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3.0 Banks 1 and 2 too lean


brianpitera

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Hello,
I recently purchased a 99 Ranger 3.0 Flex Fuel with about 184,000 miles. When I purchased it it had a fairly bad misfire on cylinder, it was noticeable at idle and driving. I have since replace the plugs and wires, ignition coil and the injector on cylinder 3, all helped a little and the cylinder 3 misfire code has disappeared, but P0171 and P0174 for banks 1 and 2 too lean have started to pop up. I most recently replaced the upper and lower intake manifold gaskets which has substantially helped smooth out the engine and driving it is very smooth and the idle is also fairly smooth, definitely much better, but the lean codes are still coming back, although it takes much longer now. I have also replaced every vacuum line I can find, tried finding other vacuum leaks with carb cleaner with no luck and cleaned the maf sensor. Tonight I tested the DPFE, with no suction it showed about 1.7 volts and with suction about 5.2, and it held suction. It also has an exhaust leak on the y-shaped pipe with the cats on it, behind the cats, which I was planning on fixing at a later point. Any help or advice on this is greatly appreciated, thank you.
 


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RonD

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Welcome to TRS :)

On a "V" engine if you get Both Banks showing Lean(or Rich) then it is a system wide issue, not a Bank issue, I know obvious but needs to be mentioned.

Lean codes do NOT mean the engine is actually running Lean, this is where codes can be confusing, lol, they often don't mean what they say.

"Lean code" means the Compter's(PCM's) air:fuel calculation is more than 15% off
PCM "knows" it is operating a 3 Liter engine, so it has a baseline of the amount of air a 3 Liter engine will be sucking in at any given RPM and throttle position.
It also has the MAF(mass air flow) sensor to fine tune that for altitude and air temp

It also "knows" the size of the stock injectors and the Fuel Pressure at those injectors, so it "knows" how much gasoline will flow out of each injector if it is opened for say, 100ms(milliseconds)

That's the background you need

So PCM does its on the fly calculation to set 14.7:1 air:fuel ratio
It then gets on the fly feedback from upstream O2 sensor on each bank

O2 sensors "see" oxygen, not fuel, too much oxygen is a Lean, too little oxygen is Rich

Say PCM sets 100ms open time for each injector, if O2 reports Lean then PCM changes to 102ms, if still Lean then 104ms, ect.......until O2 reports "good" burn
So PCM is adding more fuel until O2 reports good burn
This all takes only a few seconds so engine is never running Lean
If, in this case, PCM got to 116ms open time it would set a Lean code, 16% difference
This is called Fuel Trim, Short Term Fuel Trim(STFT), + or - 10% is normal in older vehicles

So Lean code means.........PCM is opening fuel injectors much longer that calculated, so there is a problem, and PCM lets driver know

Yes, an air leak any where from MAF to intake valve means PCM is not getting correct air data, unreported air is coming in.
And vacuum leaks are most common cause, if it effects BOTH banks then it has to be upper intake, air tube or MAF issue.

But what about fuel pressure, 1999 Ranger should run 60-70psi fuel pressure
If fuel pressure was 35psi then not as much fuel would flow out of injector in 100ms
So same Lean code

The exhaust leak at the "Y" pipe will effect Downstream O2 sensor, after the Cats, this isn't directly used in STFT but is used in Long Term Fuel Trims(LTFT)
LTFT is used when engine is cold, no O2 sensors, also called Open Loop
As any vehicle gets older it will have some air leaks and lower fuel pressure, just normal aging, LTFT is used by the PCM to Bias the air:fuel mix so it doesn't have to be "perfect".
LTFT takes a bit of time to change, Long Term, lol, and that exhaust leak sucks in air, doesn't just blow out exhaust, so downstream O2 sensor is "seeing" more air/oxygen in the exhaust after the Cats that expected, and it is biasing the base air:fuel mix, so.....
 
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JP02XLT

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You can easily check for any vacuum leaks with an un-lit propane torch, just turn the gas on, wave it around and listen for any rpm increase, much cleaner than using carb cleaner to find the leaks. I am with Ron, sounds like some un-metered air is entering the engine somewhere up in the intake portion, or decreased fuel pressure. Is it hard to start at times? Do you have a vacuum gauge to put on it to see if the engine vacuum is steady?

JP02XLT
 

brianpitera

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Thanks for the welcome and the quick responses. I spent a little time with it today, I put a fuel pressure gauge on it and it read a fairly consistent 54psi, about 53psi with the engine running and decreased to about 50 if I left the key in the on position after the fuel pump shut off. I also read the codes a few times after driving it a few times and it seems like only the p0174 code for bank 2 remains, although both banks was showing up initially after doing the intake manifold gaskets. I also bought a new code reader and read some of the live information after it warmed up, the bank one short term fuel trim read 4.7, long term read 19.5, bank two short term said 10.2 and long term said 25.0, if that helps at all, also the number one 02 sensor varied a lot around .445 volts and the number two sensor stayed much lower around .09 volts, only getting up to about .095 volts, if this means anything unusual or just confirms what is already known I'm not sure. My next step is to go get a vacuum gauge, and see what that says, also I don't think I replaced the line or connector leading to the pcv yet. I will certainly try the propane torch as well, that seems maybe a little more precise than the carb cleaner too. Unfortunately I'm leaving for a four day work trip tomorrow and wont be able to work with it then but I will continue to research and check back here. Thank you again for the help.
 

RonD

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O2 Sensor "1's" are the Upstream sensors
Bank 1 sensor 1(passenger side)
Bank 2 sensor 1(drivers side)

Bank 1 sensor 2 is the downstream(LTFT) after Cat converters O2
Bank 2 sensor 2 would only be found on Dual exhaust "V" engines

O2 sensors generate their own voltage, 0.1-0.9volts
.4 is what computer whats to maintain
O2 sensors are heated, thats what the 12volt fuses are for

Downstream O2s are after the Cats so exhaust will be cleaner, so lower than .2 or even .1 is normal

I would fix that exhaust leak then reset/clear codes
You usually can NOT clear/reset LTFT, that is normal, you just have to drive it after any repair and if fixed it will start to come dowm

Another test for vacuum leak is to warm up engine, let it idle
Unplug IAC valves 2 wire connector
IAC valve will close all the way and idle should drop to about 500, engine may even stall, either is GOOD, it means no vacuum leak
You could still have an air leak between MAF and throttle plate but not in the intake side

If idle stay at 600-700, i.e. doesn't change, then leave IAC valve unplugged and disconnect one vacuum hose at a time and plug that port with finger
If idle drops then you found the leaking hose or device at the end of that hose
 

delaware74b

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See the TSB I attached to locate vacuum-related lean codes.

FWIW, I had the same codes and everything was good - it passed the TSB procedure. Fuel pressure within specs, including injector leak-down test. Brand new OEM PCV valve, no duct leaks, no EGR on my '04 so no DPFE.

I got frustrated and changed the MAF sensor. Reset the ECM with Forscan and it was the sensor. It was under-reporting the amount of air going into the engine. I pulled it apart and found a piece of air filter material wrapped around one of the wires. No codes since.
 

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brianpitera

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Thanks for the help guys, sorry I've been away for a few days. I will try those tests tomorrow afternoon and see what the results are. I have also seen in a few responses in other threads that the elbow connector leading to the pcv cracks so I splurged on the $2.69 for the pcv and elbow, figuring I'd replace it if I end up taking the upper manifold off again. After driving it around for a while again today I read the codes and it's still just showing a bank 2 too lean code, in wondering if it's a more localized problem after all. Again I really appreciate all the help.
 

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Have you recently switched from regular gas to E85? Even for a single tank?

Sometimes the FF sensor doesn't recalculate the ethanol percentage correctly, especially when switching from regular to E85 or vice versa and it can cause rich/lean codes because the calculation of how much fuel is needed is done with incorrect starting values. The fix is to clear the KAM to force a recalculation.
 

brianpitera

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I have actually switched back and forth a couple of times, the problem has happened since I bought it so I'm not sure if the previous owner had switched or not. Do you know a procedure to reset the kam?
 

RonD

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KAM = keep alive memory
Same as Radio presets are stored in the KAM inside the radio

The PCM(computer) gets battery power all the time for the KAM, as does the Radio.

So unhook the battery, for a few minutes
Both KAM's will be cleared :)

You may experience a wandering idle as the PCM re-learns idle control settings, that should only last 2, maybe 3 drive cycles
1 drive cycle = heat up to operating temp, cool down below operating temp
 
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brianpitera

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Just finished up with changing the pcv, before I replaced it I would unplug the iac and the rpm would drop about 100 rpm, after changing it the difference is closer to 500 rpms. I unplugged the battery as I was doing the work to reset the kams and it does have a bit of a wandering idle, although it again seems a bit smoother. So far no cel but it does have a pending code for the same bank two too lean so in the next few days I'm going to look at replacing the broken part of the exhaust and digging into the tsb posted above and hoping that clears the rest of it up. Thanks again, you guys have been great.
 

brianpitera

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In case anybody is following this looking for answer, I unplugged the MAF sensor and noticed the lean codes stayed away, ended up replacing it and still no signs of those codes.... unfortunately now it’s throwing a cylinder three misfire code again, so I’ll have to chase that one down
 


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