Hey guys I have gf with a 99 ford range v6. Im pretty handy and can fix most things myself. It is coming time to do another emissions test so I need to get all these codes cleared up:

P0171: Fuel Injection system too lean, bank no.1
P0174: Fuel system too lean bank no.2
P1131: lack of upstream heated oxygen, sensor switch indicates lean, bank no.1
P1130: lack of upstream heated oxygen, sensor switch adaptive fuel limit bank no.1
P1132: lack of upstream heated oxygen, sensor indicates rich bank no.1

This is what shows up on my scanner. I have done some reading online and it seems often that it can be a vaccumm line. I find the engine bay very noisey (air blowing type noise) Maybe this is normal for this engine? I went to replace the vacuum lines and it appears you cannot just replace them with regular rubber vacuum line. They join in together and attached to a larger spot on the intake manifold. What have you guys done about this?

As for the symptoms it often stalls right after first startup. It seems to be a real dog accelerating. Sometimes It will have almost 0 power. You will have to pull over shut the truck off and turn it back on. The problem seems to come and go also.

This is relayed information from what my girlfriend is telling me. My experience it just felt like the truck was under powered from what it should be. If there is anything else you need to know just let me know.

thanks for your time,
Kevin

 

Since both banks, passenger side(bank 1) and drivers side(bank 2) are effected then problem will be something that can effect both banks at the same time.

I doubt a small vacuum line could do that.
Larger vacuum lines could, the PCV vacuum hoses, especially the elbows, often cracked after they were 10 years old.

The Lean/Rich feedback from O2 sensors is based on the MAF sensors airflow data.
The MAF sensor measures the volume of air coming in to the intake, the computer uses the 14:1 mix ratio to set "0" for that volume of air, if O2 sensor shows lean burn at calculated "0" air/fuel mix then computer adds more fuel, like +10, if O2 still reports Lean then computer adds more fuel +25, if still lean computer sets code, it has reached pre-set limit for that "0" mix, i.e. "adaptive fuel limit bank no.1"

So MAF sensor could be reporting wrong air volume, MAF uses a heated wire to determine air flow volume, it could just be dirty, you can use a MAF sensor spray cleaner to clean the wire, don't use caustic chemicals like Carb cleaner, but any electronics cleaner can be used.
Dirty MAF sensor is quite a common issue on Fords.

Also the big air plenum(air tube) from MAF to intake is a "vacuum chamber", any leak in that tube allows air to come in without passing thru the MAF sensor, so it is unreported air, the same as an intake vacuum leak.
So make sure that air tube is sealed at both ends and there are no cracks/breaks in it anywhere.
There is usually a Vent hose on this tube, it runs to oil fill tube or valve cover, it is part of the PCV system, it needs to be connected, or unreported air would come in.

Reset computer now that you have the codes, codes can remain in history a long time, while these all seem correct and related to a common problem a reset will allow you to see if any repairs were successful and only show you current issues, on the next read.

 

Thanks for the great reply. I will do exactly this. Is it possible the lean conditions could have damaged the o2 sensors? I guess it has been like this for a half a year. What can I spray on the hoses to check for vacuum leaks? does that work in fuel injected cars?

 

No, won't hurt O2 sensors, overly rich can but over many months, also rich is bad for Cat converters

Quick easier way to see IF you have an intake vacuum leak would be to warm up engine.
So idle is about 750RPMs
Then unplug IAC(idle air control) valve, this will allow it to close all the way.
Idle should drop to around 500rpm or engine may even stall, either is OK it means no vacuum leak, idle will stay high if there is a vacuum leak on the intake side of throttle plate, then remove 1 vacuum line at a time from intake, plug hole with finger and see of idle drops if so that line has a leak.

You can spray starting fluid or carb cleaner while engine is running and if idle changes then the last sprayed location sucked it in.
Best to do cold engine, hot exhaust manifold can cause spray to catch fire, and also loosen serpentine belt, so fan doesn't spin.
You can run cold engine for 2 or 3 minutes without water pump, this will make it easier to spray without it being blown around.

 

That is some good info. Where is the IDC I am not to familiar with these engines? As far as the disconnecting the vaccuum 1 by 1 and plugging it. Where they connect to the manifold it looks they all tie in together into 1 molded piece and connect there. I would have to disconnect the 3 lines runnign to the manifold all at once. Can I do this to test for leak and disconnect all 3 at once?

Thanks again,
Kevin

 

An IAC Valve is used on all fuel injected engines,
It will be located near the throttle plate(where the throttle cable connects)
It will look like a tube/can and have 3 wires on the connector.

Are you sure that's not a heater hose?

Intake should have a Vacuum manifold with several lines connected, find the power brake booster then follow it's vacuum line, it will go to the Vacuum Manifold.

 

I'll be looking at it tomorrow night. Yeah Im positive it was a vacuum line. Where it goes to the vacuum manifold it joins 3 vacuum lines into 1, its a molded rubber piece. Then it connects to the manifold with a larger piece.

Ill checkout the iac first hopefully that confirms our vacuum leak theory

 

If this "factory molded" piece (joins three vacuum lines) requires changing, you can make your own by buying a "T" fitting at any good auto parts store where they sell the vacuum line.

 

My first suggestion would be to clean the MAF sensor, as that is the most common issue.
Worn and cracked vacuum lines would be second.

MAF sets baseline air flow for computer, if that's off then everything is off.

 

So tpday i changed the vacuum lines. I was able to get an adapter to attach to the intake manifold like i said. There is one line that runs under the washer bottle. I didnt replace all of this line. When i unplugged the idle valve the truck dropped to about 400 rpms but keeps running. My code reader stopped work so i was unable to clear the codes. I also took the maf out and sprayed it with maf cleaner all over then put it all back together. Truck seems to idle at aroind 900 rpm even after its warm. Is there a spec for vacuum at idle ? I have a vacuum gauge.

I also tried using carb cleaner, didn't seem to have any success with it. I actually took a line off and sprayed it right into the vacuum line and it didn't do anything.

 

For vacuum readings look here: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine

Gasoline engines all work the same so vacuum readings are pretty standard/universal
And carb or EFI don't matter

Unplug IAC again and with idle at 400rpms carb cleaner should work better

 

After doing vacuum lines and cleaning MAF I cleared the codes, and so far it seems fine. I will e-test it friday and see how it goes.

 

Good work

 

Failed e-test. CEL came back on. But apparently the cel doesnt work so she didn't see it. Has one code. Too lean on bank 1

 

What is an e-test?

Passenger side O2 showing too much oxygen in exhaust after computer has reached its limit for adding fuel to Bank 1 injectors.

I would leave it for a few days to see if Bank 2 is effected.

If there is a miss fire on bank 1 now and then it can show lean as air is just being pumped thru the cylinder, is there a reported miss fire by driver?
Spark issue

Is there any Pinging/Knocking reported by driver?
True Lean mix will ping/knock
Injector issue

If possible swap bank 1 O2 sensor with Cat O2 sensor or Bank 2 O2 sensor, see if results follow sensor or stay on Bank 1

An exhaust manifold leak sucks in air between the exhaust valves opening so can cause lean O2 sensor readings.

 

Oops double post

 

Oh i forgot that the e-test (emissions test) does change. Basically where i live in ontario they do an emissions test every two years. It reads your obd2, it checks for any codes. If you have no codes your pretty much good to go. It also checks for readyness.

Its possible there can be a misfire. I dont hear it when i was driving it but it sure feels underpowered to me. Its hard to tell at idle because the mechanical fan runs all the time. However I am not totally used to the truck.

Unfortunately there is not alot of time to fix this car as the stickers are about to expire and will need test done for renewal. Im not sure if I can swap o2 sensors front to back I will have to look. I know on my other cars i've done the cables are very different in length and sometimes connector.

Maybe I'll try a general tune up. Plugs and wires. Would it throw a misfire code? If it doesnt fire, wouldnt it be too rich because its just passing gas through?

Kevin

Just FYI P0171 System Too Lean Bank 1

 

Only continual misfires will set a misfire code.

O2 sensor only measures oxygen, not fuel content
A properly mixed and firing cylinder will produce high CO2 and some H2O(water) with a little Oxygen
A Lean fuel mix will have lower CO2 level and more Oxygen
A Rich fuel mix will have lower CO2 level as well but less Oxygen
A misfire will shows as high Oxygen so Lean exhaust

The unburned fuel is burned up in Cat converter so it can get hotter during misfires, and if misfires are bad enough the CEL will flash during these misfires since Cat damage can occur, that will usually set a code and ID which cylinder was misfiring.

 

Ok, I am going to pickup a set of wires and plugs on my way home. Looks like its factory wires from 99 on it now. Also plugs haven't been changed in many many years.

 

I should also mention you guys have been very helpful!

 

Changed plugs and wires. Huge difference in throttle response. 2 of the plugs didnt look very well both on bank one. Look like their running hot. they were actually quite warm still also. Driving it after I finally felt that accelerating issue she was complaining about before. I stepped on the gas and it just didnt accelerate, like at all. I felt like I was in 4th gear doing about 20mph trying to accel. Have you guys had an issue like this before. This happened once in hours of driving, when I stopped at a traffic light it was fine after that.

 

I would check the voltage on the TPS(throttle position sensor).
Computer sends it 5volts, if throttle is closed the return wire(center) will show under 1volt(.7-.9), with throttle wide open above 4.5volts should be seen.
The in between voltage is what you want to check, as you open throttle the voltage should increase steadily, no jumping around or dead spots, any slight movement should change voltage.
Also make sure throttle plate is opening with pedal being pressed, I have seen stretched cables that don't move throttle plate until they are 1/4 of the way down, they "feel" OK but are stretched.
Google: ranger throttle cable mod

The TPS is what gives you faster throttle response on a fuel injected engine, the computer does see the air flow increase at the MAF but there is a lag, so fuel injection can lag behind, this could also create Lean condition.
On a carb they used an accelerator pump to squirt extra gas into intake when throttle was pressed, on fuel injection they use TPS

Hot cylinders usually indicate Lean condition or EGR flow issue, but EGR flow has several checks that would produce a Code if a problem was seen.

 

Both the lean codes did end up coming back, bank 1 and bank 2

 

That's good
Are those the only codes?
And how does the truck run?
Do you feel engine is missing or pinging under load?

If not then you have either:
low fuel pressure, computer has to open injectors longer than preset fuel trims allow for

MAF sensor is under reporting air volume, bad MAF or air/vacuum leak

or computer is bad, it is misreading MAF or O2 data

 

The engine feels really doggy to me. I expect the 160hp or so it produces to feel much more powerful. However I have not driven this truck under normal conditions. When I changed plugs and wires I did feel an improvement. I do not think its misfiring, however I could be mistaking.

As far as leaks, I did change all the vacuum lines. Could still be possible intake gasket or throttle body gasket leak.

How do I go about checking fuel pressure, or if the maf/computer is operating properly?

Thanks,
Kevin