Lean running 04 Ranger 3.0L

I have a Ford ranger that has very high LTFTs. I have been testing and chasing this problem for weeks. Maybe you guys can give me some technical input...

The truck is a 2004 Ford Ranger, engine is a 3.0L gas. Between the recent tune up and diagnostics, the list of new parts is as follows;

Plugs, wires, air filter, oil change and coolant flush, as a tune up when I got it.

Fuel filter, MAF sensor, PCV, and upstream O2 sensors, because the MPGs were terrible. I also ran some fuel injector cleaner thru the tanks.

There are NO driveability issues and the engine starts and runs fine, good power, no smoke or hesitation. The only symptom here is the high fuel trims and, occasionally it will set both P0171 and P0174, under certain conditions.

Due to the high trims, I have smoke tested the engine twice. Once with everything connected, and once with all vac ports plugged off. it was smoked with the engine hot, and with the engine cold. No signs of vac leaks. The fuel pressure tests at 65psi, engine off key on. With the engine running at idle and at 2500 rpm, the fuel pressure is steady at @65psi.

The conditions that the LTFTs hare high is odd. At idle, they will climb to 18-20%. While driving, the more load on the engine the more they will go down to a normal range of 3-5%. When you let off the gas, they will go up. Climb a hill, they go down, coast down the other side, they go up. Come to a stop sign, they go up. Drive away and they go down. Note that bank 1 always reads higher than bank 2. Also for a long time, ONLY bank 1 had this problem (not to this degree) and bank 2 was normal. Bank 2 recently started behaving the same way, but to a lesser degree. Now bank 2 us usually about 2-4% lower than bank 1. Example, if bank 1 is 18%, then bank 2 is about 15%. Bank 2 never is equal with or greater than bank 1.

I have done a hard reset on the computer (disconnected the battery, overnight with the light switch on). Once the engine warms up, the problem is back the same way.

I have also had a vacuum gauge on it, the result is normal, steady needle in range at idle, good response to throttle, no drifting shake or twitch on the needle. Good smooth normal response while driving and at idle.

The only time you notice any problem at all, is if you leave it sit and idle too long and it sets one or both lean codes. At times, its sets them pretty fast, sometimes not. As I said at idle they hover around 18-20%.

I have ruled out in my mind a fuel pump, filter, or pressure problem because the harder you load the engine, the more normal the trims run... and there is no hesitation, or lack of power, no overheating or issues of any kind under any load.

Some of my new parts might be defective, they are good brand name parts so I doubt it.

Before I start throwing more parts at it, tearing it down to put in hew intake gaskets injectors and other stuff I don't know will cure it... I would like some advice on any other test I can run, or maybe just point out something I overlooked?

You are certain there are no leaks in the intake boot?

Disconnect and seal off the purge valve, disconnect and pinch off the brake booster, and try and plug or isolate the PCV system.

Do the trims improve at idle?

As I said, I ran the smoke test with all the vac ports plugged except the PCV. I also ran it this way, at idle and 2500rpm. There was no change in the trims. The PCV is new and the hose is in very good condition.

The intake boot is good. No cracks holes or damage.

Also this problem started as a bank 1 only problem, and recently bank 2 started doing the same thing, to a lesser degree.

Just checking, so the purge is good?

Put a vacuum guage on the oil dipstick, what do you get? Pinch the PCV off when doing this.

I dont know if the purge valve is good, I know with it on and off the intake, there was no smoke. But, you have a point, I did not test it off the intake with the engine running and that port plugged. I will definitely test that again.

The vac on the dipstick I have not done... I didnt remember to try. That'll tell if the lower intake gaskets are leaking, right? PCV in and out plugged at the valve covers, gauge on the dipstick pipe.... will do.

Thanks for those reminders!

Not familiar with your engine, but I was thinking maybe run some tests on your Idle Air Control Valve. If it is a stepper motor type maybe it the motor or a pintle is sticking.

I ran a few additional tests this morning.

After plugging the PCV valve hole on bank2s valve cover, and plugging the pcv intake vent hole on bank1s valve cover, then starting the engine.... I removed the oil fill cap and stuck a nitrile glove on it tight (just the way I have always done it... quick and easy) and started the engine. There is good positive pressure, enough to slowly inflate the glove.

So... lower intake gaskets are intact enough to rule out.... I assume.

Then I put it all back together, got out a squirt bottle of water and gave a good splash on every joint hose and injector I can reach. No suction, no change in the idle. Part of the upper gasket I can't reach along with a couple injectors But I splashed enough water back there it should have reached them. Its possible it didnt.

Unless there is some other thing I am missing, I guess I will plan on putting in a new upper intake gasket and a new set of injectors at some point. I doubt they were ever changed, the guy I bought the truck from said he had it since about 2008 or 2009 and he didn not replace them or do any sort of engine work on it.

In the meantime, I assume as long as the trims are not setting a code, it fine to drive it normally with no damage being done other than low MPGs.

Which the new o2 sensors might have fixed I havent driven it much since I put them in to see. On the subject of those, I bought NKG-NTK 22500 O2 sensors for both sides upstream. NKG does not specify if they are upstream downstream or ok for both. These are the same brand and number I used for my other rangers, for upstream and they worked fine. Is it possible, for this engine, I should be using a different brand and made specifically for upstream bank 1&2? Some brands do that, some do not. I did not think it made a difference, so long as the plug fit. Maybe it does, I don't know.

What would the most logical course of action be at this point? My guess is go ahead with new upper gaskets and injectors, simply due to the trucks 200k and age its probably due for it anyway.

I notice an symptom and I don't know if it mean anything but...

When I attempt to rev the engine up and hold a higher than idle rpm, its difficult to maintain. For example, I want to hold 2500RPM, I push down on the pedal, get it up to 2500 and hold... quite often the rpm will drop on its own, to a lower RPM. Maintaining a steady RPM is a little tricky. Your foot doesn't move, the RPM just drops on its own. if you dont move your foot it doesn't come back up, you have to press the pedal a bit and try again to get it up and hold it there. My other trucks don't do that, you hold the pedal in one spot, the rpm stays in one spot.

I don't know if this problem has anything to do with the lean running problem, but I figured I better ask about it.

I found there is a TSB on this ranger and maybe this problem... Where does one go to get a full text of a TSB?
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04/08/05 Electrical and Air Conditioning NHTSA ID: 10013116
TSB ID: 04174

Malfunction indicator lamp (mil) illuminated - system lean diagnostic trouble codes (dtc's) - service tips. various models including 2004 f-series.
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If you can't find via web search, you could get a subscription to something like Alldatadiy (I think it's like $60 per year per vehicle) and you will find technical service manuals, diagrams, TSB's, color wire diagrams, etc)

Weycraze posted it for me in the other forum here.

A TSB for "find and fix the vacuum leak".

Fred Garvin wrote:

A TSB for "find and fix the vacuum leak".

It doesn't just say "find and fix the vacuum leak". There is also a capitalized caution about one of the parts that this vehicle has recently had replaced. Never mind the MAF and HEGOs.

Some of my new parts might be defective, they are good brand name parts so I doubt it.

Motorcraft from a reputable source? Not that that would guarantee they're good.

The new PCV valve is a Motorcraft part from RockAuto. The MAF is Hitachi and the O2s are NTK.

I drove it around todat for about 4 hours. Mixed driving, towing a roll of hay on a trailer for about 10 miles... some highway miles some backroads.

it started out good, but eventually when it relearned all of its stuff, its back to being about the same. Drive it over 2k rpm and the trims stay about 10-12%. Let off the gas or sit and idle, they shoot up to 20-25% or more on both banks.

Take off driving and they do fall right back down to 10-12%, if you are really going hard, it'll drop even more.

Other than the numbers on the gauge, you'd never know there was anything wrong... runs great.

I wonder about the possibility of a vacuum leak or some other unmetered air at idle. Second (and again, w/o knowing your engine), I wonder an idle air controller also ( is their a relearn procedure for an IAC on these trucks?).

I don't know about the relearn on the IAC but, That sounds like a possible cause since it only does it at idle, or when you let off the gas driving.

I had to change one of those on my other ranger once, cleaning it did no good. I might have a spare one in the parts pile. I'll look tomorrow.

The low idle is a little rough. Even so I am not sure if a bad IAC would cause this kind of issue... maybe it would, I have no idea. The last time I replaced an IAC on a ranger it was for a HIGH idle problem. This is a slow idle and a lean condition in both banks, one is always trimming about 4% more than the other. I would think a bad IAC would cause an equal problem on both banks.

its worth a shot if I can dig up another one to try here.

I have been studying the diagnostic book I bought here, (very good book, I'm learning a lot from it) and I do not think the IAC is at fault. The engine maintains a good steady idle when you turn on electrical loads, headlights, AC radio ect. Switch them on and off, the idle remains steady. There are no other symptoms of a bad IAC. As I understand it, a bad/sticky IAC will cause numerous problems, none of which I have going on.

If I understand it correctly, the IAC will not cause a p0171 p0174 at idle without some very obvious signs its not working right. Please do correct me if I am wrong here....

I will go over the vac hoses and upper gaskets again when the weather permits. I will block off the evap and climate controls ports and take it for a drive this time instead of just letting it sit there looking for a leak. Maybe something will become obvious.

What is left then is the upper intake gaskets and the fuel injectors, which in spring I will just put new ones in, because it might fix it, and in the least they probably need replaced anyway at 200K.

Which leads me to a question, if someone can answer....

Is there a condition where the fuel injectors can starve the engine of fuel (run lean) AT IDLE, but operate normally at 2k RPMs and above while the truck is being driven at speed and under loads?

Maybe weak internal parts or a clog that cause the injector to lose its proper spray pattern and strength during a short pulse time, that gets better with longer the injector pulses? (high rpm or engine loads)

or am I barking up the wrong tree?

Fred Garvin wrote:

Is there a condition where the fuel injectors can starve the engine of fuel (run lean) AT IDLE, but operate normally at 2k RPMs and above while the truck is being driven at speed and under loads?

If there is such a condition, I have not encountered it yet. :silly:

I'd stay on the unmetered air/vacuum leak path.

I agree.. when its not -20 outside, I'm going to keep chasing that probably vac leak.

As an aid to finding the problem and to keep in mind while I am doing it....

Is there ANY other condition that would mimic a vac leak and cause this condition? High LTFT at idle that gets significantly better at RPMs over 2K with NO other symptoms present?

I did find some nut shells and other vermnin leavins on top of the inake around the injectors last time I was in there... I bet one of the little buggers nibbled a hole or a wire somewhere. I'll be ab le to tell that for sure when I take it all apart to regasket the top and pop in new injectors.

But the total lack of any smoke tracks or, any sign it was sucking water in the water test points to probably not.

I had to haul some hay today so I did a few things to eliminate possible causes... If I am repeating myself a little sorry about that...

I disconnected and plugged the climate control vac port, and the Evap sys hose going to the purge valve. These were plugged at the intake. This had no effect on the STFT/LTFT at idle or any driving condition.

I plugged the brake booster at the intake, this had no effect on the trims at idle. I can't drive it without the booster, but this is an at idle problem so... kinda pointless to try.

I'm eyeballing this new MAF sensors readings. This unit also has the air temp sensor in it. The intake air temp today was around 45F. the outside air temp today was around 47F so.. its good. With the engine temp at 194F, The MAF reading is as follows;

At idle 850RPM = 3.70g/s

At 2500 RPM in park, = 10.9g/s

At 2300 RPM, pulling a trailer that is about 1200# loaded, it reads 30g/s. At this speed and load the STFT are +/- 3, LTFT are +6-10, both banks are close to the same, but bank 1 is always a little higher.

And as before, take your foot off the gas, and the LTFT shoot to 25+. The STFT seem to always run about +/- 3 under any driving conditions.

I'd appreciate input on how correct that MAF is working.

I think I have eliminated all the stuff connected to the intake as an air leak source. What I have left is the intake gasket and injector O rings. I can't think of anything else that could be sucking air. The exhaust ahead of the upstream O2 sensors have no leaks. The pipe and connections are in good shape. The intake boot to the air filter & MAF is good, no cracks or leaks.

If I missed anything, let me know.... Thanks!