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Ported vacuum switch help


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jyank
User

Jun 10, 2017, 11:50 AM

Post #1 of 16 (814 views)
Ported vacuum switch help Sign In

Have 1977 Pontiac Firebird Trans Am 400 cid 6.6 V8. Found that the ported vacuum switch that threads into the right side head was broken off causing a vacuum leak. Did not notice any problems with the running of the engine. Looks like it was like that for a long time. There are two vacuum lines that connect to the switch. Changed the switch. Now there is a rattling sound when you accelerate. Appears to be coming from the drivers exhaust from the heat raiser or exhaust dampener or what ever you call it. That noise WAS NOT there before we put this new switch in. The raiser has a vacuum control on it.
What does the switch do? Where do the two vacuum lines on the switch go to? Does the switch have anything to do with the vacuum control on the heat raiser? Or is it just a coincidence that this noise started.
Read some about it on the net. But you guys always come up with the right answer. The car is never used in cold weather. Stored for the winter. In your opinion, do you need the ported vacuum switch and the heat riser functioning. A mechanic said to remove the switch and just plug the head and remove the heat raiser. He said its only needed in cold weather.


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jun 10, 2017, 12:22 PM

Post #2 of 16 (809 views)
Re: Ported vacuum switch help Sign In

? Vacuum switch in head itself? More likely in crossing over coolant or I guess you could use the cylinder head? One side has constant vacuum (intake manifold actual vacuum to run it) and the other is sensing engine temp by your description yes could open a heat riser and hold it open or just the flap(s) that pick up warm air off of exhaust manifolds to speed up cold air to vaporize gasoline so chokes can shut down early.


The item it operates might flap? Several things are vacuum operated measure engine temp early emissions savings simply by getting choke off and engine warm both as soon as possible. Other is to disallow EGR when stone cold among some other things.


It may to air cleaner as well which is sensing temp of air coming inside to open air to the snorkel(s) and pick up air thru those not off soon hot exhaust manifolds.


IDK - almost all of that vacuum hose maze was on a sticker and hoses OE came with colored stripes to put them back where they should go. Lot of years to have OE hoses so all just black no doubt have to see what it controls as there are more than one "Vacuum Tree" I called those that snapped the plastic easily nothing could glue those back.


If need be till you have know diagrams for that specific engine - California if marked "compliant" would be different then called "Federal" standards.


If this is constantly sucking in hot air it's going to knock. If a heat riser stay in crossover mode it too hot and could knock - gasoline knock because air is too hot.


IDK - find out for sure what it operates. Other items include the rear choke pull off you really can do without and run fine none of this stuff should make noise so know if engine knock or a diverter flap is faulty. Defaults are these things will tell engine it COLD which you don't want when warmed up. They do not alone bother how the engine runs rather makes it better if operating properly,


T



Hammer Time
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Jun 10, 2017, 1:33 PM

Post #3 of 16 (800 views)
Re: Ported vacuum switch help Sign In

It's very likely the heat riser is temperature controlled, so yes it is likely related. They used those temp activated vacuum switches for timing and intake air also. You should be able to follow the hoses to find out for sure.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Jun 10, 2017, 1:33 PM)


jyank
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Jun 10, 2017, 2:09 PM

Post #4 of 16 (791 views)
Re: Ported vacuum switch help Sign In

Vacuum hose diagram sticker under the hood shows one hose going to the distributer vacuum advance and one going into a T and to the carburetor. like I said in the original post this switch was not functioning, must likely for years and I never noticed a difference until the noise after we "fixed it."


Hammer Time
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Jun 10, 2017, 2:12 PM

Post #5 of 16 (789 views)
Re: Ported vacuum switch help Sign In

If the line goes to the distributor, then it controls ignition timing and it's rather important. You should replace it.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



jyank
User

Jun 10, 2017, 2:20 PM

Post #6 of 16 (783 views)
Re: Ported vacuum switch help Sign In

It has been replaced last Thursday. I will not remove it. Do you think there is a connection when the switch was replaced and the rattle or noise on acceleration?


Hammer Time
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Jun 10, 2017, 2:22 PM

Post #7 of 16 (781 views)
Re: Ported vacuum switch help Sign In

The vacuum leak could have been robbing vacuum from the heat riser circuit.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



jyank
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Jun 10, 2017, 2:29 PM

Post #8 of 16 (775 views)
Re: Ported vacuum switch help Sign In

Just a Thought. If the switch has to do with that timing. Do you think the timing is now off and I am hearing "spark knock"? But there seams to be no loss of power or lag.


Hammer Time
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Jun 10, 2017, 2:35 PM

Post #9 of 16 (773 views)
Re: Ported vacuum switch help Sign In

The switch controls when the vacuum advance kicks in. Make sure you bought the correct switch that has the proper reaction to the temp. Some switches rest closed and open with temp, some rest open and close with temp. You need to make sure yours is doing what it's supposed to.

It would be helpful to have a service manual for the car that explains the theory of the switch.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



jyank
User

Jun 10, 2017, 2:48 PM

Post #10 of 16 (769 views)
Re: Ported vacuum switch help Sign In

99.9% sure I got the right switch. Assuming I do would that now make a difference with the timing?


Tom Greenleaf
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Jun 10, 2017, 3:47 PM

Post #11 of 16 (765 views)
Re: Ported vacuum switch help Sign In

If switch looked identical and fit proper it's probably right. To distributor is as Hammer said and that receives the vacuum when warmed up just a bit and that part might be making noise for some reason. Rubber things - hoses, the diaphragms that move things can go bad and do.
Don't just plug it off unless an open vacuum leak right now fine but next find out if it operates as it should. It's just mechanically doing what is electronically done on newer stuff,


T



jyank
User

Jun 12, 2017, 6:53 PM

Post #12 of 16 (740 views)
Re: Ported vacuum switch help Sign In

It's most likely the heat raiser making the noise. With the vacuum lines connected to the vacuum switch you can hear the rattling noise on acceleration. Disconnect the lines from the switch and drive the car no rattling noise at all. Do any of you know where I can get a brand new heat raiser assembly? Looked online only can find used ones.


Sidom
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Jun 13, 2017, 11:06 AM

Post #13 of 16 (720 views)
Re: Ported vacuum switch help Sign In

Well as HT and Tom have said.....its pretty much an emission control part from the 70s and 80s to help the engine warm up faster...
The 80s was the nightmare decade for vacuum lines and emission control parts... sure don't miss that..


That engine was designed and made with that part......


That being said....I could probably count on 1 hand.....twice.....how many I replaced with new ones......and that rattling, is the common failure pattern for those....


jyank
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Jun 13, 2017, 8:00 PM

Post #14 of 16 (707 views)
Re: Ported vacuum switch help Sign In

I want to thank all of you for your help. I now have bigger fish to fry. Heater core just started leaking today. The passenger side floor is soaked in coolant. Got the carpet pulled back and insulation. Drying it out with a heater fan as we speak. Carpet is ok but the insulation is shot. Got some to replace it once I get this fixed. Think I will bypass the core for now. Don't need heat. Car is stored in the winter months. Live in the UP of Michigan. This car is a beauty. I purchased it in 78 new. Black with red interior. But its turning into a money pit. It mostly started last year. One thing after another. Put about 4 to 5 grand into it since last summer. Going to the shop tomorrow. Pete my mechanic said the heater core replacement is a pain. He takes care of the car like it was his.


Sidom
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Jun 14, 2017, 10:54 AM

Post #15 of 16 (689 views)
Re: Ported vacuum switch help Sign In

I don't know Pete but I already like him.......Yea those are a total PITA


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jun 14, 2017, 11:17 AM

Post #16 of 16 (683 views)
Re: Ported vacuum switch help Sign In

Do yourself a huge favor by-passing heater core is do that with a "U" turn of the hoses! Don't just plug them as you need that flow on many for assorted reasons. One is critical if that is part of the by-pass system for cooling system if plugged you overheat in the rear of the engine if done that way or even if it goes back to water pump.
With rattle now I recall ton's more heat risers for assorted Chrysler products used a an offset weight and opened if exhaust flow was more and defaulted to some crossover heat could make tons of noise. Just a spring to hold them against outside of the choke plate inside unseen now it both worked as intended and quit rattling.


New wasn't a real problem to find those or as said don't allow parts that pivot to move sideways in place so much.


Memory shot - did they use a Chev engine in this or a Pontiac? They were using either in lots of vehicles and the Chev turned out with more power for a lame time stretch for real power,


T


(edit more in on that) By model year 1979 and definite by 1980 or so GM plain got rid of Pontiac engines and kept just the Chev for V8s, Olds blocks. Cadillac was making there own stuff still or used Olds depending on models..........



(This post was edited by Tom Greenleaf on Jun 14, 2017, 11:21 AM)






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