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Mike_Schriber's avatar
Mike_Schriber
Explorer
Jun 11, 2015

Ford V10 PCV system issue

I have something strange going on with the PCV system on the 6.8L V10 in my F-53 chassis motorhome.

On my rig, the right valve cover is connected to the intake tract just forward of the throttle body (which would be the "intake" side of the PCV system) and the left valve cover (with integrated PCV valve) is connected to the intake manifold (the "output" side of the PCV system).

I'm seeing oily residue inside the intake tract coming from the right side valve cover. Since this is the fresh air intake side of the PCV system I'm kinda stumped. The manifold side of the PCV system is totally clean.

I started poking around because I'll occasionally get pinging under heavy load at or near full throttle. It happens randomly and goes away if I let up on the throttle. If I immediately go back to WOT the pinging doesn't return.

Looking at the reside I'm wondering of oil coming into the engine with the air might be the cause. Either way, I'm trying to figure out why I'm seeing oil on the non-vacuum side of the PCV system. I'm pretty tempted at this point to remove the hose, cap the intake tract side and put a breather on the valve cover to see what happens.

Any thoughts?

Thanks!
  • Teeton's avatar
    Teeton
    Explorer
    Jun 12, 2015
    There's a reason why the fresh air hose is hooked after the Mass air flow sensor. Spark knock and pinging is the same thing. I just call it spark knock. I can sit and type how pinping develops and how the ecm with other parts works to reduce it. I'm at work right now and have to go. I'm job, I'm auto emissions and fuel service. Well only for the last 32 years. :)
  • Mike_Schriber's avatar
    Mike_Schriber
    Explorer
    Jun 12, 2015
    Correct. Under WOT the amount of vacuum generated is at it's lowest (which is why there's an accumulator). The "input" side of the system should never be under vacuum though unless there's a suction effect from air moving past the connection inside the intake tract. Even then, it shouldn't be enough to pull oil up into the intact tract. I do not believe that it's normal (but it might have nothing to do with the pinging).

    Removing the hose from the intake tract and capping the opening shouldn't effect the fuel/air ratio calculation since the volume involved is very small. It's a closed system though so you never know for sure what will happen when it becomes an open system. We're gonna find out though because I have a breather on order and I'm going to install it on the passenger side valve cover (well, cam cover but who cares) and cap the intake tract side. I can always add a breather to the intake tract opening as well.

    I'm not sure what you mean by "spark knock" but knocking/pinging is always from detonation and it's definitely not normal and can damage the pistons.

    Teeton wrote:
    Remember under heavy load or wide open throttle the pcv dose just about nothing. The other hose most likely have more vacuum at wide open throttle. Back a closed throttle pvc has more vacuum. The other hose will never have the vacuum that the pvc hose has. So That kinda normal (oily residue inside). You can not remove that other hose, as the mass air flow sensor is calculated with that hose on there and hooked to the vale cover.. Spark knock from time to time is also normal.
  • Teeton's avatar
    Teeton
    Explorer
    Jun 12, 2015
    Remember under heavy load or wide open throttle the pcv dose just about nothing. The other hose most likely have more vacuum at wide open throttle. Back a closed throttle pvc has more vacuum. The other hose will never have the vacuum that the pvc hose has. So That kinda normal (oily residue inside). You can not remove that other hose, as the mass air flow sensor is calculated with that hose on there and hooked to the vale cover.. Spark knock from time to time is also normal.

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