Exhaust leak after replacing Intake Manifold gaskets

[spradilak]

Hey folks a friend and I replaced the intake manifold gaskets and Valve Cover gaskets recently on my 1990 c1500 with 650k.

Aside from a bolt breaking off in the manifold it went smoothly. However now I have a quite loud exhaust leak coming from the rear of the engine. It sounds louder on the drivers side. The noise is most prominent when directly under the engine.

2 bolts are missing from the passenger side exhaust manifold but those have been missing for many years and this leak is certainly new. I bought some new 3/8 x 16 x 2 inch bolts but I can't seem to get these to thread into the missing bolt holes but anyways..

It has a ticking sound like it would be at the exhaust manifold but, I'm unsure why it would be louder after the intake manifold and valve cover swap. Xan either of these if not sealed priperly produce the ticking noise? Maybe EGR? Any input is appreciated. Thanks!

 

[movietvet]

What bolt broke off in what manifold? Are you talking about an attaching bolt for a component that attached at the intake manifold?

When doing the intake or valve cover gaskets, there is no reason to touch the exhaust manifold or any exhaust at all. The missing bolts on the passenger side are likely broke off and that is why you cannot put new bolts in it. Try to stick a pick in the holes and see if it will stop or not.

You need a mechanic's stethoscope to pinpoint the spot of the leak.

 

[Schurkey]

I have a quite loud exhaust leak coming from the rear of the engine. It sounds louder on the drivers side. The noise is most prominent when directly under the engine.

Start engine. Get underneath, stick your hand up and around the end of the exhaust manifold, where it meets the Y-pipe. If you burn your hand on the escaping exhaust gas, the donut seal is cooked.

Good luck, it'll be no fun getting that apart.

Photos from the same repair on my shorty headers:

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2 bolts are missing from the passenger side exhaust manifold but those have been missing for many years and this leak is certainly new. I bought some new 3/8 x 16 x 2 inch bolts but I can't seem to get these to thread into the missing bolt holes

Because the remains of the original bolts are still stuck in the cylinder head?

 

[spradilak]

Well thats unfortunate, I wanted to replace the manifold with something aftermarket but I'm scared all the bolts will just snap after the incident with the intake manifold, same with the flange. I would just ignore it but the exhaust leak is quite loud. Just doesn't make sense why it would be fine until after the intake gaskets.

What are the odds the exhaust leak could be from the intake manifold? I know there's an exhuast/egr passage, just not sure if it's possible to have an exhaust leak like that there

As far as the missing bolts go, I believe that the exhaust manifold is warped just enough to not allow the bolts to go into the head. The bolt goes all the way through the manifold but will not catch any threads into the head

 

[GoToGuy]

You still have not answered, are the head ex mount holes clear, how much warp is there ? You should be able to use a mirror an see what's going on .

 

[movietvet]

The manifold bolts likely broke off inside the head. Typically not leaving anything exposed/sticking out that you could grab if manifold is removed. Use the "pick" and stick it in there and see how far it goes and report back. If you ask for help, please follow the recommended steps and report back.

 

[spradilak]

What bolt broke off in what manifold? Are you talking about an attaching bolt for a component that attached at the intake manifold?

When doing the intake or valve cover gaskets, there is no reason to touch the exhaust manifold or any exhaust at all. The missing bolts on the passenger side are likely broke off and that is why you cannot put new bolts in it. Try to stick a pick in the holes and see if it will stop or not.

You need a mechanic's stethoscope to pinpoint the spot of the leak.

I just inherited the truck recently and was just doing a tune up including the thermostat and the water neck bolt broke off in the manifold. I was unable to get it out with any amount of heat or extractors..only thing I didn't do was weld a nut onto it. So I grabbed a junkyard manifold.

The exhaust manifold bolt replacement I got appears to go all the way through the manifold to the head, but will not thread in. Both of the bolts are at the very end. 1 in the front and one is the very back one.

I just went out and put a pick in the only and I believe you're right. The pick goes all the way through the manifold and like 1mm into the head on both front and rear. I assume it screws in more than 1mm into the head..Not really sure how that happened.

 

[Road Trip]

Hey folks a friend and I replaced the intake manifold gaskets and Valve Cover gaskets recently on my 1990 c1500 with 650k...

...It has a ticking sound like it would be at the exhaust manifold but, I'm unsure why it would be louder after the intake manifold and valve cover swap. Xan either of these if not sealed priperly produce the ticking noise? Maybe EGR? Any input is appreciated. Thanks!

The only thing that would explain a sudden exhaust leak sound after disturbing only the intake would be
the EGR (Exhaust Gas Recirculation) plumbing interconnecting the 2 systems.

For what it's worth, when you are trying to pinpoint the source of a leaking air sound like this, I've found
that the center cardboard tube from a paper towel roll is even better than a mechanic's stethoscope. (And
I'm a big proponent of mechanic's stethoscopes.)

For what it's worth, after 650K miles that EGR tube may be paper thin & was just waiting for an excuse
to let go... Otherwise, @Schurkey's suggestion above is also a higher probability area.

Let us know what you find. Happy hunting --

 

[spradilak]

You still have not answered, are the head ex mount holes clear, how much warp is there ? You should be able to use a mirror an see what's going on .

I replied in another comment, the pick only goes into the head by 1mm on both of them..unless there is only 1mm worth of threads in there they are definetly broken off. Guess I'm gonna abandon trying to fix that haha.

 

[spradilak]

The only thing that would explain a sudden exhaust leak sound after disturbing only the intake would be
the EGR (Exhaust Gas Recirculation) plumbing interconnecting the 2 systems.

For what it's worth, when you are trying to pinpoint an air leaking sound like this, I've found that the
center cardboard tube from a paper towel roll is even better than a mechanic's stethoscope. (And
I'm a big proponent of mechanic's stethoscopes.)

For what it's worth, after 650K miles that EGR tube may be paper thin & was just waiting for an excuse
to let go...

Let us know what you find. Happy hunting --

To add to this we started the project got the intake off, new one on..then had to take like a month break and I'm not sure if we connected any of the vacuum lines up wrong. I found a diagram and it appears we did it right but I do have a check engine light that comes on after I get up to about 50mph but the truck seems to run fine.

Idk if me taking pictures of all my vacuum lines would be of any help