The Dreaded Lean Code

[Xjorgeypoox]

Hi everyone!
New member, have been stalking the forums for a while now, and I finally got my hands on a ranger. Oldie, but seems in fair shape.
Only issue I’ve found so far, code P0174.
Pops up fairly often. Not every time but often.
Truck doesn’t idle super smoothly, but it isn’t terrible either.
I’ve replaced the egr valve as it had the original one when I purchased her. I’ve just replaced the pcv valve and breather tube.
Currently running a can of Seafoam in the tank Incase an injector is
I’ve got some images of live data and I’m hoping someone can help me decipher these and see if I can track my gremlin down.
I’m leaning towards a vac leak but I can’t seem to track it down.
Thanks in advance yall!
FYI... first image is at idle.
Second is 4th gear, low speed high throttle input
Final image is freeze frame from pending p0174 code

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[cbxer55]

Dreaded? I've been driving mine with both P0171 and 174 for years. I gave up trying to find out what's causing it and just stuck a piece of black tape over the stupid CEL. Been five or more years. Hasn't missed a beat. Had a misfire for a week or so, tracked it down to a loose spark plug. Put in new plugs, and it runs just awesome.

When I had the lean codes on my 04 Lightning, it blew so much black smoke out the tail pipes, it looked like a diesel. Lean. Yeah, right! Black smoke ain't lean.

Good luck on your mission. This tape will self destruct in five seconds.

 

[Xjorgeypoox]

unfortunately being in Ca, I have to repair in order to pass inspections... hence my current goal!!hopefully someone is able to chime in with more ideas!

 

[RonD]

Welcome to TRS

Clean MAF sensor its reading a bit high

At warm idle(only time OBD readings are valid, FYI), it should be approx. engine displacement, so 3.0l engine should be between 3-4 g/sec, assuming idle RPMs of 700 or so, if there is a vacuum leak and idle is higher then this doesn't apply until you can get RPMs down

Just FYI on throttle position, its a 0-5volts scale, and throttle sensor voltage is always between .8v and 4.5v
So 15-18% with throttle closed is correct, NOT 0%
And wide open throttle of 85-90% is correct, NOT 100%

Change PCV Valve if its not been changed in the last 3 oil changes, dirty PCV valve can be a vacuum leak if its not closing like it should


After engine is warmed up and idling, unplug the IAC Valve's 2 wire connector, it will close
RPMs should drop to 500 or so or engine may even stall, either is good, it means no vacuum leaks
If idle doesn't drop then there is a leak somewhere

You can use soapy water in a spray bottle to hunt for a vacuum leak
Spray it on potential leak points, with engine idling, engine will stumble when it sucks in the soapy water

And WAY SAFER than using a combustible spray on a hot engine, potential fire hazard
Soapy water just has a potential cleaner engine hazard,

The throttle body can leak air, and hard to detect, its often just better to pull it off and replace gasket if you can't locate a vacuum leak anywhere else

 

[Xjorgeypoox]

Hey Ron,
Thanks for the info.
I replaced the MAF but not the housing.
I’m contemplating just getting an entire housing and sensor, maybe it’s not setting in correctly...


My idle is a bit high in my opinion, normally idles about 800-900rpm, but, I’m wondering if that’s the anti diesel screw that could have been adjusted
What are the chances my o2 sensors are bad? Or that the Intake gaskets are leaking?

I have smoke tested the intake via the brake booster and only leaks I found where from the top of the iac and egr. Both were replaced less than a month ago... I do have a TB gasket coming from rocckauto. Should be here this week.

 

[RonD]

After engine is warmed up and idling, unplug the IAC valve
RPMs should drop to 500 or so
If not, turn anti-diesel screw 1/2 turn counter-clockwise(unscrew)
If RPMs do NOT drop then turn it back to where it was, its not your high idle issue

If RPMs drop then turn it counter-clockwise a bit more until engine is barely running, its set
Plug IAC Valve back in and RPMs should go up to "normal idle"

I assume its an automatic trans vehicle, manual trans should have "normal" idle at 700-750 on a 3.0l

 

[Xjorgeypoox]

No, the truck is manual. That’s why I was thinking the idle was high. I know auto trans idle higher so that was my first indicator that I may have a vac leak. Then I learned of the p0174 code. So I’m kind of thinking both may be related

 

[Dirtman]

Your fuel trims show normal at idle and high under load, this is pretty much the opposite of how a vacuum leak should show up. At idle the manifold is under high vacuum so the leak is very strong, when you increase the load on the engine manifold vacuum drops and so does the negative effects of the leak. I'm just guessing but it seems more like a fuel delivery issue to me. Being on both banks I'd throw a fuel filter at it to start since it's a cheap 5 minute job...

 

[Xjorgeypoox]

Your fuel trims show normal at idle and high under load, this is pretty much the opposite of how a vacuum leak would should show up. At idle the manifold is under high vacuum so the leak is very strong, when you increase the load on the engine manifold vacuum drops and so does the negative effects of the leak. I'm just guessing but it seems more like a fuel delivery issue to me. Being on both banks I'd throw a fuel filter at it to start since it's a cheap 5 minute job...

Is +7 at idle normal?
I thought it should be >+5?

 

[Dirtman]

Is +7 at idle normal?
I thought it should be >+5?

+7% is perfectly fine. As engines get older the numbers change. That's the whole point of the fuel trims, to be able to compensate for wear. The issue here is the amount the fuel trims change from idle to load. For example my truck runs around +10 to +12% but it does this through all throttle ranges and engine loads which is perfectly fine. Don't focus on the numbers themselves, focus on what they do.

Generally speaking when you have very high long term numbers at idle and they drop under load it points to a vacuum leak. When you have lower long term numbers at idle but very high numbers under load it points to a fuel issue. Very general rule of thumb though.

 

[RonD]

Computer runs engine Richer at idle to prevent overheating, it also doesn't use O2 sensors at idle

But Dirtman does have a point about fuel supply/pressure, Rangers never had a fuel pressure sensor
Computer just assumes 55psi in a 1999 Ranger, if it was 35-40 then that would cause Lean code

Remember a Lean code does not mean engine was ever running Lean
Lean code means computer's original calculation for injector open times was Lean
+ fuel trims means computer is opening injectors 5% longer than calculated, or 10% longer, ect....

So this could mean a vacuum leak, more air is present than computer used in calculation
OR
Less fuel is flowing in than computer used in its calculation

 

[Xjorgeypoox]

+7% is perfectly fine. As engines get older the numbers change. That's the whole point of the fuel trims, to be able to compensate for wear. The issue here is the amount the fuel trims change from idle to load. For example my truck runs around +10 to +12% but it does this through all throttle ranges and engine loads which is perfectly fine. Don't focus on the numbers themselves, focus on what they do.

Generally speaking when you have very high long term numbers at idle and they drop under load it points to a vacuum leak. When you have lower long term numbers at idle but very high numbers under load it points to a fuel issue. Very general rule of thumb though.

Awesome good info. I’ll be replacing fuel filter tomorrow. New fuel pump is on the way Just in case.On that note, Is it really that much easier to remove the bed than to drop the tank?

 

[Xjorgeypoox]

Oh wait, so one other question, seeing as I’m only getting a lean code for one bank, is that possible from a fuel issue? Wouldn’t it manifest as both banks being lean and throwing both lean codes?

 

[Dirtman]

A. Do not just throw a fuel pump at it, it's not worth it without testing it. B. Unless you bought a ford pump your buying a peice of garbage that WILL fail.

 

[Dirtman]

Oh wait, so one other question, seeing as I’m only getting a lean code for one bank, is that possible from a fuel issue? Wouldn’t it manifest as both banks being lean and throwing both lean codes?

Both banks are lean, bank 1 simply didn't cross the threshold for setting a code yet.