MK3 ABF loss of power: Problem found & possibly solved

Ahhhh... I thought you meant the 240ish BHP verison.

 

Okay was pootering around in the engine bay today and decided to replace the tiewraps on all the vac hoses. Upon removing the PCV valve I decided to give the hose a sook (no comments please) and no vac is created. So I assume that I have just discovered a whopping vac leak - letting unmetered air in downstream of the MAP sensor?

I've never had to deal with or think about how the PCV circuit works. I assume that the vacum generated, on overrun, in the inlet manifold causes a diaphragm (SP?) inside the PCV to move and hence open or close the circuit from the crankcase to the inlet boot?

Answers on a postacrd please as I know bugger all about how the breather system is supposed to work.

So I'm currently hunting around for some screws to plug the ends of the vac hose which will have to be a short term solution.

 

My pcv was broken. I had a short piece of pipe blocked off and not connected because the nipple on it was snapped. i thought it may be to do with emissions a idle or somthing similar because i have read somewhere that the breather should be dissed when checking CO. May be mixing it up with something else though.

 

I think the breather needs to be disconnected so that unburnt hydrocarbons, if present, in the oil/crankcase do not interfere with the idle CO measurement. Alternatively you can take it for a good thrash first which probably has a similar effect.

Well MPG instantly improved as well as the idle which surprised me as I though the idle was spot on to begin with. She feels stronger and now seems to pull well all through where she should pull; it's a bit subjective mind but I'll check by timing later today or tomorrow. Fingers crossed! I can check the plugs too as I have along drive ahead of me during the week - Falkirk to Banff and then home again on the same day.

 

You are probably right. I had the same effect when changing all my vacuum hoses regardless of their condition. Including blocking the PCV one. Felt like a different car.

 

hmmmm my pcv is buggered.. tell me more about this blocking off malarky..

 

get the vac hose off the pcv and bung it.

 

^^ What Matt said. Cut two lengths of short vac hose and screw in an appropriate sized bolt to seal the end of each and then fit them onto the VAC nipple on the PCV and inlet manifold.

 

you wont need one on the pcv. Only the inlet causes problems with unmetered air.

 

True but as the diapraghm is split it the PCV vac nipple will draw in unfiltered air so prob wise to plug it

 

is there a proper way of testing the PCV valve?

what do they do exactly and will not having it connected to the inlet vacuum affect anything else?

 

From what I've read it seems that the PCV is closed on high vacum/low throttle openings so I guess the the low pressure at the inlet manifold tube holds the diaphragm (SP?) closed and as you approach WOT or large throttle openings the pressure differential changes to favour that of the crankcase and the diaphragm opens and allows the crancase to breathe into the inlet system. So in short the vac hose to the inlet manifold functions as a pressure switch to open and close the breather diaphragm dependant on the relavant pressures?

In short if you can flow air through the diaphragm tube then I think it's Donald Ducked.


Still not managed to get any timing done but two up I easily reeled in a Fiesta ST that got the jump on me last nite so it seems my 16V is running a little more healthily.