P0171 & P0174 Lean codes

1999 4.0L Ranger logged these codes at 1053 rpm's

I previously used Techron Concentrate fuel additive 12oz
& 6 oz of Sea Foam engine treatment in the brake booster hose.

So I got it from both ends, I figure I messed up a sensor, not sure.

I read somewhere that additives can damage a DPFE sensor? But I have
no clue about sensors. I did a visual inspection of the MAF sensor.

Any comments will be welcomed, thanks.

I also have a '99 Ranger 4.0L. I've also experienced having the same codes which I was able to correct. This type vehicle has two 02 sensors, a pre-cat and a post-cat sensors. The code (PO171 and PO174) I believe indicated "lean" mixture. My problem however was not the sensors but a slight vacuum leak which I detected around the intake manifold. While the vehicle was idling I sprayed "carb cleaner" all around areas of possible vacuum leak. When I hit the spot in question, it momentarily affected the quality of idling. I removed the upper intake manifold and replaced the "O" ring. That got rid of my CEL code. Remember that a slight a vacuum leak , may be undetectable could cause to activate the code. In your case however since you introduced certain fuel additives, it could have affected your O2 sensor/s. One more thing, O2 sensors tend to become "lazy" (slow to respond) after a while. I replaced both my sensors. They were not that expensive and were easy to replace. As a suggestion, unless something is wrong with your lube and/or fuel system, I would not use any of the "miracle" additives. Only thing I use is the fuel injector cleaner which I add to my gas tank once every three months. Good luck.

Thanks for the reply:
I wound up doing the same thing as you, replace the three figure 8 o-rings under the black plastic intake. I went a little step further and replaced the fuel rail/intake thick gasket, underneath. That turned out to be a waste of resources, as that gasket is reliable from the factory and showed no wear, plus you have to remove the fuel injectors. Don't drop a fuel injector on concrete or it's $40 out the window. :)

The o-rings had hardened and were just barely hanging on. Effects were, poor fuel mileage, weird noises, denotation of combustion chambers and inconsistent idling. The Seafoam thru the combustion chamber just amplified the problem, although, Seafoam is a good product to use normally, in certain equipment.

May I ask you, do you get marbling noises after an oil change? Even if you fill the filter with oil before installation?

Were you able to detect any vacuum leak? Whatever you did, did it correct the "lean mixture" code? I never touched the fuel rail. Filling the oil filter with oil during oil change does not do much good or bad either. If you are worried about the oil gallery being air bound, it should not happen since the oil vents out in various places. At one time I was hearing more like slight clunking noise noticeabel while idling. That was when I was using Castrol, and then Valvoline but the noise went away when I started using Penzoil. No logical explanation except that periodically I hear owners who experienced the same thing but went away after changing to a different brand oil. When I added Lucas oil additive, it got worst. When I changed to 10W-40 same thong. So I've been using Penzoil 5W-30 for the past a couple of years now changing oil every 4K miles.

The lean code was solved with the replacement of the o-rings. I also put a real clamp on the PCV valve and hose. But I woke up this morning with another CEL. At least they are consistent. This time it’s P0113. I’m thinking all the unplugging of the MAF sensor over the years has put resistance in the wiring. If anyone reads this and can give an opinion on code P0113, please do.

I use Castrol, or did, now I use Wal-Mart brand 5W-30 ($10.00). I used the Lucas additive, it only thicken the oil and made it harder for oil to go into the smaller journals and passages. The slight clunking you heard could have been denotation due to years of fuel fill-ups with who knows what is down in those tanks. It’s hard to know what quality a stations fuel is, but I have changed to a Chevron station and the marbling has subsided.

Have you had any issues with your front brakes? Calipers or rotors?

PO133 indicates slow response from O2. As I previously stated after a while O2s tend to go "lazy". That's why I decided to replace mine. I've had no problem with my front frakes. Next brake job I will need new rotors as the ones on now are at minimum thickness.

Thanks for helping out. Have you ever had a P0113.....? It's saying something about an IAT. I think that is in with the MAF sensor, not sure.

Regarding the PO113, try this. Disconnect the air filter housing from the MAF. You will see a thin wire which changes resistance as airflow to the intake manifold changes. After a while this wire tends to get coated with oily dirt which affects its reading. Get your self a spray can of MAF sensor cleaner. Mine was made by CRC and available at Pep Boys or perhaps other autoparts store. Spray the wire and the surrounding components and let it dry. See if that does the trick. On top of keeping my K & N air filter clean, I spray the MAF sensor every time I change oil.

Do a smoke test for unmetered vacuum leaks.

Hey guys,

I also have a 4.0 liter ranger 1998 that keeps setting these lean codes, is this a fairly easy job, replacing the orings?

Hey guys,

I also have a 4.0 liter ranger 1998 that keeps setting these lean codes, is this a fairly easy job, replacing the orings?


Yeah, I did the o-ring replacement and it increased my m.p.g. to 22 hwy driving. I also had to adjust the back brakes, had a weak spring.

Have you had any issues with engine noise, such as lifter-push rod tapping? I took over a 1999 4.0L with 105,000 miles and it seems to have an oiling problem. I have had success with engine cleaners on a 1992 4.0L with poor oiling at 157,000 miles, but this 1999 4.0L seems to be harder to flush out.

Well, I tried the carb cleaner spray around the intake area. This made no change in idle. Tried with the engine cold and warmed up. I am also running a K&N air cleaner. Just for the heck of it, I replaced it with a standard air cleaner and cleaned the MAF sensor using the CRC MAF cleaner. Lets see if this does the trick, cheap try. If I can remember back this far, I started popping these codes when I cleaned and oiled my air filter last (I'm guessing). It is possible I over oiled the filter. I will keep you guys informed. By the way, my O2 sensors are original with 150,000 milkes on them. I guess they are next.