Bogs Down While Cruising

[StarFox]

2004, XLT, 3.0l, 150,000 miles

Symptoms:
Long cold start, 6-8 seconds
High idle at cold start, 1100 rpm for up to 1 minute
Almost shuts off if put in gear after cold start within the first few minutes
(Problems above have been the norm for around a year or longer)

Takes 1-2 minutes to build fuel pressure to 60 psi on cold start
Remains within 55 to 65 between idle and 3,000 rpm
(just checked this today)

System Lean bank 1 and 2 codes (pending) from torque
Fuel trims are normal at idle and appear to be elevated at cruising, +8 to +28

Last night the truck had a rough start and lopped at a low rpm for about a minute from a cold start before returning to normal. Then lost power twice while cruising within minutes. Engine seemed to bog down the more the pedal was pressed.

Fuel filter was replaced less than 30,000 miles ago
Coils, wires, and plugs replace less than 20,000 miles ago
No evidence of a vacuum leak
Fan clutch is free

The kicker is it has been fine all day today other than the post cat O2 senors reading low on occasion as well as fuel trims being between 0 and +18

I'm thinking fuel pump at the moment or maybe trash in the tank but I am not convinced so throw me some opinions and things to check please.

 

[RonD]

Welcome to TRS


After engine is fully warmed up and idling, unplug the 2 wires from the IAC Valve
RPMs should drop to 500 or so and engine may even stall, either is GOOD, it means no vacuum leaks.
If RPMs stay high then you have a vacuum leak, leave IAC unplugged while you look for it

1,100rpm cold start idle is fairly normal, depends on cold coolant temperature so outside temp after engine has been sitting, the colder the temp the higher the idle.
There is also often a surge above 1,500rpm at any startup, warm or cold, that's because the IAC Valve should be open all the way for startup, key on, and then computer starts to close it to set idle based on coolant temp.

Fuel Pressure should hold above 30psi with engine off, for a long time
When you turn on the key the computer will Prime the system by running the fuel pump for 2 seconds, that adds about 10-15psi to existing pressure.
If pressure was at 0psi then engine may not start or will struggle to start.
Try cycling key on and off 3 times before starting, so three 2 second Primes to build up lost pressure, just to test if that's the slow start issue, fuel pressure.
But above 50psi while engine is running shouldn't cause Lean condition from computer

Lean(+ fuel trims) means computer is opening fuel injectors longer than it has calculated for engine RPMs, air flow, temp and throttle position.
Engine is not actually running Lean, Lean codes are to notify driver that calculations are off.
This could be because there may be unreported air coming into the engine, i.e. vacuum leak or leak between MAF sensor and intake.
Quick IAC Valve test will confirm or deny that.
I would expect higher fuel trims at idle though, as that's when highest vacuum occurs so highest unreported air, but thats not always the case.

Fuel pump could be dropping pressure under load, it can happen, that would explain higher fuel trims at speed, but could also be the MAF sensor is reporting less air flow at higher RPMs, you could try cleaning it.
Or try watching MAF data on OBD app as you drive, it should, of course, go up with engine RPMs as air flow increases.
If you switch MAF to gm/sc, grams per second, you should see about 3.0 at warm idle, 800rpm, engine displacement
Then it should climb steadily as you reach cruising speed, maintain speed and see if stays steady

Having both banks Lean means it won't be an O2 sensor issue, for both upstream O2 sensors to fail at the same time would be unlikely.