Forgive the long post - thank you.

Thank you for accepting my request to join the forum. I am at my wits end over a long standing problem I'm having with my 2000 2.5 5speed Ranger, that has served me very well. I have been getting a persistent check engine light over emissions. As a result I cannot pass emissions and my plate is now sitting at 2018, and has been parked quite a bite until recently.

Prior to all this it had been running very well, and was getting 25 mpg on an almost bullet proof engine. Plugs and coils were replaced before that as well as the fuel pump.

Out the blue, I started getting the CEL and forever since, I've been getting mostly emission codes such as EGR and EGR solenoid and others. I've changed the EGR valve, the EGR vacuum solenoid, and DPFE sensor. I have taken the upper intake manifold off and cleaned all the passages thoroughly. STILL the codes came. I recently was forced to drive it 1000 miles. The literally 10 mpg I had on that trip, has me determined to try ONCE again to resolve the issue.

Based on the latest codes:

P0133 O2 sensor Circuit Slow Response


P0401 - Exhaust Gas Recirculation Flow Insufficient (this is the code that hasn't gone away ever)

First thing I did was run a bypass hose from the EGR valve solenoid directly to the EGR valve WHILE running. It will stall it which tells me the flow is there and the Valve is opening - therefore no carbon issue in the intake manifold. This leads me to think bad DPFE sensor once again. I decided to do one more thing first. Knowing they hadn't been replaced in forever, I bought 2 Bosch O2 sensors and hoped this would help things especially with mileage.
After fighting one of the sensor's having to go through the fenderwell, I replaced them today (Amazon promised Friday - they came today - prime guarantees mean nothing.

Good pep at first - and the engine is running strong as it always has, even with all these issues. 40 miles later, CEL light is back and it's throwing these codes:

P0136 O2 Sensor Circuit (2 brand new Bosch sensors SO WHY AM I GETTING THIS)

P0401 Exhaust Gas Recirculation Flow Insufficient AGAIN

(Pending) P1131 O2 sensor related - possible lean condition and other things but O2 is first listed (SO i AM GOING LEAN VS RICH NOW???)

In the past, the engine was running rich for sure - thus the 10 mpg on that last trip. I could occasionally smell the gas.

So I am now thinking DPFE sensor or maybe the wiring is an issue from the O2 sensor - maybe - and will look at that tomorrow. It seems I am looking at 2 issues or maybe only one, and the very old O2 sensors weren't a problem afterall. I don't know what to do with the p0401 as I have changed everything about the emissions or just about. Perhaps I had a bad DPFE sensor part to begin with. Again, this is a long running issue that has me lost and frustrated.

Is there some sort of ECU reset or anything I am missing? Any ideas or thoughts would be greatly appreciated. Sorry for the long but informative post.

Craig

 

P0132 02 Sensor Circuit High Voltage (Bank I Sensor 1)
Bank 1 is passenger side of a V6/8 engine, or the only bank on a 4cyl engine
Sensor 1 is the O2 sensor closest to the engine, upstream sensor, its main use is for air/fuel mix calaculations
Sensor 2 is the O2 sensor behind Cat converters, downstream sensor, its main use is to see if Cats are cleaning up the exhaust

You are getting P0132 because you are getting 10MPG, engine is running too Rich, high O2 voltage is rich, low O2 voltage is lean

2000 2.5l should be running 55psi fuel pressure with no FPR(fuel pressure regulator) on the engine end
So Rich running comes down to leaking fuel injector or bad computer

Easy test for leaking injector, the Clear Flooded engine routine, all fuel injected engine computers have this
Turn key on
Press gas pedal down to the floor and HOLD IT DOWN all the way<<< this will turn OFF all the fuel injectors, 0 RPMs + WOT(wide open throttle) = Clear flooded engine

Now crank the engine, it should NOT start, it should not fire at all

If it does start then gasoline is leaking in
One thing to check, to make sure you are getting WOT, use a stick to hold down gas pedal then go to the engine and make sure throttle is Wide Open, you can't manually open it any more, if so then do Throttle Cable Mod, its easy to do
Then retest using clear flooded engine

P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1
When a code starts with a 1 instead of a 0 that means its a manufacturer specific code, so Ford specific in this case, just FYI

If the old O2 sensor was the problem then your Long Term fuel trims(LTFT) maybe way off, so the new O2 sensor is correcting it
Fuel trims are the calculated open time for a fuel injector
0 STFT is what computer calculates, the LTFT is added to that, so it LTFT was -20(rich) then STFT 0 is actually -20
If the new O2 sensor is working then computer would NOW see -20 is way to Rich, so it would change STFT to +15 or more to correct it, and that would set a Lean code
Any STFT or LTFT out of the -15 to +15 should set a rich or lean code respectively


P0401 Exhaust Gas Recirculation Flow Insufficient Detected
It is a hard one to clear

EGR system has 3 parts, 4 counting the computer
EGR Valve, just a vacuum activated valve but can be opened a little or alot by varying the vacuum level

EGR Solenoid, has 12volt with key on, the computer pulse this solenoids Ground wire to open the vacuum valve a little or alot

EGR sensor, also called DPFE sensor, this has 2 hoses, not vacuum hoses, one runs to EGR pipe close to the EGR Valve, the other one runs to the EGR pipe but farther away from the EGR Valve

When the computer activates the EGR solenoid to open the EGR Valve it will see the pressure drop in the hose closer to the EGR valve, the more it opens the EGR valve the bigger the pressure drop
P0401 means computer is not seeing a big enough pressure drop

This can be from blocked EGR pipe or valve
Or EGR Solenoid valve is not opening enough or has a vacuum leak in one of its hoses
Or EGR valve has a vacuum leak
OR...........DPFE sensor is failing or its hoses are leaking or hoses are reversed

Exhaust has water vapor in it, which is why tailpipes drip water, and exhaust systems rust from the inside out, lol
So the DPFE sensor hoses get water in them, because they are connected to the exhaust system, the EGR pipe
This water vapor does get inside the DPFE sensor's chambers, so they do fail, some say metal ones are better some say plastic, but they all fail because of the moisture



One tool you may want to get if you don't have it yet, is a OBD2 Bluetooth device so you can watch Live data with engine running
You can watch EGR system and fuel trims both and maybe get a clue on why engine is running so Rich and why EGR system is not resetting

You can't fix an emissions system directly, just FYI
Once there is an EGR code the computer has to clear it in its own good time, so you can replace everything and code will stay/come back, until computer has test the system and deemed it OK
EVAP systems are the worst

Good read here on what to do for fastest clearing of emissions codes: Ford Motor Company Driving Cycle

 

Thank you for the long reply - it is greatly appreciated you took the time. I'm aware that o2 sensor codes can be triggered by another issue. They were very old so replacing them was as much a maintenance effort with the off chance the code goes away.

I changed all 3 emissions parts you mentioned. I have done the vacuum test on the EGR and it will practically stall the truck. It is my understand that clears the EGR valve as the culprit. Am I correct or have researched this correctly? Does that still mean the valve tube could be clogged. The EGR tube had also been replaced at one point, as well.

I pulled the codes with a my reader I've had for some time. I never looked to see other additional information while running. It's probably time i learn how to use all aspects of my code reader.

Do you think the issues related - the O2 sensor code and the P)401 Emissions code. Can one contribute to the other. I will try the injector test as suggested.

Thank you again for taking the time to answer me so thoroughly.

Regards

 

Ron I saw you posted this in another thread - "But the drop in MPG could mean time for a new upstream O2 sensor, they do wear out over 150k miles or so, and they do cause Rich running as they go bad, so drop in MPG without setting any codes".

By the way, I had a little exhaust smoke emanating from where the exhaust manifold runs into the beginning of the pre-cat pipe right where upstream O2 sensor resides. I thought maybe it was a little coolant that had dropped on the manifold when i separated the heater lines to gain access to O2 sensor. Are these O2 sensors I just put in, in danger of being ruined very quickly by the issues going on with the truck.

Thanks again

 

No, new O2 sensors will be fine, and you did them one at a time so each got plugged into its correct connection

You need to look at STFT(short term fuel trims) after engine is warmed up and NOT at idle to see if they are in the +10 or more range
Also have a look at the LTFT, I would expect -10 or more range

 

Did the Clear Flooded engine routine as prescribed, and it did not fire at all, so that's good.. I also checked the EGR valve again with hose off the EGR Valve Solenoid, and the engine again wanted to stall. I traced the O2 wires back to their harnesses - all intact. Because I had a can of MAF cleaner laying around for yet another CEL tragedy on a 350Z, I cleaned the MAF on the Ranger as well. I took note while driving on the scanner STFT and LTFT and attached them here. They are all over the place - neither stayed stationary. It was the same sequence of numbers from -2 to +3 on STFT % and around 0 to +3.5 on LT.

These are just screenshots but you can see how erratic this is over a 30 second period. ECU maybe?

Maybe this wil tell you something because this is something I am not knowledgeable on whatsoever. I tried to post the pictures smaller but the edit feature is not allowing it.





Maybe the ECU is just done - it has had a long life.

 

I am sure you are aware that you can only get valid STFT and O2 sensor reading after engine is warmed up, temp above 160degF

They actually look OK

Yes, STFT should jump around ALOT, +3 to -3 is normal


P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1
What did B1S1 O2 voltage look like, its a scale from .1 to .9 volts, so under 1 volt
Should jump around alot, from .2 to .6
Code would mean voltage is staying at .1 or close to it

P0136 02 Sensor Circuit Malfunction (Bank I Sensor 2)
P0136 is for the rear(downstream) O2, B1S2, this is a circuit malfunction, so wiring or the new sensor is bad
And B1S2 O2 should be a bit steadier and stay around .7-.8 but will drop and then come back up

 

I was not aware of that but this was read after I had driven 10+ miles and up to 50 mph. The scanner would not let me pull that information. I saw the option for 02 sensors and it just pulled up a screen with no data. I can screenshot that tomorrow. Also I read several places that the upstream and downstream were the same - is this not the case. There both brand new bosch same part number sensors. When I ordered them I noticed they were the exact same part number, for both upstream, and downstream. They fit fine with no wires hanging or touching anywhere. I did have to put a little wire around the rear to place it close to the socket connection point. It's not running very well still.

What do you think - bad rear o2 sensor out the box? DPFE sensor already bad? What would your thoughts be on culprits given all the shared information.

Thanks Ron

 

O2 sensor are all the same, well there are narrow band and wide band now, but Rangers all used narrow band

Difference in part numbers are the length of the 4 lead wires that plug into the vehicles harness, plugs are all the same, universal

The readings from the upstream and downstream O2s are quite different and used for different things

O2 sensors can not work until they are above 650degF which is why they are heated, to try and get them up to temp faster for best emissions control
The chemical reaction to detect Oxygen in the exhaust can only occur above 650degF
This takes a few minutes from cold start for exhaust system and cats to get HOT

O2s detect oxygen not gasoline/fuel, too much oxygen was a Lean burn, too little oxygen was a Rich burn
.1v is high oxygen, lean burn
.9v is low oxygen, rich burn

Upstream O2 is the STFT feed back, it tells computer if its calculated air/fuel mix was lean or rich, .4v is the sweet spot, so computer tries to keep upstream O2 between .2v and .6v

Downstream O2 is used to see if Cat(s) are working, Cats use remaining Oxygen to Burn Up toxic gases in the exhaust, so it voltage should be .7v and .8v this is not "rich" in this case its low oxygen, which means Cats are hot enough and working to Clean Up exhaust

 

Great information. So what does my situation suggest as I am no where closer to resolving it. I've done all things I said and still getting codes? Are you thinking that the downstream O2 is bad out the box? What about the P0401? DPFE sensor?

 

Well what does the B1S2 O2 sensor show as voltage after engine warms up?


P0401 can't be cleared, it has to go away on its own after driving for a few days
So it will come back always, then it will go away after computer confirms EGR flow is OK again
And you are sure the DPFE hoses are in correct positions?

 

I can't pull up the scanner for that - it just pulls up a menu and never loads data - I'll screenshot tomorrow. I'll check the hoses but can't imagine i had those flipped around for so long. What would that cause, if somehow this was done incorrectly? Thank you

 

The computer uses DPFE feedback to tell how much EGR flow there is when it activates the EGR solenoid, if hoses were reverse then it would show no flow, no pressure drop in the hose closest to EGR valve
One hose is larger than the other and so are the ports for that larger hose
Good read here: http://www.tomco-inc.com/Tech_Tips/ttt36.pdf
You don't need to know the technical stuff but it does show which hose is which

And I assume you have tested the hoses and both are "air tight"


If you can't test the downstream O2 voltage then swap back in the old one, as you didn't have that code with the old sensor

 

After the new upstream O2 sensor, it';s gone from 10 mpg for months to 20 mgs. I replaced the DPFE sensor and I am still getting the P0401 code after having cleared all codes. It's still running a bit rough but at least mileage is back up. That CEL and that code are really beyond frustrating.

 

Good stuff for MPG

Can you see the DPFE feedback voltage with your scanner?
Key on engine off should show .7 to 1.5volts

Next put vacuum hose on EGR valve and start engine
Apply vacuum to EGR valve and voltage should go up above 3volts or so

If either voltage is not correct then new DPFE may be faulty or the hoses on DPFE are

If scanner doesn't have that option then use a volt meter on the DPFE Brown/green wire, same tests


If voltage is correct double check EGR solenoid, and its vacuum lines
You can apply 12v and ground to the solenoid with engine running, and engine should stumble because full vacuum is going to EGR valve

 

Can't I just almost stall it out by applying vacuum from the bottom solenoid hose (that you can do when checking egr valve0? I don't have a vacuum pump. I just bought the dpfe sensor but was aftermarket.

 

Yes, any intake vacuum source can be use
I just suck on a longer hose hooked to EGR Valve, I am the vacuum pump, lol, this also tells me if EGR vacuum diaphragm is leaking, which using a constant vacuum source can't tell you
Vacuum is technically not "used up", a vacuum diaphragm should be air tight, so if I apply 5" of vacuum to a vacuum device it should stay at 5" indefinitely, but in the real world there will be small leaks on any vacuum system
So you suck on the hose once, and that should hold EGR valve open a bit, should shouldn't have to keep sucking on the hose to hold EGR valve open

 

So changing the O2 sensors has returned fuel economy from 10 to 23.4 mpg so that is great. It sometimes idles very rough but then drives smoothly. The CEL is still on and same P0401 code is being thrown, after the DPFE sensor was replaced. Vacuum applied to EGR valve causes it to almost tall so it's opening. At this point I don't know what else to do with the CEL.

On another subject - more of a generic auto/truck question, I'm getting severe vibration at 60 mph when goes away when I get to 65. I'm think drive shaft isn't balanced anymore or worn U joints. Any thoughts? Thanks as always and thanks for being such a thoughtful guy. I wish there was a guy like you on the 350Z site but there is not.