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

Vacuum Hoses

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Old Dec 19, 2011 | 09:33 PM
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Default Vacuum Hoses

Hey everyone. Yesterday I finally had time to work on my 96 Coupe. I changed the EGR Valve and started to change all of the vacuum hoses that I could fine. All of them were dried up and cracked. I changed all of the ones that I could get to because I think that's what is causing my idle to stumble a little bit. I don't have any issues driving only when I'm stopped. The idle will go up and down. When I changed the vacuum hoses that I could get to, the idle was better. However, there were three hoses that I couldn't get to. They are 2 by the battery and one underneath the battery. I saw the hose under the battery was plugged with a screw and I don't know where it is supposed connect to. Also, one of the 2 hoses by the battery goes towards the driver's side and I can't see or feel where it goes. When I was checking it, I broke off the cracked hose where it was connected to the good part of the hose but I was able to feel the hose that was deeper into the car and it seemed okay but I can't see where it leads to so I grabbed a plastic connector and connected it to the good part of the hose. I hope I'm not confusing everyone. I guess, in a nutshell, is how can I access the area under the battery and will I be able to find where all of the hoses lead to. Thanks, Ed.
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Old Dec 19, 2011 | 10:47 PM
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Have you tried taking the battery out to have a look?
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Old Dec 19, 2011 | 11:22 PM
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That's what I did when I reached in to change the hose that broke off. I still couldn't see where the hose goes or if the hose was badly damaged farther in. And the one with the screw, I can't even reach. I was thinking of jacking up the car and take a look to see if I could see where the vacuum hoses go. Is there any other things I could take off from the top or under the car? Thanks, Ed



Originally Posted by 1986coupe
Have you tried taking the battery out to have a look?
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Old Dec 19, 2011 | 11:53 PM
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you may need to remove the LH inner fender (rear section) to gain more access. the hose that is plugged with a screw is definitely a issue, and needs to be addressed. as far as your idle speed floating around at idle, you may want to clean and service your throttle body.
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Old Dec 20, 2011 | 09:39 AM
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I cleaned the Mass Air Flow Sensor about 3 months ago when I got a code and I never got the code again. Maybe I'll clean it again because that is the easiest thing to do first. When I remove the inner fender, would I be able to gain access from the top or underneath the car?


Originally Posted by Joe C
you may need to remove the LH inner fender (rear section) to gain more access. the hose that is plugged with a screw is definitely a issue, and needs to be addressed. as far as your idle speed floating around at idle, you may want to clean and service your throttle body.
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Old Dec 20, 2011 | 11:09 AM
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Originally Posted by Dr_Shakalu
I cleaned the Mass Air Flow Sensor about 3 months ago when I got a code and I never got the code again. Maybe I'll clean it again because that is the easiest thing to do first. When I remove the inner fender, would I be able to gain access from the top or underneath the car?
i'm thinking you've misunderstood me - not the MAF sensor, but the throttle body itself. i usually clean mine about every 4-5 years, or so. when i do, i remove it from the engine and get a couple cans of throttle body cleaner or carb cleaner, and blast the hell out of the thing. seems there are air passages in the idle circuit, as well as the IAC valve that are critical to a smooth idle.

when you remove the inner fender liner, you should gain access to the forward side of the battery compartment, and the underside or bottom of the same. at the bottom of the fender liner, it bends back and attaches to bottom side of the frame rail. removing that should open up the whole area for inspection...

Last edited by Joe C; Dec 20, 2011 at 11:15 AM.
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Old Dec 20, 2011 | 05:50 PM
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I have been doing the same on my 96 and I noticed that there is a hose on the inside of the car just above the clutch pedal and it goes through the firewall. I have not checked my FSM yet but thinking this is to the brake booster or clutch master. anyway maybe this is what you see on the engine side. There are also hose to and from the cruise control servo. When I find it in the FSM I will share.
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Old Dec 20, 2011 | 06:36 PM
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There is also a vacuum line inside the wiring harnass that lies next to the battery. My car was throwing codes that suggested vacuum leak. There was one part of the vacuum line hanging, could not find where the other end was. Also cruise did not work. The shop smoked the engine to look for leaks. We spotted smoke coming from next to the battery. They removed the battery and found the other half of the vacuum line going into the harnass. They spliced back together and all is fine; including the cruise.

The battery in the car is a Napa that is side vented. The vent caused battery fumes to eat away at the harnass sheathing and eventually brittled the vacuum line to the point where it just broke off. Going to replace with a sealed battery.
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Old Dec 20, 2011 | 08:10 PM
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Hey everyone, thanks for replying with possible answers. I've never had a problem with my cruise control and have never had any codes thrown suggesting a vacuum problem. The old hoses I replaced were toast so I need to get into the area by the battery. I will try to do it this weekend. I will by an FSM but since coming home from Iraq, money has been a little tight. Again, thanks for all your replies, Ed.
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Old Dec 21, 2011 | 10:40 AM
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Welcome home. Don't forget to closely inspect all the little 90 degree and other fittings that connect all those little EGR line for cracking. Suitable replacements can be found in the DIY vacuum fitting section of most parts stores if necessary.
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Old Dec 21, 2011 | 11:01 AM
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The hose that goes into the firewall is for your cruise.
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