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Old 03-08-2018, 04:23 PM   #1
ndis447
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Default 2002 wrx reading lean with negative fuel trim

I’m in the middle of getting my car tuned with iaTUNING and my short term trims are anywhere between -19 to -25, but my wideband (aem uego 4110) is showing lean afr’s. I’ve been able to confirm that the sensor is reading correctly, it reads lean when exposed to open air and rich when exposed to ether. After an ecu reset the afrs start at 10:1 and slowly lean out, sometimes reaching 16.5:1 and up. This is all at idle. Driving under light loads the car runs normally and only leans out when the engine is decelerating or the throttle is closed. I do not have any intake/vacuum leaks, I haven’t found any exhaust leaks but I’m going to smoke test to verify, my valve timing is correct, no head or intake gasket leaks, compression and leak down tests checked out. Anyone ever experience this issue? At this point I’m not sure what to do. I am running a vf23 turbo with supporting mods (Dw 750 injectors, full catless exhaust, v7 intercooler etc)
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Old 03-19-2018, 12:29 AM   #2
Nettalp
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First off, love the vf23, you're in for a treat with about 280-290hp depending on weather and tune. Best bet is to smoke test your vacuum lines and then go from there. Looks like your experiencing a vacuum leak but you'll have to confirm. Has your Maf ever been calibrated? Are you on the stock intake?
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Old 03-19-2018, 10:03 AM   #3
86Dreams
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There is a lot of stuff to consider here. Your tuner should be able to figure this out. If they cant, get a different tuner.

You need to be looking at the enleanment with respect to OL vs CL fueling.

You need to verify your front O2 is OK.

You need to make sure they tuned the correct injector latency.
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Old 03-19-2018, 09:30 PM   #4
ShinjiML
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Do you have any logs?

It sounds like you're saying after an ECU reset, during wot, the AFR starts at 10:1 and then as you drive more, the WOT pulls start to lean out?

What does your AF Learning show? If the ecu is consistently pulling lots of fuel, i.e like the -19-25% your AF correction shows, then once that carries into the wot range, it will cause a heavy lean condition because if the fuel trims pull ~20% fuel, this equates to leaning out by 2 points, i.e going from 10 AFR to 12 AFR under WOT. This certainly sounds like what is happening if the wot AFR starts going lean gradually. Your fueling issues need to be addressed and you can ask your tuner to disable AF Learning for open loop.

If Stephen is tuning your car, then he should know how to take care of it.
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Old 04-04-2018, 06:25 PM   #5
ndis447
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Quote:
Originally Posted by Nettalp View Post
First off, love the vf23, you're in for a treat with about 280-290hp depending on weather and tune. Best bet is to smoke test your vacuum lines and then go from there. Looks like your experiencing a vacuum leak but you'll have to confirm. Has your Maf ever been calibrated? Are you on the stock intake?


Sorry for the late reply, I’m just now seeing these posts. But I’ve performed several boost leak tests, starting at 5psi and going all the way up to 20psi and the system is leak free. I’ve also hooked up a fogger to double check and pressure tested with smoke in the system and there aren’t any leaks. I’m on the stock intake minus the resonator with a new panel filter from Subaru. I don’t know whether or not he calibrated the maf
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Old 04-04-2018, 06:32 PM   #6
ndis447
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Quote:
Originally Posted by 86Dreams View Post
There is a lot of stuff to consider here. Your tuner should be able to figure this out. If they cant, get a different tuner.

You need to be looking at the enleanment with respect to OL vs CL fueling.

You need to verify your front O2 is OK.

You need to make sure they tuned the correct injector latency.


He has told me more than a dozen times to boost leak test and that’s really the only advice he’s given me even though I’m 100000% sure I have no vacuum leaks. He also said the wideband could be thrown off by an exhaust leak but I’ve corrected a minor leak and still have the same problem. This only occurs at idle and the car seems to drive fine. I don’t hear any exhaust popping on decel associated with a lean condition. Front o2 was replaced by the dealer maybe 20-30k ago, the P.O. had it done. When I get home I’ll check injector latency, im using denso Dw750’s so latency shouldn’t have been changed from stock right?
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Old 04-04-2018, 06:41 PM   #7
ndis447
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Quote:
Originally Posted by ShinjiML View Post
Do you have any logs?

It sounds like you're saying after an ECU reset, during wot, the AFR starts at 10:1 and then as you drive more, the WOT pulls start to lean out?

What does your AF Learning show? If the ecu is consistently pulling lots of fuel, i.e like the -19-25% your AF correction shows, then once that carries into the wot range, it will cause a heavy lean condition because if the fuel trims pull ~20% fuel, this equates to leaning out by 2 points, i.e going from 10 AFR to 12 AFR under WOT. This certainly sounds like what is happening if the wot AFR starts going lean gradually. Your fueling issues need to be addressed and you can ask your tuner to disable AF Learning for open loop.

If Stephen is tuning your car, then he should know how to take care of it.


This is only at idle. As the car sits it would lean out gradually. Under wot afrs are 10-11.5 or so. If by afr learning you mean the long term fuel trims they were 0. Eventually he told me that we should just ignore the wideband at idle. I checked fuel pressure and it’s at 46psi at idle, I was told they should be 36psi so is there a possibility that the higher pressure is throwing off injector flow and the computer is compensating for it? I brought this up to my tuner but he didn’t have anything to say about it.
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Old 04-04-2018, 06:47 PM   #8
ShinjiML
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Quote:
Originally Posted by ndis447 View Post
This is only at idle. As the car sits it would lean out gradually. Under wot afrs are 10-11.5 or so. If by afr learning you mean the long term fuel trims they were 0. Eventually he told me that we should just ignore the wideband at idle. I checked fuel pressure and it’s at 46psi at idle, I was told they should be 36psi so is there a possibility that the higher pressure is throwing off injector flow and the computer is compensating for it? I brought this up to my tuner but he didn’t have anything to say about it.
Are you running an adjustable fpr? If not then you should be seeing around 33 psi at warm idle. If fuel pressure is set higher via an adjustable fpr then yes it will cause a rich condition. Also the dw750 injectors tend to have weird issues, ie rich idle, etc.

Are your dw750 denso or Bosch based?
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Old 04-05-2018, 02:03 PM   #9
ndis447
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Quote:
Originally Posted by ShinjiML View Post
Are you running an adjustable fpr? If not then you should be seeing around 33 psi at warm idle. If fuel pressure is set higher via an adjustable fpr then yes it will cause a rich condition. Also the dw750 injectors tend to have weird issues, ie rich idle, etc.

Are your dw750 denso or Bosch based?


I’m running the original fpr and Bosch style injectors. They’re identical to the stock injectors in regards to physical appearance. Could the fuel pressure be causing the computer to overcompensate for the extra flow? When I initially had the problem it seemed to me as if the computer was the result of the problem because after a reset the Afrs would start at ~14.7 and very quickly go rich, ~10.1 iirc, and steadily lean out
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Old 04-06-2018, 01:22 AM   #10
Airboy
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If there are no exhaust leaks and the O2 sensors aren't reading the same, then one of them is not working. Have you tried replacing the front O2 sensor?
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Old 04-06-2018, 08:15 AM   #11
ndis447
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Quote:
Originally Posted by Airboy View Post
If there are no exhaust leaks and the O2 sensors aren't reading the same, then one of them is not working. Have you tried replacing the front O2 sensor?


Front o2 isn’t that old, and it reads almost the same as the wideband does
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Old 04-06-2018, 06:39 PM   #12
ShinjiML
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Quote:
Originally Posted by ndis447 View Post
I’m running the original fpr and Bosch style injectors. They’re identical to the stock injectors in regards to physical appearance. Could the fuel pressure be causing the computer to overcompensate for the extra flow? When I initially had the problem it seemed to me as if the computer was the result of the problem because after a reset the Afrs would start at ~14.7 and very quickly go rich, ~10.1 iirc, and steadily lean out
If the fuel pressure is off and causing a rich condition beyond what the ECU can correct for then the AFRs will start going rich at cruising. The steady leaning out can be just changes in atmospheric conditions or season changes.
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Old 04-08-2018, 12:21 PM   #13
ndis447
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Quote:
Originally Posted by ShinjiML View Post
If the fuel pressure is off and causing a rich condition beyond what the ECU can correct for then the AFRs will start going rich at cruising. The steady leaning out can be just changes in atmospheric conditions or season changes.


It’s leaning out at idle only, over the course of about 5-10 minutes. But if I drive the car a little bit then let it idle the afrs go down to 14.4-15.3 and bounce around in that range
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Old 10-20-2018, 01:56 AM   #14
doinwork34
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The higher fuel pressure will mess with the injector latency. The extra fuel pressure makes it harder for the injector to open therefore you need a higher latency to compensate for the higher resistance the fuel is causing. There is a video on youtube demonstrating this, and you can see that if you increase the pressure to far, the injector will never even open since the entire final calculated pulse width may not be enough time to allow the injector to open.

In any case, if your fuel pressure is to high and you dont adjust latency, it will not be opening for long enough.
In addition latency has a diminishing affect on fuel with the increase in IPW- in other words, a bad latency will affect idle exponentially more.

So it may be worth trying to either decrease fuel pressure or increase latency.
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Old 10-20-2018, 07:40 AM   #15
Andrew2166
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02 wrx fuel psi is set for 43lbs at start up with vaccum line from fpr blocked/dc from manifold...after warm up it drops, then increases upon throttle response. One of your injectors could not be spraying properly...if you say theyre bosch, then theyre the modified oem ones and theyre known for hard fuel tuning because of uneven flow patterns...did you have your injectors checked before installed to make sure they spray evenly and dont stick open/closed?
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