Exhaust manifold gasket

[Rat baby]

84 720 4x4 if I rev my engine I get this coughing or sputtering. It’s gotten worse and is driving me crazy now. Recently replaced the muffler, and gasket at the catalytic converter. I removed the heat shield and looked for any holes. I attempted to replace the gasket  at the exhaust side of the manifold but was unable to loosen the bolts. She is running great right now other then this cough. 

[datzenmike]

I assume this is an exhaust sound? Try removing them when hot? May have to have them torched off. Then remove the manifold and heat with a torch to get the threaded studs out. Replace with stainless steel including the nuts

[Charlie69]

Check the exhaust manifold real well for cracks.  I have replaced 4 720 Z24 exhaust manifolds do to cracks.

[Rat baby]

It seems to do it less after its fully warmed up. Would a crack or old gasket cause this sort of noise?  

[datzenmike]

I had a Buick V6 head gasket that started up with a whistle that went away as the metal warmed up and expanded.

 

What I did and you should try is hold you hands around the gasket (when cold naturally) have someone start the truck and you feel around quickly for the exhaust puffing out. You have less than ten seconds but more than enough time to do this before it heats up.

[bottomwatcher]

Use soapy water and look for bubbles. You have the same 10 seconds before things start to stink as the soap burns.

[MaxChlan]

On a dead cold engine (as to not press hot air into a cold engine) what I've done is tapped a shop vac to the tailpipe to blow air into the system, and worked my way up the exhaust with soapy water looking for leaks. There is puddy that you can buy that hardens after 24 hours to fill in small cracks.As you fill in various small leaks, spraying soapy water on the exhaust manifold will direct you to any leaks. If it is the exhaust manifold gasket, they are still available from Nissan, and isn't too big of a headache to get off. I sprayed the studs and bolts with liquid wrench and let it penetrate for a few days before the job.  

Edited March 6, 2019 by MaxChlan

[bottomwatcher]

Good idea with the shop vac. Thanks for the new trick. Also when I had a header it would leak at the flanges. There are extra thick metal gaskets that are much better than the standard ones. Ran about $14 a set 10 years ago.

[MaxChlan]

9 hours ago, bottomwatcher said:

Good idea with the shop vac. Thanks for the new trick. Also when I had a header it would leak at the flanges. There are extra thick metal gaskets that are much better than the standard ones. Ran about $14 a set 10 years ago.

That's what I've ran into as of late. My truck is a little louder than it needs to be, and it's been too cold to do any major work.

Edited March 6, 2019 by MaxChlan

[Rat baby]

Hello, little update/ hoping someone can point me in the right direction. I tried yet again to free my front pipe from the manifold with a huge breaker bar. All I managed to do was sheer off one bolt.

 

I’m still needing to do the shop vac test.

 

A question I have is what are some good options if I end up replacing the manifold with a header. I would like to keep the emissions system intact (I think I do anyways) so I’m looking for a manifold that will accommodate the egr tube and the other two tubes. Please drop that knowledge :)

 

I learned to weld so I could do my own exhaust a while back. It’s ugly but it freaking works and saved me a few hundred bucks. I reused all my old pipe and it fits a little funny now. Thinking I could pull it all out and weld in some new pipe and install the header. Just lack experience here and am wary to order anything with out knowing it will work. Sorry for any stupidity. And thanks so much for the help. 

[datzenmike]

I doubt any header maker will have provision for EGR or the AIS (air injection system) It will run just fine without it.

[zrex]

FYI .. I found a uncracked exhaust manifold from a 88 D21 works on my 85 4x4 .. had to plug one hole. Oil Drain plug from a late model Volkswagen works. So much better than the Chinese manifolds on eBay ..