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Generation III Internal Engine
1997-2006 LS1 | LS6
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Old 01-01-2012, 07:12 PM   #1
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Question '98 pontiac trans am vacuum problems

Hey Guys,
I have been having alot of trouble figuring this out do to the lack of not being able to find an exact diagram of the vacuum lines and that I have a proCharger installed which has changed thing around a little bit from stock.

Anyways the problem goes... for starters when I get on the throttle with the vents on high (a/c or heater,defrost, vent, dosnt matter) the air completly cuts off and stops blowing out the vents. Then once achieved speed (say 70 mph) the air would come back on. Now, just recently it has stopped blowing all together at high speed. If I am going 70 mph and the heater or a/c or vent is on high, I can hear it blowing inside the dash blowing but nothing comes out of any of the vents no matter what settings. The fan inside is definatly spinning though.

The reason i think it is vacuum is because this engine has been rebuilt and not by the guys who did the supercharger. These new guys really did a number on mixing crap up. I gave them my ProCharger manual but i dont think they even opened it up seems.

I explained this problem to a friend and he said sounds like my vacuum lines are maybe mixed up.

has anyone ever heard of this or got a diagram or some pictures of where what lines go where haha? Im getting desperate.
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Old 01-01-2012, 07:22 PM   #2
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i would agree with your friend, i think it is a vacuum problem. if you can't find a diagram you could always remove the hvac controls and unplug the vacuum plug on the back, pick up a vacuum gauge from the local parts store, and check to see if you are losing supply vacuum at the control head. if you are then follow that vacuum line through the dash to where it goes on the engine. along the way you will probably see where it is broken just replace it and be on your way. i have also seen where the control head (the vac switch in it to be specific) will malfunction and air will not come from any where, but the blower still spins. lets hope for a vac line becuse its a lot cheaper. good luck and keep us posted
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Old 01-01-2012, 07:36 PM   #3
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Arrow Pictures

Looks like I have 2 hard black plastic vacumm lines coming from the "passanger side". One comes out of the firewall and the other comes from the back of the engine block "feels like". Then it connects to all this crap in picture 2 and runs down finally into a black cannister that looks like it blocks the pressure or somthing. It is weird, I never seen one before.
does that all look right?
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'98 pontiac trans am vacuum problems-sam_1728.jpg   '98 pontiac trans am vacuum problems-sam_1729.jpg  
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Old 01-01-2012, 07:43 PM   #4
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Here this might help a smidgen... Does everyones look like this?
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Old 01-01-2012, 07:56 PM   #5
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Then on the driver side.....
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Old 01-01-2012, 08:42 PM   #6
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Quote:
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Here this might help a smidgen... Does everyones look like this?

Air flow from both back lines is going straight into the black cannister. SO the air just gets blocked... That cant be right, right?
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Old 01-01-2012, 10:44 PM   #7
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Quote:
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Here this might help a smidgen... Does everyones look like this?
the black canister is a vacuum canister that "stores" vacuum. the bulge in the lines where they split and go from the engine to the firewall and canister looks like a check valve. you need those two things even more than a stock car becuse if your vac line goes straight to the engine then your vac actuators in your dash (the ones that hold the air doors open) would close when you make boost. i would look at mine and compare but it is in storage for the winter. if i have time tomarrow i will go look and take a pic. i would have to say that the black plastic line going in to the firewall is probably your vac supply line for your hvac controls. i would get a vac gauge on it to see if it has vacuum. (at idle it should be between 18hg and 22hg). that number may vary a little depending on your mods ie: big cams=less vac. you could disconnect the line to see if you feel it sucking air in. if you wanna get real fancey you could get a hand vacuum pump and apply vacuum to the dash side of the vac line to see if it moves the acuators inside. (just turn the heat on once the vac is applied and turn the **** to see if it changes where it flows from.)
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Old 01-02-2012, 01:12 AM   #8
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Okay, so your saying the line going into my firewall is the Vacuum line that controls the dampers, right? And the other line beside it on the right is the one that goes to the back of the engine, what does it do, and the canister works in conjunction with the firewall line right?

What I think is going on is how the check valve is connected to the lines. There are 3 lines plugged into this check valve and i dont think there plugged into the correct spots. Since the check valve only allows air too pass through one way, this could be the problem right? somehow when i create boost all my vents close off but the air blower is still blowing in the dash. can you look at the pic and see if you think each line is plugged into the right spot? whenever you get a chance.
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Old 01-02-2012, 11:50 AM   #9
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vacuum is negatve air pressure, so the opposite of boost. on a NA motor when you go to WOT your engine vacuum goes from around 20hg to less than 3hg. the cannister holds vacuum and the check valve keeps it from leaving the canister when you go WOT. the black hose going to the back of the engine should be your vacuum supply line. that is the line the supply's the canister and and the acuators in your dash. it will be a couple of hours but i will go check to see where my lines are connected to and post up a pic for ya.
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Old 01-02-2012, 01:58 PM   #10
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Yeah its definatly my check valve lines arrangement that has it all mixed up. Mine was set different than what I could tell in most pictures so I set it like what I have seen online. Its now set like the picture below. I hope your is like that, i got my fingers crossed.
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Old 01-03-2012, 12:57 AM   #11
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That looks right. I bet hooking it up that way will fix your problems.
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Old 01-04-2012, 08:45 PM   #12
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I finally got out to the car to check it. Here is a pic labeled to where they go. Keep us posted iam interested to find out what it was. Good luck.
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Old 01-05-2012, 02:33 PM   #13
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Have You taken the a/c heater control assembly off and apart as the cold/hot and the outside/inside air are controled by vacuum and the little orifices in the a/c switch panel are really small and become clogged and actually the vacuum lines that feed vacuum to those controls could be clogged ,,,,,,,,,,getting any and all dirt out usually restores proper function . It is fairly easy to do once You have that control switch panel off .
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Old 01-05-2012, 02:33 PM
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2000, 98, air, check, diagram, heater, line, lines, motor, pontiac, procharger, pump, ta, trans, vacuum, valve, working


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