2004 5.3 tahoe, Mobil 1 since 5,000 miles, now 55,000. Slight oil on top of both valve covers. Shop says there is no PCV valve but only a tube with a orfice that may be plugged up causing back pressure. Can I use Berryman's choke spray ? Which end is the orfice ? Plenum or valve cover end ? Thanks. *BW*

Hello And sure sorry your having such a problem. The Pcv comes out of the valve cover and goes directly into the manifold and it about a 1/4 Inch Inside diameter and about 3/8 so what you want to do is to clean both of them some chevy's have two clean both. and they come directly out of the valve cover straight to intake manifold. I hope that helps you out, I have been doing this for about 20 years so I see about everything. Also if that does not fix your problem after you clean it out feel free to ask me for free. I know one thing about those 5.3 they have a intake gasket problem that makes them run rough when cold and oK when warmed up but not great. like it should be. And Again So sorry about Your Problems and if there is anything else call on me.

Here is how to replace the pcv valve. The valve is on passenger side and is hooked to a vacuum.

Hi,

Your post "...light oil on top of both valve covers..." is to be expected. This would be residue of heated engine oil that evaporates out of the crankcase and has accumulated overtime. Pls note how it is dispersed, most of the oil would be almost powdery since it has binded to the surrounding dust, grime and dirt. Not unless there is excessive oil that is still in liquid form, then that should be a cause for worry. If so, a check/replacement of the valve cover gasket has to be considered. Generally, "Slight oil on top of both valve covers" as stated earlier is to be expected over time and therefore could not be avoided. Best would be regular engine wash/cleaning.

Use of Berryman's choke spray (or any other de-greaser/cleaner) would serve the purpose of cleaning.

There could possibly be two types of PCV valve used by most GM engines that just might fit your engine:
P/N 25179136 - PCV Valve (original type)
P/N 12572717 - PCV Valve (fixed orifice type)

You should not feel any vacuum at the valve cover end, on the contrary, it should be more of a rapidly pulsating positive pressure (with the engine on idle/running).

Unto your other concern "Sea Foam in the fuel", is basically for the cleaning up any carbon build up in your engine and is meant to target the fuel rail/delivery system as well as the combustion chamber.

Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

Thank you for using FixYa.

See also if link below helps
http://www.pdfoo.com/result-2004-chevy-tahoe-service-manual.html

Shouldn't be plugged if you use mobil 1 and have changed regularly. Do you actually see drips/runs anywhere? It could be the valve cover gaskets themselves. Your best bet is to get the factory service manual which will give you everything in detail that is what the dealer mechanics use
http://cgi.ebay.com/ebaymotors/2004-Tahoe-Suburban-Yukon-Chevy-Service-Repair-Manual_W0QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247QQcategoryZ34216QQihZ025QQitemZ380006789512QQrdZ1QQsspagenameZWD1V
Let me know if you need any further assistance.
Thanks,
Lee

You can use the choke spray for cleaning it, if you do, remove and clean the entire tube from end to end, not just the oraface. However, this part is fairly cheap, around $10 at any automotive store, I suggest replacement.