Mercury Grand Marquis Problems

EVP Sensor Failure May Cause Drivability/Fuel Economy Issues on Mercury Grand Marquis

Problem Description and Possible Solution

The EGR valve position (EVP) sensor can fail on this vehicle. The EVP sensor measures the EGR valve position and transmits the date to the engine control computer. If it fails, drivability and fuel economy can suffer, the Check Engine Light will commonly illuminate.

(31 people reported this problem)

Mercury Grand Marquis Vehicles With This Problem

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Average mileage: 85,442 (14,300–150,000)
11 model years affected: 1990, 1991, 1992, 1993, more1994, 1995, 1996, 1997, 2000, 2001, 2005
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Viewing 1-10 of 10 comments
severe bucking when slowly accelerating and also when after shifting into cruise gear at about 50 mph. when cold bucking is not hardly noticeable.. replaced all ignition parts "plugs , wires, distributor , ignition module. Disconnected the EGR valve and lessened the bucking about 50 percent.. replaced the throttle postion sensor still bucking.. just about going nuts.. tranny is not the problem according to 2 experts in the tranny business.. oh yes when I jam the gas pedal to the floor the bucking does not exist.. so I try to drive always flooring the gas.. also the morning startups it turns right over.. the tps did help there also..
Check Engine light come on only after the engine is hot The codes are 172/176 C for continual. Code reference ( Engine running to lean.) Replaced vacuum lines and sensor at charcoal canister. replace Both Oxygen sensors, replaced sensors on EGR. I can drive for hours and the light will not come on. After I stop the engine for a period of time say within 40 minutes the light will come on. If I drive with the light on for 10 to 15 miles, the light then will go off. If I stop the engine and restart the light goes off. Driving me nuts Can someone make a suggestion. as to what it could be. I have been told, that it could be a leak in the intake manifold. That was taken off and put back on with a new gasket, when I had Valve guide seals put on. The person that put them on is a longtime mechanic and have used him for years. The engine does not change, as far a running is concerned ,it still runs smooth. No miss, no Idle problems, no hesitation, nothing changes ,other than the Check engine light coming on. The Dealer had it for 2 days and could not find anything wrong. The Vacuum level stay`s steady, does not move. What am I looking for. It has to be something with the mixture, or air intake. I just don`t know. HELP
EGR pressure sensor (DPFE-4) failed. Replaced with new OEM part and failed again within 6 months.
Replaced the EGR 3x (was not aware of the issue) then replaced the snsor with the 3rd EGR. It worked fine for quite some time then the same error occured (P401 - I think?). Cleaning the PCV valve FINALLY did the trick.
Had the same reading and too much vacuum on fuel sensor. We had to take the gas tank down and a lines above it was broken. $325 at the dealer for the part. Less than $40 for 2 at the junk yard. Problem solved.