The air injection system on my 348 makes a rattling noise that's most noticable near the quarter window air inlets. The manual indicates that the system is activated at a coolant temp of 15C and turns off at 50C. This approximately coincides with the coolant temperature when I hear the rattling noise. The noise starts abrubtly (if the ambient air temp is below 15C at startup) and goes away just as abruptly when the water temp gage reads a little over 60C. I would like to know if this is normal or not? The sound itself isn't particularly bothersome. I just want to ensure it's not a malfunction. Thanks, James
If you are hearing a rattling it could be that something is loose. All the air injection does is heat up the air going into the engine, to help it warm up faster. It is to help reduce the emitions of the car. Have a look to see if your gas cover its what is making the rattling noise. The next time you start the car try popping off the air inlet toobs that are attatched to the air box, and see if that changes anything. Look to see if the Mass Air Flow Sensors haven't gotten loose. There are two screws on each that hold them to the air box. Check the hose that runs from the air injection valves to the bottom front of the air box, to see if those are loose. Also check to make sure that the four nuts that hold the air box to the subframe haven't gotten loose. More than likely it will be something that isn't tightend down properly, and the extra harmonics, created by the injection valves being open, are causing,whatever it is to vibrate and make the rattling noise. Either that or you have something cracked.
Hi James, sorry, don't have anything constructive to contribute to your issue. Just wanted to make a comment on Ernie's statement... It is my understanding that air injection systems pump air (i.e. oxygen) into the exhaust to help burn off unburnt hydrocarbons while the engine and cats are cold. Thus, it is an emissions device as Ernie stated. Not sure if that's what you meant Ernie. This isn't meant to be nitpicking, just wanted to make clear of that so it wouldn't be misleading. Unless, of course, it is something else that your speaking of, cause I know you know cars Ernie... Good Luck James!
Eric, I think the intent of the system is just as you described. Thanks for the suggestions Ernie. I take it you aren't experiencing the same noise and that I indeed have to find/eliminate the source.
It is normal for the air injection system to make a pulsating vibration/noise when it is operating. I wouldn't call it a rattle, but it is loud and car be heard and felt above the engine noise on a car with a stock exhaust. Brian
Normal air injection noise I've noticed is just a faint high-pitched whine. A rattle would definately stand apart from that. I guess the generalized diagnosis would be an issue with the air pump or it belts, but I have no specific ideas beyond that.
I have a similar situation with my car. When I first start up on the driver side I get a noise that is louder then the engine for a while then it stops - prob same thing?
Eric: the 348 is a passive injection system so it doesn't have an air pump, however I'm certain the noise is related to the injection system. If I hold the injection air line coming from the airbox in my hand while the car is warming up I can feel the vibration start and stop at the corresponding temperature set points. You should try this too Andy.
I have that same noise! It goes away after the car warms up.You can hear it in the rear window air duct. I will try and look into it this week.If you guys find the cause I would like to hear what the problem was.
James, You aren't having a problem... the 348 "gurgles" for the first couple of minutes after a not-warm engine is started (the engine doesn't need to be "cold" for the gurgling to occur). My car does it and so should all. It's the air-injection, as you indicated.
Thanks for the replies. It makes me a bit more comfortable knowing others are seeing the same behavior. On a related note, has anyone here disconnected and plugged their 348 air injection system. I know some here have removed cats, and with those gone the injection system is less important.
Wow! So this is an issue everyone has? It has driven me nuts recently wondering where this noise was coming from. It is definately coming from the airducts. I only hear it when i first start the car cold, last a couple minutes then silence. Does anyone know what it is that actually makes the noise, and is there anything you can do to silence it a bit without interfering with whatever it is doing?
Yes to two of the proceeding questions. 1. the noise is the sound of the unmuffled exhaust that is being fed from just below the headers where they are bolted to the engine to the aircleaner[ look at the stainless tubing that is routed from that area to the valves that operate at the temps noted] to the lines that connect this system to the aircleaner. 2. I've removed this plumbing, plugged the heads. No more noise!
Markie: What did you use to plug the heads? I've seen plugs advertized for the 308, but not the 348. BTW, I think the air goes from the airbox to the exhaust, not the other way around.
Harmony, you are absolutly correct, I had my head up my A**pump. As previously stated on this thread, the air injection system is pumpless, and I think the air from the cleaner is drawn into the exhaust by the relativley lower pressure in the exhaust manifold to add oxygen so that it runs hotter and lites off the cats faster when told to do so by the computer [that certain temp range]. I plugged the inlets that are just above the manifolds where they attach to the head with 19 mm x 1.50 stainless cap nuts. It's amazing how much room there is in the engine bay when you remove some of the "non essential" equipment!
