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1997 Mountaineer 5.0 P0402

Discussion in 'Stock 1995 - 2001 Explorers' started by Meadowlark Lemon, October 10, 2019.

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  1. Meadowlark Lemon

    Meadowlark Lemon New Member

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    Hi everyone,

    Apologies in advance since I know this topic has been covered numerous times, but none of the other threads point me in quite the right direction.

    Part of the problem is I am not sure if I have an early or late model 5.0, since they apparently changed the EGR system between 1996 and late 1997. I believe this dictates whether I have a DPFE or not.

    Vehicle is a 1997 Mountaineer 5.0, AWD, tow package, 185,000 miles. Burns about 1 qt of oil per 1000 miles, averages about 15 MPG in mixed driving. EGR is located on the back of the upper intake elbow, almost under the cowl.

    Symptoms are as follows:

    Pretty consistent P0402 EGR excessive flow. Sometimes a P0153 - Heated O2 sensor1, bank 2 slow response. Even more rarely P0351 Ignition CoilA, primary/secondary - circuit malfunction. It is not present now and I don't remember exactly what it was.

    Possibly unrelated, but I think the trans shifts a little later than it should (1-2 and 2-3) and an occasional surging feeling cruising at moderate speed (35-45 mph). That could just me being a little too picky.

    Diagnosis steps so far:

    I've removed the vacuum tube from the EGR valve and if I pull vacuum on the tube at idle, the engine will stall out, so the diaphragm appears to be good and the valve is not completely stuck.

    I've driven with the EGR valve disconnected and I get only a P0401 - EGR insufficient flow.

    This leads me to believe the EGR valve is not a the root of this issue, but some sensor that tells the ECU / PCM the valve position is out of range.

    Any ideas?

    Thanks,

    Andrew
     
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  3. 1998Exp

    1998Exp Well-Known Member

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    The older system, without a DPFE uses a potentiometer mounted at the top of the EGR valve to sense the pintle position. It should be easy to tell if there is one or not (also note that the newer, sensor-less EGR doesn't have any electrical connections). If you have the newer system, your P0402 is from a failed DPFE or from a broken/disconnected tube leading to it. If, as I think, your system doesn't have a DPFE, the most likely cause of that code would be a bit of carbon accumulation on the valve seat that's preventing it from closing completely - a common problem. On my, now long gone 1985 LTD, I used to remove the EGR, pull some vacuum to raise the pintle, and scrape the seat clean, which always solved the problem. Good luck!
     
  4. Meadowlark Lemon

    Meadowlark Lemon New Member

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    Thanks for the quick response. The EGR valve definitely has an electrical connection, so it sounds like I've got the older system without the DPFE. Looks like I will be pulling the EGR valve. I've read the easiest way is to remove the intake elbow to get access to the EGR bolts (basically removing the EGR valve on a workbench. Do I need any gaskets for reassembly? Either for the EGR valve or the intake elbow? Is there coolant running through any of these joints?

    Thanks,

    Andrew
     
  5. 410Fortune

    410Fortune Firewood Season Staff Member Moderator

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    Correct, sounds like you have the 96-97.5 GT40 engine not the P heads
    The EGR plumbing is inside your lower and upper intake manifolds.
    NO DPFE on this model
    No coolant in the intake elbow
    There is an EGR gasket, base gasket between the intake and the egr valve
    There is also a gasket at the intake elbow to upper plenum, good time to replace that also if you plan to remove the whole elbow.

    P0402 usually means the diaphram has a hole in it or has worn out
    Use a good replacement, not a cheapo.
     
  6. Meadowlark Lemon

    Meadowlark Lemon New Member

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    Hi guys,

    Thanks again for all the great advice. I am getting ready to pull the EGR and inspect it and there are two different gaskets coming up when I search RockAuto and advance auto - with screen and without. Is there any way to tell which I need before I tear things apart? There is a couple of days lead time so I would rather have the part on hand so I can get things put back together straight away.

    Thanks,

    Andrew
     
  7. 1998Exp

    1998Exp Well-Known Member

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    Hmm, P0402 means excessive fllow. In this case there is no flow measurement, but just a position sensor on top of the DPFE, and this sensor is detecting that the valve is open too far -- or more likely, partially open when it should be closed. A hole in the diaphragm would cause a problem with opening, not closing. Could be a week spring, or as I pointed earlier, carbon deposits on the valve seat preventing it from fully closing.
     
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  8. 410Fortune

    410Fortune Firewood Season Staff Member Moderator

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    P0402

    Exhaust Gas Recirculation Flow Excessive Detected

    indicating the engine exhaust gas recirculation (EGR) valve is flowing too much recirculated exhaust gases when it is commanded to open the flow of gases into the intake manifold.

    • The EGR valve is opening all the way or more than needed due to a blocked vacuum diaphragm in the EGR vacuum back pressure valve.

    • The EGR temperature sensor is registering too much of a temperature change when the EGR valve is opened from a partly blocked exhaust catalyst causing excessive back pressure in the EGR system.

    • The EGR is stuck open due to binding or carbon deposits holding the valve open.

    You are correct the carbon deposits may be holding the valve open

    Remove the valve and inspect it
    Also the plumbing leading up to it, for you the plumbing is inside the intake manifold and throttle body elbow

    What I said:
    A hole in the diaphram would not allow the valve to open and close, I suspected this simply because the last 2-3 EGR valves I replaced on the GT40 intakes had a hole in the diaphram, I have never had carbon holding one open, but that does not mean it does not happen!

    What you said:
    As you suggest blockage would keep the valve open = excessive flow detected. GOOD CALL!!!

    In either case you likely need a new valve
    Before I buy new parts I ALMOST ALWAYS remove and inspect the old ones
    Lets see what you find out!
     
  9. Meadowlark Lemon

    Meadowlark Lemon New Member

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    Well I finally got around to pulling the EGR on my Mountaineer, and it does not look nearly cruddy enough to get stuck open. I took a stab at testing the EVR with and ohm meter and got the same results with the valve all the way open or all the way closed - no continuity across any pair of pins. Too me that points to the EVR being bad - is it serviceable or is it just included in the new EGR? Is my EVR test remotely useful or am I doing it all wrong?

    upload_2019-11-10_9-53-5.png upload_2019-11-10_9-53-21.png
    Thanks,

    Andrew
     
  10. CDW6212R

    CDW6212R Hauls the mail. Elite Explorer

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    Interested, I've got plans that need a decision on which EGR type to use.

    That looks like the older EGR type, with the sensor on the EGR valve. The non-P head 302's have a flat top on the elbow where the EGR goes to the backside. The P head elbows(uses DPFE sensor) are rounded with no flat top surface.

    I want to use the late 97 PCM to run a 347 in my old 92 Lincoln, with a 98 4R70W trans I've got. The EGR type is one detail I'm not sure of still, and the DTRS/range trans sensor.
     
  11. 410Fortune

    410Fortune Firewood Season Staff Member Moderator

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    dtrs range sensor was analog signal 1994-1007 then went digital in 98+
    so use whichever sensor the PCM is expecting to see

    The EGR I have run into before I do not see a way to run the 96-97 style with the 98+ PCM and vise versa... Maybe a tune could change it?
    I have never tried to do this, close as I have come is using a 96-97 PCM just to run a 98+ truck so we could move it around and see that it runs while we troubleshoot other things
     
  12. 96eb96

    96eb96 Well-Known Member

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    Those are junk, I had that style on an 85 302 crown vic. You should vacuum test it first of all to see if the pintle moves off the seat. You may be able to use engine vac. I think there is a solenoid that controls it too, it could be always open and letting in air (I had that issue too with the 85). There is your excessive flow.

    I know I had issues with it at high mileage, both the valve and the sensor. Clean the pintle. You can check the pot on the ohm scale as the position changes. Not sure about pinout but it should be easy to find. You can certainly remove the pot and replace as an assembly. I looked up the part and it is the same as the old crown vic.


    So, either the pintle isn't sealing or the sensor is messed up reporting the wrong position or the solenoid is bad. Best bet could be a scan too to see the egr voltage at idle. Look into forscan.
     
  13. CDW6212R

    CDW6212R Hauls the mail. Elite Explorer

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    As 96eb96 referred to above, I think the DPFE EGR system is better. That was used in the late 97 P head trucks, yes, so that's what I'm aiming to use with a 97.5 PCM. I thought I did have to use the analog DTRS, just make sure the wire pins matched the 98+ VB wiring. This is for my 347 that I plan to use a ported Explorer intake on. The intake elbow will not be used though, I'm not sure yet how to integrate the DPFE type EGR, into the Mustang TB spacer, and which throttle(and CC) cable to use. Minor details, the rest is much harder(whole car wiring).;)o_O
     
  14. 410Fortune

    410Fortune Firewood Season Staff Member Moderator

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    97.5 pcm = analog dtrs
    I like to upgrade older 4r70w as you said, with the 98 solenoid through plug and internal wiring harness

    Basically before 98 the 4r70w had 3 power wires that entered the case to power the solenoids
    In 98 they reduced to one and moved all the wires around????

    PITA to re pin in the truck but can be done through the center floor access panel fun fun
    here is the info
    [​IMG]

    [​IMG]

    I too prefer the dpfe EGR system keep your sampler tubes in good shape, replaced cracked p head external EGR tubes, and use the plastic DPFE .....otherwise never really have any issues

    the 96 style I always had rips in the orange diaphram on the EGR valve itself, otherwise they were good too but the elbow and internal intake passages do gum/carbon up over time.....tick tick tick
     
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