I've got a ranger that after driving for 15-20 minutes, sometimes the check engine light will come on. I did the KOER test, and came back with 41, which was I found described as a lean condition, is this correct? Would anybody care to give me some direction as to where to begin to look for the cause? Thanks!

 

Yes, code list here: https://www.therangerstation.com/tec...gitcodes.shtml

Engine must be warmed up set a Lean or Rich code, thats why the delay

Engine is not actually running Lean, these codes mean the computer is opening the fuel injectors longer than it calculated to keep O2 sensor voltage at .4volt
O2 sensor voltage is .1 to .9 under 1 volt
.1 is lean, too much oxygen in the exhaust
.9 is rich, too little oxygen in the exhaust

Once engine and O2 sensor warms up the computer uses the O2 sensor to fine tune the air/fuel mix, sweet spot is .4volt
Computer "knows" how much fuel the 2.9Liter engine will need at any RPM and throttle position, thats the "calculation"
If there is still too much oxygen in the exhaust, say .2volt, then computer adds more fuel to get it to .4volt
If it has to do this constantly then it will notify driver with code 41, because something isn't right

You have only 1 O2 sensor on your 2.9l V6, later model V6 engines had 2, one on each side of the engine

O2 sensors use chemicals to detect Oxygen in the exhaust, so they do wear out, use up the chemicals
Recommended life is 100k-150k miles, so if the O2 sensor is very old then it may be done, and they do cause Lean code at that time

Other causes would be a vacuum leak, this is less likely when using a MAP sensor, vs MAF sensor, but can happen
Extra air is coming into the engine which throws off computers calculation, so it has to add more fuel

Lower fuel pressure, computer expects 25-35psi fuel pressure, if its 10-20psi then less fuel is flowing in so computer has to open fuel injector longer than it calculated
Dirty fuel filter lowers pressure
You would also notice lower fuel pressure at highway speeds, engine might stumble a bit because its "running out of gas" at high speeds

 

Thanks Ron. Could a damaged air filter housing be causing it? There is some sort of sensor on the housing. This truck has a damaged air filter housing, that someone tried to repair with gorilla tape. They did a pretty good job of sealing it up, but I've been looking around at salvage yards for a replacement, but haven't had any luck yet. Seems there isn't a lot of 2.9's in junk yards around here, and the 2.3 and 3.0 housing that I've found are all different (even on what appeared to be the same year 2.3).

Also, you gave me the advice to change the fluid/filter in that old A4LD and i want you to know it did help to some extent. Still have a bit of a harsh/delayed engagement when you first start it and put it into gear, but that seems to be the only time it happens is when you first put it into gear on a cold start. The sorta clunky 1-2 shift has smoothed out somewhat as well. I dont drive it much because I work close to home, but I've put about 150 miles on it or so since the change, and I drove it quite a bit yesterday and I noticed that shifting is smoothing out, I'm not sure if that has to do with the new fluid cleaning stuff up, or what.

Ball joints and wheel bearings are probably in my future, as you might imagine with 29 year old joints and bearings. But I wanted to thank you again, it was really your post about the A4LD that pushed me out of that fear of changing the transmission fluid, and I'm glad that I did.

 

I'll look into just replacing the o2 sensor also. The good thing about this old truck is everything seems to be reasonably priced. At the low end, an o2 sensor is only $18.

 

Oh and about the fuel filter, I was planning on replacing that today actually.

 

The sensor on the air filter box could be for air temperature if it has 2 wires
If it has 2 vacuum hoses its for the air diverter on cold starts

But neither should effect engine operation enough to cause the 41 code

If it was an IAT(intake air temp) sensor issue there would be a different code for that