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HELP needed , engine running to lean .

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Old 12 September 2017, 12:55 PM   #1
ducske916
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Default HELP needed , engine running to lean .

Hey ;

I have a stock impreza wrx 02 from a client that is running way to lean .
Also getting the faultcode p0171 . ( system to lean )
First off corse checked all the vacuumhoses and even blocked them off compleet . Stays the same . Car even starts cold at 17 AFR .
fuel trim go's directly to the max of 25% and even then it come's to a afr of 15.5 - 16 .


Things done :

- New fuelpump
- New lamdasonde ( first one )
- Other tmic
- AF sensor changed from a car that run's fine ( even from 2 different cars already )
- Changet the complete intake manifold incl injectors and fpr )with other one inc new gaskets and intakehose
- Checked timing belt ( is correct )
- Swapt ecu from other bugeye

Nothing that even chaged a bit the afr .
I'm realy with my back against the wall now....

Is it possible with let us say bad closing valve's you get a lean afr ?
I have no more idea's for the moment to look at .

Last edited by ducske916; 12 September 2017 at 12:58 PM.
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Old 12 September 2017, 01:12 PM   #2
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what make was the front sensor that was fitted ?
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Old 12 September 2017, 01:14 PM   #3
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Denso .

But can't believe even it as somting to do with the lamda sensor because it runs even lean at cold startup ( so still in open loop and not using the lamda sensor )
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Old 12 September 2017, 01:50 PM   #4
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try resetting the ecu to clear everything.
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Old 12 September 2017, 03:02 PM   #5
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Done the ecu reset ( with proecu , ecutek )
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Old 12 September 2017, 04:43 PM   #6
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maf?


I'd have said front lambda sensor (pre-turbo) too. Are you sure the new sensor is ok?
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Old 12 September 2017, 06:19 PM   #7
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take a look at your fuel trims, if the long term and short term have high positive numbers then it could mean a fuel delivery problem of some kind or fuel leak hence the lean condition.
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Old 12 September 2017, 06:39 PM   #8
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i checked all above items .
Now i did get the tip to disconect the maf , then the afr go's to 14.8 .
So maybe a problem in the maf wire's to the ecu . will check this first now .
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Old 13 September 2017, 08:51 AM   #9
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try another maf if you can get one.
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Old 13 September 2017, 09:22 AM   #10
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Any pre turbo exhaust leaks.
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Old 13 September 2017, 11:52 AM   #11
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also try cleaning the maf wire, spray with some carb cleaner/ brake cleaner and let it dry before refitting. theres videos on youtube if your unsure,
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Old 13 September 2017, 06:16 PM   #12
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checkt the maf sensor, 12v ok - ground ok and signal wire i put a wire direct to the ecu but still the same problem .
Maf is already bin changed with 2 other one's from fine running wrx'es ( and cleaned also with maf cleaner )


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Old 13 September 2017, 08:15 PM   #13
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Possibly a pre-turbo air leak. The standard turbo inlet pipe is prone to splitting where it joins the turbo compressor cover.

This would cause a maxed out fuel trim and 'system too lean' fault code to be generated.

A smoke/pressure test on the inlet would be a good idea.

Last edited by little'un; 13 September 2017 at 08:17 PM.
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Old 14 September 2017, 07:18 AM   #14
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Already changed the inlet pipe ( was a perrin one on it, changed it out together with the intake manifould to a oem one )
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Old 14 September 2017, 12:58 PM   #15
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Temp sensor?
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Old 14 September 2017, 01:23 PM   #16
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Manifold, upipe leak? Allowing oxygen into the exhaust and making sensor think it is too lean? The pulsing nature of the exhaust can pull air in as well as leak exhaust out.

Measured the actual fuel pressure in the rail?

Can you not read live sensor values using SSM? That would probably give a clue.

Is it misfiring? Running lean could cause a misfire, but a continual misfire may show lean on the O2 sensor, because of the excess of oxygen now in the exhaust.
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Old 14 September 2017, 03:05 PM   #17
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Up-pipe is new
fuel pressure with running engine 2.5bar @ rail
and like said, it does this even at cold start so then the lamdasensor even doesn't work ( open loop) so a exhaust leak can not be the problem
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Old 14 September 2017, 03:41 PM   #18
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Quote:
Originally Posted by TECHNOPUG View Post
Temp sensor?
CTS typically makes them run rich.
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Old 18 September 2017, 10:47 AM   #19
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You can't put the MAF in the wrong way round on these can you?
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Old 18 September 2017, 10:50 AM   #20
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Stock air box? Cone filters etc can muck up MAF readings.
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Old 19 September 2017, 09:41 AM   #21
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Quote:
Originally Posted by ducske916 View Post
Up-pipe is new
fuel pressure with running engine 2.5bar @ rail
and like said, it does this even at cold start so then the lamdasensor even doesn't work ( open loop) so a exhaust leak can not be the problem
that seems a little low to me unless you only checked with the VAC pipe connected? check at the filter hose you should get around 3bar with the vac pipe to the fuel pressure regulator disconnected.

If it runs OK with the MAF disconnected then your most likely going to be chasing a faulty maf sensor or an air leak somewhere. If you can smoke/pressure test the intake/intercooler/manifold it may give you a clue. Also check the IACV operation and gasket orientation as that can give you bother.
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