2004, 2.3L Ranger Persistent Rich Condition
 

Hi folks,

First sorry for the long post but wanted to share what I’ve done so far to try to solve the problem without leading anyone astray. I’ve been pulling out my hair since last August with a persistent Rich Condition. Backstory:

I replaced the cylinder head last June/July to fix a misfire issue (burnet exhaust valves on cylinders 1 and 2). Upon restart in early August, the PCM threw a Lean Condition code (P0171). Cleaned the gunked-up MAP sensor, which resolved the issue. Engine shook a bit so replaced all 4 injectors. Engine ran pretty smooth. After 100 miles of driving, the PCM threw a Rich Condition code (P0172) in mid-August and I’ve been struggling to figure out what’s causing it.

What I know:
1. Short Term Fuel Trim (STFT) hovers around -0.8 to about +1.0 at idle. It does go down to about -7.2 to -5.5 at idle after highway driving but eventually settles down to -0.8 to about +1.0 after idling for about 10-15 minutes or so
2. Long Term Fuel Trim (LTFT) is the problem. It starts at about -15 or so but eventually drops to -25 after anywhere between 30 and 100 miles of driving which then throws the P0172 codeAny ideas on what can be causing this Rich Condition is appreciated. Truch won’t pass emissions inspection otherwise. I’ve included a list of things I did and parts I replaced.

Questions:
1. PCM: Does the PCM need to be reprogrammed after replacing the injectors and/or cylinder head?
2. Timing: Can bad timing cause a rich condition? Engine runs smooth and no knocking/detonation and it responds like I would expect from a small 4 cylinder engine on a heavy vehicle
3. P01650 code: The PCM throws a P01650 code (Power Steering Pressure Switch out of Self-Test Range when I do a KOEO (Key On Engine Off) test. I can’t find a new PSP pressure switch anywhere so I’m living with the code for now. Can there be a relationship between this P01650 and the P0172 Rich Condition code? (Truck will not pass inspection with a P01650 code in my state)

Things I’ve done and observed so far, all with no luck:
1. Drivability: Fuel Trims move become more positive when applying throttle when driving (although LTFT doesn’t do better than -15). This is expected since more oxygen is applied to the A/F mixture. Given this, I assume the PCM is working well. Thoughts welcome
2. Exhaust: White smoke, no smell of raw fuel
3. Today: Measured compression (cyl 1 = 190 psi; cyl 2 = 190 psi; cyl 3 = 185 psi; cyl 4 = 190 psi). Given these results, I assume the cylinder head job
4. Spark plugs: Changed them out in early 2017 to try to resolve the misfire issue. Regapped them today. No change to fuel trims
5. Spark plug picture attached: Their conditions look normal to me. Thoughts welcome
6. IAC valve: Replaced in early 2017 to try to resolve the misfire issue
7. Coil pack + spark plug wires: Replaced in early 2017 to try to resolve the misfire issue
8. Catalytic converter assembly: Replaced this past weekend as it was bad
9. Upstream and Downstream O2 sensors: Replaced at same time as Cat. Upstream was a bit erratic and downstream seemed pegged at 0.08V. Upstream now transitions from Lean to Rich to Lean smoothly. And downstream fluctuates between 0.08 and 0.15 at idle (I would expect this)
10. Leak at exhaust manifold gasket: Replaced with a high quality Felpro at same time as Cat replacement
11. Exhaust system leak test: Did a leak test with soapy water, including exhaust manifold gasket. No exhaust gas leaks
12. MAF sensor: Replaced 8 weeks ago as it was fluctuating between 0.01 lb/sec and 0.03 lb/sec. Now transition between 0.01 lb/s to 0.07lb/s depending on throttle position, rpm, etc
13. Cylinder Head Temp sensor: Replaced about 4 weeks ago as it was pegged at 265°F. Now reads between 215°F and 225°F
14. Evap Solenoid Purge Valve: Did a bench test this past Friday with a power supply and vacuum pump. Holds vacuum. Also did an EVAP system test with my scanner. All checks out good
15. MAP sensor: Did not replace. Measured PSI with scanner with engine off. Readout was atmospheric pressure for my area per the Weather Channel app and it changes to between 4.5psi and 7.5 psi at various rpms. I assume this means it’s operating correctly. Thoughts welcome
16. Crankshaft sensor: Replaced at same time as cylinder head as a precaution. Used the adjustment tool that came with the part
17. Throttle body + plate: Cleaned at same time as cylinder head replacement
18. Did a fuel pressure test about 8 weeks ago. Results follow:
a. At idle: 65 psi (I read a post by RonD that, from 1999 on, normal fuel pressure for Ford trucks is between 60 psi and 70 psi, so I assume 65 psi is normal for my Ranger)
b. T0 (engine shut off): pressure drops to 58 psi within seconds
c. T10 (10 minutes after engine shut off): pressure at 54 psi
d. T20: pressure holds at 54 psi
e. T30: pressure holds at 53.9 psi
It doesn’t appear fuel injectors are not leaking, which could have explained the Rich Condition. Thoughts welcomeCan fuel injectors be injecting too much fuel into the combustion chamber even if the fuel pressure is good and the injectors are not leaking?

Lean or Rich is the open time for the injectors not "how the engine is running", engine is not running Rich

Once the upstream O2 sensor is warmed up to 650degF it will start working, takes a few minutes for that
Computer calculates open time for the fuel injectors "on the fly" once O2s are warmed up
Computer has a table in memory for this 2.3l engine that gives injector open time for all RPMs and all throttle positions
Computer then uses MAF sensor, coolant/head temp sensor, intake air temp sensor data to Off-set the table data in memory, and that is 0 STFT
If 0 STFT shows high O2 voltage after it's burned(rich) then computer changes to -2% STFT, if still Rich then -4% STFT, ect..........until O2 shows correct voltage, this all take a second, maybe 1.5 seconds, so happens very fast
And it is a percentage, -10 or +10 STFT means computer calculated 0 STFT was 10% off low or high
-10 STFT means computer is adding 10% LESS fuel that it calculated
If engine is not Pinging/knocking then all is well its not actually running Lean

Rangers all used standard O2 sensors, they are heated, and generate there own signal voltage once heated up above 650degF
.1 to .9volts is the range, your reader may be adding a 0
.35 is the sweet spot for correct Oxygen levels in upstream exhaust, .1 is Lean(high oxygen),.9 is Rich(low oxygen)
Upstream O2s send out an analog voltage so changes are an up and down wave of voltage between .1 and .9, the OBD reader shows static voltage moment to moment, so should change very fast on the Reader

Down stream O2 should be around .7 all the time, changes very slowly
The Computer does add more fuel than needed every few seconds, thats for the Cats, it keeps them Hot

LTFT is what it says Long Term fuel trim, it is used to off-set computers calculations as an engine and system gets older, and lso used on Cold Starts before O2s warm up
So actual fuel trim is STFT + LTFT, so if STFT is +2 and LTFT is -10, then actual fuel trim is -8
And the +2 STFT will slowly pull the -10 LTFT down to -8, so LTFT is a LEARNED parameter, not static
And it can not be Cleared by most OBD readers, some can clear it, I know Ford Dealers can

If you have +20 or -20 LTFT and do some repairs, then it can take a week or two for the LTFT to come back closer to 0

Whats you MPG like?

If I understand your reply, RonD, the rich condition might be due to “learning time” for LTFT, so I should ignore the check engine light and give the PCM time to relearn the injector on/off cycle?

Also, you mentioned the the downstream O2 sensor should always read about 0.7V, even at idle? Mine definitely reads 0,08V to 0.15V at idle and hits 0,65V to 0.75V when cruising. Is this normal?

I’m getting about 17-20 mpg city/highway combined, depending on driving style. Better than the 12mpg before I cylinder head swap and all the other parts I replaced. Truck has 196k miles

MPG seems a little low, even with winter fuel, for 2.3l DOHC, may be someone with one can comment, I don't have one so can't say

An O2 sensor reads Oxygen levels in the exhaust, RPM doesn't matter
Now the computer does ignore O2 sensors at idle and at WOT(wide open throttle), at both times computer runs the engine Rich on purpose.
At idle an engine will over heat if fuel mix is too lean, so you should see + STFT at idle, or lower - STFT(so it it was -4 it should move to -2, a richer mix)
At WOT its all about power so computer uses tables for RPMs and ignores O2

When heated up the Cat converter should burn up or store most of the oxygen in the exhaust, regardless of RPMs, so you should see .7 volts from downstream O2 all the time
The .1 volts means High Oxygen in the exhaust after the Cat, which may mean new Cat is not doing its job, or could be because mix is too lean, the Cat NEEDS unburned gasoline to keep it Hot, so it should get hotter at idle with Richer fuel mix

It may be different with your OBD reader or in a 2004 2.3l never work on one, so the drop in Downstream O2 voltage at idle could be normal, the .65-.75 while cruising is expected and normal

Yes drive it a bit more and see if LTFT is coming closer to 0, longer trips will help, hour + drives at high way speeds, stop and go driving doesn't help much to reset LTFT

Update following driving test: After getting the P0172 rich condition DTC, I drove the car for 100 miles over the past 1.5 week in the hope that the ECU "learning" would make the LTFT less negative. Driving was about 80 miles highway and 20 city/hwy. LTFT stayed pegged at -25%. I'm nearing the end of my skill set and knowledge. I've replaced known bad or poorly performing sensors and parts, including confirming fuel pressure, as I mentioned in the original post, but to no avail; P0172 keeps coming back.

The only thing I can think of is I could possibly have not set the timing right when I replaced the cylinder head in July/August of last year (I also replaced the timing chain, tensioner and crankshaft position sensor with new parts). I also replaced the spark plugs to copper core on the odd chance the previous iridium plugs did not create a strong enough spark. No change to the LTFT.

Question: Can an overly advanced timing potentially cause LTFT to be extremely negative generating the P0172 code? A freeze frame snapshot from today follows:

Ignition timing advance for #1 cylinder: +20 degrees (it drops, then rises when I rev the engine, bouncing between about 17 degrees and 21 degrees when engine rev stabilizes)
STFT: 0
LTFT: -23.4
MAP reading: 4.35 psi (KOEO readout was 14.7 psi. I live pretty close to sea level)
Engine RPM: 801 (idle, car in Park)
Intake air temp: 39F
MAF readout: 0.01 lb/s
Calculated load: 20.4%
Engine doesn't knock, no detonation and exhaust at the tailpipe is white and doesn't smell of raw fuel.

Any ideas are welcome. I'm at my wits' end with this P0172.

PS: Stay safe anyone who's in the path of the storm.

Only thing left that I could suggest before replacing the PCM(computer) or having Ford Up date it with new software., is...............

Replace the PCV valve on the drivers side of engine, a real pain to get to through the drivers side wheel well
Ford recommends changing this every year, lol, but at least every 2 years IMO

It's a long shot but not a no shot, the blow-by in the engine has to go somewhere and its either sucked thru the PCV filter or it goes out the Vent(breather) hose and into the intake air tube, and that could cause lower oxygen levels.

BUT...............my problem is the normal STFT, -5 to +5 , and the high LTFT which doesn't make sense, so thinking a computer issue, i.e. "its carrying the 1" lol, a math goof

I replaced the PCV in 2016, about 4000 miles ago but will replace it again (yes, it's a royal pain, but it's worth a shot seeing it costs only a few bucks …). So the ignition advance looks good. Thanks for the confirmation (if nothing else, it gives me a positive feeling that I probably didn't mess up the cylinder head job, at least not significantly, anyhow :smile:).

Couple of more things, Ron, that I did a few days ago to eliminate potential causes of excessively negative LTFT:

1. On Thursday, I remove the EGR tube that feeds into the intake. I sealed the hole and checked for leaks by spraying brake cleaner. No vacuum leak. Unfortunately, no difference in LTFT so I assume the EGR valve is good
2. I filled up with premium gasoline yesterday. Long shot but it was worth a shot. No change in LTFT, not even a sliver
3. I contacted a local Ford dealer to have the airbag recall taken care of. They'll call me when parts are in. At the same time as that service, I'll try to talk to a technician if there's any value to reflashing the ECU (vs asking the service adviser for his/her thoughts who'll surely want to do that even if it's a needless service)

I'll be incognito for a few weeks pending the recall service, but I'll report back with a status. And, after all is said and done, I'll do a write up like I did for the cylinder head job with lessons learned and other things I learned.

You can use a vacuum gauge, $20, to test for valve and ignition timing, plus a host of other engine issues, one of the "old tools" that still works on all gasoline engines, lol.

Tests to do and results here: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine

You want a high, warm engine, vacuum, because you are close to sea level, so 19"+, if lower valve timing could be off
Also do blocked exhaust tests, that will cause persistent false Rich readings

But it really is looking more like computer goof up in the math, and no real way to test for that outside of what you have done...........eliminate other possible problems and what ever is left is most likely problem.

Rich Condition Solved
 

Good work

Would not have thought injectors, were they the same LB?

I have used Dorman shackles, no complaints
You do need to grind off the rivets to get factory shackles off, new shackles come with bolts
And so far I have had to burn out 6 of the 8 leaf bushings on my Rangers because bolt couldn't be removed
Used a small propane torch, and ran water in the bed above to prevent paint damage from the heat, or if replacing more than one shackle just pull off the bed, WAY EASIER to work on that way
Bed comes off easily, its not heavy but you will need a friend to help because it is awkward

Just guessing but lb/hr for pounds per hour

Yes, sorry, injectors are rated in pounds per hour of fuel flow because air/fuel ratios are weight ratios, gasoline is 14.7 to 1 ratio, 14.7 POUNDS of air to 1 POUND of gasoline
Or 14.7 grams of air to 1 gram of gasoline

The computer is programmed for the LB rating of the stock injectors and the average fuel pressure, so it "knows" if it opens an injector for say 100milliseconds, XX gasoline will flow in from that injector
If you change to a different LB injector then computer will set lean or rich codes because its still using the the old LB rating in its calculations

2006 Ranger 2.3 p0172 rich code.
 

Have you replaced and/or excluded any potential parts that can contribute to the issue?

Ranger 2.3 rich.
 

Sent you a private message