has anyone experienced a leaking exhaust manifold? The truck has a much louder than normal "knock" when excelerating. At first I thought and had some bad fuel in the tank. I eliminated that with a full take of good fuel and some STP but the "knocking" continued. Then I thought that perhaps it wasn't firing on all cylinders but it felt like it had full power. I took it to my mechanic and he said it as a exhaust manifold leak. He said that he has never replaced the exhaust manifold but that it was a "nightmare" and expensive. He also said that it's not a safety issue but on the long run the leak would cause the truck not to pass its emmission test. He said the problem was with rusted bolts that would be difficult to remove. Has anyone else had this problem? What did you do about it? Expensive?
Thanks

 

i have the exact same problem. the bolts have snapped off and the engine sounds terrible when accelerating. i have an exhaust guy i know who says it is common on these trucks and the best move is to replace the manifold with hedders. it is a pain to do especially if the bolts have snapped inside the heads then they have to be drilled out. plus it is a poor design because they use steel bolts in an aluminum head. i'm putting on hedders but i don't know if my engine is 2 valve or 3 and i need that info to buy the correct hedders.

 

A leaking exhaust manifold will have make "ticking" sound. On the 2V modulars broken manifold studs are extremely common.

An exhaust leak at the manifold is absolutely bad for a vehcile with O2 sensors. The leak will throw off the O2s which will in turn throw off the a/f ratio and can cause other problems. With a bad leak its not uncommon to lose quite a bit of power.

One reason I put headers on my 6.8l at 18k miles to avoid the broken stud problems. My dad got the studs on his 6.8l replaced for under $500. His studs were stainless and they still snapped off from constant heat/cool cycles. Eventually fatiged the bolts and broke off.

Spend the $$$ and get the studs fixed. If you have the extra $$$ spring for headers.

 

Good evening brent penfold and bcwood.... I see that both of you live in NY and I just wanted to invite you to stop by the NY chapter. Here is the link NY Chapter
If you are interested in joining, just click on the link in my sig and it will take you to the proper place to request membership. Thank you for your time and I hope to see you around the board.

 

The broken manifold actually is a safety issue, as is any leak that is in front of the converter. The reason is that exhaust that has not passed through a converter will almost always have potentially deadly levels of carbon monoxide, and when these leaks are in front of the cab, the gases can get into the cab. Repeated exposure to even small amounts can gradually expose you to enough to make you sick, fall asleep at the wheel, etc. I know because my brother went through just this and fell to sleep at the wheel and almost crashed. This was from a cracked manifold, so I know from experience that it can be dangerous.

And it is absolutely true what was said about O2 sensors. On a vehicle with a properly tuned exhaust, there will be vacuum in the manifold, and oxygen from the outside gets drawn into the exhaust. The O2 sensors detect the added oxygen and tell the computer to add more fuel to compensate. The added fuel produces a rich mixture that guarantees the formation of carbon monoxide.

 

any reason that you can't use some exhaust patch kit to stop the leak? I saw the type that is a cloth roll, dip it in a solution and wrap the area with the leak. There are other types of puddy and sealers for exhuast leaks.

would this work?

 

Not for very long. The patch kits really don't hold up the heat well enough to work, and they don't expand as much as the metal they are attached to, so it pretty much flakes off But it might last long enough till a more permanent repair or replacement can be made.

 

Vacuum in an exhaust manifold??? Your definition of "properly tuned" exhaust.jd

 

If you have broken manifold bolts, the leak will more than likely be at the manifold flange where it bolts to the head. Hard to patch that. A cracked manifold can be repaired. Any type of glue or putty isn't what I would call a permanent fix.

 

Yes, I did, but if you look up other articles I've written you will see that I said relative vacuum. And it does depend on application and conditions. For exhaust, you might get vacuum under cruise and light throttle, but once you punch the throttle, it can because a pressure region. AS often you are taking this outside context. Everyone should know that the hot expanding exhaust represents a great deal of pressure in the form of a pulse. I have always argued that it is in the wake of these pulses that vacuum exists.

So both statements are true, and I do deal with both cases all the time. For example, on Honda Civics, the converter fails when the manifold cracks, causing an incorrect O2 sensor reading. This cause a rich mixture which ruins the converter. This effect would not be unique to a Civic, and on the same crack you will find both problems I am talking about. If you read the O2 sensor and the fuel trim, that will indicate a lean condition that is being corrected by adding more fuel, and yet you can smell exhaust in the vicinity of the manifold. If you fix the leak, the fuel trim drops back down to normal, and the fuel consumption decreases.

I never said constant vacuum in my articles, and if you think about it, you have high pressure high velocity gases escaping the cylinder. It is in the wake of the pulses that the the vacuum exists. So many leaks work both ways.

If it were me, for the labor involved in replacing a manifold, you might as well pay for smog legal headers and get a little performance out of the deal. This is especially true if you are paying someone to replace the manifold.

 

nothing wrong with the exhaust mani, the piples connecting to the exhaust mani were not properly sized/bent, so the bolts never pulled the pipe tight. there is a large gap where exhaust is escaping. i am having new pipes and a new flange installed to seal both sides of the exhaust. this should quiet the thing down.

 

I have seen your half page dissertations on such subjects as yournturi effect," to the "Bernoulli effect," etc., and your attempts to connect them to exhaust flow. I have also noticed that you are not only an expert in exhaust flow, but also transmissions, carburetors, engines, and on down the line.

I am always in awe of someone with such a varied knowledge and proficiency, and wonder where such knowledge was obtained. Do you have an auto repair facility? How many auto repair technicians do you have? Where is your facility located? Were did you receive your automotive training? How many degrees do you have?

As far as the theory of exhaust manifolds taking in outside air that will create a fault to the point of creating damage, I have a problem as this not the case in all applications as you implied. A couple examples. My personal truck, a 1996 F150, 5.0, has had an exhaust leak on #4 cylinder where the exhaust manifold joins the head for almost a year. No cel, and no problems, no burned up converter, etc.

Early 90's Toyota Corollas, and Chevy equivalents, exhaust manifolds cracked almost immediately. Many, many miles driven with absolutely no problems such as you indicate.

There are many others, while I suppose there are exceptions, stating for certain that an exhaust leak must be repaired immediately before damaging components would be incorrect.

If exhaust manifolds could drawn in outside air, there would be no need for injection pumps, just run a pipe to each exhaust outlet and put a muffler on the end of it. But that is not that case. Air must be pumped in to overcome the pressure that exists in the manifold.jd

 

Trying right now to find something I can pick up at an auto parts store for a temp fix. It only has to last me 2-3 week tops. Looks like the tube part up near the flange section by cylinder 1.