QuestionI have a 2000 Ford Expedition and there is a knock in the engine. We replaced the EGR valve and some vacuum hose. The code reader stated that there was trouble in the emission control. If I'm remembering correctly, it was a P401. Also, I can get the knock to go away by retarding the timing, by manually sucking on the vacuum hose. Could you please enlighten me as to what this could be?
Thank you so much.
AnswerI have yet to see a code P0401 caused by the egr valve. 99% of the time this code occurs is due to a faulty EGR sensor, or DPFE.
You didn't specify if the engine knock is a noise all the time, on cold startup, or on accel, or what engine you have. Some of the 5.4 engines had a piston slap that sounds like a knock on cold startups, as far as I know Ford says this is not a problem. and the noise usually decreases as the engine warms up. If this is the noise you have make sure the oil you use is 5/20 and good quality.
Sometimes an inoperative egr can cause a knock or ping on acceleration, this could be due to the sensor reading incorrectly and the PCM not regulating the egr valve normally.
As far as code readers, those are not always accurate, and there is more to the code than just reading the code. Each code is pretty specific as to what the problem is, knowing how to interpret and diagnose a code is what makes the difference between buying unneeded parts or fixing the problem right the first time.
