Engine 1993 doesnt want to idle

I’ll try to explain how it works and differences in hose routing between natural aspiration(non boosted) and boosted applications.

The Pcv valve is a check valve that gets plugged into a hole in the rear center of the lower intake. A hose should be connected to it that goes to the upper intake where it gets its vacuum source. The vacuum from the upper intake pulls crankcase fumes back into the engine to be burned during the normal combustion cycle. This part of the pcv system can be the same for either application. The reason is, the pcv valve , being a check valve should only allow air to flow in one direction which is from the crankcase and to the intake. When the intake is under pressure from boost, the pcv valve blocks air movement from the intake and prevents the boost pressure from getting into the crankcase. So you don’t need to change that part of the pcv system on a boosted application. It just stays the same as stock.

Under vacuum, the air being sucked out of the crankcase through the pcv valve needs to be replaced by air coming into the crankcase at some other location. In stock form on these typical 5.0 Foxbody engines, there’s a hose/pipe that goes from the passenger side valve cover to the side of the throttle body. The drivers side valve cover is sealed and has no vent. This way, all air sucked out of the back of the lower intake through the pcv valve gets replaced by air coming from the intake track prior to the throttle blade but after the MAF. This setup is important because it draws clean air through the filter and also draws this air through the MAF which includes that air in the measurement sent to the computer for A/F adjustment made by the computer. So for non boosted application , that’s it.

On a boosted application , there’s a bit of a problem with this crankcase “supply” hose that is normally connected to the throttle body. Under boost, the entire throttle body internal is under pressure. If the supply hose for the pcv is connected here, boost pressure will be shot down into the crankcase. In addition to loosing boost pressure and less performance, it can also blow out oil seals in the engine.

So, on boosted applications we need to find an air source for the pcv system that is not subjected to boost, but is still filtered and entered through the MAF.

There may be other examples and I hope others can chime in with them. However, on my setup I just followed the lead in the Vortech inst. They provide an inline filter for the inlet hose and a fitting to connect it to the air box upstream of the MAF.

Here is the connection at the passenger valve cover



Here is the inline air filter




Here is the connection at the air box upstream of the maf allowing pcv air to be metered an included in data sent to computer

Oh, one more pic. Here is the stock connection point for pcv air supply hose at the throttle body. I pulled the angle pipe out and plugged it with a bolt and sealer on the threads.

John Dirks Jr said:

Oh, one more pic. Here is the stock connection point for pcv air supply hose at the throttle body. I pulled the angle pipe out and plugged it with a bolt and sealer on the threads.

Click to expand...

Excellent explanation. What is the best way to replace the pcv and filter from behind the intake?

On a stock setup there is no pcv filter to change. The stock setup uses air pulled through the regular air intake filter.

To replace the pcv valve, you pull it and the hose it’s connected to out from the back of the intake. Remove the valve from the hose, put a new one in the end of the hose and insert it back in to the intake.

Sometimes the pcv valve is just gummed up with crankcase sludge. Sometimes a you can clean it by spraying carb cleaner or similar into it. If it’s clean and functional, you should be able to blow through in one direction, but not the other.

Check the hose too. If it’s hard, brittle or cracked, toss it and replace with a new one.