Rumbling like an exhaust leak

[kcabpilot]

Over the past week or so I've been hearing a rumbling that sounds like like a "hole in the muffler" for lack of a better description but it's coming from up front on the passenger side. Today while I was listening to it at idle I discovered that if I disconnect the vacuum sense line to the right SAI solenoid it stops.

All SAI tubing secure and fittings are tight

Any ideas?

 

[discostew]

One or both of your check valves are probably leaking back into those pipes.

 

[kcabpilot]

So you mean it is sticking? Makes sense since it seems to be intermittent. I'll look it up, didn't actually know there were check valves or where they are.

 

[Hubacek]

I may have a similar problem happening very intermittenyly; Only after it rains or even high humidity atmosphere, I will get that rumble, "hole in the exhaust note" sound from under the hood but when having a look I'm unable to find anything suspect. It continues as I begin driving, but will cease by the time I reach destination. No places where rain water can drain into the engine and like I said, doesn't even have to actually rain but reacts to the density of the air. I will have to try what you did the next time that happens

 

[discostew]

So you mean it is sticking? Makes sense since it seems to be intermittent. I'll look it up, didn't actually know there were check valves or where they are.

I always figure carbon build up causes them to either stick or just not seal even if its not stuck. You might want to make sure the vac. hose going to them doesn't have vacuum in it. The solenoids stick, usually stick closed but I don't see why it wouldn't stick open.

 

[kcabpilot]

Okay well I think I'm on the right track then at least. This all started after I R&R'ed the intake plenum to clean the injectors and replace the coil packs. When I pulled the sense line off the RH valve and the noise stopped it did have vacuum on it. I need to read up on the SAI section of the manual because frankly I don't really have any idea how the thing works.

 

[Hubacek]

Okay well I think I'm on the right track then at least. This all started after I R&R'ed the intake plenum to clean the injectors and replace the coil packs. When I pulled the sense line off the RH valve and the noise stopped it did have vacuum on it. I need to read up on the SAI section of the manual because frankly I don't really have any idea how the thing works.

Reading is always good. But basically you have the pump on PS, the valve on each side connected to the cylinder head by that manifold with double brass flex pipes. Then there is the solenoid wired in next to the infamous purge valve. The ECU has its designated parameters that will activate the SAI to assist the heating of catalytic converters by pumping that extra air in on cold startup. Right?

 

[discostew]

I think you crossed the two connectors that are near each other. The purge valve and the secondary air solenoid. I bet its getting duty cycled and your purge valve is just getting opened on a cold start.

 

[kcabpilot]

Finally got around to looking at this and yup, that's exactly what I did. So it was working okay except that when the SAI pump shut off after a cold start the vacuum to the control valves did not release so they stayed open and the "exhaust" rumble I was hearing was indeed exhaust backflowing through the open valves and the non-running pump. I found that all I had to do was momentarily disconnect the line to one of the valves and it stopped and would not reoccur until the next cold start. Finally I got tired of doing that and read the f*cking manual so now it works the way it's supposed to. lol