Blocked exhaust

I suspect that my converter or muffler may have collapsed internally. How would you confirm this without tearing apart the system?

One could either unbolt the header pipe from the rest of the exhaust and test drive it sans converter/muffler (a bit noisy) or use a vacuum gauge. I prefer the latter.
A vacuum gauge is cheap, easy to use, and will last you forever.

If you purchase a gauge it will probably come with an instruction sheet on how to read it. If not, simply connect it to a vacuum line at the intake manifold.
With the engine at idle you will have a reading of 16-20" of vacuum (this varies based on altitude, barometric pressure, etc.)
Rev the engine quickly and you should see the needle drop to zero instantly.
Allow the throttle to close quickly; the needle should return to the original reading (16-20) instantly.

If the system is clogged the needle will return to something a bit higher than than the 16-20" and will then drop slowly back to the original 16-20". If it does this then you probably have a clogged converter. Hope that helps.

vacuum gauge is the best way ,as in post above,but the specs are WAY off base,consult a service manual.

good luck.

The vacuum gauge is much more elegant and probably more reliable, but - similar in principle to unbolting the header pipe but easier and quieter is to pull the O2 sensor(s) - it doesn’t open up the pipe quite as much but does a similar thing.

Pull it - drive around and if the power is better you likely do have a clog

if the blockage is severe,one will never notice a difference, a VAC gauge is the perfect tool,it will tell you ,valve issues,timing issues,restrictions,and many more things .if one learns how to read it properly,just like a multimeter.except this works great for the breathing of the engine,and when dechipherd correctly will answer all need to do more work than nessecery.

hope that helps.

What specs are way off base?

I had the same question.

You are mostly right, of course. But I figure if the OP has a vac gauge and knows how to use it they wouldn’t be posting about this. Thinking from my own situation, it would take me an hour to go out the store and back to get the gauge, and then another who knows how much time to figure out the specs, hooking it up and interpreting the output. (Then, of course, there’s the annoying drone from the wife about how every time I work on the car I have to buy another tool). Meanwhile, I can pull an O2 sensor in about 5-15 minutes and find out if anything is different. So to me (and maybe the OP), the vac gauge might be the things that is more work than necessary.

And I would think that with a major blockage it would be easy to notice the difference. A minor blockage would be where it should be hard.

In any case, as I said, you are mostly right. I would suggest to the OP that if they frequently do have to mess with cars to spend the time/money on buying and learning the vac gauge. I have recently decided that it is high time that I did as well.

A vacuum gauge is a cheap investment. A vacuum gauge and fuel pressure gage should be in any wannabe mechanics toolbox. The vacuum specifications and the sample instructions are in most repair manuals. A repair manual is another required tool. Either, Haynes or Chilton’s are ok for the novice.

sorry fellows,did want to step on anyones toes,I apologize. I only say the specs are because,I dont know what theOP is working ,and Ive had cars with higher readings at idle and the service manual said that was ok for that particullar vehicle. the specs given are dead on in a general sense.the best way to see a restriction is to use a tach,run the engine to 3k RPMS,gauge will drop to zero,than rise between 5-8psi and stay there,depending on the size of the restriction.

sorry again

No apologies necessary at all; just curious about why you disagreed with the vacuum specs. I’ve seen some service manuals that make reference to 22-25" of manifold vacuum but have never run across a vehicle that would approach those numbers.
The elevation above sea level here is a shade over 1000 feet and most have run about 17-18" of vacuum Seems like I vaguely (very vaguely) remember a vehicle once that was hovering around 20 with a few others in the 15-16" range.
I suppose certain engines could hit in excess of 20 if at sea level with the right atmospheric conditions involved.

This kind of falls in line with something that has always puzzled me and this in regards to pulling a vacuum on an A/C system. Many manuals state to pull them down to 29" and I’ve never, ever been able to come close to that number.
Air operated vacuum pump, new or used Robinaire electric vac. pump, and a totally sealed tight system has never gotten me anything better than 21" even after pulling a vacuum for an hour and a half.

Slightly off-topic but just wondering’.

I only said that because I’ve seen cars where the02 sensor is not even visable,whithout the use of a lift,then when you can see it you need a special tool,which price wise ,could well exceed the price of a vac gauge. I only say that for the fact that I have hundreds of dollars invested in 02 removal tools.just trying to make it the fact 40% of sensoor are crossthreaded from factory,and other reasons.


Would bad cat cause engine to not want to run above 50 mph and cause brakes to become hard, losing vaccum surely. restarts in 5-10 minutes but is rough. Losing vacuum led me to rule out TCC Will get new vaccuum gauge tomorrow to test. Thanks