Stupid Question.....

[tomtom72]

....but important ( I think it's important ) maybe to me. How cold does an LT5 have to be before you can pull the plenum?

Yes, I truly do not know the answer to that question.:o

The reason I ask is that I rent garage space and may not work on the car there. I have to drive it to my apartment to do any work, and by the time I get to my parking space my car is fully hot, water and oil.

I need to pull my plenum as I have an audible vacuum leak coming from under the plenum.

TIA
:cheers:
Tom

I know I should have left it in my space when I finished my work on the car yesterday. I was a bit spent & not thinking clearly. Maybe I was a bit pi$$ed off when I started her & heard the vacuum leak....oh, and my vacuum pump's switch failed at the same time....guess I'll use my spare.

[Aurora40]

I suspect it's not like pulling plugs out of a hot aluminum head, where you have to worry about stripping things. I suspect it's more a matter of how hot of a plenum can you handle pulling?

You'll have to open the cooling system, so you will at least need to wait until the cooling system pressure drops.

[tomtom72]

Good Morning Bob! Thanks for the thoughts. I have gloves so the heat I guess would be okay on my skin. It's just that my or these motors retain heat for a long time once they are to proper operating temps.

The thing I have in my head dates back to the late 60's & early 70's when aluminum engine parts were sort of rare and most of the old time mechanics used to say "do not unbolt hot aluminum parts!" I've never considered the question from a point of view that something bad, like warping, would happen because I've never worked on my LT5 when it was hot. I guess that is my fear and reason for my stupid question.

Thanks for your time!

Tom

[Kevin]

when i was having injector problems i gently limped mine from the hotel to the ncm and parked it for a bit before gordon and I tackled swapping them out. it wasn't cold by any stretch of the imagination

[tomtom72]

Thanks a bunch Kevin! I am thinking that Gordon is as good a source as I can find. Thanks for passing that info along!

:cheers:
Tom

[Kevin]

Thanks a bunch Kevin! I am thinking that Gordon is as good a source as I can find. Thanks for passing that info along!

:cheers:
Tom

forgot to mention i thought it was a coil problem so we fired it up and let it run for a bit while we pulled wires to see if that was the problem before we dug into the motor.

[jrd1990zr1]

Hey Tom,

If you want to drive it up by me we can pull the plenum in my garage. I've got a lift so you can change the oil, if needed too! Downside is the travel distance. Let me know.

John :cheers:

....but important ( I think it's important ) maybe to me. How cold does an LT5 have to be before you can pull the plenum?

Yes, I truly do not know the answer to that question.:o

The reason I ask is that I rent garage space and may not work on the car there. I have to drive it to my apartment to do any work, and by the time I get to my parking space my car is fully hot, water and oil.

I need to pull my plenum as I have an audible vacuum leak coming from under the plenum.

TIA
:cheers:
Tom

I know I should have left it in my space when I finished my work on the car yesterday. I was a bit spent & not thinking clearly. Maybe I was a bit pi$$ed off when I started her & heard the vacuum leak....oh, and my vacuum pump's switch failed at the same time....guess I'll use my spare.

[tomtom72]

John, you are the man! Thanks, I'll let you know as I have an al fresco plenum pull scheduled for this Friday afternoon, no rain. I've done some diagnostics with my hand vacuum pump last night. I have vacuum integrity on the line from the vacuum pump. So the check valve & tank are good to go.

I'm figuring either I have a bad control solenoid, or a hole in one of the actuator diaphrams the size of the grand canyon....or a mouse got in there & chewed on a vacuum line. She is hissing like all get out at idle, and when you try to get in the secondaries it sounds like it's drowning.

:cheers:
Tom

[Aurora40]

If it holds vacuum with a hand pump and the engine off, why would it hiss at idle? Everything should be the same, except the engine vacuum supply line also has vacuum. I believe that comes from the driver's side front of the plenum?

[tomtom72]

I do not know Bob. That is the symptom I'm seeing. It has a hiss at idle, and until you call the 2*'s it runs normally. When the 2*'s should come on she starts to gurgle like it's drowning. I'll have to admit that I was not insistent on calling the 2*'s. As soon as I heard the gurgling I got out of the gas. I didn't even think to turn the key "off" and test it that way. I should have, but I just didn't think of it at the moment. I blew that one I know!

I was a bit distracted when I was doing a brief diagnostic in the garage where I park so I had to be quick as it was a bad time to be under the hood in the garage, too many people around.

I went back last evening & repeated the pump line test and it does hold vacuum with the motor off. I was going to start it up, pull the left vacuum line, plug the nipple and apply vacuum to that line....but I had bad timing again & there were too many people around again.

Soooo, my diagnostic plan will be to go bring her back to my building on Friday after work ( hopefully no rain! ) and test her with the key "off" and the key "ON" on the way over hoping that will give me some more info to narrow down my search. The hissing is, to my ear, coming from under the plenum as far as I can tell. :o

:cheers:
Tom

[jrd1990zr1]

Tom,

Before you pull the plenum or the engine gets warm, check to make sure the vacuum line to the MAP sensor is still hooked up to the back of the plenum. Just a thought. Also make sure the PCV valves are seated and there are no leaks. I have quite a hissing sound on mine as the air flows through the PCV system. Again just a thought. Did you change out the PCV valves and possibly get a bad valve?

Don't forget I still have those 4-917 PCV valves for you!

John

[tomtom72]

Yea, I did change the PCV's. That will be added to my check list, thanks for the idea. I eyed them up while I was looking the first time but did not get to touching them to look for them as a leak source. Think I'll bring another set with me & do that just for chits & giggles. I get what you're saying about when they are operating & the air flow noise they can make, but I'm going to check them over just to be sure that is not my hiss.

Yea I even eyed up the MAP line the first go around & I felt along it & both ends were on....my stuff is never that simple! :-({|=

Oh well, at least I have my Cobalt...it runs fine, slow, much slower, but it's not hissing at me!:sign10:

:cheers:
Tom

Oh yes I did not forget. You want me to send a check? I thank you for snagging them for me!

[mike100]

It's probably the big hard plastic hose with the curly-q bend in it. It goes to the evap solenoid and to just behind the throttle body on the driver's side.

[tomtom72]

It's probably the big hard plastic hose with the curly-q bend in it. It goes to the evap solenoid and to just behind the throttle body on the driver's side.

That's the larger one of the lines that come out of that double connector, right?

Those are still connected, how well I'm not sure as my double connector is the original and it looks like the both lines are not the tightest of fits. Maybe some judicious use of zip ties is in order? :icon_scra

Thanks Mike for your time & thoughts! :handshak:

[mike100]

Mine was still on the plenum side, but the double connector on the solenoid is where most of them pop off (maybe from repeated backfires?). I sanded mine rough and reinserted it hard- it's fine now. you would have to really pull on it to get it out.

you might have another leak on another line, but if your secondaries still work, it's probably that line for the evap.

[tomtom72]

Mike, thanks for giving me the heads up. :thumbsup:

I'll go look at the evap canister when I get to her today. I would not have thought of the evap system as a suspect.

:cheers:
Tom

[mike100]

Mike, thanks for giving me the heads up. :thumbsup:

I'll go look at the evap canister when I get to her today. I would not have thought of the evap system as a suspect.

:cheers:
Tom

oh yeah, the 1990 model...the 91's have the can in the back fender, but the line routes out on the side of the engine where you can squeeze it closed to test for air leaks at idle.

What I did to be able to hear the hiss better was to remove the air cleaner duct and block the front of the air horn with a very stiff piece of cardboard from a real thick box (a notebook binder or clipboard has been suggested as a better thing to use) while the engine idles. I also clamped the evap line and the blocked the two vac connections on the sides of the plenum. If the engine is actually still running by then, you should really be able to hear it struggle for air through the vac leak under there.

After that, it's about a 45 minute job to pop off the plenum, 20 minutes of that draining some of the water out of the radiator. I'd suggest getting it up on jacks to get at the rad petcock and to take off the front tires to be able to work closer and not wreck your back. btw, put rags over the brakes to keep the mess off of your pants. So half the time is in prep- the plenum itself could be taken off in 10 minutes if you get really good at it.

the evap solenoid is is usually open when the car is running and up to temp, but the actual tank one-way check valve should only allow ventilation when the gas tank pressure gets high (like it is real hot outside)...basically there should be no leak there. If the line popped off, you're going to have a 1300 rpm idle.

[tomtom72]

Thanks again Mike. I went over the evap system and as far as I can tell it is not my 'hiss'. It's looking like it is a vacuum leak in the 2* system. It runs fine with the key off, but key on it sure don't want to get up & boggie and the SES light flashes at me....it will not set or stay on but it winks at me. It's proly laughing at my sorry butt too!

Yea, it's been a while since I had to pull the plenum. Oh well if it cools down enough and if it don't rain on me I should be able to get to it in a coupla hours in earnest. I hate not having a garage! :mad:

I'll post up what I find as it may serve as some info for others.

:cheers:
Tom

[tomtom72]

Okay just to put a period on this......the 2*'s not working and the vacuum leak saga.

This falls into the area of back yard wrench error. :o I took out the overflow bottle to clean it. When I put it back I got the vacuum hose from the pump behind the two mounting ears that hold the tank to the frame rail. When I tightened down those two bolts I crushed the vacuum hose to a fair thee well!

So of course attaching a vacuum tester to all the hoses going under the plenum didn't show any issues. The pump ran like a race horse & I had to unplug it to save it committing suicide, but failed to realize that the 2* circuit would still have a vacuum leak from the crushed hose when I tried to engage the 2*'s! :o

The moral of this sad tale for me is: Watch what I'm doing and try not to work in the dark!

:cheers:
Tom

P.S. I never found the issue. JVD's shop fixed it for me down at the Gathering this year. Thanks Jim!