• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

Question regarding vacuum at PCV port on intake manifold--4.0 SOHC


IronHorseDriver

New Member
Joined
Sep 28, 2015
Messages
2
Reaction score
0
Points
0
Vehicle Year
2003
Make / Model
Ford
Transmission
Automatic
Hey Folks,

The Vehicle: 2003 Ford Ranger Edge, 4.0 SOHC

The Question: There is a port on the forward right side (passenger side) of the intake plenum (manifold) where the PCV elbow and hose is attached (the PCV valve is on the rear of the left valve cover). Should I get full engine vacuum (18-20") at this port?

The Background and Analysis
: I rebuilt this engine last year. It ran fine for about 1200 miles (no Check Engine Lights) then suddenly, early on New Year's morning, the lower O ring on one of the injectors failed, causing the injector to drop lower into the port in the head, causing a loss of fuel pressure and fuel spillage at the top where the injector is attached into the fuel rail. The engine shut down. a fair bit of fuel spilled, but I was able to get it started and limp off the expressway into a parking lot. Two days later, I went out to the vehicle, removed the intake plenum to access the fuel rails and injectors, and I replaced all O rings on the injectors. Given my less-than-ideal working environment (a parking lot in 30 degree weather), rather than completely remove the plenum, I kept the PCV hose and the coolant lines that attach to this port attached and just swung the plenum out of the way. While it was up and out of the way, a couple of ounces of oil spilled out of the plenum ports for the #1 and #2 cylinder. When I was finished replacing the O rings, I reinstalled the injectors and rails, reinstalled the plenum, started it up, and got it home. About a day later, the Check Engine Light (CEL) came on, and it showed a P0172 code (Bank 2 system too lean). Then, a couple of days later it showed both P0172 and P0171 (Bank 1 system too lean). The vacuum gauge showed 18" of manifold vacuum.

While in my troubleshooting, I pulled the PCV hose off of the port where it attaches at the manifold. As soon as I pulled it off, I noticed that there seemed to be full vacuum at that port, and the engine died instantly. Hence my question for this forum, since I am not sure if it is supposed to have full vacuum there.

A week later, while the truck was in my garage, I checked the PCV hose and elbows, and as a precaution I replaced both the hoses, the elbows, and the PCV valve. Prior to replacing the hoses and elbows, I removed the intake again to check for loose or missing gaskets, but they seemed to be OK. I reinstalled everything again, but that damned CEL came on again, this time only showing a P0171 code (Bank 1 system too lean). The engine runs fine.

Since the weather is supposed to be relatively warm this weekend, I plan on removing the plenum again, this time completely removing it, so I can check for possible cracks in the plenum. or a gasket that is not seated.

Although the P0171 code can have several causes, I am suspecting a vacuum leak because, when I first ran the engine after rebuild last summer, I had a vacuum tester on it and it read 20". Now it is only reading 18.

The reason I asked the question about the port for the PCV valve is because I am wondering whether there is supposed to be a restrictor in that port (or in the plenum where the port connects) to prevent full engine vacuum from developing in the PCV hose assembly. If there is supposed to be something of that sort, then it is possible that it got knocked out of the way or broken when I pulled the intake while fixing the truck in the parking lot.

Thanks to all for your advice.
 


Rock Auto 5% Discount Code: 70D65189E6D8FF: January 5th, 2022

adsm08

Senior Master Grease Monkey
Supporting Member
Article Contributor
Ford Technician
TRS 20th Anniversary
Joined
Sep 20, 2009
Messages
34,623
Reaction score
3,566
Points
113
Location
Dillsburg PA
Vehicle Year
1987
Make / Model
Ford
Engine Type
4.0 V6
Engine Size
4.0
Transmission
Manual
2WD / 4WD
4WD
Tire Size
31X10.50X15
The hose should have full vacuum all the time. The PVC valve itself is open most of the time, and really only closes at high or full throttle when intake vacuum is low, but can still open up then if crank case pressure gets too high.
 

RonD

Well-Known Member
Joined
Jun 2, 2012
Messages
20,406
Reaction score
4,091
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Yes, full vacuum on any hose connected to intake manifold between throttle plate and valves/head.
But not thru PCV Valve if it was connected to that hose.

PCV valve closes more at high vacuum, idle or deceleration, and then opens more when accelerating.
It is a reverse taper valve, there is a spring and weight(the thing you hear rattling when you shake it) inside, vacuum pulls up the weight against the spring and closes the valve, the higher the vacuum the more the valve closes so the less the flow of air out of the valve cover/crankcase.

All piston engines have blow-by, when the air/fuel mix ignites in a cylinder some of the hot burning gases "blow-by" the piston rings, and into the crankcase, the hot gases vaporizes some of the oil on the piston sides and cylinder walls as it passes by, this is where 99% of the oil vapor in the engine comes from, bearings and valve train spray oil, they don't vaporize it.

In the "good old days" there was just a vent tube on the upper oil pan or lower block pointed down at the ground, the "blow-by" pressure and oil vapor would go out this vent, some of the oil would condense and drip out the vent tube.
Newer engines have less "blow-by" but all engines have it, older rings more "blow-by".

The PCV(positive crankcase ventilation) system was added and the vent tube removed.
At idle "blow-by" is not high, low RPMs and no engine load, so PCV valve closes, it never shuts tight, but closes, as throttle opens vacuum drops and "blow-by" increases, so PCV valve opens more.

PCV system also depends on a semi-closed system, PCV system does have a vent hose, opposite valve cover of PCV Valve on a V engine usually, which is hooked to air filter housing or air tube between air filter and throttle plate.
This area has low vacuum when engine is idling and higher vacuum when accelerating, this is called a "ported vacuum", this allow fresh air circulation and balances the air flow.

Because the system is semi-sealed if you were to remove the oil filler cap or PCV valve while engine was running it would create an imbalance, but if PCV Valve was attached to the hose it should have been a smaller vacuum leak, raising RPMs, vs out right stall, may be time for a new PCV Valve.



Both banks with lean code means upper intake vacuum leak, MAF sensor air tube leak(ported vacuum), MAF sensor itself, or Low Fuel Pressure.

Both O2s failing at the same time is too much of a long shot.

Lower intake leak would effect one bank.

Exhaust manifold leak will also cause lean code, but only on that 1 bank.

Computer doesn't/can't measure fuel pressure, 1998 and up Rangers got Returnless fuel system and 65psi fuel pressure, earlier Rangers had 35psi.
If fuel pressure drops down to say 40psi engine will still run OK but computer will have to open the fuel injectors longer.
The "open time"(pulse width) of the fuel injectors is what sets Lean or Rich codes.

Computer calculates 14:1 air:fuel mix based on MAF sensor data, this is 0 fuel trim(STFT), computer opens injectors(based on 65psi) to get that amount of fuel added, that mixture is then burned in the engine and the computer gets Oxygen Levels in the exhaust from O2 sensors.
Too much oxygen is Lean, too little Rich.
If lean, computer opens injectors a little longer, +1 fuel trim, if Rich it closes injectors sooner, -1
Engines normally run from -5 to +8 fuel trims, and it is constantly changing.
If fuel trim(open time) gets up to +20 then computer sets Lean code for that bank.
-20 would be Rich code.
Engine is never actually running Lean, computer is adding the needed fuel, the CEL and the code is to let driver know the math the computer is doing isn't adding up.
 
Last edited:

enjr44

Active Member
U.S. Military - Veteran
Joined
Mar 24, 2013
Messages
1,142
Reaction score
9
Points
38
Age
77
Location
Renton, WA
Vehicle Year
02 2X4; 08 FX4
Make / Model
Ford
Engine Size
4.0 SOHC
Transmission
Automatic
02 4.0, had left bank lean code. Couldn't fix it. Finally took it to Ford, they said it was bad PCV valve elbow. Said, should of had lean on both banks, could not explain why not.

So .....
 


Top