[rockyklg]

hi everyone,
a few days ago my truck started running really rough suddenly after a quick stop at the store. 260K and burning a bit of oil i immediately thought plugs. after i replaced the plugs i noticed it was leaking exhaust from the heat riser shaft pretty badly. plugs made almost no difference. i checked spark and they are all firing strong. could the heat riser be the trouble??? any ideas?
thanks

[FarmerTed]

The heat riser is just a tube that directs heat from the exhaust manifold up to the air intake. If there is exhaust coming from there then it sounds like you may have an exhaust manifold leak. It could be just be the "horn" rings leaking but with the rough running it sounds more like you may have an intake leak as well. Since these "share" a single gasket it may be time to replace it.

[rockyklg]

well the exhaust is coming out of the shaft with the spring wound around it on the exhaust manifold. i thought that was the heat riser. do you think the intake and exhaust manifold gasket went at the same time and that is what is causing the problem?

[jeepgod]

Can someone tell me what it runs like and sounds like when you have a intake/exhaust mainifold leak/

[FarmerTed]

Originally Posted by rockyklg

well the exhaust is coming out of the shaft with the spring wound around it on the exhaust manifold. i thought that was the heat riser. do you think the intake and exhaust manifold gasket went at the same time and that is what is causing the problem?

You can pull the air cleaner off and the heat riser/shield is held on with two bolts. If you pull that off you will be able to see where the exhaust is coming from. Whether it is the "horn" or the head to manifold gasket, either way you will need to pull the intake/exhaust manifold to repair it so a new manifold gasket is a given. I just went through this. It is a pain but fairly straight forward. There are lots of write-ups here on mud that will help greatly.

[Outdoor Adventure]

Try carb cleaner sprayed on the intake manifold. Improvement will confirm a leak. The heat riser is not a tube; it is a flap that rides on the shaft. The flap opens and closes according to engine temperature, hence the spring. The front of the shaft rides on a bushing, no longer available, and the rear end of the shaft is fitted with an exhaust restricting cap/plug. When the bushing and shaft wear and/or the rear cap is missing, you'll get an annoying exhaust tick. You can remove the horns with the manifold attached if you have to replace the rings. My sense is that the exhaust issue is separate from the rough running. The intake manifold is aluminum and susceptible to cracks and/ or gasket leaks.

[rockyklg]

yeah its all pretty well striped and desmogged so i can see quite clearly that it is coming from the shaft. do you think this is why it is running so rough?

@jeepgod sounds like a ticking noise for a small leak and kind of a whopping noise for a big leak

[2mbb]

so the original poster is finding exhaust coming out from the heat valve which sits in the exhaust manifold directly underneath the carburetor. This is a flap that is moved by a bimetal spring. When the engine is cold exhaust gases are directed to heat the air inside the intake manifold and when the engine is warm, the valve moves to direct the exhaust gases away from the intake manifold.

This is not the HAI valve or inlet tube which gets hot air into the air cleaner by collecting air from around the #1 exhaust port

The shaft on the heat valve doesn't really have a seal. It's just a shaft through a bushing, especially on the front side (the side with the bimetal spring). Some leakage might be expected. If you have a lot of exhaust leaking (and it's not from something else like a crack, etc.), then I would begin to suspect that you have excessive back pressure in your exhaust system.

[rockyklg]

@2mbb what could be causing the extra back pressure? could the heat riser valve be stuck in the closed posistion? no cat installed, pretty new muffler (6 mos or so).
thanks for the replies

[2mbb]

I suppose the heat valve could be stuck closed, but I don't think that would cause the leaking. when the engine is cold, you can try and rotate the end of the shaft to see if it's stuck.

Pretty much that only thing that would cause back pressure in the exhaust is the cat, the muffler, or a collasped pipe. If your muffler is new and no cat, then that's probably not the problem.

With that information I would say that the leak is probably a red herring and your problem is unrelated.

[rockyklg]

thanks mbb!!
that image def make me think its not the riser blocking flow... when done with work im going to see if i can find an intake leak somewhere. guess im gonna have to check compression too.. hopefully its not something really bad.. im open to any advice.