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High LTFT. Need advice and opinions


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Brianorina
New User

Jan 12, 2017, 6:32 PM

Post #1 of 9 (767 views)
High LTFT. Need advice and opinions Sign In

Using OBD2 on my 01 CELICA GTS. At idle my LTFT is at about +26% and STFT runs around 0 to +8%. O2B1S1 seems to be running fine, but O2B1S2 is running constant at 0.7V. @1500RPM to @2500RPM LTFT shows minor changes going between +25% to +30% as STFT shoots up to about 10% to 15%. Both O2 sensors drop to 0.1V anytime RPM goes over 1000. @4000+RPM LTFT drops to 0% with STFT going to +18% to +20%. I notice the CEL goes on when fuel trim hits +35%. I have changed fuel injectors, fuel pump and strainer, fuel filter. I checked for vacuum leaks on intake side using Carb Cleaner but found nothing. Need ideas as I am getting more than just frustrated. At the very least, I've done a decent maintenance procedure as far as fuel delivery.


Discretesignals
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Jan 12, 2017, 8:14 PM

Post #2 of 9 (760 views)
Re: High LTFT. Need advice and opinions Sign In

Honestly sometimes the carb cleaner trick for finding vacuum leaks doesn't always work, especially if the leak is somewhere the cleaner can't get to. A smoke machine is really good for finding vacuum leaks. Check for leaks when the engine is cold.

Pinch of the brake booster hose and see if your trims go normal.
If you have propane, inject that into the engine while it is running to see if you can get O2s to go rich. Short term trim should also go negative when you hit it with propane. You just want to make sure the B1S1 isn't stuck low and causing your issue.

If that is good, inspect your air inlet ducting for cracks, tears, missing hoses etc. A MAF sensor that is reporting less air than is actually going into the engine will cause lean conditions at idle, acceleration, cruising, and WOT. If the MAF sensor resistors are dirty, clean them with electrical contact cleaner to see if that makes an improvement.





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 Jan 12, 2017, 8:15 PM)


Brianorina
New User

Jan 12, 2017, 11:55 PM

Post #3 of 9 (741 views)
Re: High LTFT. Need advice and opinions Sign In

Well I appreciate the advice. As far as my MAF, I am sure it's reading normally as I had just replaced it about a week ago. If anything I'll try to spray it again with electrical cleaner to test for any changes. Will also try to see if running rich changes anything on the O2 sensor. Any ideas as far as another option for finding vacuum leaks? Wish I could smoke test but don't have the machine to test for leaks.


kev2
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Jan 13, 2017, 3:49 AM

Post #4 of 9 (727 views)
Re: High LTFT. Need advice and opinions Sign In

did you check ECT, fuel pressure, MAP?


Discretesignals
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Jan 13, 2017, 5:29 AM

Post #5 of 9 (721 views)
Re: High LTFT. Need advice and opinions Sign In

The most concise method for finding leak is with a smoke machine. If you can find a shop in your area that has one, that would be your best bet in finding any leaks. As stated check it when the engine is cold. Besides using smoke, water, and brake spray tricks, I don't know any other way of finding vacuum leaks.

Watch out for those aftermarket MAF sensors. I've had quite a few dudes. If you can get your hands on a MAF off a known good running vehicle for test purposes, that would be great to see if any changes occur. You can test a MAF with a scope, but it really only checks its ability to respond to changes and max amplitude. MAF sensor signal output is determined by air flow, so if you have a bad running engine or air leaks after the sensor, it's really hard to judge if the sensor is the issue. If you can drive the vehicle and do a wide open throttle (WOT) run with it, watch your O2 sensors to see if they go full rich around (0.9 volts). If they go rich and stay as long as your holding it WOT, that means MAF and fuel pressure is probably good. Use safety when doing a WOT run.

I don't think that it will have a MAP sensor, but another thing to look at is calculated BARO if your scanner displays it. The PCM will change the fuel curve depending on the BARO pressure it calculates. Make sure the BARO value is equal to the atmospheric pressure where you live.

As stated, check ECT. Compare ECT to IAT datastream values after the vehicle has sat over night. Both should be close to the same values.





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 Jan 13, 2017, 5:33 AM)


Brianorina
New User

Jan 13, 2017, 1:46 PM

Post #6 of 9 (699 views)
Re: High LTFT. Need advice and opinions Sign In


In Reply To
did you check ECT, fuel pressure, MAP?


ECT runs great. Fuel pressure I've yet to check and still wondering how I would be able to set that up as my FPR is in-tank and I don't exactly have a test port. My car uses a MAF.


(This post was edited by Brianorina on Jan 13, 2017, 2:07 PM)


Hammer Time
Ultimate Carjunky / Moderator
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Jan 13, 2017, 2:14 PM

Post #7 of 9 (687 views)
Re: High LTFT. Need advice and opinions Sign In

Where the regulator is, is not important. Usually the best way on those is use an adapter at the fuel line connector in the engine compartment.





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

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.



Brianorina
New User

Jan 17, 2017, 10:17 AM

Post #8 of 9 (655 views)
Re: High LTFT. Need advice and opinions Sign In


In Reply To
The most concise method for finding leak is with a smoke machine. If you can find a shop in your area that has one, that would be your best bet in finding any leaks. As stated check it when the engine is cold. Besides using smoke, water, and brake spray tricks, I don't know any other way of finding vacuum leaks.

Watch out for those aftermarket MAF sensors. I've had quite a few dudes. If you can get your hands on a MAF off a known good running vehicle for test purposes, that would be great to see if any changes occur. You can test a MAF with a scope, but it really only checks its ability to respond to changes and max amplitude. MAF sensor signal output is determined by air flow, so if you have a bad running engine or air leaks after the sensor, it's really hard to judge if the sensor is the issue. If you can drive the vehicle and do a wide open throttle (WOT) run with it, watch your O2 sensors to see if they go full rich around (0.9 volts). If they go rich and stay as long as your holding it WOT, that means MAF and fuel pressure is probably good. Use safety when doing a WOT run.

I don't think that it will have a MAP sensor, but another thing to look at is calculated BARO if your scanner displays it. The PCM will change the fuel curve depending on the BARO pressure it calculates. Make sure the BARO value is equal to the atmospheric pressure where you live.

As stated, check ECT. Compare ECT to IAT datastream values after the vehicle has sat over night. Both should be close to the same values.



I have noticed something that's been bothering me for quite some time. Rpm@1500 & rpm@2500 the LTFT goes up but when I hit rpm@5000+ the LTFT drops to right around 4to8% and stabilizes there. STFT goes straight to 0. With that and the O2 data, my gut is telling me to give the fuel system another go. I haven't had the time or funding to grab a fuel pressure test gauge as I've been waiting on people to pay me back. I'll make the run today and check the pressure.


kev2
Veteran
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Jan 17, 2017, 2:54 PM

Post #9 of 9 (642 views)
Re: High LTFT. Need advice and opinions Sign In

I noticed this reply "ECT runs great." I like some more details....there are no other codes- and vehicle is stock no modifications.
is the eng reach @220degF?






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