C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

90 Plenum Vacuum Lines

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Old Jul 10, 2016 | 02:11 PM
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Default 90 Plenum Vacuum Lines

I'm just wondering where the 3 vacuum ports on the passenger side plenum are supposed to go. The last port closest to the firewall is for the HVAC line, but what about the others? MAP sensor and fuel pressure regulator? I can only find reference to the HVAC line, which I noticed was hooked up wrong on my car. It was on the front port. Would that affect HVAC controls? I cant find reference to the MAP sensor anywhere.

Thanks.



Last edited by jimmers; Jul 10, 2016 at 02:16 PM.
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Old Jul 10, 2016 | 05:36 PM
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I'm going to assume the order doesn't matter, as they all go to roughly the same spot on the plenum.
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Old Jul 10, 2016 | 06:21 PM
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if you're standing on the RH side of the engine looking at the ports, the forward port (the open port in your pic) goes to the HVAC - it routes in front of the distributor and connects to a two-port, check valve on the left side of the engine - one side to the HVAC, and the other to the cruise control module. there might be another "tee" in the line going to the emissions system. the middle port connects to the fuel pressure regulator, and the aft port to the MAP sensor. BTW, your MAP sensor is not configured correctly - looks like it mounts to the funky-looking "L" bracket, because of the fuel gauge. that might be part of your vacuum line mix-up. a better setup would look like this -



hope this helps.

Last edited by Joe C; Jul 10, 2016 at 06:53 PM.
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Old Jul 10, 2016 | 08:09 PM
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Originally Posted by Joe C
if you're standing on the RH side of the engine looking at the ports, the forward port (the open port in your pic) goes to the HVAC - it routes in front of the distributor and connects to a two-port, check valve on the left side of the engine - one side to the HVAC, and the other to the cruise control module. there might be another "tee" in the line going to the emissions system. the middle port connects to the fuel pressure regulator, and the aft port to the MAP sensor. BTW, your MAP sensor is not configured correctly - looks like it mounts to the funky-looking "L" bracket, because of the fuel gauge. that might be part of your vacuum line mix-up. a better setup would look like this -

hope this helps.
Thanks for the reply. That clears things up a lot. My MAP sensor was like that when I got the car. Looking at pictures trying to get an idea how the vacuum lines are routed, I noticed it looked a little funky. The bracket that I have won't mount to the car properly like in your picture. It looks like it was custom made. Does the bracket come with a new MAP sensor or do I need to find a proper bracket somewhere?
Thanks for the help!
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Old Jul 10, 2016 | 08:44 PM
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Originally Posted by jimmers
Thanks for the reply. That clears things up a lot. My MAP sensor was like that when I got the car. Looking at pictures trying to get an idea how the vacuum lines are routed, I noticed it looked a little funky. The bracket that I have won't mount to the car properly like in your picture. It looks like it was custom made. Does the bracket come with a new MAP sensor or do I need to find a proper bracket somewhere?
Thanks for the help!
as I recall, your bracket looks to be part of an accell fuel rail pressure gauge kit.



I bought the same kit for my 90, but pitched the bracket in the trash. the brass elbow allows for locating the gauge aft or left of the MAP sensor using the stock MAP sensor bracket, to maintain the stock configuration. the only mod I did was notching the aluminum distributor cover, and tilting the gauge for better viewing. to answer your question, i'm not aware the mounting bracket comes with a new sensor. you will need to find a correct bracket and mounting hardware - scrounge fleabay or various used parts vendors. it looks like your MAP is riveted to the "L" bracket, so you'll have to undo the rivets.

here's a fleabay bracket with hardware, but to me, way too pricey....

http://www.ebay.com/itm/90-92-Camaro...1W1HOC&vxp=mtr
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Old Jul 10, 2016 | 10:20 PM
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Originally Posted by Joe C
as I recall, your bracket looks to be part of an accell fuel rail pressure gauge kit.



I bought the same kit for my 90, but pitched the bracket in the trash. the brass elbow allows for locating the gauge aft or left of the MAP sensor using the stock MAP sensor bracket, to maintain the stock configuration. the only mod I did was notching the aluminum distributor cover, and tilting the gauge for better viewing. to answer your question, i'm not aware the mounting bracket comes with a new sensor. you will need to find a correct bracket and mounting hardware - scrounge fleabay or various used parts vendors. it looks like your MAP is riveted to the "L" bracket, so you'll have to undo the rivets.

here's a fleabay bracket with hardware, but to me, way too pricey....

http://www.ebay.com/itm/90-92-Camaro...1W1HOC&vxp=mtr
Thanks. I'll try and find a stock bracket and fix the fuel pressure gauge.
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