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Discussion Starter · #1 ·
Hello all,

Lately my Cougar has been throwing a P0401 code (insufficient EGR flow) along with symptoms like engine shaking at cruising speeds, reduced fuel economy and a quite high 1000rpm idle when warm.

Many posts on the forum have led me to suspect a bad DPFE sensor, so I plugged my computer to the car and drove around for a while to check DPFE voltage values with Forscan.

During this drive, the voltage curve stayed totally flat at .15v, whether at idle or under full throttle acceleration. I'm not quite an expert at reading DPFE values, but I guess the voltage should vary depending on engine load and everything which leads me to think the sensor is definitely bad. Do you guys also think so?
 

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1999 3.0 SilFro
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The EGR only functions at PART-throttle, never at idle or at WOT.

If your DPFE is tested good, then the reason for the insufficient flow is due to build-up in the passages between the EGR valve and the intake manifold. Begin by removing the throttle body, as most of the buildup occurs behind the gasket there. Clean out the grooves behind the mating surface, and that might solve the problem. You can also use a wire or pipe cleaner to clean out the path inside the manifold, between the EGR valve and those channels, but it's rather inaccessible.
 

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Discussion Starter · #3 ·
Thanks, you just taught me something. In fact to be more precise, the .15v voltage didn't change at part throttle either, the curve just stayed totally flat while driving.

I also forgot to mention mine is the 2.0l engine. I removed the throttle body to give it a slight clean and replace the gasket a few weeks ago, didn't notice any carbon buildup into the intake manifold
 

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There's a great troubleshooting guide here
 

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Discussion Starter · #5 ·
There's a great troubleshooting guide here
Thanks for this very complete guide which I'll definitely keep on my hard drive. Correct me if I'm wrong, but the guide says with the plastic housing DPFE, which I guess is the one mounted on my car, a 1v value should appear when no pressure is detected and increase while driving? If that's right, I guess my DPFE is fried.
 

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As you follow the troubleshooting guide, you can use intake manifold vacuum in place of a handheld vacuum pump. The system should be pretty easy to troubleshoot.
 

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Don't forget to make sure the tube leading to the exhaust manifold from the egr valve isn't clogged either.
 
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