Loud Exhaust Note after going 55mph

[militarydave]

My little truck has gone through some rought times. sat for about a year while my happy ass was in Iraq. came back, i replaced all the electrical components: Ignition coil, distributor, plugs, wires, module, coil pack, ECM, Fuel Pump, Fuel Filter, Fuses, Relays, Alternator, belt, pulleys, muffer/exhaust, battery.... etc. etc.

its basically new. strong little 2.9 V6. but, when i'm on the freeway and hit about 55-65 mph in 5th gear... i start hearing a really loud monotone exhaust note. not a nice one, but just LOUD, right underneath the cabin. when i replaced the muffler, i didn't replace the headers. i'm guessing i have an exhaust leak, but after changing all gaskets... i got nothing. still loud noise only when i hit fifth right underneath the cabin.

any ideas?

thanks,

-dave

 

[CraigK]

Could be the dreaded manifold to Y-pipe flange leak.

 

[militarydave]

looking at it now... it is coming form the Y pipe, just before the catalytic converter. so... i need a new Y pipe flange or the entire manifold/header assembly?

-dave

 

[Tedybear]

Careful planing can save a headache. The Y-Pipe is one thing...and the only annoying part is getting the 02 sensor out if you are re-using it. (trust me...most of the time it's well worth the money to just replace it LOL....)

As for the manifold? Here's where the planning helps. Soak the daylights out of the bolts going to the manifold at the Y-Pipe. Those 2 bolts may not look all that awful....but they can be damn near welded in place!!

(if you have access and the know-how to use a torch for heat? It'll come in handy.)

I'd NOT recommend trying to replace or remove the exhaust manifold. The bolts going into the head have a nice side effect known as breaking off...after that? It's another headache to extract the bolts.

S-

 

[militarydave]

so soak it with a can of PB Blaster and leave it penetrating for a day or 2? i can replace the 02 sensor... thats fine. no biggie. i just dont wanna mess anything up!

-dave

 

[CraigK]

My O2 sensor was a disaster waiting to happen. You don't want to strip this baby. Soak it with penetrating oil too. Then soak it again. I sawed off the top of my O2 sensor with a hack saw so I could use a short, high quality, SIX-SIDED socket (worth buying just for this - as opposed to a twelve sided socket, which strips bolt heads easier). Then I used a long extension on my rachet.

Craig

 

[militarydave]

wow, so the thing is that delicate! i'll take that into consideration. i have a new 02 sensor now. seems to be quite the tight fit!

-dave

 

[IRKillroy]

well instead of replacing it, why don't you take it to the welders in your maint section and have them fix the leak?! I'm sure they won't mind hooking you up... I know the welders in my Maint Bn in pendleton never had a problem doing stuff like that (as long as it wasn't aluminum welding... that wire is expensive)

then you just bolt it back up in the truck without spending 500 dollars on a new y-pipe

 

[CraigK]

"just bolt it back up in the truck without spending 500 dollars on a new y-pipe" ?????


http://www.autozone.com/R,1022875/v...partType,00856/shopping/partProductDetail.htm

 

[militarydave]

very nice! i'll see what i can do. if i have no luck on the 02 sensor, i'll just by the Pipe. i get hooked up by autozone anyways!

-dave

 

[militarydave]

Ok, so i've replaced the Y-pipe exhaust flange... but i still hear that monotone noise when cruising after 55 (mostly on the hwy).

any other thoughts?

 

[militarydave]

could it be hole or leak in the catalytic converter?

-dave

 

[Hahnsb2]

Doubt it. Exhaust leaks will be most present when accelerating and aren't monotone.

 

[JackSchitt]

do you have a long bed or short bed? reason i am asking is because if it is long bed there may be a carrier bearing thats going bad. thats what is sounds like to me. is it a humming sound? any vibration?

 

[BRUTUS_T_HOG]

mine does the same thing, its my differential.. only does it at 55mph, no lower, no higher.. and only up hill or towing