Jump to content

Recommended Posts

Help Please :(

I'm getting some sort of knocking noise coming from around the airbox. I have traced the fault to an electrical cylindar thing that is attached to the box just bellow the MAF meter. it also has two small pipes one goes to the air inlet bit and the other pipe goes somewhere behind the air box. I can feel this pulsesating when i put my hand around it.

Is this normal :(( and what is it

Link to post
Share on other sites

I've found out what it is and its meant to do it. It's a pulse valve thingy controlled by the ECU and it starts to pulse when the engine warms up, it's venting fumes back into the air intake.

I did search on it here and found a post about it in May/04. It was explained a lot better by Keywhire i think thats the guy. I'll try and dig it out again

Link to post
Share on other sites

Here you go

quote1117099078=kevhaywire]

Well done Snyper. You explained that better than I did. That's precisely what I was trying to say!

CC freq valve. OK, now this is on OBD1 cars, not 100% sure what OBD2 cars do but what it does is vent petrol fumes into the throttle body. It's called a frequency valve because it responds to pulse waves from the ECU. During the 1st 2 minutes of a cold start, the valve is closed and the O2 sensor is going through it's preheat cycle. At this point the ECU is ignoring the O2 sensor and just blasting a rich mixture in. Also worthy of note, at wide open throttle, the 02 sensor is again ignored. All clever stuff really.....

Anyway, back to that valve....after 2 mins, you will feel the freq valve pulsing slowly as it vents vapours from the CC into the inlet. As the revs increase, so does the frequency of pulsing in the valve, and thus more vapours are allowed into the engine.

Link to post
Share on other sites
  • 3 years later...
×
×
  • Create New...