Tracing Down Exhaust Leak - 300-6

ceetwarrior · #1 (**permalink**) 10-03-2009, 11:19 PM

Hey guys, so I have this exhaust leak somewhere in the front of the exhaust system on my '94 300-6. It only makes noise under LOAD so I am positive it's not valve-train noise.

Upon inspection I noticed small amounts of black soot where manifolds meet block. So I pulled off both exhaust manifolds today and was very surprised to find no gaskets! So I filed the manifolds clean, applied 700* Ultra Copper RTV and reinstalled. No cracks, no leaks at the cats/piping, nothing. Everything is tight and right. Let it dry, 16hrs and still have the noise.

I checked all the EGR/smog tubing and it's all in good condition, no leaks/holes. Is it possible that the EGR valve itself is leaking? I am going to try the stethoscope in the morning and check the EGR valve for 'noise'. Even though I can only hear it in the cab when under load.

Any other ideas?

Hilux · #2 (**permalink**) 10-03-2009, 11:36 PM

That's the same thing my 93 F250HD is doing , I hope someone has an answer .

ceetwarrior · #3 (**permalink**) 10-04-2009, 12:55 AM

I started the engine and I was poking around and found (at least) one of the 6 little tubes were leaking right where they meet the head with the ferrell nuts.

Can those be filled with copper RTV to keep them from leaking? Looks like the upper intake needs to be removed to get to the main tube....

SammichTheStout · #4 (**permalink**) 10-04-2009, 09:07 AM

My 95 300L6 does the same thing. Tick-tick-tick-tick, but only under load, I was convinced that the upper exhaust wasn't sealing up. I'm going to ask my mechanic on monday what that sound might be. I hope its not an injector.

uhoh826 · #5 (**permalink**) 10-04-2009, 11:11 AM

I found a few little leaks on my truck that had me puzzled. The base of the egr valve that mounts to the intake had a micro crack running through it. would leak only when i got on it but i believe it gave me one of the egr codes. the base of the egr valve is cast aluminum i think but i only caught sight when i cleaned the back of the valve for a new gasket.
The egr pipe was leaking where it tied into the exhaust manifold. Again only heard it when i was on the throttle. Tried loosening and retightening, thread sealers nothing worked so i just got a new pipe and that fixed it.
I have a 93 but i think the motors are the same. Your exhaust manifold and lower intake share one common gasket. They also use the same bolts to tighten the manifolds and intake to the head. If there wasn't a gasket under the exhaust manifold then there probably isn't anything under the lower intake either. The tabs on the side of my intake manifold that pinch it to the head were all broken. Gave me a really bad intake leak and the truck ran like crap. If you pull off the upper intake and fuel lines you can get a good look at the head and where the manifolds bolt to it. I'd bet your leak is somewhere in there.

ceetwarrior · #6 (**permalink**) 11-04-2009, 09:53 PM

Hey guys, I replaced my AIR tube and it fixed the problem for two weeks. Then it came back worse than other one morning when I started my truck. I traced it down again to the NEW air tube. Pulled off the upper intake again and found that the air tube has pushed out about 3/4". So I take a hammer and beat it back down into place. Then tighten up the farrel nuts some more. I have those nuts soo tight I am afraid that I am going to round off the heads.

Has anyone ran into this problem before where that tube wont hold tight? I was thinking about making a bracket from the fuel rail bolt to hold the AIR tube tight.... any thoughts?

F150xlt · #7 (**permalink**) 11-04-2009, 11:07 PM

When I rebuilt my 89 300 it was impossible to remove the air tube from the head with out damaging the joints where the individual air tubes were crimped to the main air tube.

I removed the air tube and installed allen head type NPT pipe plugs in the head. As far as I know, air is only injected into the exhaust ports during cold start up. No codes are set with the air tube removed.

brett12396f150 · #8 (**permalink**) 11-06-2009, 10:04 PM

@sammich- could be a rocker making the tick noise.

SammichTheStout · #9 (**permalink**) 11-06-2009, 10:08 PM

How would a rocker make that distinctive ticking? I smell exhaust in the cab with the heater on, so I'm pretty sure its an exhaust leak. I can always check my clearances the next time I have the valve cover off.

brett12396f150 · #10 (**permalink**) 11-06-2009, 10:17 PM

What kind of a ticking is it? lol Only reason i said rockers is cause u said ticking noise maybe injectors, kinda close. High pitch or low pitch tick?

SammichTheStout · #11 (**permalink**) 11-08-2009, 07:23 AM

I don't know that it has a pitch, its just a ticking sound that happens only when accelerating.

ceetwarrior · #12 (**permalink**) 11-09-2009, 08:33 AM

If you are poking your head in the engine bay and you hear a ticking noise, thats just normal valvetrain noise. They all do it. If you can hear anything inside the truck during 'load', that's an exhaust leak. Like a clacking sound, not a tickin sound.

94shorty · #13 (**permalink**) 11-09-2009, 10:07 AM

I got one for ya. I have a noticeable banging noise(tung tung tung) under load that sounds like a u-joint going bad. I thought that's what it was and planned on replacing them this weekend, until I happen to hear the noise in idle(faintly) and while stopped in-line at the drive thru. It's definitely not coming from the engine. Also, it's intermittent, won't do it everytime, but most. Gotta crawl under there one of these nights to figure out where it's coming from.