Originally posted by Bradness:
Roger: When you refer to "..engine wear, crud buildup...), " is it possible you're referring to valves, valve seats and/or seals, rings or other mechanical wear items? I ask as my car has relatively high mileage (143,000 miles). I am planning an engine transplant next summer so maybe I should just get a set of earplugs for now!

Thanks again.



Yes, of course.

Wear and crud affecting compression and intake runner air velocity directly impact intake air reversion.


When a Duratec engine is started and is high idling at 1000 rpm., the cylinders are firing at a rate of 3 times 1000 per minute. This equals 50 reversion pulses per second, or 50 Hz. If the intake system and control system start to resonate, you get a very loud 50 Hz. The exact frequency of the combined systems will vary some. A few people have even reported moosing at harmonic frequencies (multiples of the original at higher RPM's).

Breaking the cycle requires detuning the intake tract and/or feedback mechanism (hence the different resonators and IAC), brute force supression of amplitude (the TH fix), or a homebrewed solution affecting amplitude or resonance or hysteresis.

Cleaning the intake or clearing plugged CAT's would come under the heading of supressing amplitude. Changing the distance between the IAC and MAF, or getting a new and more responsive MAF affects hysteresis. The size and length of the combined intake ducting, as well as the shape and interior surface affects acoustic resonance. Changing the response of the ECU or IAC is out of most of our hands.

"Those who cannot remember the past are condemned to repeat it" -George Santayana