yah...probably the cat

about $250-$300 for an OEM style....

--Dylan

 

I've seen them for around that much with the downpipes, but a replacement cat by itself runs about $80.

 

yeah i meant with the downpipes...sorry about that one...;-)

You can get by alot cheaper with just a replacement cat but unless you're real good with your welder you might want to send it out for repairs...those pipes are not the easiest things to seal weld in the position in which they sit

When I did my exhaust I removed the cat (yes the new one) and just ran straight to the flowmasters , I think it sounds much better without it and since I have 'farmer' plates I dont have to worry about smog testing during inspection...

Best of luck...
--Dylan

 

You got that right. I just put a high flow cat on my truck, and it's a real pain to weld under there, especially with the vehicle sitting on the ground. I ended up tacking it in place, then dropping the downpipes and finished welding it off the truck.

 

Ok, let's think about this... The sound is more pronounced when you are opening the throttle. Since you have LESS vacuum in your manifold with the throttle open, it doesn't make sense for it to be a vacuum leak (which would be more pronounced with a higher vacuum).

I suspect the hissing sound is coming from your "Idle Air Controller" (IAC) which is located on the back side of your throttle body. It's purpose is to regulate the amount of air entering the engine when the throttle blades are closed (at idle). When you open the throttle, the IAC throttles shut (since the engine is now getting it's air through the butterfly valves). The hissing/whistling sound is likely coming from the air going through the IAC opening on the TB when the IAC solenoid is nearly shut. This can sometimes be cured by cleaning the IAC port in the throttle body (TB). Remove the TB from your manifold, remove ALL sensors/solenoids from the TB. Clean the TB with THROTTLE BODY CLEANER (use a Q-tip in the IAC port). You should also clean the actual IAC, but be careful NOT to allow any cleaner to get into the solenoid motor (electrical part), and do NOT twist the plunger. The internals are easily damaged if you are not gentle with it. Just lightly rub it with a rag with some TB cleaner on it.

This is actually regular maintenance that should be done at least twice a year.

 

Well my first post, I used the search and found this old thread. Hope some one gives it the time of day. I have a 98 1500 2wd 5.9. I have this same hising/whistle in my engine bay however I was able to pin point it with the air cleaner off I could stick my finger in the rear of the throttle body and could feel the air being sucked or pushed (what ever we want to call it) when the sound was happening and when it went away I did not feel it. Does this mean it is the IAC? I will try taking it off and cleaning it sunday to see if there is any change. Just wanted to see your guys opinions seeing the inactivity in the thread I assume you got yours fixed. Thanks In Advance.-The Rev

 

no love on the old thread.....

 

I know this thread is REALLY old, but I have the exact problem mentioned. Did anyone ever figure out the culprit for sure?

When I accelerate I hear a whistle. Only on acceleration. ??

 

this recently came up in another thread... OI believe the noise is normal on some trucks on startup for a short time and them should go away I would sometimes notice it on mine...

 

Check and see if the gasket between the throttle body, and air filter box is still there.