Well I've had the 401 code for a few weeks now, figured I needed to clean the TB. But have not been able to with all the snow we've had plus I live in an apartment. The P0171 just came back even after cleaning the MAF and IAC 2 weeks ago. But today I noticed that my idle is very rough and stumbly. This is the first time this has ever happened. On top of this, the exhaust if I rev it high turns greyish and smells horrible. And also, my gas mileage is very low, maybe 10mpg combined city/highway, hand calculated.

All my O2 sensors are less then a year old, fuel filter is too, which needs changing. Plugs are 18 months old.

What could I be looking at that would be causing the above problems?

Truck is a 1998 F150 4.6L 4X4 auto tranny w/3.55LS with 175k on it. Other then the hole in my exhaust after the cats at the tranny, truck runs dam good.

 

follow the pcv hose to the back of the intake while running and see if the elbow is leaking. thats one of the biggest causes of the p0171. the po401 is usually the dpfe sensor failing, but if the egr ports are clogged it could cause the same code. start the engine and try using a piece of rubber hose and hook it to the egr vacuum port and try to suck the diaphram open or use a little vacuum pump to open it. the engine should die or want to die if the egr opens and the ports are clean.

what brand plugs did you use?

 

I'll have to check to see if that hose is shot. Right before my wedding in October 2008, I had everything that can be changed, changed. All fluids, filters, pcv valve with the hose. Well hopefully the hose was replaced. I had a hole in it 2 years ago and had to rig up a small piece of hose to fix the issue. If thats still there then I know the hose was not replaced.

The plugs should be motorcraft. My mechanic is good about using oem only and since there is motorcraft parts warehouse a few blocks away its not hard getting the stuff.

We'll see if i'm able to get a piece of hose to do the check.

 

Ok, its been just over a week and I have not been able to check my truck. Now I have 4 codes, P0171, P0174, P0401 and P1000. On top of all of this i now hear a wind swirling noise coming from the passenger side of the motor that I didn't hear before this past Saturday. Truck starts very rough now with a large plume of wht/greyish smoke once it fires up. Idle will stumble and buck down to around 300RPMS if i come to a sudden or hard stop or if I rev the motor up real quick to 3000RPMS. And finally another hole in my exhaust opened or the pipe from the drivers side ford header came loose and my truck sounds like a beat up p.o.s chevy from the 70's. Its beyond embarrasing.

 

The new exhaust leak could be the EGR pipe rusted through or off at the manifold. Find the EGR on the intake and the approx 3/4 inch diam pipe that goes from it down to the manifold. See if it has a hole or broke loose down there.

Large smoke when you start up sounds like you have something leaking into intake, cylinder or exhaust. If intake gasket it is not so bad (not so good either....), if head gasket that is a big job. Are you losing any coolant or oil? Keep an eye on them to see if they are dropping levels.

You can unblot the EGR and see if the passage in the intake is clear. You may have to remove the throttle body and then the elbow. Then you can clean it out with a drill bit, it has intersecting drilled holes. The DPFE is also a known failure item and that can cause the codes you have, as mentioned above.

I have similar stumbling problems on mine after letting off gas and idling, I think I still have something not right in my EGR system, although not throwing any more codes yet.

 

im going to be very pissed if the EGR tube is shot. When I had my entire exhaust done, ford shorty headers and custom piping I had to have a new EGR tube, bolts and such replaced. Original pipe connecting to the stock manifolds was unrecognizeable. You didn't know if it was welded on or rusted, thats how bad it was. If this dam rain would go away i'de get under the hood.

As for coolant and oil, both are good. Levels are fine, no leaks except for the oil pan gasket or maybe dip stick where it goes into pan. Just had oil done last week.

 

Check the vacuum lines coming off the EGR solenoid. They run near the EGR pipe, and can come into contact with it and melt. Take the plactic tubing off the line and verify there isn't a hole. This will cause a P0401 code.
Not uncommon to have to tighten up exhaust bolts after they heat up a few times, after putting new ones in.

 

ok i'll check those too. I did a quick look as I was still in my work uniform. There is a noticeable noise coming from teh passenger side of the motor. I cannot pin point exactly where. I checked the pcv valve and it seemed normal. Not sure what i'de be looking for if it wasn't working properly. Truck was running like crap to while doing the checking and acutally died on me while making a hard turn into the parking lot. When the engine did buck and catch its regular idle a small puff of smoke came out of the hole in the exhaust.

 

If the EGR is dirty and stuck open, it will not idle correctly, but I think that will throw a P0402 code.
Also, is your IAC on the passenger side of the intake? The PCV hose should connect to intake at the same location as the IAC. A vacuum leak there could cause idle issues along with that noise you here and possibly the PCV codes. The EGR works off vacuum also, so I suppose if you are low enough caused by a leak, it might not open properly. This could cause a P0401 code.
I would check all the vacuum lines first. If you have a hand pump that would be great. Just pull off each hose and give it 20 inches of vacuum and see if it holds.

 

will see what I can do tomorrow. Supposed to be 60 degrees out finally. And yes the IAC is on the side of the TB elbow and not on the backside.

What about a stuck IAC aswell?

 

Ok i replaced the PCV valve and I went to a motorcraft parts warehouse and picked up a DPFE sensor, $85. Easy as hell to replace, bolted kind. The stock one was pretty gross. ONe of the ports was filled with this orange crap and other was just dirty and yucky. I'll see if I can take a pic later.

Truck seems to run a lot better. Idle does not jump around or buck, or dip and then shoot back up. Only time it stalls or dips is on hard turns. Only done it once. I'de reset the battery and all that but the pioneer radio I have is impossible to program.

 

I just want to pull my hair out. I thought I had the CEL/stumbling/rough idle/dying problems solved. I replaced the DPFE sensor (motorcraft) and pcv valve (napa). Truck was running great till last night and then this evening. Truck starts much better, no huge puffs of smoke. Acceleration is somewhat better. Truck when idleing is smooth most of the time. But once the stumbling and wanting to die happens the idle is very rough, drops to about 300rpms or so, recovers to 700ish and puffs of smoke come out from the exhaust and then it goes back to normal idle.

The truck has died twice. It has died only when slowing down for making turns. It has come close when im coming to a complete stop.

What i dont get is, why on turns and coming to complete stops does it want to die? Oh and im definitely sucking as down. My needle after filling up does move till I hit about 30-35 miles, today it moved once i hit about 15-20miles.

 

Sounds like the EGR valve itself is hanging open some. That will definitely cause that problem, -no doubt about it.

As mentioned by cking2600, -that SHOULD be a PO402 (poppet valve failure), BUT that problem doesn't always produce the 402 because it has to do with insufficient flow (PO401) at the same time. To much flow may also bring on the PO171.

I suggest working the valve with engine running @ idle,- to determine proper function. Take a section of hose (3' or so) / Disconnect the green line from the valve / Plug your section of hose into the valve / Suck on the hose like your drinking a milk shake.

It's called the "suck test". Your idle should deflect, drop down and almost stall the motor when you yourself supplies vacuum with a section of hose. If nothing happens differently with idle, and while performing test, the valve is bad and you need a replacement.

 

Jbrew, will do. Im going to tackle this tomorrow. I'll pick up some hose from autozone or wherever. I gotta finish working on some HO scale train models today/tonight.

 

How do fit HO scale trains in your apartment ?

Anyway, try tapping the valve, - if it's hanging open it may close if you smack it a few times. But, it will just open again once you hit cruising speeds and hang again.