Hey, been a while since I've posted, but I have encountered an issue and ya'll have bailed me out ever since I've been a part of this site. I have a 1998 Ford Explorer Sport 4x4 with the 4.0L OHV. For the past week or two, I have noticed an idle issue, when I first start the truck, the RPM's shoot higher than normal then drop lower than normal and will sometimes stall out. Well, I thought, maybe IAC, had that issue with my 94 Ranger, replaced that and solved my problems. So I took a multimeter to it, everything checked out. Still confused I was waiting for another sign. Well, today that sign came in the form of a CEL. I happened to be rolling up on an advance auto when the CEL came on and I asked them to pull the codes for me, well, one code popped up,

P0171: System Too Lean(Bank 1)

The guys at advance suggested O2 sensor, but I wasn't 100% sure, sounds like a possibility but I decided to check with ya'll before playing with anything. I did a search in the forums and found a lot of threads with both banks throwing codes, but I only have 1 and was wondering what ya'lls suggestions would be. Thanks for ya'lls help

 

Maybe a faulty O2 but maybe it's telling the truth. Have you changed the intake gaskets yet? These are prone to leaks on these motors. Once it warms up, the expansion of materials can make a good seal but when cold, leaks. An intake leak will run lean. Lean spikes can rev the motor up as you mention.

 

The CEL came on when the engine was warm, not when it was warming up, so would it still throw a lean code if the intake is leaking? I mean, I had been running for about an hr and a half when the code finally popped up. It was the longest I've run the thing since August. Since then, the longest ride was maybe 25 minutes sitting in traffic, this was 1.5 hrs wide open highway. I know the intake gasket could be an issue, but it just seems awkward that it would do it then when the engine was warm, that would be something I would have expected while it was cold, unless it's finally just gave out.

Edit: I just changed the PCV last week, it was clogged up. I noticed no change from the revving issue, but it needed to be done. I'm going out tomorrow in the daylight and gonna check out the MAF see if it's gunked up at all and clean it if it needs to be. I checked some EGR hoses because I had had an issue with the upstream hose melting, and no hoses are damaged from what i can tell.

 

buy some carb cleaner, and use the small straw on the side to concentrate the spray. While the motor is running, spray around the intake, pcv valve, hoses, and all vacuum lines. If you find a spot that is leaking, the motor sound will change. If you have a misfire on that side, it will also throw a lean code.

 

One thing to add to what vloney said.....check for vacuum leaks with the engine cold. They are usually worse then and show up easier.

 

I sprayed around the Intake Mani, nothing changed, cleaned the MAF and Throttle body, MAF was as clean as can be, throttle body was slightly dirty, pulled the IAC and sprayed it down and wiped it, and everything seems ok for now, but I've also been cranking on and off and it would normally stop the revving on about the 2nd-3rd start. I cleared the code, and so far so good, it hasn't returned. I'll keep ya'll updated, if it does it again i'm going to crawl up under and take a multimeter to the O2 sensor and see what it tells me, would have done it now, but the engine is starting to get warm and I don't wanna go play with that right now, we'll let it cool down before I touch that. I will probably go back out in about an hr or so, and we'll see what kind of progress I've made.

 

ok, well, it's still doing the same thing, and the code came back, I haven't had a chance to take a look into anything else bc of classes, homework, work, and me being sick. Any other ideas, it'll probably be monday or tuesday before I get a chance to poke around again, and any other ideas would be greatly appreciated.

 

Im Having The Same Problem With My Explorer Sport 2000. Im Going To Try Putting In A Set Of Motorcraft Spark Plugs .

 

Ok so far everything checks out, but i'm starting to notice a little bit of a different tone, sounds like my engine is gurgling on the drivers side, then I popped the hood and it sounded like there was air being sucked through on the drivers side as well. Starting to make me think the gasket, but when i sprayed the carb cleaner around it like earlier stated, no tone changed. I don't have time to dive into pulling the intake mani off this week, but I would also like to see if this could be what it is, if that sounds like what it is, or if there is something else to look at. I was given an idea by a friend to check the EGR, I replaced it not too long ago bc it had melted the upstream portion, could there be an issue with that causing my problems. And the stalling is getting worse, I started it today and it died almost immediately and would not refire, it'd turn over and start catching then just keep spinning, gave it some gas and it finally caught and ran like a champ.

As was stated earlier about a misfire, wouldn't it throw a secondary code as a misfire code? I've messed with a neon(don't ask) that threw a misfire and lean code simultaneously. Plus the plugs and wires aren't too old, maybe have 3000-4000 miles on them.

 

You have a vacuum leak. The O2 is reading correctly.

On the Sport Tracs when this happens it is the hose on the passengers side, in between the cylinder head and the upper intake, near the front of the engine and it wraps around the from molded part of the front cylinder of th intake. It is actually part of the PVC hose. You can't find it because it cracks on the bottom.

I have pictures of this but am not sure how post them on this site as I have them at another site. But here is the link to them.

http://www.zjstech.net/~library/2290...e/Hose%201.jpg

http://www.zjstech.net/~library/2290...e/Hose%202.jpg

 

I checked all the hoses I could find and still nothing. I am stumped as can be. about to give up and hand it off to a mechanic to look into. Now, when I was looking through my haynes manual for a better defination of the trouble code and it says fuel adaptive too lean(bank 1), so yeah, this is extremely frustrating.

 

I have a 98 Ranger 4x4 and it just threw the 171 code at me. I reset it by removing the batt cable for a while but it came back. Figured it would. Looked at all the vacuum lines, even the ones to the front hubs. No bad lines that I can spot. I'll have to check the PVC valve, haven't looked at that in forever. I did pull the idle air valve. Not carboned up but it's old. Still seems to work.

One other thread mentioned changing the fuel pump, pressure problems. I had an Aerostar at one point and going up a long steep hill I'd hit 3/4 throttle and it would just suck air, no power. Fuel pump.

I'll keep you posted.