PCV Tube Help

[PCGUY112887]

I am using the PCV tube off my 3100 on my 3500. For some reason, even though the valvecovers are the same, I can NOT get my PCV tube to stay in the rear valvecover on my 3500. It sorta presses in there, but it just doesn't stay with just a press fit like it did on the 3100.

It keeps turning around and ends up just hanging there. I know that is just sucking in hot, unmetered air into my motor. I want to stop it! What can I use to force my PCV tube to stay in the valve cover? I wanted to use some black RTV around it to make it stay but I'm afraid I will end up sucking some of it into the valvecover or something.

Ideas?

Thanks.

[WrathOfSocrus]

If you aren't fond of glue or rtv then you could try wrapping some duct tape around the outside of the hose to make up the difference in diameter. As long as it is wrapped secure around the hose it should never come off and you can build up enough tape until it doesn't slide in and out of the grommet easily. Black duct tape is less gawdy =)

[3400-95-Modified]

That's actually not the PCV tube, its a rear valve cover breather vent. All that's doing is pulling in the fumes and burn off in the crankcase into the engine, Its more of a emissions thing. The PCV system is ONLY the tube that runs from the VAC side of the TB to the front valve cover.

I used a 3500 one and it works fine... I'm half tempted to remove that from the system and just put a tube with a breather filter on it somewhere, a good amount of oil residue gets pulled through that and into your intake, and I'm not too fond of that.

[WrathOfSocrus]

That's actually not the PCV tube, its a rear valve cover breather vent. All that's doing is pulling in the fumes and burn off in the crankcase

So it pulls in Positive Crankcase Ventilation?

[3400-95-Modified]

Actually to be quite honest, I got it wrong myself...

If everything is working correctly that tube should actually be pulling air INTO the engine, not pushing it out or pulling a vac on the engine.

Going by how a PCV system works, the breather tube on the rear valve cover is there to induce filtered air INTO the crankcase, where the PCV valve is there to pull a vacuum on the crankcase and create a draft.

Picture I found once I looked it up.



So my option still stands true, you can eliminate this tube going to your intake, and just find a way to seal/hold in the plug that goes there and run it to a little breather so it can pull clean air into the motor, since really that tube should not be sucking air through it into the intake.

[robertisaar]

well i just learned something new.... i always thought it was odd that there were essentially 2 PCV ports....

[3400-95-Modified]

well i just learned something new.... i always thought it was odd that there were essentially 2 PCV ports....

Same here after I googled it.

If you think about it PCV is basically useless at WOT since both ports are at the same pressure, aka 0 VAC, so its not doing anything... The PCV only works where there is a VAC on the PCV valve part which means part throttle cursing... So I guess you can say if the car is not being daily driven, and doesn't have to meet any emissions standards then the PCV is useless... unless of course the PCV track has less restriction than the air filter, if not then the motor will never try to pull air through it at WOT. This is where a Vac pump comes into play I'm thinking about one of those too...

[pocket-rocket]

part throttle cursing...

I'm always part throttle cursing. Full throttle is where it's at, baby!

[AaronGTR]

So my option still stands true, you can eliminate this tube going to your intake, and just find a way to seal/hold in the plug that goes there and run it to a little breather so it can pull clean air into the motor, since really that tube should not be sucking air through it into the intake.

You can do that, and it will run (I ran that way for a while) but it will throw off the fuel trims on MAF equipped cars slightly at low engine loads. When there is a vacuum behind the TB and the engine is pulling vapor through the front PCV valve and line, it is pulling fresh air in through the rear valve cover vent. If you have a breather installed there instead of a line going to you intake (behind the MAF), then you are pulling in and burning un-metered air.

Same here after I googled it.

If you think about it PCV is basically useless at WOT since both ports are at the same pressure, aka 0 VAC, so its not doing anything... The PCV only works where there is a VAC on the PCV valve part which means part throttle cursing... So I guess you can say if the car is not being daily driven, and doesn't have to meet any emissions standards then the PCV is useless... unless of course the PCV track has less restriction than the air filter, if not then the motor will never try to pull air through it at WOT. This is where a Vac pump comes into play I'm thinking about one of those too...

This is true. At WOT with higher combustion pressures it develops positive pressure in the crank case and will evacuate the blow by gases on it's own. Sometimes there is even enough pressure that the flow reverses and comes out both PCV ports (front and rear valve covers) and into the intake stream. The PCV is really only meant to work and evacuate those gases when there is no crank case pressure (ie low throttle daily driving) and it needs vacuum to do so.

A vacuum pump would be very cool to have indeed. You eliminate the PCV system and just pull off one of the valve covers (breather on the other) and put a catch can in the line. Problem would be finding an electric vacuum pump that isn't too big and heavy or expensive, and that makes enough vacuum to be useful. I haven't looked for one yet honestly, but most of the vacuum pumps I've seen are belt driven for V8's like Moroso's. They also create a pretty high vacuum so they make negative crank case pressure even at WOT, the benefit being they help the rings seal better so racers can use low tension rings for less friction. I don't know if this kind a theory could be practically applied to a street driven V6 or outside of racing?

[robertisaar]

i think the only issue there is that most of the vacuum pumps aren't really designed for a DD, so they're used to only running for short amounts of time. if there is one out there meant for long-term use, go for it, can't hurt, so long as you can mount it.

[pocket-rocket]

Do they make vacuum regulators? If so you could probably get something like the vacuum pump out of a Cady for the brake booster to use. Now that I think about it, when I worked at Four Winds building diesel pusher class A motorhomes, they had vacuum pumps they installed to run the HVAC controls...

[robertisaar]

Caddies have vacuum pumps? well this is new to me... if its in a caddy, it was built to last. any idea as to which years/models?

as for the diesel: most diesel vehicles have some type of vacuum pump, usually for brakes, but one rated for HVAC use would fare better in a street car...

[pocket-rocket]

IIRC I think it was the older ones (around the 80's era). It could have been the diesels, idk. Using my vacuum pump to try to figure out how much vacuum they created, it was around 10 inHg through a small hose (3/16"ID). I have no idea where you could find one of these. I wish I still worked there. Well, ok, I lied. I would rather be unemployed then work at that hell hole again, but if I would have realize those things would have benefited us, you can best believe I would have gotten a few of them. I wonder if any of the RV surplus places around here would have them... BTW, these were Freightliner chassis that these were on. I worked there from 2006-2008, so I saw 2006-2009 model years go through. Not that I've ever seen an RV junkyard anywhere...

[AaronGTR]

I doubt they make enough vacuum to have the same effect as the belt driven vacuum pumps I mentioned, but they could possibly be sufficient to use only for the PCV line if you didn't want to route the PCV into your intake. Of course, then you wouldn't be emissions legal if you live in a state with inspections. For everyone else though, I think it would work if you could get a pump that would produce at least 14 in/Hg or better.