P0171 & P0174 with Knocking

[SnowOptix]

Hello all,

I have a '99 4.0 4x4 XLT that's doing something interesting. I noticed that there was a knocking sound in the upper part of the engine that got progressively worse over time, but only sounded while idling. I've been running with a CEL for a while. I finally got the codes read and it's P0171 and P0174. According to Ford, that's a lean mixture.

Well, I found out what the "marbling" was according to this excellent forum. It was carbon buildup on the top of the heads. I ran water through a vacuum line to steam clean it (I know it's bad for the O2's) and that blasted all the carbon out. It idled fine for a few weeks. Now it's starting to knock again.

This tells me that I'm getting carbon buildup on the valves/heads, and that could be due to a rich mixture (from what I know). Could the issue with the presumably 2 dead O2 sensors be causing the engine to run rich and build carbon? I'm not completely familiar on the vacuum line system on newer engines, but if one were leaking, would it cause carbon buildup?

I'll be ordering new O2 sensors soon. Let me know what you guys think. Thanks!!

 

[Earl43P]

Common causes of those lean codes a e vacuum leaks (PCV elbow, etc.) and the notorious upper and lower intake manifold gaskets.

http://www.explorerforum.com/forums/showthread.php?t=171819

The O2's may be telling you the truth.....

 

[adsm08]

Have you actually watched the waveforms of the O2 sensors? If you haven't or they aren't throwing codes don't assume they are bad (but there is a 100K mile service interval on them).

Try running some seafoam or ATF in the oil for 10 to 15 minutes and then change it, and throw some fuel treatment in the tank.

 

[mentalbreakdown00]

WHen it flags a code for running lean it means it has added as much fuel as it's programming will allow for emissions, but is still running too lean. The common causes for this have already been stated, except for an exhaust leak before the O2's will also cause the same code.

 

[snake]

Above posters correct, vacuum leak through the PCV hose is the most common problem on most Fords- they collapse then a hole rips through causing unnmetered air to get past the MAF. Let us know what U find.

 

[LearjetMinako]

Things to try and look for:
1.) Vaccum leaks, check hose that are disconnected or ripped
2.) Clean the MAF sensor, pickup a can of MAF cleaner and give it a good cleaning.
3.) Carbon build-up, SeaFoam works wonders
4.) O2 sensor is fautly, change this last
5.) Spark Plugs, doesn't really cause this problem unless the engine is running rough also. Worth to check them anyways.

 

[SnowOptix]

Thanks for the input guys (and sorry for posting in the wrong section). It appears Learjet summed it all up, so I'll be doing that soon and posting what I find. The carbon buildup seems to form relatively quickly, so I'm assuming it's definitely a problem with what/how things are being burnt.

 

[88_Eddie]

when in doubt, seafoam it out

 

[SnowOptix]

Update! I hesitated posting but I would like to archive this for future drivers of Rangers who might encounter this problem. I'd like to thank every member of this forum, as the information I have gathered here has solved something that 2 dealerships and a private mechanic could not diagnose-- and my god was it easy!

The dealer paperwork for my Ranger showed that the PCV had been changed within 10K miles, so I didn't even look at it as a possibility for a vacuum leak. I went around, spraying starter fluid/carb cleaner in areas that a potential leak might form. It's dangerous, but nothing would really surge my RPMs like that stuff. After checking many a hose and seal, I was checking near the driver's side of the engine and checked the hose above the PCV inlet. In that area, I got a surge.

I pulled off all hoses in that area, including the PCV and was a bit dumbfounded at what I found. The dealership had replaced the PCV alright, but it came off of that hose so easily-- a lightbulb went off. The hose needed replacing-- it had no cracks, but made a horrible seal on the valve and inlet from the valve cover. A quick trip to PepBoys and I returned home with a new hose. Placed that on and cleared my code. I did a quick cleaning of the MAF (didn't have a security torx to do it right) so I just sprayed cleaner liberally all over the sensor while still mounted in the intake (engine was off, didn't start it for several minutes while the stuff evaporated).

To clear the pinging, I Sea Foamed the valvetrain and cleared all carbon that was contacting the pistons. Needless to say, I'm safe after 500+ miles of driving. She runs so smoothly now and after I changed all the fluids in her (both differentials, everything you can think of) she's like new again. MPG is really high-- around 22-23 highway. Absolutely happy with results.

Thank you all, sorry for the somewhat lengthy update.

 

[warment]

Just fixed this issue in my dad's 2002 Ford Ranger FX4 with 4.0. He had a large crack in the passenger side PCV elbow near the front of the engine. A piece of 5/8" hose was used to replace the elbow. Ford wanted to sell me the entire PCV hose system (hard lines and elbows) for over $40. No codes since Saturday.