I have a open element air filter on my 5.9. When I accelerate I get a hissing noise much like its sucking in air. This came on my truck and I have never heard it with the stock setup. From doing searches on this forum and Google I see that some time the sound can come from a clogged or clogging cat. Then I read further that if that was the case I could crack my head on my 5.9 motor. So I have done my plenum with the Hughes plate and did the thermostat to what they suggested. I have had my 8th cylinder miss fire come on once more since the job was done. I took out the plug looked at it and its burning light brownish so that seems good. When this was happening I could go to the passenger side of my truck and hear a light ticking like when a spark is shorting through a wire... tick... tick..... tick..... Rev'ed the truck up and it disconnected the neg battery terminal and all has been well. No check engine lights or anything. But I am one of those people where I read that if the cat is clogging then I may crack a head.... So now in the back of my head when I accelerate I hear that hissing and I am wondering is that my Air intake or my exhaust trying to get to my cat that could be tighter then a rats ***???


Now for the 4 thousand dollar question. I am in NH we have a ODB2 test when we get inspected. If I punch my cat will I get a O2 sensor light come on? Or is there enough leeway on the sensors to do this?

 

An open element WILL make a sucking noise since your engine is sucking in air at a high rate.
If your cat is done, it will limit your engine badly. It will just stop accelerating at high speed.

 

BTW before the plenum I got the 8th cylinder misfire code. Po308 or something like that. I did Cap, rotor, wires, plugs.

I have a cherry bomb on the end of the cat so I can punch it out pretty easy.

 

Yeah I hit 80-90 on the highway with out issue...

 

You should be good then.

 

Thanks for the piece of mind sir!

 

Keep in mind that if the plenum was blown, it was ruining the cat. For the misfire, get a couple bottles of Techron+ and run it through the gas. (may be carbon build up on valves) Also you can try Seafoam through the intake. I'd have the cat pressure tested.

 

Zman my plenum was blown not to bad (in my opinion) but the entire in side of the intake had a fine layer or coat of oil on it. I have ran sea foam through the gas tank upon fill ups. I was worried about putting it in the intake since i dont know how the intake be able to suck the fluid through since the pickups are pretty high on the sides of the intake. I would guess it would just pool at the bottom of the intake on my new plenum plate. Has any one actually done seafoam into the intake through the throttle body??? And then check to make sure it is not just pooled up on the bottom of the intake? I have yet to put it through my oil..... I have used about 4 cans through 4 tanks of fuel just to clean everything up.

 

How do I do a pressure test, is there a special tool? I understand I need to drill a hole in the pipe in front of the cat but what type of "valve" do i put in there to get a pressure reading?

 

There is a special tool/gauge. And it can be done by removing the o2's and using the adapter with the tool. I have one, but I suggest you just take it to a muffler shop.