2.3L ('83-'97) Vacuum where it shouldn't be.

[Harp 1]

A little back story before getting to issue. About 3,000 miles ago I had to have motor overhauled, cylinders honed, new rings, new rod and main bearings, due to low compression on number 3 cylinder and truck running like crap. After reinstalling motor still had same issue with how it was running, extremely rough idle, missing in low rpms, but after about 100 miles it started to smooth out some. Now it is back to rough idle and missing at lower rpm but runs smooth once above 25-30 MPH. Now to the current issue, while pulling codes yesterday we got a cylinder imbalance error so i was thinking possible low compression again, maybe rings didn't seat so i pulled oil filler cap to see if I had any blowby and I didn't, but engine smoothed out a little bit. I pulled hose from valve cover to throttle body off of valve cover (picture 1) and you could hear air "sucking", I have vacuum sucking back into the valve cover. I also noticed something that sounded like wire loom may be vibrating against something, so I got to moving wire loom around and brushed against the hose from the PCV valve to intake manifold and the sound I heard was the ball in the PCV valve. I pulled the valve and it does move when shaking it but motor runs smoother with the valve not in the rubber grommet (Picture 3). According to all the valves I have checked at parts stores, that is not the correct valve as they show one with connections for vacuum lines and this one does not have them (picture 2). I have no stray vacuum lines anywhere in the engine compartment so there is no way I can even start to check with moving lines. The codes that were pulled are 116, 327 (egr is unhooked at this time waiting in new style connector), 411 and 538. Is there any chance that I may have a PCM issue with the age of the truck and what would cause vacuum at the valve cover? I did an edit and posted a picture, number 4, of what the parts stores show as the correct PCV valve.

 

[franklin2]

That is what the PCV valve does, it is a controlled vacuum leak, it puts a vacuum on the valve cover/interior of the engine to pull bad stuff out of the interior of the engine. It keeps the oil cleaner as it pulls out fuel, water, and other blowby gases out of the engine.

But there are different PCV valves with different flow rates. You need to make sure your PCV valve is the correct one for your 4 cyl engine.

 

[Harp 1]

That is what the PCV valve does, it is a controlled vacuum leak, it puts a vacuum on the valve cover/interior of the engine to pull bad stuff out of the interior of the engine. It keeps the oil cleaner as it pulls out fuel, water, and other blowby gases out of the engine.

But there are different PCV valves with different flow rates. You need to make sure your PCV valve is the correct one for your 4 cyl engine.

I have vacuum sucking back INTO the valve cover, it should be sucking OUT of the valve cover back in the throttle body

 

[Mechrick]

it should be sucking OUT of the valve cover back in the throttle body

No.

At idle, if you unplug the hose going to the top of the valve cover and put a vacuum gauge there (on the valve cover) the vacuum should slowly increase as the PCV valve pulls the crankcase into a vacuum. Engines that have blowby can have positive pressure there, even at idle, but it's supposed to be negative pressure.

The hose nipple is the fresh air intake for the crankcase and should be filtered air from between the throttle plate and air filter. The PCV valve is the polluted air out of the crankcase to the vacuum side of the throttle plate.

PCV valves can stick, and as someone mentioned, have different flow rates by application.

 

[Harp 1]

No.

At idle, if you unplug the hose going to the top of the valve cover and put a vacuum gauge there (on the valve cover) the vacuum should slowly increase as the PCV valve pulls the crankcase into a vacuum. Engines that have blowby can have positive pressure there, even at idle, but it's supposed to be negative pressure.

The hose nipple is the fresh air intake for the crankcase and should be filtered air from between the throttle plate and air filter. The PCV valve is the polluted air out of the crankcase to the vacuum side of the throttle plate.

PCV valves can stick, and as someone mentioned, have different flow rates by application.

Mechrick, Thank you. That is a new one on me but then again I am not much on all the fangled engine systems. Give me back my old points and condenser, distributor, coil, and carb motors. As far as the PCV valve goes you can see in the pics that what they show and what I have are different but same part number. The one they show has the 2 hose ports on it and mine doesn't.

 

[tomw]

If you pull the oil filler cap on a 2.3, engine at idle, or pull the hose leading from the filtered air inlet duct heading to the throttle, and cover the inlet, you should develop a slight vacuum after a short while. The ducting supplies filtered air to the inlet to the crankcase.
The air flows through the crankcase, down to a fitting on the side of the block underneath the intake manifold. It looks like a sheet metal oval with two halves that are attached. It has a largeish pipe going into the side of the block(never took one off) and a smaller, about 5/8 or 3/4" outlet that has what looks like heater hose on it. The heater hose heads forward along the side of the block, and has a PCV valve stuffed into its end. The other end of the PCV is stuffed into another length of heater hose, and leads up to the underside of the large upper manifold that is bolted to the regular horizontal manifold. An 85 has the tube connected on the underside of the upper manifold where it is horizontal. So, the PCV is kind of hidden in-line of the tube from the oil separator(oval thing on the side of the block) to the intake. The intake will have vacuum, and will pull on the PCV valve, which has a weak spring and a ball bearing that close the valve as needed when vacuum is low.
As the engine runs, some air will flow from the air cleaner assembly, through the oil filler or other fitting on the cam cover, through the crankcase, through the separator, through the heater hose, the PCV and back up the the intake manifold.
If it quits working, you likely will have oil coating and rustproofing your engine bay. Most have leaking cam cover gaskets, and this will add pressure and increase that leakage.
I found after owning for 20+ years that a rubber gasket is THE BEST, and the rubber/cork are CR*P, the cork are even worse. I tried them all. So now I do not have oil leaking from the cam cover any more. Yippee.
tom