My 2001 Ranger suddenly began to bog, sag and buck with feeling of no power under load at part throttle when driving the other day, even showing a flashing CEL. After limping home, FORSCAN showed codes 0171, 0300, 0301 and 0302. I removed the intake manifold and checked all vacuum lines the next day, finding that the PCV valve hose had split, and replaced it. After smoke testing for other leaks and finding none, on the test drive it showed the same symptoms only worse. Here's what today's FORSCAN log showed at a couple of points during an 87-second test:

at 4 seconds after starting:
IMRC1M 0.02 V Intake Manifold Runner Control Monitor
LONGFT1 -5.47 % Long term fuel trim 1
SHRTFT1 1.42 % Short term fuel trim 1
ENGLOAD 20.96 % Engine load
MAF 4.15 g/s Mass Air Flow
MAN VAC 44.03 kPa Manifold air pressure
O2S11.VOLT.OBDII 0.26 V Heated Exhaust Gas Oxygen Sensor (bank 1, sensor 1)
O2S11_V 0.55 V Heated Exhaust Gas Oxygen Sensor (bank 1, sensor 1)
O2S12.STFT.OBDII 99.22 % Short Term Fuel Trim (Bank 1, Sensor 2)

At 5.47 seconds in

IMRC1M 2.48 V Intake Manifold Runner Control Monitor
LONGFT1 2.34 % Long term fuel trim 1
SHRTFT1 -1.49 % Short term fuel trim 1
ENGLOAD 34.43 % Engine load
MAF 10.96 g/s Mass Air Flow
MAN VAC 37.26 kPa Manifold air pressure
O2S11.VOLT.OBDII 0.83 V Heated Exhaust Gas Oxygen Sensor (bank 1, sensor 1)
O2S11_V 0.28 V Heated Exhaust Gas Oxygen Sensor (bank 1, sensor 1)
O2S12.STFT.OBDII 99.22 % Short Term Fuel Trim (Bank 1, Sensor 2)

The manifold vacuum was fluctuating wildly, even at constant revs.

I'm pretty sure I have found and sealed all the vacuum leaks. I can't afford to just throw parts at the problem when a MAF sensor costs $300. Can anyone here help me diagnose this so I get the right part? I can run additional data in a FORSCAN log tomorrow if necessary.

Thanks.

 

Welcome to the forum

Why are you diagnosing a Lean condition?
Or are those reading after the repairs?

STFT is -1% so that's Rich and could be that way because it WAS Lean before and computer is correcting LTFT by closing injectors early, as it should

2001-2003 2.3l Duratec Rangers had one common issue, the IMRC(intake manifold runner control), it caused your described symptoms when it was acting up

But it should set codes in the P200X area, i.e. P2004

The P0171 - System too Lean (Bank 1), code was from the misfires most likely, O2 sensors can only see Oxygen, its what the "O" stands for, so when a cylinder misfires no Oxygen is burned up with the gasoline, so its dumped into exhaust pipe and O2 see the extra oxygen as Lean condition

 

Ron, thanks for the reply. I had a slight lean condition for a long time due to a vacuum leak, and when it got bad enough that the engine wouldn't start (back in January) I bought a smoke tester, found a leak at the top of the PCV valve hose and repaired it. Then last Thursday it started showing the symptoms described above. On Friday I removed the intake, found and fixed that leak. The readings above are from yesterday after I thought I had fixed everything.

 

After doing some more things, here is what I know. This is a DOHC Duratec engine with a timing chain.

1. Today replaced the MAP sensor. No improvement.
2. I was able to do a 20-mile round trip to NAPA to get the new sensor. At very low throttle openings, it ran smooth and made power. If I opened the throttle to 1/2, it bogged. I was able to nurse it by going in one gear lower than normal and keeping the revs up. CEL did not light up until I tested opening the throttle. Immediately threw codes 0171, 0302, 0303.
3. I find it interesting that only cylinders 2 and 3 show misfires. There is a vacuum hose to the IMRC that connects in the middle of the intake manifold between these two cylinders. Once the engine cools down I will pull and inspect that hose.
4. Alternately, I wonder if there is some dirt between the manifold and the head, or a damaged intake gasket, that I missed when reinstalling the intake on Friday,

If I were to remove or gut the cat, would that throw a CEL? I can't pass state inspection with a CEL showing.

And typically for me, when I went to take the wife's car to the market yesterday, its display said to fill coolant. Did so, coolant spilled out on the ground. Sure enough, there is a crack in the radiator. I've ordered a new radiator which will be here on Saturday. But right now my only capable motor vehicle is the riding mower.

 

The 302 and 303 codes are probably causing the 171 code, not the other way around or you would get random misfires

Yes, you could have an air leak causing the misfires specific to those cylinders

The Vacuum hose you mention should run DOWN to the IMRC control valve on drivers side lower engine, then another vacuum line from that control valve up to the IMRC actuator
This other vacuum line is know to come off or crack/split at its sharp bend coming off the Control valve
Have a look at these vacuum lines

You can do a smoke test to check for air leaks, cheap cigar and a large glass of whiskey, cigar is optional :)

 

Thanks, Ron. I have done several smoke tests and am satisfied that there are no leaks. That vac hose to the IMRC was in good condition.

A friend suggested it might be a plugged cat. Certainly the engine ran with a lean condition for many miles before it was bad enough for me to find and fix the vacuum leak in the PCV hose. Is there a definitive test that would determine whether the catalyst is the problem? I have not had any P0420 codes at all, which I believe is for the cat.

 

Here is part of a scan I did earlier today. I don't know if it will help. The forum won't let me attach the forscan log file. I also did a compression test today; all cylinders are good.



I'm starting to think it might be a bad catalyst. The vacuum readings and negative fuel trim are confusing to me.

 

You can use a vacuum gauge to test for blocked exhaust

Engine at idle should have 18-21" of vacuum
Raise RPMs to 2,000 and vacuum should drop and then come back up to that 18" level when RPMs stabilize, if vacuum come back buy is slowly dropping then exhaust is blocked

Then at idle "blip" the throttle, open quickly then let it snap closed
Vacuum should drop QUICKLY to 0-2" then QUICKLY come back to 18-21"
Slow drop and slow return is a blocked exhaust

 

It was a bad coil.The misfires were causing the lean condition as the PCM reacted to perceived rich mixture in the exhaust. The clue was that only these two cylinders were misfiring. That led me to replace the coil and now it's as good as new.

 

Good work

Thanks for posting the update and the fix