67mustang302

What pcv valve are you guys with h/c/i setups running, the stock one? What about those of you with carb'd setups, stock 85 valve? Does anyone know if there's even a chart or something that lists what valve or how to select one for flow?

mjr46

on my 85, I run the stock one, however I run it to a catch can then to an oil seperator then back to the intake, on my 92 I sold I had a stock 85 that had a provision for one in the oil filler cap, never an issue

67mustang302

Hmmm....ok. I think mine might be bad, figured I'd see if the stock 85 one works well or if something works better.

mjr46

I HAVEN'T had any issues with mine to my knowledge, what is yours doing??

67mustang302

I'm not even sure it's the pcv valve. Did the cam swap recently and while it runs better, I'm still trying to work a wierdo tuning bug out. My pcv valve has been on there for a while and could probably stand to be replaced just as a matter of maintenance. But the next step is to just plug the pcv system and drive without it to see if it's even having any affect.

Fwiw though, the car basically under WOT goes from slightly lean right now under 2k rpm....and right at 2k the afr takes a dump to 11:1, then cleans out after about 2,700rpm and holds at around 12.5:1 from 3k-6.5k. Seems like no amount of timing, jetting, air bleed or emulsion bleed changing or any combo therein will make it go away.

I was thinking that the pcv might be doing something odd and sticking shut suddenly etc, engine loses additional air from the pcv system and causes a spike in booster signal momentarily. It's a long shot, but it's a free check to just plug the pcv line and see if it has any affect.

mjr46

SO ARE you trying to keep it at 11:1?? the initial rich may be a result of the shot the squirters dump in??

67mustang302

If it ran fine at 11:1 I'd leave it be. It still runs a lil rough through the 2k rpm range then cleans out, so it would probably be fine at 11.5:1, and definitely at 12:1. It's the laziness and running rough in that rpm range that's a major issue for me though, 2nd gear at 2,500rpm for autox and road racing, it has to have immediate and clean response.

It's most likely not the pump shot though, cuz if I pull in 4th from a little off idle, it runs a bit lean at first(mech secondary, 4th gear, 1,200rpm haha) and does ok at WOT until it hits 2krpm, long after the pump shot has expired. Then it suddenly drops from a leanish 14:1 down to 11:1 and runs rough, then cleans out at around 3k.

I suppose it's possible the pump shot is too large and the fuel is just puddling on the bottom of the intake, and once engine speed picks up enough to move it out, it gets a raw fuel dump into the cylinders.

petrock

Don't plug the PCV system. Its to relieve crank case pressure. If you plug it up, the pressure has nowhere to go and usually the first thing to crap out are seals and/or gaskets and you'll start to leak.

If the PCV valve is getting stuck closed, then you either have a vacuum leak somewhere in the PCV system or the PCV system is clogged. You should feel noticeable suction at the PCV valve when the engine is idling.