I just noticed a loud hissing noise coming from my engine bay and it was coming from this.



I've had the car for about 10 yrs and its not my daily driver but I've never noticed this noise before. It doesn't do it right at startup but about 30 seconds later it just starts blowing air out the grey top. Not sure if its called and AIR pump vacuum solenoid or an egr solenoid. Is this normal or did it go out?

 

Well, it is not EGR, but AIR, however I don't have one on my car, so I don't know what it should sound like.

 

Thanks shoebox. So do anyone have one of these still on their car? Would anyone mind going out and seeing if yours has a loud hissing noise coming from the top of this?

 

From Shoebox's AIR recall components diagram, that's the vacuum solenoid that appears to connect to the shutoff valve on the main AIR discharge line. There should not be any pressure in the solenoid, if everything is functioning correctly. Is the hissing due to pressure in the valve? If so, is there a flow out of the valve? If so, is it warm? Does is continue after about 3 minutes from startup, when the AIR pump should shut off?

I'm wondering if:

-the shutoff valve and the check valves have failed, and somehow exhaust is blowing through the vacuum line, into the solenoid?

-the AIR pump is not shutting off like it is supposed to, and when the shutoff valve closes, the pressure from the AIR pump is bleeding through the vacuum line to the solenoid?

http://shbox.com/1/air_pump_recall.jpg

 

The hissing does continue after 3 mins. It did it the entire time my car was idling in the driveway for about 15 mins. It was HOT air coming out of the top of the solenoid. I dont have access to the car right now. I'm stuck at work for 24 hrs. I'll have to look at it in the morning. I'm trying to figure out what steps I need to take to track down this issue. I was hoping it was just a bad vacuum solenoid.

I was thinking about just deleting the air and egr, but I have Lts with emissions so I could pass a tx state inspection. I'm pretty sure that I have to have 3 out of the 5 showing "Ready" to be able to pass. Is there any way around this? The car is a 96 and it is still an OBDII in case anyone was wondering.

 

I doubt is is supposed to be hissing. That would mean vacuum is escaping. Probably a bad solenoid if you have already checked the hoses for cracks or leakage.

 

Does anyone know the part # for the solenoid? I cant find it on gmparts direct, autozone, or o'reilly autoparts websites.

 

If anything is blowing out of the valve it's not vacuum. Vacuum would be pulling air in. It would hiss, but not feel like hot air escaping.

 

The solenoid was part of the recall components and was not in the original parts books that everyone has access to. You will probably have to contact the dealer.

 

Update: I took off the grey plastic top on the solenoid to find that the rubber in it was in pieces. Not sure if it was a diaphragm or what, but that's where all the hot air was blowing out. Guessing that the solenoid was bad. So I went to 2 dealers and both of them don't have access to the part #s of the recall components. They both tried to tell me that it was the bleed valve pictured in green. They called it a secondary air injection solenoid with two vacuum ports. Then they brought out the part and realized that it was completely different. After that they tried to say that it was the shutoff valve pictured in red until they brought out that part as well. I tried explaining to them that it was a vacuum solenoid pictured below in yellow but their diagrams don't even show the part and do not even have a part # for it.

 

Update # 2. I decided to just plug the bad solenoid back in. It was not showing a check engine light anyway so I just decided to bypass it. I connected the 2 vacuum lines going into solenoid together with a 90' vacuum fitting. One of the lines comes from the shutoff valve then goes into the bad solenoid. From there it comes out of the solenoid then up to the side of the intake. Do you think this will hurt anything? Not sure exactly what the solenoid did to begin with. The car started right up. No more hissing, it idled fine, no check engine light. I just didn't drive it.

 

The solenoid appears to operate the shutoff valve. As I've said before, there should not be any "hot air" in the solenoid. The fact that the rubber in the valve was rotted could be indicating the diaphragm in the shutoff valve is damaged, possibly due to a faulty check valve at the manifold, and is allowing exhaust gas to reach the solenoid. If that is the case, and you simply connected the shutoff valve to the intake manifold, bypassing the solenoid, it wouldn't be good for the engine.

Have you examined the rubber elbows at the check valves? If there is any evidence that they are overheating, it would point to the above idea that you have a faulty check valve.

Appears you aren't really open to this line of thinking, so I'll post this once, and the rest is up to you, since my previous input seems to have been totally ignored.

 

Not really sure how I'm not open to this line of thinking or how I have totally ignored your previous imput? I have inspected all of the AIR pump components and the pump itself. I have seen no visible damage to any of it besides the rotted rubber under the plastic cap of the vacuum solenoid. Could this possibly be because of the fact that it has been on the car since 96? The rubber elbows at the check valves are fine. I do not know of a way to check the solenoid, the shutoff valve, or the check valves off of the exhaust to see if the are working properly besides a visual inspection for evidence of overheating. Which I have already done. So what have I completely ignored? I have seen these type of responses from you before to previous posts that other members have written. Most of them are for new members that haven't used the search function 1st, others are from people reposting every 5 mins. All I was trying to do was get input from the forum that has helped me in the past, not to get talked down to like I am some 16 yr old with no mechanical experience. I appreciate your help in the previous posts and in the past but that last comment was unnecessary.