Clogged cats causing lean condition?
- Thread starter metroplex
- Start date
- Status
i know you will have alot of back pressure. the vehicle probably will not run up to 3000 rpm and then start to cut out. it might cause it to lean out for the simple fact that its not burning all of the mixture its putting in because its not excaving it completely. so my best guess its doing both, but youll never know unless you have a scanner. hddm3
yes a clogged cat will cause a lower vacuum reading. Particularly if you idle, take the reading, run it at 2500 rpm for a while, then idle again and get an even lower reading.
A very hot exhaust will heat up the front 02 depending where it is and skew its reading, pretty sure in the lean direction. 02 sensors are actually pyrometers and lean exhaust is hotter.
A very hot exhaust will heat up the front 02 depending where it is and skew its reading, pretty sure in the lean direction. 02 sensors are actually pyrometers and lean exhaust is hotter.
A lean mixture will misfire, causing unburned fuel to enter the cat. Inside the cat all this extra fuel is ignited, causing the cat to overheat. The cat will eventually break apart internally clogging the exhaust system. Misfires are one of the catalytic converter's worst enemies. Lean mixtures which cause misfires will damage the cat.
Once a cat is clogged, an easy way to confirm diagnosis is to bring the engine up to operating temperature. Use an infrared no-contact thermometer gun to measure the temp on input and output sides of the cat. On a clogged cat the output temp will be considerably cooler. Example numbers for a clogged cat would be say, 400 degrees F input side, 150 degrees F output side.
On a good properly functioning cat the output side will be 50 to 100 degrees F warmer than the input side. Example numbers for a working cat might look like 420 degrees F input, 480 degrees F output.
A vacuum gauge and an infrared no-contact thermometer gun are two of the most useful tools to have when diagnosing a bad cat or restricted exhaust.
Once a cat is clogged, an easy way to confirm diagnosis is to bring the engine up to operating temperature. Use an infrared no-contact thermometer gun to measure the temp on input and output sides of the cat. On a clogged cat the output temp will be considerably cooler. Example numbers for a clogged cat would be say, 400 degrees F input side, 150 degrees F output side.
On a good properly functioning cat the output side will be 50 to 100 degrees F warmer than the input side. Example numbers for a working cat might look like 420 degrees F input, 480 degrees F output.
A vacuum gauge and an infrared no-contact thermometer gun are two of the most useful tools to have when diagnosing a bad cat or restricted exhaust.
My vacuum at idle is 16 inHg, and I thought it could be an intake manifold vacuum leak. But this is a 2000 Crown Vic and it idles fine (has aftermarket cams and non-standard intake), but I did these mods 2 years ago and it has run fine up to 2 months ago when I think bad 87 octane gas could have fouled my O2 sensors, causing the cats to plug/burn up.
Vizvo, that's some good info to know, thanks for the tip.
- Status
