lurk520

It was smoke tested at an exhaust shop and they said it was leaking around the intake manifold gasket and throttle body. When it's cold the metal contracts causing the leak/noise. Once it heats up the metal expands and seals the leak enough to stop making noise.

dave1123

Here's another old fart's trick I'd like to pass on. If you're looking for a vacuum leak, take a propane torch, crack the valve open a little bit. Don't light it! Then play the gas around the intake gaskets and vacuum hoses. The engine will speed up when the gas gets sucked in.

lurk520

That's good info Dave. I plan on tackling this project tomorrow. I also just read in the troubleshooting section of my Haynes manual that intake manifold and throttle body leaks can cause starting problems too (Jeep starts up but dies immediately after), which my Jeep has done since I bought it a year and a half ago. So hopefully I can kill two bird in one stone, one hell of a stone any way.

dave1123

Throttle body base gasket leaks are common and something most people overlook. This happens quite often when people take it off to clean it and don't inspect the gasket or replace it. Or it could be loose.

Base gasket problems were more common with carburetors because of the presence of fuel. The old Quadrojet carb was noted to be a piece of junk because the base gasket would swell up and close off the vacuum port for the metering rods. If you trimmed off this swell, they worked fine.

Now that I think about it, this could be a problem with throttle body injector systems as well.

lurk520

Got er done fellas! Man was that a PITA! Took a good 8.5-9 hours. Had to take off the fuel rail after everything was put back together because an o-ring was busted. The new manifold gasket seems to be much better quality than the original which was just a very thin piece of sheet metal. Put on a new TB gasket as well. Did not have to disconnect the exhaust manifolds from the exhaust pipes. Can't believe I was able to get all those bolts back on and torque them down to spec and in order, guess it is possible. Once I started the Jeep back up the engine bay smoked really good for a while from all the gas and PB Blaster. Seems to be starting a little faster and smoother so far but need more time to tell, even seems to shut down a little smoother. Thanks for all the info and tips guys.

dave1123

Well, now you know how to do THAT job. Feels good to get it over with, doesn't it?

lurk520

Yep. I hope to never do it again.

lurk520

So guess what? I don't think the sound is gone. I've heard it a couple times for about 2 seconds on start up. I'm wondering if It's something with my oil pump because my gauge has been on the fritz as well, all though that never worked on my last jeep 4.0 either. Or something with the fly wheel. Theres also a TSB for the duty cycle purge solenoid that causes a ticking sound, I will be addressing that next.

lurk520

Just found this ***** on the exhaust pipe as well.

lurk520

Put some inferno metal repair on it.

lurk520

Day 2 with the putty patch and so far no ticking/clicking sound. No cold weather though either. Hitting almost 90 degrees here already. We'll see how it goes.

lurk520

Still no clicking sound. I'm almost sure now it was that scuff on the exhaust pipe. Although I do notice a slight improvement in performance and even gas mileage with the new gaskets. Still starts funny on warm starts, fine with cold or hot. Don't know if I'll ever figure that one out.

dave1123

I've discovered sort of the same problem with my WJ 4.0. If the engine is warm and the exhaust pipes cold, it stumbles a little until the pipes warm up. I think we've tracked it down to the 02 sensor. When the sensor is cold, the PCM gets confused because the engine sensors say it's warm, therefore the mixture isn't right until the 02 sensor gets hot. It only takes 30 seconds or so to catch up, longer if the air temp is below 0*

lurk520

Could be. But today I started it up on a warm start, and once again I heard a clicking sound for a couple seconds. So now I'm wondering if it's the starter or the fly wheel. One of our company vans had a bad fly wheel and it made a similar clicking sound, but it made it the whole time it was running, not just intermittent. And when I say a warm start, I mean it's either been sitting in the sun but hasn't ran in 5-6 hours, or I drove it around for a while but it's sat 1.5-2 hours. The thing runs and handles like a dream though otherwise.

PS I've also read these things have vapor lock issues and I've kinda wondered if that could be it, maybe the heat shield is too worn out. But it really doesn't have trouble starting, it just stumbles a little.

lurk520

I've also read about piston skirts being broken..... So who knows