I have had my check engine light on for quite some time now and its really started to annoy me. Im dealing with a 1998 4.6 V8, and I am having an egr problem. I have taken the truck to a few different mechanics, and all of them did what they could but I still havent gotten the problem fixed . I got my trusty snap-on scanner out and as of ten minutes or so ago these are codes that I have:
P0401 EGR insufficient flow
P0174 System too lean (bank 2)
and I occasionally get a P1408 EGR flow out of range.

I have done the following to try to rid myself of the codes with no success.
pressure and vacuum tested all vacuum hoses
replaced EGR vavle,DPFE sensor, 02 sensors, EVR solenoid, and PCV valve
removed exhaust manifolds and replaced gaskets as well as a fresh set of bolts
replaced elbow on PCV tube that I was told is known to leak
new fuel pump as well as throttle position sensor,cam position sensor and idle air control motor
removed and thoroughly cleaned throttle body and EGR tubes as well as EGR intake ports
new spark plugs and wires and cleaned mass air flow sensor

I wondered at first if my catalytic converters had anything to do with, but I have no loss of power. As a matter of fact it has plenty, so I decided not to mess with them. I tried to get out the WD-40 or carb cleaner and spray around to see if I could find a vacuum leak but I could not for the life of me find anything. It has caused my fuel trim to go crazy, and I have tried just about every octane booster, injector cleaner, and fuel system treatment I could get my hands on. My scanner is telling me I have no faults on my injectors so I dont plan on replacing them. I have no clue where to go from here, but anything at this point would be great!

 

First off, don't throw parts at a code. Most likely problem with the p0401 is blocked passages inside the throttle body elbow. To confirm, pull a vacuum on the egr valve with the engine idling. If the engine doesn't change tune, the ports are clogged. The engine should almost cut off if everything is ok. As far as the p0174, you HAVE a vacuum leak on the drivers side of the engine somewhere. Good luck.

 

On the P0174, check the line that goes from the driver's side valve cover underneath the intake assembly. It joins the intake right in front of the throttle body.
I am the resident expert on not solving the P0401, so ask away, I can tell you what hasn't worked. But one thing you should check carefully is if the EGR tubes that go from the DPFE to the EGR pipe have not been crossed. I had a dealer replace a bad DPFE 2 years ago, and I think that is when they got crossed. They had also replaced the tubing from the EGR pipe, and the tubes would only connect one way. But they were on there back wards. I just recently made that discovery. IT ruined the new DPFE and I haven't replaced it yet. I'm hoping when I do it will finally fix the problem.
Everything that has been written on this site has already been done twice or more to fix my problem. The passages in the throttle body are clean enough to eat on, and have been more than once.

I just haven't had the time to get to replacing the DPFE since the people here helped my isolate that problem(Thanks jbrew).

Bigbronc made a post that confirmed to me which dealership crossed the lines to the DPFE because he recognized the type of tubing that was used.(Thanks Bigbronc).

 

who was the manufacturer of the DPFE and EGR?

isn't there sometimes a problem with non motorcraft parts in these areas?

 

Okay, well ill take it all apart and check it again but I swear it has not been two months since i had the thing in pieces and practically soaked in carb cleaner and then scraped inside and out with a wire brush. And as far a the 174 there are only 3 places that it could leak, which would be on the fuel pressure regulator, EGR valve, or EVR solenoid. When I did a vacuum test they did not leak. Do you think that If I wrapped them with electrical tape that it may solve the problem?

I know it looks like I have been throwing parts at it. I have been trying to solve this issue for about 3 months now. At first I had no clue, and I was just buying stuff mechanics told me that I needed to fix it. Im kinda learning as I go, and I hope that when I figure it out I will be able to help someone else out. I know this has been a real pain to me.

 

Okay, I will be sure to check it out while im cleaning out the throttle.. again. And as far as the DPFE sensor, I dont think the tubes are crossed. The longer tube is first coming from the manifolds and it connects on the farthest DPFE port. And of course the shorter covers the other. I hope that is how they go on there. It has been like for a couple months, but it is a brand new sensor. I guess if I screw it up there is always the warranty .

 

I have been using nothing but motocraft. I think the only time that I have not used motocraft was when I put in some Bosch spark plugs, but I dont do that anymore.

 

Does this mean your running Motorcraft plugs - Now? Why did you change the exhaust gaskets? Do you have any pics of the engine compartment? Did you do the intake -upper and lower gaskets ? Are you absolutely sure there is NO exhaust/egr tube leaks?

 

Yes as far as I know. Why? The only reason I changed is because of people telling me that f150s dont like bosch plugs. I have asked mechanics and they say it doesnt matter. I could not tell a difference when they were in there, but I had the 9 dollar bosch plugs.

 

I can't help yuh, use the search bar.

 

Im sorry I did not know you edited what you wrote before. Im a little confused as to why you ask me about the spark plugs and then said you could not help. I changed the exhaust gaskets because I was searching for a suggested exhaust leak, because I was told that an exhaust leak could cause my 1408. I was looking around under neath and noticed one of my manifold bolts was gone. Come to find out it broke off in the block, so I drilled it out. Then replaced the gaskets, and put new bolts on both sides. I will get some pictures in the A.M. I have not messed with the upper and lower intake gaskets, because the mechanic told me when he sprayed carb cleaner on those areas that they were not leaking.

 

Yea, I usually edit for 5 minutes,-as more things come to mind lol.

I couldn't help if you were running Bosch Plugs. If you had that many mechanics tell you that it doesn't matter,- then how could I help ? Bosch plugs are just bad news in that model IMO. For some they have worked out, so they say,-for most they haven't. It matters, and those mechanics can't be modular guys lol. I wouldn't work on the problem until the correct OEM spec plugs are installed. Bosch = wrong heat range - doesn't meet spec.

Carb Cleaner - Who do you have working on your truck ???

You have a vac tool right? -A Mighty Vac or something ? Just plumb it into the manifold. Throw a T in-line w/main vac. That can help diagnose the problem. I can send you a chart from Ford Service. You plug into the vac harness/throw the gauge up be the wipers somewhere, so you can read that and watch rpms at the same time. - You vac tool may have come with instructions. I believe, you can even check the cats this way.

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What's your warm idle at ?

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Test the DPFE real quick w/multi meter. Connect to center wire (SIG RETURN) @ the DPFE connector / Connect ground to battery.

Readings should increase w/ rpm, like this -

http://picasaweb.google.com/jbrew393...07882591006386

If not = Bad.

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Fuel Filter? I haven't seen that mentioned..?

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The 1/4" vac lines/harness likes to break between the battery and firewall. You have to pull the battery to check them all thoroughly. This problem is usually from something missed. I asked for pics to see how you have the lines routed.

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Well, your P0401 is out of range from factory set parameters. They are BOTH flow codes and yes and exhaust leak can definitely cause them.

P1408 (Circuit) EGR Flow Out Of Self Test Range. = P1401 (Circuit) . Yea, you better check the bottom wire (VREF) on the DPFE; -check it KeyOnEngineOff (KOEO). Should be more than 4.96 volts. 1408 IS a KOER self test, so check it running @ idle as-well.

The DPFE sensor is tested for out of range values (typically >4.96 volts, <0.195 volts) and if this is detected the DTC P1400 or P1401 is set.

The system checks the EGR for correct gas flow. During steady state driving with moderate loads and engine speeds the EVR duty cycle (operating rate) will keep increasing until the sufficient flow rate is produced. If the EVR duty cycle reaches 80% (ie 80% open) the PCM checks the DPFE sensor voltage with a table in memory to check that the gas flow is within parameters. If the voltage is too high it indicates that there is insufficient gas flow, and this stores the DTCs.

It's posible to lean out from problems within this system. If the system is not gas-tight then air can be drawn into the inlet system instead of inert gas. This can weakens the mixture sufficiently to cause misfiring, and manifests itself as a noticeable misfire/hesitation at speed and light throttle, not present when accelerating. If the leak is serious enough it may manifest itself as a hunting/rolling idle, caused by an unmetered leak of air into the inlet.

 

Mine would only fit one way also, so I just assumed they were right. But the tech that replaced them cut them the wrong lengths, is why they only fit one way, (the wrong way). Chances are you don't have the same problem. But a mechanic not paying attention to what he was doing, caused the problems I've had.

 

I had one of my really good friend's dad working on it when he did the whole carb cleaner thing. He is a mechanic for a living and has been for almost 30 years. I thought I should trust him, because I myself dont know that much about mechanics. As far as Bosch plugs, people telling me what you are saying now is exactly why I changed them. I definitely have alot of stuff to do as far as this list, but I will get back to you with all the info later on today.
Right now, the truck is off to get a new set of wheels put on so I am not going to have it for a little bit. Ill be sure to get some pictures up as well, so you can see how I have everything.

 

Okay jbrew, I am back with a little bit of info. I did the DPFE test like you said and it ran 5.05volts (VREF) and .02volts-.05volts on the (SIG RETURN). The results running were near the same. I manually applied vacuum to the EGR valve while idling and it had no effect on the engine. I could hear the diaphragm moving up and down. Does this mean I need to give the throttle body a really good clean-out?

Im going to tear it all down on saturday and do the upper and lower gaskets, and I will also clean out the throttle body really well also. I did not have time to do it today, and my wheels were late. Hopefully I can get this all figured out. Thanks a ton for all the help so far!