1973 l48 pcv

[Douglas C.]

Hello. Trying to confirm correct PCV and T fitting. Is it PCV 6487530? Can't find T fitting number. Tks. Doug

[Joe L.]

Re: 1973 l48 pcv

Hello. Trying to confirm correct PCV and T fitting. Is it PCV 6487530? Can't find T fitting number. Tks. Doug

Douglas------

Valve depends on engine option. L-48= GM #6487532 aka AC CV769C. L-82= GM #6484525 aka AC CV746C. The tee was GM #3970076. All of the aforementioned are GM-discontinued.

[Douglas C.]

Re: 1973 l48 pcv

Douglas------

Valve depends on engine option. L-48= GM #6487532 aka AC CV769C. L-82= GM #6484525 aka AC CV746C. The tee was GM #3970076. All of the aforementioned are GM-discontinued.

Thanks Joe. What is the best source for these items? Doug

[Joe L.]

Re: 1973 l48 pcv

Thanks Joe. What is the best source for these items? Doug

Douglas------


You might find them on eBay. Keep in mind that there were many slightly different iterations of the PCV valves over the years without a change in part numbers. So, if you are after absolute correctness, you have to obtain the version of the valve that was used in 1973.

The tee is probably also available in reproduction.

[Douglas C.]

Re: 1973 l48 pcv

Douglas------


You might find them on eBay. Keep in mind that there were many slightly different iterations of the PCV valves over the years without a change in part numbers. So, if you are after absolute correctness, you have to obtain the version of the valve that was used in 1973.

The tee is probably also available in reproduction.

Thanks. I did find the T. See pic. Does the T allow manifold vacuum to the canister? If so that seems odd, I would think there would be some internal valve to stop vacuum to the canister. 12922_1-B_253f38ec-d469-41e4-8e47-ffc5fe721aaa_400x400.jpg

[Jimmy P.]

Re: 1973 l48 pcv

Doug,
Maybe this helps explain things....The earlier C3 EVAP Canister thru 73 has a valve on top that will open when the engine runs above idle to allow manifold vacuum to draw the air through the Canister. At idle, the valve is closed so that extra air and vapors don't upset the idle mixture. At higher rpms more air goes thru the engine and the EVAP has little effect on the mixture. Manifold vacuum supplied to the Canister on the earlier systems comes from the hose that runs to the "T" connector attached to the PCV valve. The canister valve is controlled by the level of vacuum it receives from the smaller hose that goes to the timed port on the carb.
I've attached a photo of the top of the '73 EVAP Canister and a photo of an original '73 L82 CV746C PCV valve "T" assembly as well as a photo of an original L48 PCV valve 'T' assembly.....Note the original sealant used as well as the clamp. The emission system is explained in great detail with many color photos in the 3rd Edition of the 73-74 TIM&JG.

[Douglas C.]

Re: 1973 l48 pcv

Doug,
Maybe this helps explain things....The earlier C3 EVAP Canister thru 73 has a valve on top that will open when the engine runs above idle to allow manifold vacuum to draw the air through the Canister. At idle, the valve is closed so that extra air and vapors don't upset the idle mixture. At higher rpms more air goes thru the engine and the EVAP has little effect on the mixture. Manifold vacuum supplied to the Canister on the earlier systems comes from the hose that runs to the "T" connector attached to the PCV valve. The canister valve is controlled by the level of vacuum it receives from the smaller hose that goes to the timed port on the carb.
I've attached a photo of the top of the '73 EVAP Canister and a photo of an original '73 L82 CV746C PCV valve "T" assembly as well as a photo of an original L48 PCV valve 'T' assembly.....Note the original sealant used as well as the clamp. The emission system is explained in great detail with many color photos in the 3rd Edition of the 73-74 TIM&JG.

Thanks Jimmy, very helpful. So, brings me to a question. I am trying to cool down the engine. Disconnected the TCS wire and running full vacuum to distributor. Issue is high idle speed. Original carb just restored with adjustment to idle restrictors. Idles around 1,000 but I think I need to limit vacuum advance from 16 to around 10 degrees. Also on canister, if I plug off PCV hose to canister rpm drops a little. Is there maybe a vacuum leak at the canister?

Thanks for your help. Doug

[Jimmy P.]

Re: 1973 l48 pcv

Thanks Jimmy, very helpful. So, brings me to a question. I am trying to cool down the engine. Disconnected the TCS wire and running full vacuum to distributor. Issue is high idle speed. Original carb just restored with adjustment to idle restrictors. Idles around 1,000 but I think I need to limit vacuum advance from 16 to around 10 degrees. Also on canister, if I plug off PCV hose to canister rpm drops a little. Is there maybe a vacuum leak at the canister?

Thanks for your help. Doug

Doug,
I'm not a mechanic, so I'm not going to be much help on adjusting vacuum and idle to help cool down your engine. I'm sure there are quite a few guys on here that can help with that. However, since you asked about a possible vacuum leak at the canister... I've attached a couple photos to show the check valve assembly on your '73 and earlier EVAP canister. You could check yours to see if the rubber seal is in good condition...If not...it
could be part of your problem. Hope this helps

[Douglas C.]

Re: 1973 l48 pcv

Thanks again Jimmy, this is very helpful.
Doug

[Douglas C.]

Re: 1973 l48 pcv

Doug,
I'm not a mechanic, so I'm not going to be much help on adjusting vacuum and idle to help cool down your engine. I'm sure there are quite a few guys on here that can help with that. However, since you asked about a possible vacuum leak at the canister... I've attached a couple photos to show the check valve assembly on your '73 and earlier EVAP canister. You could check yours to see if the rubber seal is in good condition...If not...it
could be part of your problem. Hope this helps

Ok. Going to replace rubber hoses and have a new PCV T fitting ordered. Do I have to remove the canister or can I reach down and pop top, check rubber top gasket, and unbolt washer fluid canister out of the way?

[Jimmy P.]

Re: 1973 l48 pcv

Ok. Going to replace rubber hoses and have a new PCV T fitting ordered. Do I have to remove the canister or can I reach down and pop top, check rubber top gasket, and unbolt washer fluid canister out of the way?

[Douglas C.]

Re: 1973 l48 pcv

Thanks Jimmy. I believe I have a small vacuum leak at canister, I hope to find the spring under the cap. I guess I can make a rubber gasket if needed. Is there an open vent tube at bottom of canister? If so can that be a source of a vacuum leak. And....glad to be in touch with another L48 4 speed member! Doug

[Jimmy P.]

Re: 1973 l48 pcv

Thanks Jimmy. I believe I have a small vacuum leak at canister, I hope to find the spring under the cap. I guess I can make a rubber gasket if needed. Is there an open vent tube at bottom of canister? If so can that be a source of a vacuum leak. And....glad to be in touch with another L48 4 speed member! Doug

Doug,
There is a drain tube on the bottom of the Canister. Its purpose is to let any raw gas that may get into the Canister from a faulty fuel seperator valve back at the fuel tank drain out. You would certainly notice the raw gas smell or see it on the garage floor. There is also a filter in the bottom of the canister that should be changed all the vendors and NAPA stores sell it. The hoses down at the canister might be cracked and dry rotted causing your problem ( leak) I've attached photos to show the bottom of the Canister and the filter. Problem is to change the filter you'll need to remove the splash pan under the canister to get to it.

[Douglas C.]

Re: 1973 l48 pcv

Doug,
There is a drain tube on the bottom of the Canister. Its purpose is to let any raw gas that may get into the Canister from a faulty fuel seperator valve back at the fuel tank drain out. You would certainly notice the raw gas smell or see it on the garage floor. There is also a filter in the bottom of the canister that should be changed all the vendors and NAPA stores sell it. The hoses down at the canister might be cracked and dry rotted causing your problem ( leak) I've attached photos to show the bottom of the Canister and the filter. Problem is to change the filter you'll need to remove the splash pan under the canister to get to it.

Ok, good info. It looks like to remove the access panel I need to remove the lower body aluminum to get to one bolt holding the under body panel. At that point I guess best to remove the canister. Does the bottom snap or twist off the replace the filter? Doug

[Jimmy P.]

Re: 1973 l48 pcv

Ok, good info. It looks like to remove the access panel I need to remove the lower body aluminum to get to one bolt holding the under body panel. At that point I guess best to remove the canister. Does the bottom snap or twist off the replace the filter? Doug

Doug,
Here are a couple pics from my Restorer article I did on this very thing a while back. Yes the bottom lid just pops off using a small screwdriver in the marked slot and then snaps back into place.