Question-------------------------
Followup To Thank you Clay, I followed your advice and they diagnosed my problem as an EGR valve problem. The tech at Auto Zone said it probably was carbon in the EGR tubes or a vacuum leak. We recently had air conditioner work done and they said that a vacuum line might have been left off or lose. They advised that I try these things first before replacing the EGR valve. My problem now is they could not seem to tell me exactly where this valve was on my engine. They thought it may be on the back of the engine. I would like to know exactly where it is located and how to go about cleaning the EGR valve tubes? I purchased a Haynes repair book on Ford Explorers & Mountaineers,but it does not show the location on a 5.0 liter engine. Any advice that you could give will be greatly appreciated.
Thank you, Donnie
Question -
1997 Mercury Mountaineer V-8 engine. My Check Engine light stays on constantly. If you unhook the battery it will stay off for about 20 miles then back on again. I have replaced both of the oxygen sensors and the gas cap. It runs fine and all the gauges are registering normal readings. What would you advise my next step to be to help correct this problem.
Answer -
Donnie, the check engine light means that the PCM has detected something that is out-of-range, and doesn't necessarily mean that a sensor is bad. Dont' replace anymore parts until you know what code is stored!
If you don't have a scan tool, take it to a shop that does and allow them to perform a diagnosis. The code will tell you which system to investigate, and then you'll have a chance at finding the correct cause of the problem.
Now, don't let them replace parts just based on the code. For example, if a Code P0401 is stored, that means the DPFE reading has been less than expected at some time.... it doesn't necessarily mean the DPFE sensor is bad. It could be a cracked DPFE hose, a plugged EGR port, a faulty EGR valve, or a burnt wire to the DPFE sensor or EVR solenoid. A good shop will have the equipment to make appropriate tests and know which parts are needed to fix the concern. Ask them what was the bad reading the sensor was giving, and what would have been an acceptable reading - they should know!
Hope this helps....
Clay
AnswerGreat, Donnie, you're on the right track! The helpful guys at AutoZone gave you the code, so you now know which system to investigate.
Chances are the DPFE sensor is bad - it is fairly common. But before replacing it, I would want to verify EGR operation and see what the sensor is reading.
First, locate the EGR valve. I think it is near the back of the intake manifold, remotely connected via a flex-tube to the exhaust from the r/side exhaust manifold. The EGR valve might be brass colored or painted black, and it has a single vacuum hose connected at the top.
Unplug the vacuum hose and apply about 15" vacuum to the top of the valve, with the engine at idle - it should make the engine run very rough, perhaps even stall. If it does, the EGR ports are clean enough to allow EGR when the valve opens, and valve is opening properly.
Then, remove the vacuum hose and the engine should idle smoothly again - the EGR is closing OK, so the valve is OK.
You will need a scan tool or a voltmeter to test the DPFE sensor readings. It is a silver or black box that has two hoses and one electrical plug connected to it, and it on the side or back of the intake manifold. The electrical connector has three wires, and I can't tell you which is which... one is 5 volt reference voltage from the PCM, one is the ground side through the PCM, and the other is the signal voltage that is returned to the PCM.
Unplug the connector and identify which has 5 volts with the key on.. now you know which wire you are not going to be testing!
Plug it back in and test from ground to one of the other wires... one of them should read about 1 volt with the key on, and the other should read about 4 volts.
The 1 volt wire is your signal voltage. Now, crank the engine and see if that 1 volt will increase to about 3 volts or more as you apply vacuum to the EGR valve - it should. A faulty DPFE may read '0' or may read 4 volts all the time... either way will set a code.
Now, all this testing is much easier with a Ford scan tool that the dealer has... if you pay them for an hour's diagnosis, they should be able to tell you the results and advise you if there are other problems as well.
Good luck! The voltmeter and vacuum pump method will work, but is a little slower and cumbersome.
Clay
