This has me STUMPED! My rebuilt '90, 302, 0.40 over, roller rockers, 255 Comp Cam, continues to have problems with the PCV valve sticking open after starting up after sitting several hours. I have replaced the PCV with a new EV140 and yet continues to exhibit the same thing.

My only thoughts on this is that the Oil Catch Can I have between the PCV valve and the Plenum is creating somewhat of a Vacuum Resevior so as to not allow the ball in the valve to come to a lower resting place. Has anybody got any other ideas to why this valve would stick open? Do I need to recalibrate the base idle with the PCV valve installed? I did the base idle calibration per Fords specs, but maybe someone has an idea on what to do next....then again maybe I've been the only one to have this problem...

 

I don't understand what you mean by "sticking open". It's supposed to be "open" in that air should be flowing whenever the engine is running. The only time the valve is supposed to close is if the engine would backfire.

 

I understand it's suppose to be open. That's the given here as it helps pull in crankcase gases, blowby and route them into the intake to be re-burned and to prevent pressure in the crankcase from blowing seals. My problem is that when starting up say after several hours, the calibrated amount of air isn't there and it's nearly Wide-Open, thus in turn creating an air leak that the PCM cannot understand nor control. With my Autometer gauge, I watch the HEGO sensor's reaction to the problem. IT's stuck in full RICH. The DTC that pops up from this is of course a Lean condition since we have an unmetered, large air leak. As soon as I remove the PCV valve from the rear of the valve cover and plug the bottom of it with my finger the engine smooths out and the gauge returns to Lean and Rich as the PCM adjusts the air/fuel ratio controling the pulse width to injectors and such.

I should also note that after I remove my finger from the bottom of the PCV valve and re-insert it into the valve cover that engine operates as it's suppose to do. So as I said, it's only after starting up when the motor has had time to cool down. If I shut the truck off right getting it started when it's exhibiting this problem, the PCV valve works as normal and the engine returns to normal.

On another note, I am using emission's hose and not heater or fuel line house. 11/32's is the I.D.

 

First off, are you running a MAF or SD system? Since you referred to metered air, I'm assuming you're running a MAF-based setup. The gases coming through the PCV valve into the intake should have already been metered, as the fresh air side of the PCV system should draw from the intake tube AFTER the MAF. Is this the case on your truck, or are you drawing fresh air from someplace else?

 

Actually I'm running an SD setup, but the metered amount allowed through the PCV valve when it's completely open @ idle, is greater than the PCM can control for this motor given it's fuel trim is pre-programmed and only computes for strict amount of variables...

EDIT: That didn't make complete logic to me, I'll try again. It's not suppose to be completely stuck open at idle, but it seems to stick Wide open @ idle and in turn the PCM sees this as an unmetered air leak and throws a DTC , # 41, Lean condition, but I see it as a Rich condition on my autometer gauge since the PCM is at the limit with Fuel trim to compensate for the unmetered amount of air.

I have the emissions setup exact with the hose connected to the nipple on the oil filler neck and the air filter box.

 

The air going through the PCV is not in anyway metered then. It sounds like you're operating on the fringe of the capability of the SD system with your extra displacement and aftermarket cam. The air coming through the PCV system is putting it beyond what the stock tune can correct for.

 

The valve should be wide open at idle, as you should be pulling 16+ inHg of vacuum against it.

Honestly, the easiest solution would be to run both valvecovers to a vented catchcan and delete the PCV system. The other options would be to convert to a MAF-based system, or tune your SD-based system.

 

Darn...I didn't think that the PCV valve should be @ wide open when it was @ idle. I only thought it should open a certain amount based on vaccum from the manifold. Well I feel even more dumb than before. I thought I had read that somewhere..

I went with the largest cam I go with and that was it with the SD system. Anything other than that would require going to a MAF setup.

Well, I guess I'm left to explore other other possibilites mentioned here. Thanks Gentlemen for the info and the help!

 

The PCV is sized to allow a certain amount of air thru based on engine size. However, it has no "metering" capability to where it varies the amount. It's either ON or OFF. Even if it could meter, then the max air flow would be at idle when vacuum is the highest.

 

I'm not sure why it is sticking open, but it should restrict airflow when manifold vacuum is at its highest.

 

This is incorrect. At high idle, the pintle in the valve is sucked up to the top of the valve into a position which restricts airflow. Maximum flow occurs at lower intake manifold levels.

Now, if the pintle ISN'T moving up and restricting airflow, the resultant higher-than-normal airflow through the valve will definitely affect the engine operation in a negative manner. And this sounds like what is happening.

I ran into this way back when, while troubleshooting a friend's car (which they had taken to several shops and nobody could figure it out) - the guts had fallen out of the PCV valve into the valve cover! It would barely run at idle due to the lean mixture.

 

This is not true, the PCV valve is by definition a metering valve:

How does a PCV valve work exactly? - Corvette Forum : DigitalCorvettes.com Corvette Forums

Start at post #7

 

If that is the case, then it sounds like the OP's cam isn't generating enough vacuum at startup (IAC at high duty cycle, high idle rpm, lower manifold vacuum than at hot idle) to pull the pintle up high enough into the body of the valve to restrict flow.

I stick by the solutions I presented earlier. I would either run both valvecovers to a vented catchcan, or swap to a MAF-based system. Routing both valvecovers to a catchcan would remove the source of additional air in the intake tract. A MAF-based system would meter the additional air in the intake tract and trim fuel accordingly.

 

I agree that this could be the source of the problem, I wonder if the OP was to remove the PCV valve from its grommet (with vacuum hose still connected and engine running) and manually push the pintle up, if it would make any difference (not that this would be a permanent solution, but it would test this theory at least).

I also agree with you that a different crankcase venting system may be the solution.

 

I had an issue like this years ago on a stang I built. Back then it was common to take a holley #111 jet and install it in the top of the pcv (only works on metal pcv's) push it in there with some jb weld or rtv to hold it and drill out the main jet as needed to set the right flow. All it does is acts as a restrictor.