Too lean, both banks, under load... fuel pressure?


Jack Schmidt

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2003 4.0 SOHC, ~120k mi.

I'm getting too-lean trouble codes on both banks. Here are two freeze frames, a day or two apart, the second one after MAF cleaning:

DTCFRZF P0174 P0174
FUELSYS1 CL CL
FUELSYS2 N/A N/A
LOAD_PCT(%) 56.1 87.5
ETC(degF) 190 189
SHRTFT1(%) 12.5 13.3
LONGFT1(%) 20.3 24.2
SHRTFT2(%) 10.9 18.8
LONGFT2(%) 25.0 25.0
RPM(/min) 2366 2708
VSS(mph) 70 40
SPARKADV(deg) 29 16
IAT(degF) 66 88
MAF(lb/min) 5.456 9.074
TP(%) 29.4 44.7
O2B1S1(V) 0.095 0.290
SHRTFTB1S1(%) 12.5 13.3
O2B1S2(V) 0.665 0.390
O2B3S1(V) 0.13 0.265
SHRTFTB3S1(%) 10.9 18.8


When I unplug the IAC the engine dies immediately. Cleaning the MAF sensor, I removed virtually zero gunk. O2 sensors are probably original.

I started getting the trouble codes very shortly after I manually tripped the fuel line gravity switch (for anti-theft), returned to the truck and tried to start it before remembering to reset the gravity switch, then switched it on and started the truck normally. I don't know if this has anything at all to do with my trouble codes.

I installed a new fuel pump assembly a few months ago, supposedly OEM from NAPA Auto Parts. And I installed a new fuel filter and fuel relay about 1k miles before that.

At the moment I suspect the fuel pump, even though it's almost new, or maybe something else in the fuel path? When I turn on the fuel pump I hear the normal "zzz" of the motor but the pitch starts high then goes low and stays low, exactly like the sound made when starting from zero pressure due to a bad fuel check valve. Along with the "zzz" I hear a "shhh" in the tank as if air or foam is being pumped. I don't think I've ever heard the "shh" before. After I turn off the fuel pump the "shhh" continues, fading out over about three seconds. The tank is completely full. I don't smell fuel anywhere.

I don't have a fuel pressure gauge but would like to get one. What's the best way to install one? I don't mind if it's just under the hood or even temporary. My previous ranger had a pneumatic valve on the fuel rail but this truck doesn't.

Am I jumping too quickly to blame the fuel pump?

Maybe the gravity switch? I tried tripping it and resetting it and tapping on it -- no help.
 


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RonD

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Yes those stats are showing computer is having to open fuel injectors longer than it has calculated, so LEAN code would be set

If engine is running OK otherwise, no big drop in MPG, and no Vacuum leaks, then fuel pressure could be the problem

2001-2003 4.0l SOHC engines often didn't have a test port for fuel pressure

Fuel filter should have 3 ports
One is a return line to the gas tank and has a pressure regulator in the tank I think???
Maybe it has gone bad and that the new noise you are hearing
You wouldn't smell gas because it would just be flowing back into the gas tank
 

Jack Schmidt

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Yes, three ports on the fuel filter. Yes, the fuel pressure check valve is part of the fuel pump assembly which resides inside the tank. The previous one died about a year ago but it didn't make this "shhh" sound. Maybe the previous one wasn't as leaky as this one.

I'm going to study up on the gravity cut-off switch. Maybe it's simply another pressure relief switch that dumps the pressure back into the tank.

Edit:

The gravity switch is actually called an inertia switch, and it's all electrical, so it can't be my problem. Also, I found a pressure port with pneumatic fitting on the back end of the passenger side fuel rail. It points aft and is a bit buried under the PCV(?) hose. I'm going to look for a pressure gauge that will mate with this fitting. If the pressure is low I'll hit NAPA up for a replacement under warranty.

The valve on the end of the fuel rail is called a "Schrader valve."
 
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RonD

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A schrader valve is what was used as a test port on the fuel rails, so good find

There is also a Pulse Damper with a vacuum hose on the end of the fuel rail.
When Ford went to Returnless system and 50-60psi fuel pressure in 1998 the opening and closing of fuel injectors would cause pressure waves in the rail that would cause computer to have "fits", lol, because when an injector was open for a few milliseconds its flow was not consistent because it could be in the trough or peak of a pressure wave
Pulse Damper is just a "rubber" diaphragm that prevents pressure waves from reflecting off the end of the rail, 1997 and earlier had the Fuel pressure regulators diaphragm on the fuel rail that did the same thing
The Vacuum hose on the Pulse Damper is just for safety, in case diaphragm should leak fuel wouldn't drip out, it would be sucked into the engine, causing Rich codes
 

Jack Schmidt

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I was going to buy a dedicated fuel pressure gauge and fittings, but I got too impatient and just tested with a tire pressure gauge. I'm reading 30 PSI with engine off and only the fuel pump running.

After a quick search here I didn't find a fuel pressure specification but your message makes it pretty obvious that I'm way below spec.
 

RonD

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Yes, 55psi is spec with engine running

Fuel pump shouldn't run with engine off, its a safety thing?

Unless you jumper the fuel pump relay
 

Jack Schmidt

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Yeah, I jumpered it. In fact, I wired up an extra switch and relay a couple years ago when my previous fuel check valve was leaky. I used the cigarette lighter as the extra switch. I installed it because I didn't want to replace the fuel pump assembly just for a bad check valve and I didn't want to put lots of cycles on my key switch. Instead I would just push in the cig lighter for 5 seconds before starting the engine. The extra switch came in handy for this diagnosis as well.

Heading off to NAPA right now to find out about the warranty.
 

RonD

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Then I would expect 60+psi engine off fuel pump on, so yes I would think either pump or pressure control is not working as it should
 

Jack Schmidt

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I have a lifetime warranty on the NAPA fuel pump assembly, so I won't be out any money, but it's a chunk of time to drop the tank. Been there, done that.

Unfortunately, I have ~17 gallons in the tank now. I'm going to connect a long hose between the Schrader valve and a couple 5-gallon tanks and run the pump to drain the tank. Maybe shuttle some gas into my wife's car. What a pain.

I wonder if my truck is somehow killing fuel check valves. I'll check the tank for dirt when I have it out. Wish I could study the bad check valve but I know from previous replacement that the fuel pump assembly is a damn complicated piece of hardware.

Thanks for all your replies, RonD. Love this site and the guys on it.
 

RonD

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Much easier to lift the bed, 6 torx 55 bolts, 3 phillips on filler tube

Put rear 2 bolts back in but not tight
Have 2x4 handy and lift up the bed, put 2x4 in place to hold it

Or disconnect tail lights wires and slide bed back 2 feet, or enough to pull out assembly

Or install one of these for future use: http://www.stealthdumptrucks.com/forduplarge.jpg

:)
 

Jack Schmidt

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I fear my torx bolts are seriously rusted in place. I'd also have to buy the torx socket, but I suppose it's not expensive. In fact, given the full tank, this is the time to buy the socket and replacement bolts. Gonna go right now.

> http://www.stealthdumptrucks.com/forduplarge.jpg
:)
 

RonD

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Independent shop will loosen them with impact air wrench for CASH :)
Takes about 5min so offer $20, see what they say

But you still need the T-55 to take them out and reinstall
 

alwaysFlOoReD

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I've busted a bunch of t-55 sockets. Buy more than one and take back any that don't break.
 

Jack Schmidt

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Well, I needed transportation for a while so I drove a while with lean codes and 30 PSI fuel pressure I kept off the accelerator and the truck ran fine. Yesterday I finally replaced the fuel pump assembly.

I took the advice above and removed the bed rather than dropping the tank. Really good advice, thanks! It was MUCH easier to disconnect and reconnect the hoses than when I dropped the tank. It took me about 2.5 hours. The plastic on my bumper got a little scratched, though. The T55 socket from NAPA, Carlyle brand, is only 3/8" drive but didn't break even though I used a 3/8-to-1/2 adapter and a 1/2" breaker bar. I re-installed the six bed bolts with anti-seize compound yet they still went in with effort so I suppose the nuts are distorted-thread lock nuts.

Now the fuel pressure, with engine not running, pegs my 60 PSI pressure gauge. No more "shhh" sound from the fuel pump, and no more lean codes. Yay!

Thanks!
 

RonD

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(y) Good work

Thanks for posting the FIX

Just FYI, Lean code doesn't mean the engine is actually running Lean, it means the computer's calculated open time for the fuel injectors is showing high oxygen content in the exhaust, via O2 sensor, High Oxygen level = Lean Burn, Low Oxygen level = Rich burn
So computer opens injectors longer to get correct oxygen levels in the exhaust, this only takes 1 or 2 seconds of run time
If the extra open time for the injectors exceeds more than 15-20% of calculated open time then computer will set Lean code.

STFT(short term fuel trim) numbers are a %, + or no sign means open time is being extended, +2 or 2 = 2% longer open time, -2 would be 2% shorter open time, would set Rich code at over -15%
Long term FTs are also a % but are used to offset computers base calculations, computers calculation is 0 STFT
So if LTFT is +15% and STFT is +10% thats actually +25% fuel trim
LTFT is there so vehicle can age gracefully, lol, there will be small air leaks and fuel pressure will drop down a bit, LTFT is used so computer doesn't have to re-learn every time its started up, also on cold start when O2 sensors are not working

Computer bases open time on air flow and fuel pressure at the injectors, for 1998 and up that's 60psi, +/- 8psi
So the lower average fuel pressure from the failing pump caused the Lean codes, but engine was never actually running Lean, so safe to drive.

If an engine is actually running Lean it will ping/knock during operation, and that can cause damage to engine
 
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