P0401 Insufficient EGR Flow

[ConfederateTyrant]

My 95 Grand Marquis has had this error code, P0401, for the last 6 years and I'm wondering if anyone has had this error and fixed it themselves. I found two solutions, replace the sensors or remove the elbow that attaches the throttle body to the intake and clean the EGR ports which tend to clog with carbon.

I attempted to remove the throttle body elbow, but due to space issues I could not pull it off to clean it, also I didn't have the correct gasket. The EGR valve itself is not faulty, I believe that the ports are clogged, and a friend believes the sensors are faulty. There is a website that I found which showed the ports and I see where they are located.

I was thinking of using some Amsoil Power Foam to clean it, by spraying it down the throttle body and letting it soak around the port openings. Perhaps that would help dissolve enough carbon, if they are clogged, to get a constant flow going and turn off the light.

Anyone got any better suggestions, or better instructions?

 

[Matt_S]

6 years?

A simple soak won't be enough. You have to get it off far enough to manually scrape and brush the carbon deposits. Soaking with a cleaner will help, but it won't do the whole trick. You might try searching for wavinwayne's posting about cleaning up the EGR passages in his Expedition. He posted some pretty good pictures that will probably be helpful.

 

[punisher]

Easy to test, apply vac to the EGR valve (at least 5" worth) so it opens. If it stalls the engine at idle or causes it to run really rough, then chances are your EGR ports are clean and you likely have a PFE/DPFE problem. Verify your vac lines from the EVP and manifold vac aren't broken, those plastic lines can and do break.

The dealer has the base gasket, they do often separate when you remove the intake elbow, it (gasket) only fits one way so pay attention. A small screwdriver works to clean the 3 ports and main channel in the manifold. Using any kind of cleaner to soak the deposits is fruitless, they are soft and come out easily. Use some compressed air to blow the excess carbon out and reassemble. Bet you wish you had a 8mm magnetic socket when this is over with.

 

[ConfederateTyrant]

Yes yes, go ahead and laugh (I've been laughing every time the tape falls off and someone goes "hey that says 'Check Engine'"...haha).

I saw wavinwayne's pictures, the setup is similar, but he has a lot more room to work with than I have. His EGR ports are on the piece which holds the throttle body, where as mine are on the mounting location on the intake manifold. Now the code went off by itself a few times, so maybe it's not really clogged up all that bad and a soaking may help out enough, or could be the sensor.

I managed to get all of the bolts loose and could get the elbow to move, but so much crab happens to be located back there, which prevented me from lifting it out of it's space. I'll give it another shot along with the soak.

Thanks Punisher, I already wish I had a lot of magnetic tools, that also happens to be one of them.

 

[m2200b]

Test for DPFE function first with punishers test.

 

[ConfederateTyrant]

I found a website, http://autoclinic.net/article/ford/marquis_p0401.htm, but it's now asking for a login. It shows some great pictures.

To test for DPFE function, I do that by using a voltmeter and measure the change when using a vacuum to pull the EGR valve open? That is what was done on the website and the DPFE sensor did not change voltage when the EGR was pulled completely open, which concluded that the ports were clogged.

I'll do this one weekend when I have nowhere to be and have plenty of time to do it. Thanks for all the input.

Punisher, does the dealer sell this gasket by itself or can I only get it in a intake manifold gasket kit?

 

[wavinwayne]

O'Reilly Auto Parts is where I got my gaskets when I did the Expedition's EGR port cleaning. I had to get 2, & they were about $3 each.

 

[punisher]

Dealer sells them (gaskets) by themselves, might be available aftermarket, but I do not know.

I find it easier to remove the EVR assembly from the bracket at the rear of the elbow and take the bolts (8 or 10mm head) from the PFE bracket and leave the bracket and PFE there while you remove the elbow.

Seriously, don't even worry about testing the PFE/DPFE. Just apply vac to the valve and if it still idles good, clogged ports are the culprit. I usually don't recommend not testing something, but a PFE/DPFE will give you an out of range code when it goes bad. The black/grey plastic single inlet PFEs are reliable as **** and don't usually cause problems. An insufficient EGR flow code on that particular 4.6 is 99.5% plugged ports.

EDIT: In addition, it can be a pain to test PFE/DPFEs because they have different "null" voltages and different scales depending on calibration. There are 3 different plastic PFE sensors and at least two different metal DPFE sensors in the mix.

 

[Ramblin Fever]

Same thing here, mine has been going on/off since October - same exact code.

I'm gonna clean the MAF next, after that I give up.

I've cleaned the EGR valve, replaced all O2's, and it goes on/off every 3-4 days at random.

Truck runs fine, am not too worried about just letting it go.

 

[ConfederateTyrant]

The gasket I need is available in an intake manifold kit from Advance Auto, O'Reilly, and Auto Zone, but I'll contact the Ford dealer about it to see.

Punisher, I am following a good bit of your instructions, just want to clear up some things. The EVR is the sensor and bracket assembly that is attached by a 10mm or 8mm (can't remember but I've removed it several times) bolt on the top rear of the elbow? What would the DPFE sensor look like and where would it be located? I've probably removed it once or twice before.

I agree on your statistics of these Fords, everyone whom I spoke with has the same issue, even my previous mechanic told us not to worry with it, since he had a car that had the same code for over 10 years and no issues. However, his mechanics were prone to leaving stuff disconnected, and they did some work around the EGR area, it's noticeable with a mess of wires and crap back there, which should be neat. I'll never take it to his shop again.

My biggest problem with removing it were the two vacuum connections on the right side (driver's side) of the elbow, as they were very stubborn at budging.

 

[punisher]

The EVR is the vac regulator, it has two plastic vac lines and a single connector running to it. It is on the pass side of the bracket to the rear of the elbow. I pull it out (1 nut and rotate it to disengage the tab holding it to the bracket) to get to the bolt underneith it holding the bracket to the elbow. Removing the actual PFE sensor, especially the plastic one, is a deceptive PITA, hence leaving it there along with the bracket. The actual PFE sensor is black/black grey, or grey plastic square mounted to the middle of the bracket, 1 sensor line and 1 electrical connector running to it. Some emission specs had the DPFE sensor which is a metal box with 1 connector and 2 sensor lines running to it, same location.

http://www.tomco-inc.com/Tech_Tips/ttt33.pdf

 

[ConfederateTyrant]

Punisher, you have any idea what that gasket would be called at the dealer? I looked on the local Ford dealer's website, Allan Vigil, and I found a "manifold gasket" for $8. There was no other intake manifold gasket or gasket similar to that.

 

[punisher]

I delayed in answering because I thought I had an extra gasket inside the plastic package with the part number on it, I went through my toolbox and couldn't find it. I think I used it a couple years back on my own Grand Marq. So no info there.

I think it is a "plenum gasket" or an upper intake gasket. I just tell the parts guy it is the gasket from the lower manifold to the 90 degree throttle body plenum, then we look at their parts diagram and find it.

 

[ConfederateTyrant]

Punisher, thanks for that info, I have no problem with your delay. I believe it is the upper intake gasket, Advance Auto, Auto Zone, and Rock Auto do not have pictures unless you view the intake kit. I'll tackle this job sometime soon, any idea of what the proper torque is for those 4 bolts that connect the elbow? I don't have a torque wrench but I've leared how to guage up to 30 ft. lbs. by hand.

Thanks for all the help.

 

[ConfederateTyrant]

Punisher, I wanted to say that I found the part number, Fel-Pro MS94800. The Fel-Pro website had a picture up and it looks just like the mounting area. That is also called the Upper Intake gasket, so you were right on with that.

 

[Mud]

Punisher has good advice - in most cases with that code, if it's not due to clogged EGR port passages, it's the DPFE sensor. I don't think that the EGR valve fails that often on the 4.6's.

Soaking with the foam will not do much - you really do need to get in there and clean it all up as described. Be sure - first thing - to put a rag down into the intake so that debris will stay out of the engine. When I did this on my 95 CV, I used a shop vac to suck up any carbon bits. Note - not being a wiseguy, but be SURE that you remove that rag too! While I had the elbow off I also removed and cleaned the throttle body with CRC TB cleaner - worked very well and did not mess up the coating inside the TB. Also replaced the TB gasket with a new one.

The 2 vacuum hoses (low and high pressure readings) that connect to the EVR are connected to the exhaust. Sometimes the fittings or the hoses are corroded/broken. The EGR is mounted to a pipe that connects to the exhaust as well and it is not uncommon for the pipe to crack. All this stuff can throw the same code. From your description of the shop leaving stuff undone, you would be well off to recheck any sort of vacuum line that is in the area of the EGR and intake elbow.

I have always tightened the 4 bolts to a reasonable amount without any problems and I use a very light coat of anti-seize on the threads of almost any bolt that is reinstalled anywhere.

 

[ConfederateTyrant]

Mud,
I do not hear of the EGR valve being the true cause very often. I heard once that if the DPFE fails, then it will show a high EGR flow code (P0402, I believe) which will lead to engine stalling and crappy performance. Those hoses were not cracked or corroded, as I checked them when I attempted this job back in December, I realized I had the wrong gasket. I'll check the EGR tube, my Hayne's manual shows a good picture of where it connects into the exhaust manifold, so I know where to check. There are no sounds of vacuum loss and no extra air blowing through the back of the engine, just the air thrown from the large cooling fan.

I was thinking of using a vacuum of some kind, shop cleaner or household vacuum cleaner, to remove loose carbon deposits. Throttle Body is plenty clean, I have cleaned it multiple times in the past year, and will clean it again when I clean the EGR passages as well.

I don't believe the shop ever removed the throttle body or upper intake elbow, but the sensors in the back were hanging there instead of being fully bolted in or connected to their mount points.

 

[punisher]

If you look online you can find directions for doing a KOER EEC test. This test also checks EGR operation. Now, with clogged EGR ports it will set a code, but if you suspect the ports are clogged anyways, just hook up a vac gauge to the vac line connected to the EGR valve during the KOER test. The PCM will actuate the EVR near the end of the test and you will see the vac gauge indicate a vacuum (at least 5") at the EGR valve. This proves out your vac lines, EVR and electrical operation of the system. While the engine idles, apply vac to the EGR to see if the engine stumbles, this will eliminate EGR valve and clogged ports as a cause. If all of the mechanical and vac components of the EGR check out, then suspect a PFE/DPFE. The plastic PFE is solid, the metal DPFE was a problem child.

As far as EGR valves, in years of working on '91-95' 4.6s, I only replaced 1 EGR valve, and that was because I broke it by crossthreading a replacement EGR tube I was installing. Rare to see a Ford EGR valve with that kind of longevity.

As far a torque, best I could find was 75-105 inch/lb. I never knew that before. I just got them tight as Mud indicated.

 

[ConfederateTyrant]

Finally! I cleaned out my ports.

I have to say, it wasn't that hard to do, just takes some time and patience, took me about 3-4 hours, but that included time to goof around. I haven't done enough driving to see if the check engine light will stay off, but the EGR ports were full of carbon, it took some Amsoil Power Foam to soften the carbon so I could get most of the gunk off the sides and bottom of the ports. Then after scraping all the gasket material, along with a little more carbon, I took a shop vac and sucked all the crud out and reinstalled everything.

I was going to use a magnetic socket, and a friend of mine was going to let me borrow his, but I tried something else before that. Just got some double-sided sticky tape and put it on the opening of the socket and let the bolt push the rest of it inside. That helped hold the front two plenum bolts in the socket while I lowered them into the hole. I just put the back two bolts in the plenum and carefully lowered it onto the gasket, I used the red straw from the power foam to hold the gasket aligned so I could get one more bolt in there and tightened each bolt to where it did not budge anymore, without stripping it out of course. Sprayed some foam around the mating surfaces to check for leaks, RPMs did not rev up or down so it seemed that the foam was not sucked into the intake.

Punisher, Mud, thanks for all the advice.

 

[punisher]

Glad to hear you got it done sir.