


The intake plenum was removed twice to do the plugs and coils. I am wondering if that gasket may have been damaged. Could a
bad plenum gasket cause a vacuum leak and error only on bank 1 though? Check for vacuum leaks, use the old school spray trick...
Why did you NOT replace gasket AND depending on where leak is no idea what is affected...


gausse
Novice

Jul 30, 2016, 11:55 AM

Post #4 of 16 (1213 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

Has a brand new Cat Converter (2 weeks old).


gausse
Novice

Jul 30, 2016, 12:09 PM

Post #5 of 16 (1208 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

Little more background. It was running poorly as described and I was getting error codes P1155, P0300,P0302,P0306.

I took it into repair shop for diagnosis. They ran diagnostic tests and recommended motor vac and new O2 sensor. Also noted that rear sensor was at 0.0 volts and said they tightened a loose vacuum hose on throttle body. Ran the same after visit and vacuum hose tightening. Said is was running very lean.

I replaced the O2 sensor and used some fuel system cleaners. The P1155 went away and was replaced by the P0171 error I have now.


(This post was edited by gausse on Jul 30, 2016, 12:13 PM)


gausse
Novice

Jul 30, 2016, 12:22 PM

Post #6 of 16 (1203 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

Don't have a vacuum tester/fuel pressure gauge yet.
If the pressure were bad, would it create a problem only when warm? Works fine when car is cold (1st 5-10 minutes).


kev2
Veteran
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Jul 31, 2016, 8:36 AM

Post #7 of 16 (1177 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

OK so no scanner, no fuel pressure tests, no vacuum leak testing.....
Did you want to guess Or troubleshoot ?


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 31, 2016, 9:30 AM

Post #8 of 16 (1174 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

I guess you'll be needing this





~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 31, 2016, 1:01 PM

Post #9 of 16 (1158 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

Watched right along.


Quote from top line........
">>I have a 2002 Toyota Highlander V6 with 250k miles.<<"


Need anyone do anything till this is declared worth touching anymore at all?


T



gausse
Novice

Jul 31, 2016, 9:24 PM

Post #10 of 16 (1138 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

The questions I had were more general, to better understand how the systems work:


1. If the car runs fine when cold, can fuel system issues be ruled out?
2. Would a bad MAF cause errors on both banks, rather than just bank 1?


Can a car run well when's it is cold and then when its warm (and computer kicks in) still have fuel system (pressure, etc.) problems? Wouldn't fuel problems be there when its cold as well? Is fuel pressure constant or is it adjusted by the computer?


Can a bad MAF sensor or vacuum leak cause the bank P0171 error? It's a V6 and only one bank is reporting the error, but not both. Wouldn't a MAF problem cause an error on both banks?


The auto shop had it on the scanner as part of the testing and did not report fuel pressure or vacuum problems. Plan to pick up a vacuum tester and give that a try. Have a basic code reader, but not one that reads live data. Will get a better scanner to get more detail.


gausse
Novice

Jul 31, 2016, 9:32 PM

Post #11 of 16 (1137 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In


In Reply To
Watched right along.


Quote from top line........
">>I have a 2002 Toyota Highlander V6 with 250k miles.<<"


Need anyone do anything till this is declared worth touching anymore at all?


T


Have had it since it was new and the 250k is mostly highway miles. It's in good shape for its age and can't afford a new one right now. Would love a new one though, it has been a great vehicle.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 1, 2016, 3:07 AM

Post #12 of 16 (1123 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

Good to know you've known the vehicle. It's impossible to know what "highway" miles really mean as if that doesn't count for use or something? A vehicle's parts all traveled that far and even so much as springs in seats, arm rests, knobs, handles, upholstery can get to a point it's just time to give up.


The question of can a vehicle still be totally useful for much longer at about this age and miles totally depends on how much has already been done or still totally good for more without endless surprises. It's hard to know all that situation by situation.


Every wire and hose has gone along for those miles begin to all be suspect long before this age. BTW - retired and all my own vehicles are much older that this but no miles, out of harsh conditions except one I must use others don't see so much as rain if I can help it - not the norm.


IMO - driveline hard parts can do the 300K mark with exceptional care. You almost never hear of much more than that,


T



Discretesignals
Ultimate Carjunky / Moderator
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Aug 1, 2016, 4:37 AM

Post #13 of 16 (1116 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In


Quote
1. If the car runs fine when cold, can fuel system issues be ruled out?
2. Would a bad MAF cause errors on both banks, rather than just bank 1?


1. Yes and no. Fuel system includes many things that could work fine when cold and fail when hot. Scan tool interpretation of the data (fuel trim, engine load, ect. O2 sensor voltages) can help paint a picture on what is happening.
2. Yes, a MAF sensor issue will affect both banks.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Aug 1, 2016, 4:39 AM)


gausse
Novice

Aug 17, 2016, 8:40 PM

Post #14 of 16 (1053 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

Getting long term fuel trim (LTFT) of 50 on bank 1 and bank 2 is normal (close to 0). The LTFT is around 50 at 1000-1800 RPM and drops down to 13.3 at 2179 RPM and 6.3 at 2643.

Did a vacuum gauge test but couldn't detect the problem that way (it was steady at 22, dropped to 5 on revs and recovered quickly).

The fact that the LTFT is bad on bank 1 and not bank 2 should rule out fuel pump or MAF correct? So maybe a intake leak? Could it be a bad plenum gasket? Had the plenum off twice for plugs and coils but gasket was reused.


(This post was edited by gausse on Aug 17, 2016, 8:44 PM)


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Aug 18, 2016, 4:15 AM

Post #15 of 16 (1038 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

What happens to the long and short term fuel trims if you pinch off the brake booster hose?





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


gausse
Novice

Aug 18, 2016, 9:04 PM

Post #16 of 16 (1011 views)
Re: Higlander is running lean on bank 1 (P0171) Sign In

After I drove home tonight I clamped the hose and checked the live data. The LTFT was -0.8 to 0 with a couple frames at 5.5 and 7. STFT was in the -0.0 to 3.6 range.

The strange thing to me was that even when I unclamped the hose the STFT and LTFT values didn't go back up to what I was seeing before. Took it back out for test drive and it was still bogging down on acceleration as before. When it is cold (open loop) it runs good and after warm it bogs on acceleration and seems better at higher RPMs.


(This post was edited by gausse on Aug 18, 2016, 9:08 PM)






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