A P0172 SOHC mystery

[Alligator Wrangler]

Hello, everyone. I'm new here, wondering if you can help me out with some truck troubles.

I have a 2005 4x4 manual Ranger with the 4.0 V6 SOHC (166K miles). It seems to run all right but has had a P0172 code for the longest time. OBDII data shows that the long term fuel trim is extremely rich in bank 1 (-25%), and even bank 2 has about -4%. It smells strongly of gas around the truck. Just a few days ago it sent out a P0420 code (cat), and I'm wondering if the rich condition is damaging the cat.

Upstream O2 sensors (Bosch), alternator, PCV valve, air filter, MAF sensor, and a bunch of EVAP components have been replaced. Cleaned the throttle body and IAC. The truck's wiring is pretty bad (previous owners did janky stuff), so there could still be something connected incorrectly.

My mechanic couldn't figure it out. His thought was either a leaking fuel injector or a timing chain problem. Compression test was normal. Balance power test showed cylinder 2 was low. No vacuum leaks, no exhaust restriction. I know that the SOHC is infamous for timing chain issues. I tried fuel injector cleaner additives but it hasn't made a noticeable difference.

I'm thinking about replacing/cleaning all the injectors and swapping the timing chain tensioners. I've never removed an intake manifold before so this is a big job for me. Do you think this would be worthwhile to try? Or do you have another idea?

Thanks for any input you might be able to provide.

 

[Alligator Wrangler]

As an update, I just got an automotive stethoscope. All my injectors make a consistent clicking noise. So it's probably not them.

 

[RonD]

Welcome to TRS

Try "Clear Flooded Engine" test

All Fuel Injection computers have this "mode", called Clear Flooded Engine mode

Key on
Press gas pedal down to the floor all the way and HOLD IT DOWN
(At 0 RPMs and throttle sensor showing WOT(wide open) computer will not open fuel injectors while cranking engine over, so driver can "dry out a flooded engine")
Turn the key to START
Engine should just crank and not fire or start, no fuel, but spark is still on
If it fires or starts then you may have fuel leaking in to the intake

Besides injectors leaking there is a Vacuum hose on the Pulse Damper, its on the fuel rail passenger side near the firewall, pull off this vacuum line and check it for gasoline, should not be any of course

If engine started using "Clear Flooded Engine" test
There is one more thing to test, to make sure your throttle sensor is showing WOT to computer
Key off
Put a stick against the seat holding gas pedal down all the way
Open the hood and see if you can open the throttle manually a bit more, if you can then computer was not seeing WOT, your throttle cable has stretched
Google: Ranger throttle cable mod

Simple fix

Once WOT is confirmed and you still have firing or start up with test then you can ID which injector is leaking
(assuming no gasoline in that vacuum line)

Unplug coil packs 4 wire connector, so no spark
Cycle key on and off 2 times to build fuel pressure
Now repeat test and crank engine over a few times with gas pedal to the floor
Pull out spark plugs and check the tips, all should be DRY
WET tip means that cylinder's injector is leaking
Start on bank 1(passenger side) since that is what code points to


High fuel pressure
Longshot since BOTH Banks use the same fuel pressure source, so should be equally Rich on both sides
Electric fuel pump in the tank produces 80+psi fuel pressure
There is a Fuel pressure regulator(FPR) also in the gas tank
The FPR is set for 60psi in a 1998-2011 Ranger
Your running pressure at the engine should be 55-65psi
There probably is no fuel pressure test port on a 4.0l SOHC, you can add one but as said its a longshot if one bank is effected more than the other bank


Yes, Richer running causes Cats to run hotter so shortens their life, also fouls spark plugs faster

 

[Alligator Wrangler]

Howdy, RonD. Thank you for your great reply. I appreciate the welcome to TRS.

Well I'll be. With the engine cold, she starts right up with the throttle open. She just cranks when already hot. I slapped some zip ties on my (loose) throttle cable and got the same result.

I wasn't able to find/access the pulse damper, but someone in a forum said you might need to remove the intake to get to it. I think I'll just go ahead and take off the intake to get to the injectors, and swap out my timing chain tensioners while I'm at it...

I appreciate the tip.

 

[Alligator Wrangler]

UPDATE: Overall apparent success.

I pulled the intake manifold and replaced all the injectors. The injector seals and o-rings looked terrible and the engine head was covered in dirt. I cleaned everything and replaced the worst seals. While I was at it, I also swapped out the thermostat and its housing, intake manifold gaskets, fuel filter, and forward/rear timing chain tensioners. This was my first time doing this and wow, what a job - it took a few days and a lot of podcasts and country songs to get it done.

(TIPS: If you swap the injectors or work with the fuel system, make sure to cut fuel pressure before you start! You can do this by starting the truck and pulling the fuel pump relay from the fuse box. There will still be fuel in the line so have lots of paper towels on hand to soak it up. Also, make sure that your valves are closed or at least stick a paper towel underneath the injector port to catch the dirt before it falls into the cylinder.)

I think the injectors were the true problem. Overall, the truck seems to be running better now. All the codes cleared initially, and long term fuel trims for both banks now sit at about 2-3% at 2000 rpm. Much better!

It still smells pretty badly of gasoline around the truck. After about 30 miles of driving without any DTCs, the computer threw code P0420 again. Fortunately the rich condition is still cleared but I imagine the fuel trim imbalance damaged my catalytic converters... though my OBD2 scanner emissions mode says the catalyst passed (and only flags evaporative system). I'm not sure why there's a difference there.

I might use this opportunity to upgrade my whole exhaust system, unless someone has another idea.

 

[RonD]

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

I assume you have a OBD2 reader so can view Live Data
O2 sensors only see Oxygen
O2 sensors generate their own voltage
O2 sensors can't generate voltage until they are heated above 650degF
0.1volt = high oxygen "lean"
0.9volt = low oxygen "rich"

The upstream O2's are used to balance air/fuel mix on the fly, computer varies injector open time based on feed back from these O2s
Sweet spot is 0.4volt, computer tries to get that as an "average", so 0.2v to 0.6v is the range you should see, as voltage changes rapidly

Once exhaust passes thru cat converter, the converters have burned up most of the oxygen to clean up the exhaust
So downstream O2s should have a steadier voltage at 0.75v to 0.85v, LOW oxygen as its been burned up
If downstream O2s get below 0.75v then computer will see that as Cat converter is NOT burning up the oxygen so "Efficiency Below Threshold" code
This can be from failing Cat or Failing O2 sensor, O2 sensors use a chemical reaction to generate voltage, as they run low on chemicals the voltage goes down
If O2 shows 0.0v then bad wire most likely


"evaporative system", EVAP system is the system that applies negative pressure(vacuum) to the gas tank when vehicle is running, this prevents gas fumes from polluting the air as gas sloshes around in the tank when driving
Fumes are sucked into the intake and burned just like fuel from injectors
EVAP systems can be a pain in the but to troubleshot and correct, lol
Can be as simple as a loose gas cap or pain like the pressure sensor on the top of the tank

 

[Alligator Wrangler]

Hi @RonD thanks very much for another great reply. I looked at my live sensor data - yeah, both post-cat O2 sensors are fluctuating wildly between 0.1 and 0.8 V. Those are original sensors as far as I know. Do you think it's worthwhile to replace them or should I just look at getting new cats? I'd rather not because cats are expensive! Thanks again.

 

[RonD]

You can swap one with an Upstream sensor
O2s tend to go to low volts, 0.1v-0.2v when they run out of chemicals

You want a steady high volt for Downstream sensors if the Cats burned up all the Oxygen
Your description reads like the downstream O2s are reacting like the upstream O2s so the Cats aren't doing anything

 

[Alligator Wrangler]

Update - catalytic converters were replaced with magnaflow aftermarket cats, with resolution of the P0420 code. Downstream O2 sensors now hover at about 0.7 volts.
I ordered the magaflow direct fit cat system, but it doesn't fit with the 4x4 manual (annoying.) Muffler shop was able to help. Thanks for your help, everyone.