Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner
1 - 12 of 12 Posts

·
Registered
Joined
·
2,024 Posts
Discussion Starter · #1 ·
I know this has been discussed before, but do we have an actual PCV valve on the 4.2? :confused: I know the breather line is up front on the cam cover & taps into the intake silencer for it's (non-vac) filtered air source. I've had the silencer off of my 2005 & poked around, but I cant seem to find a PCV valve/hose/line/tap? :undecided It's gotta be there somewhere? There has to be a vacuum source to sweep the crankcase of vapors. Some PCV valves now are integrated into the valve cover, so I am assuming ours is hidden around the back or intake manifold side?

Thanks!
Joel
 

·
Registered
2004 chevy trailblazer_ls_ext
Joined
·
477 Posts
MTPockets,
There is no PCV valve used on the 4.2 engine. Fresh air from the throttle body is supplied to the crankcase, mixed with blow-by gases and then passes through the crankcase ventilation pipe into the intake manifold. The vacuum used to "sweep" the crankcase in that which is created in the intake manifold. When the throttle is opened manifold vacuum decreased. At this point in time, crankcase pressure are higher and crankcase gases rush down the ventilation pipe, into the engine and are then combusted together with the normal fresh air/fuel mixture.
Also, GM also states that the crankcase ventilation has no serviceable components, so no maintenance of the system is required.
 

·
Registered
2002 chevy trailblazer_ls
Joined
·
2,235 Posts
No valve to replace. It has a passage between the crankcase and intake manifold. How it works forever without eventually getting clogged, I have no idea.

From a GM technical overview

4.2L L6 engine with the following features:

Emission controls that include one catalytic converter, a Positive Crankcase Ventilation (PCV) system without a PCV valve, an enhanced Evaporative (EVAP) system and no Exhaust Gas Recirculation (EGR) system. (Uses VVT overlap for that purpose.)

Also, PCV air intake to the top of the valve cover is before the throttle body- taps into the resonator upstream of the throttle body, for filtered air.
 

·
Registered
Joined
·
2,024 Posts
Discussion Starter · #4 ·
Bringing an old one back to life here..:eek: I was under the hood again today and I am still totally puzzled by this!?! I know the breather line is up front, up top on the cam cover & plugs into the intake silencer for it's clean air source. That would be your 'fresh air goes in' portion. Where the heck is the vac side to purge out the crankcase vapors? A PCV system cannot work with one hose. There's got to be a port, hose, line.. tied into a vac source somwhere!:crazy: Is it cast into the intake manifold somewhere like tblazed says?

Joel
 

·
Registered
2002 chevy trailblazer_ls
Joined
·
2,235 Posts
Look on the driver's side of the engine, from beneath the intake manifold there is a hose that connects and makes a 90° bend and goes to the block. That's the crankcase ventilation hose. What regulates or meters the vacuum apparently is a fixed orifice of some sort that is not serviceable. I guess you could take the hose off and clean the passage with spray cleaner. :undecided
 

·
Registered
Joined
·
2,024 Posts
Discussion Starter · #6 ·

·
Registered
Joined
·
2,024 Posts
Discussion Starter · #8 ·
Yeah, you see more & more engines now with just a metered orifice instead of a PCV valve. IMO- it's better. No chance of installing a cheap, faulty aftermarket valve, no chance of leaks, bad check vlvs, etc.. Actually, the design on the 4.2L is pretty slick! There is no way for oil to pool in the intake (like soooo many other vehicles) since the PCV line dumps at the tops of the #3 and 4 intake runners. Oily crankcase vapors get swept right down the runners. Another plus for the 4.2L IMO.

Joel
 

·
Registered
2002 chevy trailblazer_ls
Joined
·
2,235 Posts
Yeah, you see more & more engines now with just a metered orifice instead of a PCV valve. IMO- it's better.Another plus for the 4.2L IMO.

Joel
I hope so. It'll work as long as doesn't get clogged. However in the diagnostics section of the manual there is clogged PCV system and the internal passages in the engine block mentioned, so I guess it's possible.

I had a perfectly good AC brand PCV valve clog completely on my '88 S10 4.3 and I didn't catch it until a lot of sludge had built up in the engine. It was tough getting most of that gunk cleaned out. Pulled the valve covers because of leaks and OMG what a mess... all seems OK now and pressure good, oil not too dirty, engine runs quietly.
 

·
Registered
Joined
·
2,024 Posts
Discussion Starter · #10 ·
You could probably disconnect the PCV hose from the intake and blast some intake cleaner, seafoam, etc, into the hose to back-purge any junk into the crank case. IMO- you'd want to do this just before an oil change as the cleaner would wind-up in the oil. Getting at the stub on the side of the block would be a task!:undecided

Joel
 

·
Premium Member
'05 Chevy TB EXT
Joined
·
5,153 Posts
You could probably disconnect the PCV hose from the intake and blast some intake cleaner, seafoam, etc, into the hose to back-purge any junk into the crank case. IMO- you'd want to do this just before an oil change as the cleaner would wind-up in the oil. Getting at the stub on the side of the block would be a task!:undecided

Joel
Don't do that unless you are prepared to complete the cleaning. I have posted before about this system and I'll try to find it .....
 

·
Registered
2004 chevy trailblazer_lt
Joined
·
40 Posts
1 - 12 of 12 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top