Fuel trim after rebuild
#1
Fuel trim after rebuild
Recently finished my 4.6 rebuild(crower cam, new cam bearings, head gaskets, compete new cooling system, new front cover and oil pump assembly, new injectors, new every seal I could possibly get my hands on) and my fuel trims are wacked the heck out.
I initially had 2 vacuum leaks on reassembly(cracked vacuum fitting for the booster connection, leaking clamps on the IAC valve) which I rectified and reset my adaptations afterwards. Within 5-10 miles, my LTFT will be about 20% on both banks and my short term fluctuates from -3 to +9 or so across different throttle and load conditions. upstream sensors appear to be cycling correctly, and rears appear to do their job as well when watching the voltages with my scan tool. MAF is reading about 10grams at idle and maxes out at 100 under WOT(don't know if those 2 figures are right)
I set a p0174 twice in quick succession this past weekend when cruising on the highway, but it cleared and 60+ miles since, and no returning faults.
Any ideas? I have smoked the system and I see no vacuum leaks anywhere
I initially had 2 vacuum leaks on reassembly(cracked vacuum fitting for the booster connection, leaking clamps on the IAC valve) which I rectified and reset my adaptations afterwards. Within 5-10 miles, my LTFT will be about 20% on both banks and my short term fluctuates from -3 to +9 or so across different throttle and load conditions. upstream sensors appear to be cycling correctly, and rears appear to do their job as well when watching the voltages with my scan tool. MAF is reading about 10grams at idle and maxes out at 100 under WOT(don't know if those 2 figures are right)
I set a p0174 twice in quick succession this past weekend when cruising on the highway, but it cleared and 60+ miles since, and no returning faults.
Any ideas? I have smoked the system and I see no vacuum leaks anywhere
#3
LTFT is the car adjusting its base fuel settings to account for issues in the running condition. Ideally? your LTFT should be 0, that would indicate that everything is running perfect and the car is not compensating for anything. A high positive fuel trim means the car is adding fuel to combat an issue, and the reverse is witholding fuel to combat an issue. STFT should just fluctuate no more than a handful of % points
I don't know what our gram flow rate for the MAF is supposed to be, to be honest
I don't know what our gram flow rate for the MAF is supposed to be, to be honest
#5
Check fuel pressure when engine has warmed up. I'm assuming its +20 so its running lean. I went through the 171/174 code thing. Redid head gaskets because they started to leak...did injectors ,etc while in there. Put all back together and LTFT was badly leaning out on both banks...all vac hoses had already ben replaced. Checked fuel pressure and it was 20 psi....spec is 50.. I couldn't believe that engine drove and ran with only 20 psi...lol.. Replaced fuel pump and now fuel trims good.
#6
#7
#8
LTFT is the car adjusting its base fuel settings to account for issues in the running condition. Ideally? your LTFT should be 0, that would indicate that everything is running perfect and the car is not compensating for anything. A high positive fuel trim means the car is adding fuel to combat an issue, and the reverse is witholding fuel to combat an issue. STFT should just fluctuate no more than a handful of % points.t
Ideally STFT should fluctuate between -5% and +5%. That's normal. Readings from 5-10% either way are not uncommon however, but they should not persist and if they occur STFT should return reasonably quickly to the 05%/+5% range.
Last edited by mln01; 11-01-2018 at 11:41 AM.
#9
Only way to read fuel pressure is through the shraeder valve
Same thing happened to me with my rebuild, I was around 7%-12% LTFT and intermittent/pending P0101, P0441, P0505, 121. I can't be certain what actually fixed it, but now I sit exactly at 1.56% LTFT with no fluctuation.
I suggest picking up a cheap intake pressure pressure ($15 bucks) and testing the vacuum in the intake. You can also use it test if the exhaust is clogged.
Some things I did
- redid intake manifold gasket
- replaced brand new genuine purge valve with a Hyundai unit (go figure)
- replaced MAF
- new air filter, o-ring
- new fuel pump (bosch)
- different brand spark plugs (in the OE spec heat range)
Same thing happened to me with my rebuild, I was around 7%-12% LTFT and intermittent/pending P0101, P0441, P0505, 121. I can't be certain what actually fixed it, but now I sit exactly at 1.56% LTFT with no fluctuation.
I suggest picking up a cheap intake pressure pressure ($15 bucks) and testing the vacuum in the intake. You can also use it test if the exhaust is clogged.
Some things I did
- redid intake manifold gasket
- replaced brand new genuine purge valve with a Hyundai unit (go figure)
- replaced MAF
- new air filter, o-ring
- new fuel pump (bosch)
- different brand spark plugs (in the OE spec heat range)
#10
Checked the fuel pressure today after work, steady 50, and when revved it blips down to about 45 and then returns to 50. Car off, pressure falls to about 45 and holds there indefinitely, looks like the pump is OK
I did smoke it again, and I do have a small vacuum leak... coming out of the throttle shaft of the throttle body looks like I will need a new throttle body unless there is an available seal option for the throttle shaft
I did smoke it again, and I do have a small vacuum leak... coming out of the throttle shaft of the throttle body looks like I will need a new throttle body unless there is an available seal option for the throttle shaft