2003 Ranger 4.0 liter 64,000mi since new

I posted a question a while back but didn't have all the PIN readings (Live Data) to assist in diagnosing for a LEAN BANK 1 & 2 Long Term Fuel Trim codes (P0171 and P0174). Bank 1 and 2 LTFT are BOTH 25

I now have every reading imaginable that the scanner could provide, so if any of you could help me diagnose the problem I would most appreciate it. I photographed the screen and can list whatever numbers you might think helpful.

Let me start by saying that the truck runs well, with no discernable poor running conditions under any circumstances. I sprayed EVERYTHING with flammable brake cleaner to try to find a possible air leak. With only 64k on the truck, all lines (plastic/rubber) look GREAT, and no leaks could be found.

Erasing the codes and running the truck takes maybe 500mi for the codes to return (but the LTFT readings are immediately evident). The STFT is also 25% now (the graphed readings bounce between 22-26).

Readings: (All taken at idle, 55 def F at 300ft Above Sea Level)

LTFT #1 25%
LTFT #2 25%
Manifold Pressure 0 psi (shouldn't it read atmospheric, or a vacuum like 20 or so in at idle?)
Mass Airlfow Status: "No Error"
Mass Air Flow 5.1 gr/sec or 0.66 lb/min
Mass Airflow Volts: 0.91v
Baro Pressure: 13.38psi
Engine Misfire Detected: NO
EGR Status: "No Error"
EGR Evaluated: YES
EGR Sys Eval Test Ready: "Not Ready"
EGR Vac Regulator Fault: "No Error" (Is this the DPFE?)
STFT #1 29% +/- 4% variable
STFT #2 28% +/- 3% variable

I DO now have a DTC P1000 OBD Readiness Test Incomplete which I suspect is just because I reset the previous codes, and the Readiness Monitors have not completed their drive cycles.

Some suggested hose/elbow vacuum leaks.
Others said Mass Airflow Sensor Bad
Others said DPFE Sensor bad
Hopefully the above readings will assist.

Questions/Comments/Ideas Much Appreciated?


Thanks,
Bob

 

Just so you know STFT is open time for fuel injectors, 0 STFT would be computer calculated open time for each injector based on AIR WEIGHT at that moment

As an example, computer calculates each injectors open time as 100ms(milliseconds) based on air flow(WEIGHT)
After that 0 STFT fuel is burned, the O2 sensor shows Lean(low volts)
So computer changes to +2 STFT, and injectors open for 102ms, so open 2% longer to let in more gasoline
Then O2 sensor still shows Lean, so computer tries +4 STFT, then +6, then +8 ect...........until it gets O2 sensor to read .45volts, good burn

Same happens for Rich except, -2 STFT would be 98ms open time, the 96ms(-4 STFT) ect..............

Gasoline's air/fuel mix ratio is 14.7/1, this is a WEIGHT ratio
14.7 POUNDS of air to 1 POUND of gasoline
14.7 grams of air to 1 gram of gasoline
So pre-vaporizers or 200mpg carbs were never possible, it just doesn't work that way, lol

So when the computers calculations are off by 25% it will set a code, in this case +25 so a Lean code, -25 would be Rich code, and on both banks so its common to the engine as a whole

The computer already KNOWS its running a 4 Liter engine, so it knows 4 liters of air will come in at WIDE OPEN THROTTLE every 2 RPMs, so computer already knows how much air VOLUME is coming in at ANY RPM and throttle position, its just math
But it doesn't know the WEIGHT of that air volume
"Hot air rises', why? because its lighter than cooler air
Its harder to breath at 5,000ft why, because there is less air, lighter air

The MAF sensor is used to calculate the weight of the air passing by it
The IAT(ACT) sensor is used to calculate the temp of the air
A vacuum leak can cause Lean code because MAF is showing less air/lighter air than there actually is, because air is leaking in

The computer does NOT have a fuel pressure sensor, this is important because computer calculations are based on each fuel injector having 55psi pressure behind it, 1998 and up Rangers
If fuel pressure was say 30psi..............then less fuel would flow in in the 100ms open time, so.................yep, Lean code, and computer has to open injectors longer maybe 25% longer

Simple vacuum leak test
Warm up engine, let it idle and unplug IAC Valves 2 wire connector
RPMs should drop to 500 or engine may even stall, either is GOOD, it means no vacuum leak
If RPMs do not drop then there is a leak

Fuel pressure needs to be tested, just to take that off the table or you can chase your tail around and back again if it is a fuel pressure issue
1998 and up Rangers have fuel pressure regulator in the gas tank on the fuel pump assembly, just mentioning that because if fuel pressure is low you change the whole assembly

 

Good answers, thanks.

Does this engine have Schraeder valve on the fuel rail to check the fuel pressure?
I didn't see any is why I ask I don't have a shop manual for it yet). I haven't dug around seriously, so it could be there I guess.

If the fuel filter or sock on the fuel pump were clogged, resulting in low flow/pressure of course at 75mph the supply wouldn't be enough to run the engine w/o
surge/misfire and that's not the case.

So fuel pressure is obviously Job 1!

Thanks,
Bob

 

Engine can run fine on 30psi pressure, at any speed, thats what 1997 and older Rangers used, but computer was programmed for that pressure, so no running issue just Lean codes on 1998 and up if pressure is low

I know on some early 2000's 4.0l SOHC Ranger there was no schrader valve, 2003 should have one

If its there it will be on passenger side on fuel rail at the back by the firewall after the last injector on that side
It will have a blue or black cap on it

At the very rear on that fuel rail is the Pressure Damper, it will have a vacuum hose attached, it absorbs pressure wave build up in the rail, can't use it to test pressure

 

Thanks, I will look there.

Yes, low fuel pressure will cause the ECU to lengthen the injector open-time to compensate for less fuel per unit time, and that can handle up
to a certain lack of pressure after which you will experience poor running.

First order of business is to check the pressure. I hope the thing has a Schraeder valve to make it easy. :)

 

OK, problem discovered.



I managed to bend my hand around and got my fuel pressure gauge on the Schrader valve expecting to see low pressure, but it was 65-66psi so went ovr to my friend's shop to use his smoke machine, but he thought maybe the IAC motor gasket was leaking cuz the idle was hight a about 1050rpm, and while the cover was off the top of the throttle body he shot some brake cleaner where I couldn't get earlier and found a small crack in the plastic intake manifold runner set. When the engine was cold, no crack, but let it sit and idle a while and pull on the trottle body for more leverage, and the brake cleaner made about a 75 rpm higher idle speed.



So it looks like I'll be replacing the runner set. About $200 so not too bad, and it looks like a reasonable job.



I would have thought it would have taken more that such as small crack, but any crack is too big, so we'll see if that fixes it I guess.



Thanks for the replies and ideas-

Bob

 

Good work

Crossed fingers on the results