alright guys im at a breaking point, 99 ranger 4.0 v6 automatic, here are my codes p0171- fuel system too lean cylinder bank 1, p0113- IAT sensor circuit high input, shift solenoid B ( just bought it putting it in tomorrow) p0174- fuel system too lean cylinder bank 2, p0303- cylinder number 3 misfire detected, so heres where im stuck, every now and then its different codes or its just one code, trying to chase this misfire at freeway speed is killing me, ive replaced the mass air flow sensor, IAT sensor circuit high input, plugs n wires, coil pack, pcv valve. ive checked for a vacuum leak but did not find one, i have a lousy connector on my IAT sensor, i checked compression, all the cylinders were 165-170 all the way around, the check engine light starts flashing when i either step on the gas decently hard when at 40-50 MPH or going up incline and hold a steady throttle, anybody on here have this problem and fixed it? the only thing i haven't checked is fuel injector or resetting the the light,any help would be greatly appreciated. TIA

 

Start by checking your fuel pressure.
There will be a schrader valve on the fuel rail.
Should be at 60 to 65 PSI.

Test it with the key to the "on' position, at idle and revving it to 3000rpm or where the RPM hits at 40 to 50 MPH.

You will need to rent or buy a fuel pressure tester.

 

Simple quick test for vacuum leak is to warm up engine to operating temp
Unplug the two wires on IAC Valve it will close all the way
RPMs should drop to 500 or engine may stall, either is GOOD, no vacuum leaks
If idle stays high then there is a leak, or someone has messed with Anti-Diesel screw on throttle linkage, it is NOT an idle screw, lol.

Lean on both banks is a system wide vacuum leak, so upper intake not lower, and as Jeff said could be fuel pressure issue.
Computer expects(no sensor) fuel pressure above 50psi at the injectors, and bases its calculations on the amount of fuel that will flow out of each injector on that pressure.
If pressure is low then calculations would be off so Lean Code set.
Lean or Rich codes doesn't mean the engine is actually running Lean or Rich, the codes mean the computer's calculations are not correct, so it is letting the driver/owner know something is wrong.
For Lean it means there is MORE air than expected or LESS fuel than expected

Flashing CEL means engine damage may occur, usually from misfires, so back off gas pedal when that happens.

IAT(intake air temp) sensor should be part of the MAF sensor, MAF sensor has 4 wires, IAT 2 wires, so if your MAF sensor has 6 wires then outer 2 wires are for the IAT sensor
The Grey/red wire is the Reference voltage shared by pretty much every sensor on the engine, TPS, DPFE, ECT, and two trans sensors, not solenoids
Test grey wire for 5v key on

 

I forgot to mention the fuel filter as well.
If it's partially blocked then the engine may be starved for fuel under load (hard acceleration or going up hill).
This will also set a lean code.

 

thank you guys for the input im gonna do the IAC trick right now and then go get a fuel test

 

i disconnected the IAC valve and engine dropped to 500 RPMS

 

So vacuum leak is off the table as cause for Lean codes

 

That leaves fuel pressure and computer itself

MAF maybe but MAF and TPS(throttle position sensor) are compared by computer.
Each computer "knows" what size engine it is running.
i.e. a 4 LITER engine will pull in 4 Liters of air every 2 RPM at Wide Open Throttle(WOT)
So from there computer can calculate air flow based on throttle position and RPM
MAF sensor is used to fine tune that, based on the WEIGHT of the air, i.e. sea level or 5,000ft elevation, if out of correct range computer should set TPS or MAF code

And just FYI, "New MAF" just means you installed a NEVER TESTED MAF sensor, new used to mean "tested and working", new now means "you test it we will replace it if broken", lol.

 

so i checked my fuel pressure and its at 42 psi and drops to 40 psi when rev it up to 3,000 rpms, i replaced the fuel filter and didn't change anything, the scanner gave me these codes
p0171- fuel system to lean cylinder bank 1 p0174- fuel system too lean cylinder bank 2 p1504- air control circuit malfunction, the scanner is saying i don't have a misfire anymore, but when i pull the cap off the coil pack the idle doesn't change, my only misfire was cylinder 3 im at total loss trying to chase the problem, also when i got to step on the gas leaving a stoplight, or pulling out of somewhere, my truck stutters till i hold consistent throttle but while at speed i press more and it sputters then goes to normal any ideas?

 

Yes, fuel pressure is too low, spec is 55-65psi on 1998 and up Rangers
It is actually listed at 65psi +/- 8psi, so 57-73psi, but most I have tested were 55-65psi when they ran well

1997 and earlier use a different system, with 35-45psi

p1504 was from when you unplugged the IAC Valve

Cylinder 3 may be at the end of the fuel rail, not sure on '99 but if it is then it could misfire from too lean a mix with the lower fuel pressure, while the other cylinders are getting just enough

Could be there is a leak in the tank's lift line from pump to top of tank, but in any case you will need to pull or lift the bed and checkout or replace the fuel pump
If factory it is 19 years old now

 

is there anyway to test the fuel pump? or easy ways of actually diagnosing the problem?

 

I thought you just did test it??
Try tester on a different engine just to be sure, but if you are confident that pressure test was valid then thats the problem

42psi, didn't pass the test, so that is the actual problem, at least for the Lean codes and probably the misfire on #3

or at least the first problem to fix, lol, truck is 19 years old so won't be the only problem

Just a quick how it works
Computer expect 55psi minimum
So it opens each injector for 100ms(milliseconds) to let in the correct amount of fuel.
It looks at O2 sensors on each bank
O2 sensor shows Lean
So computer opens injectors for 102ms, adds more fuel
Then checks O2s again, and Lean again
So 104ms, then 106ms then 108ms, 110ms, 112ms, 114ms, 116ms(this is where lean code gets set) then 118ms, then 120ms then 122ms and now O2's show OK not lean, all this takes about 4 seconds in real time, so engine was never running lean

116ms is 16% over 100ms and computer sets codes when there is a 15% difference between its calculations and actual open time needed for injectors, this is to let driver/owner know there is a problem, but it continues to run engine at 122ms, or whatever makes O2s show correct mix

So 55psi, 10% of that is 5.5psi, so if fuel pressure was at 49.5psi it would be 10% low, at 44psi it would be 20% low, so 42psi is over 20% lower than expected
In above example 122ms is at 22% open time longer than 100ms, so correcting for 20% lower fuel pressure

So yes, 100% thats the problem as far as lean issue but can't say it is the only problem on a 19 year old used car, lol.

 

yeah sorry i spaced out when i asked the questions i have so many things im trying to figure out how to do on this truck, should i replace the fuelpump or no

 

Yes, replace the fuel pump....

If the truck has been in Arizona all its life, the bed bolts should come out easy.

If you have rear mud flaps, removing those makes it easier to lift the box over the rear bumper.

 

so i went out to my truck this morning and pulled the wire off cylinder #3 and theres no misfire, i checked a different cylinder to see if it would drop the idle just as much and it did, i havent driven it yet but i think we solved it

 

???

 

What did you solve ?

You're fuel pump is putting out 42 PSI, the minimum is 50....

Eventually what will happen is, the truck will get so little fuel it won't start one morning ?

 

now i have a knocking sound
sounds like the motor on passenger side