Pressure Tester Gauge for Measuring

[duke16]

Measuring Exhaust Back Pressure

I'm trying to verify my front cats are clogged. Can I use a Compression Test Gauge ( http://www.autozone.com/autozone/ca...e=Tools&parentId=cat30101&subPartId=prod62339 ) connected to the oxygen sensor port on the exhaust to measure the pressure after the cats?

 

[Dilbert5]

No, that gauge is for testing cylinder pressure, the range is far too high to use for testing you cat.
They do make a pressure gauge that is a much lower range. Look up this ebay auction #

Basic Exhaust Back Pressure Tester Set w/Oxygen Sensor Item number: 250455327464

 

[duke16]

Thanks.

Is this the best way to test a cat?

 

[Dilbert5]

The gauge will give you a positive reading, of course you could check engine vac while bringing it up to a fast idle, then back down. Then pop out the O2 sensors and re-check the vac readings.

 

[duke16]

So I got the above pressure tester ( http://cgi.ebay.com/ebaymotors/ws/e...&item=250455327464&viewitem=#ebayphotohosting ) and hooked it up, and I'm getting a reading of practically 0.

I have my two rear cats removed. So my setup is 1 cat per downpipe, with an O2 sensor before and after each. I hooked the gauge up to the O2 port closest to the engine (before the cats). Both sides are basically reading the same, 0 bar at idle, 0 psi at 2500rpm. The strange thing is, the needle is bouncing around ALOT. It will not hold steady, so it may be above 0, but I can't tell. Below is a picture of the gauge. Have I done something stupidly wrong? Should the needle be bouncing around like that?

Thanks

 

[Dilbert5]

It is normal for the needle to be bouncing around. Since the pressure is remaining near zero, it would appear that your cats are not clogged.

 

[budwich]

I guess the question is why do you think that your cats are clogged???

 

[duke16]

Sluggish acceleration, loss of power, bad gas mileage. And I had a rattle from 1 of the cats soon after having my cat-back system installed. It's gone away now.

In addition, I had been driving on a bad spark plug for some time (not intentionally, but I did have some bad misfires, enough to blow out the header gasket). So putting all that together, I thought it was a sure thing at least 1 of my cats was clogged.

 

[budwich]

thanks... that will help us more. IF those conditions still exist, you might want compression test a few cylinders especially the mis-fired one to see if they are "good". Some times, in addition to washing cylinders with gas to cause a cat problem, mis-firing (non-firing) can cause ring/compression problems depending on how long the condition existed. Perhaps cleaning some components (eg. MAF) might be worthwhile.