Hey guys! I have a 94 xj with the 4.0 aw4 and about 165000 miles on her.
About 500 miles ago I replaced my old cracked exhaust manifold wit an APN header. I also replaced all the intake/exhaust bolts and studs for good measure. The included gasket that came with my header was used along with some of that Permatex ultra high temp copper rtv for added measure. Everything was torqued down to spec and all was fine and dandy until now.

I let my jeep sit for about 4-5 days and then drove it earlier this week. It started up just fine, but by the time I got to work (about a 2.5 mile drive) there was an audible whistle noise. I popped the hood and could instantly tell I had some kind of intake/vacuum leak coming from near the rear of the valve cover. I was able to pinpoint the leak as being at the intake gasket right next to injector #6. I can actually touch the top edge of the gasket and hear the pitch of the whistle change. I find it funny that one day there is no leak, the next there is.

Now, it only does this once I'm at operation temperature, never when the motor is cold.Other than the audible whistle you'd never know there was a problem, the jeep idles perfectly and has all of its power. So today I got under there and retorqued everything to spec for good measure.... No dice, it still whistles.

So, all that to say, am I looking at taking the intake and exhaust back off and redoing the gasket? It was a real PITA to do the first time and is right on the edge of my comfort level with engine work. What's my worse case scenario? Thanks in advance guys!

 

It doesn't hurt to remove it and see if there's foreign matter between the gasket and surface, or if there's any scoring on mating surfaces that the gasket wasn't able to seal up fully.

 

In the meantime, is it ok to drive it? Or will I wind up hurting it?

 

Has anyone had bad luck with the included APN gasket? Thinking about trying the felpro gasket if I end up taking everything back off...

 

Is it running different or rough? No, you're not going to ruin your motor, but, it needs to be repaired. I've always had good luck with felpro gaskets. I don't have any experience with the one you used. On an intake/exhaust manifold, I've only ever used a gasket....no rtv.

Have you checked the torque on the bolts? Maybe one came loose or never got torqued down?

 

It seems to be running just a tad rough. Nothing major though. I'll try the felpro gasket next. Yes, this past weekend I rechecked all the bolts and torqued them all to spec. 24 ft lbs I believe it was.

 

I advise not running it hard/hot long till you fix it. Some risk of burning a valve I think.

Very little aftermarket header experience here. (plenty of stock though!) What comes up...the thickness of the flange of the header. If it's thicker or course the intake won't be sucked up right. I'm not sure of a cure.

I know you put your finger right on it...still though do be sure it's not the bottom O ring on #6 injector. It's so close in there. I had thought MY intake was leaking, only to find it was that O ring was not in right.

 

Thanks Flintstone! Fortunately I'm working very close to home right now (2.5 miles) so I don't have to drive very long or hard . The flange thickness of the apn always concerned me and I'm thinking of switching back to an OE style header. Which stock replacement header brand do you recommend?