Exhaust plugged up

Now does the cat rattle?

Some muffler places will drill a hole near the entrance of the cat to determine backpressure. I have removed a plug (02 sensor) to determine that.

What is the engine doing or not doing? I always recommend rechecking the camshaft timing!!!

No, banging on the catalytic converter indicates sound innards.

Reason I'm asking the question is because I had a bad coolant sensor in the past. It took me some time to figure it out, a month. The tailpipe is badly blackened, engine was running very rich.

Are you saying to physically remove the O2 sensor to see if there's difference in engine power at higher rpms, like climbing hills on the highway? If so, I can see that's markedly decreased in my observations.

My cat. conv. rattled, but it rattles no more! Exhaust sounds different too! lol

If something is wrong......fix it! If you want someting better...........change it! ;-)

No don't just change the 02 sensor to another location unless you have to. Now if you install another exhaust manifold and downpipe and neither had a spot for the multi-wire 02, then put it on the cat. :-)

Apparently, there's no test for a plugged catalytic converter per your reply. THAT is what I'm trying to determine before jumping to something else. Just dust in the wind is what I'm getting... Nevermind.

Is this still that '88 Fox?

If you try running the engine with the 02 sensor unplugged/removed then the engine should run differently. ;-) Usually poorly if the 02 sensor still functions! 8^o

WOW I answered that question about a test for a plugged catalytic converter a couple of posts ago..........I will bring it back to the top now. If the cat. conv. is clogged then the back pressure will be very strong BEFORE the cat. I also feel the exhaust coming out of the tailpipe! If it is strong then I will assume that the cat is fine!

Now if yours is a VW up to 1992 then you might have a CO pipe that has an easily removeable cap on it. Take that cap off and determine the back pressure. Just a little exhaust should come out of it if it is not clogged.

Camshaft timing and ign timing can make the engine run well or poorly. Also vacuum leaks can make the engine run poorly.

one way to check for a plugged cat is with a manifold vacuum gauge. under light throttle at cruising speeds up to about 70mph the vacuum should stay higher. If it drops off it maybe a sign of a bad cat.

The easy test is to get out on the freeway and accelerate up to the speed limit (will maybe a little over) in a bit of a hurry. If it is blocked, you should feel a lack of power and slow acieration. It may hit like a brick wall. This is not a sure test, but it works well most of the time.

If you don't know, likely it is not overly clogged.

Why do you think it is clogged?

I was looking for something like gas pressure near the entry of the cat vice the exit side of the cat. Guessing with near-plugged cat, the pressure on the inlet side would increase dramatically as rpms increase near full throttle.

The vacuum side on the intake could point to that as well. Where's a good connection point for such a vacuum gauge on the intake?

The easy test is to get out on the freeway and accelerate up to the speed limit (will maybe a little over) in a bit of a hurry. If it is blocked, you should feel a lack of power and slow acieration. It may hit like a brick wall. This is not a sure test, but it works well most of the time.

If you don't know, likely it is not overly clogged.

Why do you think it is ------ >>This is correct. Lack of power is common when stepping on the gas. You still need to remove the converter to examine it and see if anything falls out. its just a few bolts and clamps. The symptoms vary depending on how much its plugged. And how the engine was running before it became plugged. And maybe caused the malfunctioning converter problem . I find that people who don't want to remove their converter are usually afraid the exhaust pipes will fall apart from rust. And this is reason enough to suspect a plugged converter. Especially if a piece of delaminated exhaust pipe might be in the converter.

Cat was replaced some 6 plus years ago. Aftermarket version, welded in place. So, the loosen a couple of bolts to remove is not valid here. Local Midas shop put the car on a lift and banged both mufflers and the cat listening for loose internal components, nothing. All the piping has little if any rust on it.

Again, I suspect cat blockage as the car ran very rich due to a faulty coolant sensor for almost a month. And, has noticably slowed at highway speeds at same amount of throttle. High speed acceleration is practically nil.

Due to another response, I went out and got a vacuum gauge for checking the intake vacuum. It reads 17 In/HG at 800 rpm idle. That area of the gauge says possible late ignition timing. So, now I have to hunt down a timing light.

Got a compression checking tool. Cylinders read the following: #1: 137 psi #2: 137 psi #3: 138 psi #4: 135 psi

Loosing coolant someplace. Filled the reservoir to spec, ran it till it warmed up. Let it cool overnight, normal level for cold. Ran for about a month, found coolant reservoir empty yesterday after driving back from town. Filled to spec again, drove it a few miles. Don't seen any apparent leak or dribble of one. Oil is clean colored, no milky shade. No antifreeze smell inside the car.

With a welded cat you eliminated my favorite visual test. I look at both intake and outake looking for meltdown. I had had chunks fall off the back so it looks clear but converter chunks acted like potatoes in the pipe before the muffler causing quite a restriction

I have seen my car leak at the flange coming off the drivers side of the head (USA drivers side). The aluminum had corroded to the point of leaking. A new plastic flange from VW fixed that leak. Check your antifreeze every day you drive it to see if there is some pattern like driving it for a 100 miles in one setting cause a greater leak that a week of 10 mile trips. I have had the radiator leak and a few hoses. No head leaks in the years I owned Rabbits.

should have just had the aluminum ones machined and/or filled the pits with JB weld and filed flat, the plastic ones are known to warp and... wait for it... leak.

nate

There should be no more than 3psi of exhaust pressure at WOT. 2.5psi is excessive IMHO. Make up a gauge setup, pull your O2 sensor and cycle your engine to WOT to get an idea. Anything under 2psi is great. Fuel pressure is important, but don't ignore fuel VOLUME/Delivery as pressure isn't the only factor. Flow is just as important in the fuel system as the intake system flow- (read: Lose the K&N filter if you have it.) BTW: If you had a serious 'rich condition' for extended periods, your Cat. Conv. will likely suffer damage.