Running so rich it's fouling plugs and stall,codes.

[ben_2_go]

2000 Ranger 2.5 automatic 4x2 is running so rich it's stalling and fouling spark plugs.It's also pumping black smoke out the tail pipe from idle to about 3000rpm.The codes says it's running lean,but it's far from running lean.The codes I get are P1131 and P0171.Surely a bad O2 sensor wouldn't cause this.

Recent work includes all filter changes,new timing belt with water pump,thermostat,new spark plugs,new spark plug wires,pcv valve,and all vacuum connectors and hoses replace.I also checked to make sure no wiring problems between the harness and O2 sensors.Another note,the truck is all stock.No modifications at all.

 

[RonD]

On the 2000 you will run 65psi fuel pressure with a Pulse Damper on the end of the fuel rail, it will have a vacuum line attached, remove this vacuum line and check it for fuel.
If diaphragm in Pulse Damper fails the vacuum line is there to prevent fuel from leaking on to hot engine, so a safety feature.

But with the Lean codes it really reads like a computer issue or O2 issue, if possible get a scanner to do a live read of the O2 sensor.
Also check for exhaust leak on manifold.
Exhaust manifold actually has negative pressure when engine is running, proper exhaust pipe tuning cause a suction.
But what can happen with a leak is that air is sucked in making exhaust look lean so computer cranks up fuel trim.

Lean code means computer has added more fuel but O2 still shows lean...............but MAF sensor is still the baseline

 

[ben_2_go]

On the 2000 you will run 65psi fuel pressure with a Pulse Damper on the end of the fuel rail, it will have a vacuum line attached, remove this vacuum line and check it for fuel.
If diaphragm in Pulse Damper fails the vacuum line is there to prevent fuel from leaking on to hot engine, so a safety feature.No fuel and it holds vacuum.It's running rich and blowing raw fuel out the exhaust, so I am pretty sure it isn't fuel system related.

But with the Lean codes it really reads like a computer issue or O2 issue, if possible get a scanner to do a live read of the O2 sensor.
Also check for exhaust leak on manifold.Checked the exhaust mani while I had the engine apart doing the timing belt,water pump,and hoses.
Exhaust manifold actually has negative pressure when engine is running, proper exhaust pipe tuning cause a suction.Scavenging,I am familiar with this.
But what can happen with a leak is that air is sucked in making exhaust look lean so computer cranks up fuel trim.Exhaust is completely stock with no leaks or damage.

Lean code means computer has added more fuel but O2 still shows lean...............but MAF sensor is still the baselineCleaned the MAF but failed to mention it in my first post.Same results.

I am at a loss and ready to scrap this heap.I'll try O2 sensors.I can't afford getting 140 miles per tank.I used to get between 350 and 400.

 

[Earl43P]

Change just the upstream O2, the one after the cat can't cause that.
It's just an efficiency monitor. Save a few $.

 

[RonD]

Yes, the upstream O2 is the main fuel trim sensor, downstream just checks that Cat converter is working.

What about a leaking fuel injector?

Simple test is to use the "Clear Flooded Engine" routine
Engine warmed up
Turn key on
Press gas pedal to the floor and hold it there
Turn key to start

Engine should crank but not fire, if it fires then gas is leaking in from somewhere.

With key on engine off, and you push down the gas pedal all the way the computer sees above 4.5volts from TPS(throttle position sensor) this tells the computer to shut off fuel injector pulses(clear flooded engine mode) but spark will still be on.

If engine doesn't fire or start then injectors are not leaking
As soon as you let off the gas pedal fuel injectors will start and engine will start

If engine does fire you can disable the coil(s) and repeat above test, but don't let off the gas pedal while cranking.
Then pull one spark plug from each cylinder and see which one is wet with fuel, so you can ID faulty injector.

You have sequential fire injectors so there will be 4 Ground wires, one from each injector, running back to computer, the computer Grounds an injector to open it.
Each injector gets 12volts when key is on, so if one of the 4 Ground wires gets a bare spot and grounds to a metal part, that injector will open with key on.

 

[ben_2_go]

Rechecked everything again.Did the test described above with a no start out come,so no injectors are leaking.Everything keeps coming back to the O2 sensor, which I ordered last night.Should be here this weekend,I hope.I am going to clean the MAF again when I install the new O2 sensor.

 

[adsm08]

The computer thinks it is running lean, it is adding as much fuel as it can.

Check for air leaks, check the MAF.

 

[ben_2_go]

The computer thinks it is running lean, it is adding as much fuel as it can.

Check for air leaks, check the MAF.

I had to remove the intake to get the PVC valve out.I used all new gaskets and torqued everything to spec.I rechecked all my new vacuum hoses and fittings today.Nothing is out of sorts there.the duct from the MAF to the intake is tight and I checked it for cracks when I had it off.I cleaned the MAF when I did all the other repair work.I'll clean it again when I install the new o2's.

 

[tomw]

If your fuel pressure regulator fails, you might get full pressure all the time. That will cause the symptoms noted. Have you checked fuel pressure? The vacuum line on the regulator is used to modulate pressure. High vacuum -> lower fuel pressure. Low vacuum -> high pressure. Low vacuum would happen with the throttle open, as when you step on the gas, so it would need more fuel. Hi vacuum would be with throttle closed, as in at idle, thus low load, and less need for fuel.
I've seen 4.0 regulators (over $100!!!! made of gold?) fail, and the pressure was high, and fuel mileage dropped to ~10mpg. Just about half. Replaced, and mpg went back to normal, no black smoke, and it ran well.
tom

 

[ben_2_go]

If your fuel pressure regulator fails, you might get full pressure all the time. That will cause the symptoms noted. Have you checked fuel pressure? The vacuum line on the regulator is used to modulate pressure. High vacuum -> lower fuel pressure. Low vacuum -> high pressure. Low vacuum would happen with the throttle open, as when you step on the gas, so it would need more fuel. Hi vacuum would be with throttle closed, as in at idle, thus low load, and less need for fuel.
I've seen 4.0 regulators (over $100!!!! made of gold?) fail, and the pressure was high, and fuel mileage dropped to ~10mpg. Just about half. Replaced, and mpg went back to normal, no black smoke, and it ran well.
tom

I checked the regulator to make sure it's holding a vacuum.If it's holding vacuum and not leaking fuel,it should be good.I keep the filters changed so there shouldn't be anything holding it open internally.My fuel tank is clean inside.I pulled it last year when I had a fuel line break.I was surprised to find there was no sediment in the bottom and the pump screen was clean.

 

[tomw]

You said: "If it's holding vacuum and not leaking fuel,it should be good."

I would not bet on it. You can borrow a gauge from a parts store and actually check it and know. Borrow for no cost if you don't break the gauge.
The regulator on a friends 4.0 went bad, and the mileage dropped to about 1/2 of normal. It held a vacuum, but the pressure was wacked out high. You could not see any problem externally, but the regulator DID NOT WORK. The computer cannot compensate for unregulated pressure no matter how much it tries to lean out the mix.
It is worth a check IMO.
tom

 

[ben_2_go]

You said: "If it's holding vacuum and not leaking fuel,it should be good."

I would not bet on it. You can borrow a gauge from a parts store and actually check it and know. Borrow for no cost if you don't break the gauge.
The regulator on a friends 4.0 went bad, and the mileage dropped to about 1/2 of normal. It held a vacuum, but the pressure was wacked out high. You could not see any problem externally, but the regulator DID NOT WORK. The computer cannot compensate for unregulated pressure no matter how much it tries to lean out the mix.
It is worth a check IMO.
tom

None of my local auto part stores have a fuel pressure gauge on their loaner program.I tried Auto Zone,Asvanced Auto,O'Riliey's,and NAPA'er.

 

[tomw]

Did you check their price on the shelf? I bought one at Advance for <$20, I think. It has the gauge, a couple adapters, and a drain line connected to a relief valve so you can catch the flow to measure capacity(volume over a measured time).
Ask at a local station that does mech work if they'll let you check the pressure in their drive ... it just takes a few seconds. Or see if they'd do it for a light gouge to your wallet.
tom

 

[ben_2_go]

Did you check their price on the shelf? I bought one at Advance for <$20, I think. It has the gauge, a couple adapters, and a drain line connected to a relief valve so you can catch the flow to measure capacity(volume over a measured time).
Ask at a local station that does mech work if they'll let you check the pressure in their drive ... it just takes a few seconds. Or see if they'd do it for a light gouge to your wallet.
tom

Yep,all the places around here price them around $45 to 50.I ordered both for $45 shipped from Rock auto.They are slow to ship things to me but I have my motorcycles to get around on until the O2 sensors arrive.

I just realized you were talking about the fuel psi gauge.None of the stores have them in stock but all offered to order one for me.I didn't bother asking the price.

 

[tomw]

Well maybe you can get a mechanic friend to check the pressure for you. On their lunch hour, so to speak. I expect that most shops bill a minimum 1/4 hour, so having it done would be close to the cost of the gauge.
Does removing and attaching the vacuum line to the pressure regulator have any effect on the exhaust? Removed, the mix should go rich and possibly give black smoke.
tom