I foolishly bought a 2002 Ranger 2.3l in part because I thought it had no check engine light. Turned out that 8 bulbs in the instrument cluster were burned out including that one. Dumb purchase on many levels. But I'm trying to bail myself out by getting it to pass inspection.

Fixed the P0125 in no time--thermostat was stuck open. I used the trick on this forum of putting in a 2004 Ranger thermostat and adding a 1.2k ohm resistor to the heater wire connector to prevent a PCM problem. Works great.

The other code is the P0172 System Too Rich. I have read every post about it here. MANY possible causes.

First thing I did was clean, then replace the MAP sensor because its reading didn't change above 17" vacuum. Pump it to 25", no increase. Replaced with one from Rock Auto. Also verified good readings from the TPS. Replaced the air filter. Cleaned the MAF. Cleaned the IAC and put on a new gasket. Also cleaned the throttle body and put on a new gasket. IOW I did the easy stuff. P0172 returned in 20 miles.

Then I took it to a trusted mechanic who told me: "You need a new engine. You should get rid of the truck, maybe trade it in somewhere. How much did you pay for it? THAT much?!?" (I told you it was a foolish purchase--he agrees). His idea is that rings are old and leaky (184K), and the excess blowby confuses the PCM because it is 'air' entering the intake that is not metered by the MAF, so it screws up the mixture. Too much blowby, he says, is causing the System Too Rich condition. I don't get it. Shouldn't it be causing a Too Lean condition?

By the way, this mechanic coached me that if I plug the PCM entry to the intake manifold and remove that tube from the PCV, then install a breather cap on the valve cover I probably will be able to pass inspection. Odd because if he 'notices' the cap he'll have to fail me, and he's an upright but sympathetic guy. After doing that improper mod, including plugging the hole in the intake downstream of the MAF where the tube from the valve cover used to fit in, the trucks runs about the same, but the fuel trim numbers look a LOT more normal (they were very negative). Still, P0172 returned. Incidentally, off idle the truck is intermittently very hesitant, maybe a bit less so when fully warmed up, but it always smooths out and has decent pep as soon as it hits 2000 rpm.

Finally I bought an ELM327 wifi sender and checked my sensors on FORScan Lite. (What a fantastic thing this is, to watch your sensors on your phone!) So this post is my request for advice about what the sensors are telling me.

--Coolant temp and Cylinder head temp look normal, somewhat above 200F. I had put in a 194deg thermostat.

--TPS looks fine, runs from about 0.8V closed to around 4.0V nearly floored.

--Short term fuel trim once I hit 2000 rpm and above fluctuates between -5 and +5, averages near 0, maybe slightly negative. At idle it runs from -6 to +4, lots of gradual fluctuations, no sudden jumps.

--Long term fuel trim was quite negative until I did the breather cap trick, now also runs between 0 and 4 when running. Once in a while briefly goes negative. After running for a 10 mile drive I let it idle, and LTFT runs from +3 to +4 with a little fluctuating out of that range.

--MAP sensor runs from about 0.8V to around 4V.

--IAC looks odd to me. It runs in the 40-55% range all the time, even above idle. At 2500 rpm it is still open around 50%. Is this odd?

--MAF is the other one which looks very odd to me. Going down hill with the throttle closed it drops to 0.32 lb/min. At idle it runs about 0.36 to 0.42, and floored at 3000 rpm it jumps up much higher, maybe 4? 5? I didn't write it down. But the point is that my virtual meter in FORScan Lite has a scale from 0.00 to 0.14 lb/min. So even at idle I am way off the scale. I'd like to know whether those lb/min values are way high (bad MAF) or if the scale is wrong in the software.

--Finally looked at the heated O2 sensor of bank 1. Can't figure out how to interpret it. Its value of course fluctuates. Maybe I need to monitor some other aspect of the sensor(?)

Thanks in advance for looking at this. Eager for suggestions.

John
Chapel Hill NC