2005 f 150 4.6 has -20% LTFT'S on both banks

2005 f 150 with 4.6 drive by wire with -20%LT fuel trims on both banks .It stays at -20%LTFT at all loads and rpms . My second issue, is that it also has no power and very poor throttle response at dead stop in 1st gear/reverse. when I push the gas peddle to accelerate normally ( half throttle) nothing happens for 2-4 seconds while rpm is limited to 1600. During this event the truck rolls forward very slowly, as if i'm only applying 10%throttle. Then finally after reaching about 8 mph in that state, it will finally rev up beyond 1600 rpm and acts normal. it has plenty of power, and responsiveness in all other gears and speed ranges beyond 8mph.

fuel pressure is at spec .( 38 psi at idle) and jumps to 45 psi when push the throttle. (Has 45 psi during hesitation)
oxygen sensors are oscillating from .1 to.9 like they should. +/- 5% on short terms and respond instantly to vacuum leaks and added propane.

parts i have replaced with no change to the above mentioned conditions.
1 MAF sensor
2 EGR module with MAP
3 up stream 02's
4 throttle body/TPS
5 FPDM
6 All coils, its not misfiring.
7 all injectors,with KAM reset. it relearned - 20% LTFT on both banks agin.

I have been trying to find the issue for a year now unsuccessfully . it just doesn't want to rev up at a stop and pulling out in front of people is a concern because sometimes it accelerates fine but some times it just slowly eases along no matter how hard i push the peddle. ive gon over all the causes of neg fuel trims and cant find the cause, any input is greatly appreciated

Have you checked exhaust back-pressure?

i have checked manifold vacuum , it stays in the green zone at 22 inches.
fuel pressure is in spec with no decay after shut down so its not a leaky injector.and its -20 on both banks so i would have to have a leaker on both sides i think.
i have unplugged EGR with no change to trims. i have pinched off evap line going to intake with no change to trims. its been doing the same thing for over a year now but has not got any worse

Is the air filter totally plugged or is there something stuffed in that intake tube? Is the ECT sensor reporting properly? Check the values in global OBD2 and not enhanced mode in case you are getting substituted values. Do these have fuel pressure regulators where it could be leaking?

Nissan Technician

Hi guys,

I think is also convenient to check calc. Load and throttle position at wot.

Due to is a drive by wire system, pcm could be restricting power delivery. Why? We don't know yet.

the fuel trims... are they LTFT or STFT ? post both for each bank please...

negative fuel trims indicate a fuel delivery issue. the engine is getting too much fuel so the pcm is taking it away. while watching the fuel pressure with the engine running, pull the vacuum line from the fuel pressure regulator. Does the pressure change?

The fuel trims look upside down to me also, what happens to the trims if you give it some propane or carb cleaner in the intake.

new air filter, the air filter box runs over to the driver fender well where its drawing in all its air. i pulled it away from that location (thinking it may be restricting air flow) how ever it had no effect. thanks for replying

when i add propane or create a vacuum leak the 02's and fuel trims respond instantly the way they should.
Its an electronic returnless fuel system with a pressure sensor on the fuel rail.(I have changed it also) when i remove the vacuum line on the sensor, scan tool shows no change on scan tool psi, but on a mechanical gauge it rises to 47 psi. when i disconnect the FRPS scan data says 75 PSI but mechanical gauge says 20 psi .
These are my pids at idle after getting the engine to operating temp.
rpm 700
calculated load 25-30% at idle with all accessories off. ( i think its high)
STFT1 +/- 5% LTFT1 -20% up stream 02's are both switching like normal with current trim numbers
STFT2 +/-5% LTFT2 -20%
ECT 190 'F IAT 79 ' F
MAP 5.1 psi MAF 0.01 lb/s
FRP 40 psi EVAP % 34.9%
BARO 14.9 psi / 159.66 HZ
SPARK ADV = 12.5 degrees

While gathering this data just now, my LTFT on both banks maxed out at -26.6%, which puts it in open loop fault and then trims go to 0's and codes p2196 and p2198 set (02 sensor signal biased/stuck rich). I have never seen it get this bad until now. I drove a few miles and checked again and they settled back at -20 on the long terms. .

Attachment below

duty cycle on fuel pump is staying at 50%. the cycle is controlled by the pcm from input from the temp sensor and rpm. temp looks low... should be around the 210 mark. check rpm signal as well. cycle should drop to 25% after startup.

ok i believe i can check that at the fuel pump driver module with my vantage pro.
however i just spent an hour reading threads on what the temp is supposed to be, and cant really get a good answer. then when i search for replacement thermostats, they range from 180 -192-195 degrees . Then searched for OEM replacement (motercraft) and they are 190 degrees .

Maf: 0.01 lb/s instead of 0.1 lb/s? Please confirm.

Maf reading at idle

Sorry I don't know why pics are flipped

Yes . maf reading at idle is 0.01lb/s, and with a WOT snap it maxed at .32 lb/s

Flex fuel?

0.01 lb/s x 60 sec = 0.6 lb/min.

This is a low number for me. I would expect at idle about 4 lb/min.

I was thinking that too, but am not sure about the g/s conversion, so that number might be ok?

Nissan Technician

coolant range for ford 4.6 is 190 to 225. that is the thermostat opens at 190. is the upper coolant hose hot to the touch? might want to test that coolant temp manually.

the .01lb/s comes out to 4.5g/s for the MAF as it should be.

I still think the coolant temp is too low causing the engine to run rich. Maybe someone else can comment on this to confirm... fuel pressure is controlled by the speed of the pump motor.