Stupid Question.....

[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!


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]

Originally Posted by 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.

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?

Thanks Mike for your time & thoughts!

[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.

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.


Tom

[mike100]

Originally Posted by tomtom72

Mike, thanks for giving me the heads up.

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.


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!

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


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. 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!

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


Tom

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