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Old 15 Nov 2009, 12:46 PM   #1 (permalink)
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Started running leaner

Hi guys

I've noticed that my v6 sti has started to run leaner to the point where it now concerns me.
I have a LM1 ( recently calibrated with new sensor ) and Apexi PFC.
Car was tuned to around 11.5:1 in boost but recently has started to lean out, now around 13:1 and only richens up slightly higher in the RPM range.
The Apexi MAF voltage readings are the same as always and the MAF was recently changed for another reason ( problem started a while after maf change), so im ruling out MAF failing at this point.

Im showing no knock

Im thinking fuel pump failing? I seem to recall this started happening after i run quite low on fuel so maybe intank sock has picked up some crap? I have receipts for uprated fuel pump from back in 2005, so for piece of mind will be changing to a new genuine Walbro regardless, but looking for other suggestions also.

Thanks for reading.
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Old 15 Nov 2009, 04:58 PM   #2 (permalink)
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Re: Started running leaner

Fuel pump is whining too, never noticed it before...

Have swapped MAF to rule out, and still the same. New Genuine Walbro on order and should be here in a few days.

Any other suggestions?
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Old 15 Nov 2009, 05:13 PM   #3 (permalink)
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Re: Started running leaner

Quote:
Originally Posted by GotBoost View Post
Hi guys

I've noticed that my v6 sti has started to run leaner to the point where it now concerns me.
I have a LM1 ( recently calibrated with new sensor ) and Apexi PFC.
Car was tuned to around 11.5:1 in boost but recently has started to lean out, now around 13:1 and only richens up slightly higher in the RPM range.
The Apexi MAF voltage readings are the same as always and the MAF was recently changed for another reason ( problem started a while after maf change), so im ruling out MAF failing at this point.

Im showing no knock

Im thinking fuel pump failing? I seem to recall this started happening after i run quite low on fuel so maybe intank sock has picked up some crap? I have receipts for uprated fuel pump from back in 2005, so for piece of mind will be changing to a new genuine Walbro regardless, but looking for other suggestions also.

Thanks for reading.
Just thinking the Maf is Original Subaru Part???? a wise choice the uprating of fuel pump to rule that out but if the Fuel Pump dont fix the problem be worth fitting a Knocklink device as for a 2nd opinion to make sure it not detonating
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Old 15 Nov 2009, 05:20 PM   #4 (permalink)
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Re: Started running leaner

Not registering knock over 10 on the PFC, i do have a KS4 here so will hook that up to be sure, although im not driving the car hard until the pump arrives.

Yes, both mafs tried are Subaru items and less than a month old each!!
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Old 15 Nov 2009, 05:44 PM   #5 (permalink)
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Re: Started running leaner

Quote:
Originally Posted by GotBoost View Post
Not registering knock over 10 on the PFC, i do have a KS4 here so will hook that up to be sure, although im not driving the car hard until the pump arrives.

Yes, both mafs tried are Subaru items and less than a month old each!!
Be interesting when pump fitted so hopfully sort your problem
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Old 15 Nov 2009, 08:49 PM   #6 (permalink)
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Re: Started running leaner

Could it be a faulty FPR at all? thats what retains the fuel pressure, if it was weak then it wouldn`t hold the fuel pressure so could maybe cause it to run lean, I think this is why a lot fit the SARD after market type.
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Old 16 Nov 2009, 12:38 AM   #7 (permalink)
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Re: Started running leaner

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Originally Posted by bugeye_bob View Post
Could it be a faulty FPR at all? thats what retains the fuel pressure, if it was weak then it wouldn`t hold the fuel pressure so could maybe cause it to run lean, I think this is why a lot fit the SARD after market type.
Ya true didnt think of that
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Old 18 Nov 2009, 10:50 PM   #8 (permalink)
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Re: Started running leaner

New Walbro fitted, no difference. ( Used Walbro for sale now LOL )

Strange thing, sometimes its fine, sometimes it runs leaner with slight hesitation....

I have a Sitek FPR here so will fit that asap and bump fuel pressure up a bit until i can get the the cause.

Other Suggestions?
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Old 01 Dec 2009, 12:59 PM   #9 (permalink)
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Re: Started running leaner

Hi guys, still struggling with a large variation in AFR on the Scoob, basic spec is a 99 STI 6 with Apexi PFC.

Problem -

Sometimes the fuelling is spot on and the car drives great, sometimes it runs overly lean and the car stammers, the difference is around a full AFR point ( ie instead of 14:1 it runs around 15:1 and so on ).

The MAF sensor is brand new and i have logs of this happening showing that the MAF voltages and commanded injector duty cycles are the same when this problem occurs, so im ruling out the MAF/ecu/wiring etc being at fault and fairly sure this is a fuel supply issue.

As an example, i have a 3bar fuel map and a 3.5bar fuel map for the car, when running the 3.5bar fuel map and the problem occurs ( lean ), if i load the 3 bar fuel map it brings it back into the correct AFR zone, of course when the problem goes away randomly it runs overly rich again and i can reload the 3.5bar map and it runs correct.
Again, logs show same map points, MAF volts, and commanded Injector duty cycle when problem occurs and not, on the same map and same FP!

NEW Walbro fuel pump and Sytec FPR fitted.

Same problem persists and im running out of ideas. Anyone?
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Old 01 Dec 2009, 01:08 PM   #10 (permalink)
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Re: Started running leaner

Sounds like a fuel supply issue but it could be an air leak ... have you checked hoses, headers, up-pipe etc ?
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Old 01 Dec 2009, 01:16 PM   #11 (permalink)
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Re: Started running leaner

I would agree with the air/ vacuum leak idea, but this occurs in vacuum and boost. All the while the MAFv at idle stays around the 1260mv, if there was an intermittent vacuum/boost leak i would expect the MAFv to drop when the problem is present. At idle, atmo or boost, the logs show repeatable MAFv and INJ duty in the same map locations.

Wideband is located in OEM position on downpipe, obviously running open loop.
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Old 01 Dec 2009, 01:19 PM   #12 (permalink)
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Re: Started running leaner

Have you checked vacuum hose to the FPR ?
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Old 01 Dec 2009, 01:28 PM   #13 (permalink)
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Re: Started running leaner

Yep, recently replaced when the new FPR was fitted, straight to IM with no T's off it. If your thinking its just getting atmo pressure then it would run rich at low load / idle, its lean throughout when the problem is present.

Registers 3 bar at idle vacuum and 3.5bar with pipe disconnected ( atmo ). Idles in cell N1P2 at 1260mv MAFv.

Its really annoying, i'll change something, quickly redo the fuelling and it'll be spot on, then a few hours later ( or randomly ) it will play up and either run lean or rich, depending if i corrected the fuel map when the problem was present or not.....

I could do with logging fuel pressure really, but at the moment its not an option.
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Old 01 Dec 2009, 01:40 PM   #14 (permalink)
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Re: Started running leaner

I am presuming that the LM1 is correct as the leanness is actually manifesting itself on the car aswell... so... just throwing some thoughts out :

- wiring to MAP sensor iffy ?
- fuel cap loose .. this can cause a weird effect sometimes.
- fuel filter or fuel return pipework
- fuel getting very hot
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Old 01 Dec 2009, 01:46 PM   #15 (permalink)
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Re: Started running leaner

Yeah, first thing i done when the problem started was use a new sensor and free air calib, still the same.

Wiring - maybe, but i beleive this would show in the MAFv logs
Fuel cap - Has been on and off for a number of fills, and holds pressure fine.
Fuel Filter - I havent changed the fuel filter yet, so thats an easy one to try!!!!!! Simplest things are often overlooked.

Will change fuel filter this afternoon and report back. Thanks for your help mate.
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