Measure the back pressure on the catalytic convert

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I have a 1992 Dodge grand Caravan with a 3.3L engine. I would like to measure the back pressure on the catalytic converter to see if it is clogged. There are many YouTube video’s showing how to use a vacuum gauge to measure back pressure at a RPM. But the actual pressure and RPM you should use is somewhat vehicle specific and older cars are supposed to be considerably different than new ones. My Haynes manual has no spec for my van. Does anyone here have access to such information.
 

wally6934

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Originally Posted By: NHGUY
Put a vacuum gauge in the 02 sensor port.
I am looking for the spec for pressure and the RPM to check it at.
 
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Would be interesting to know. I've seen front/back temps readings taken, but no pressure readings.
 
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I had a Chevy Impala that had a blocked converter, it had NO pickup at all, was hard to get up hills, and took forever to get up to 50 mph! Shop was stumped too, until they put on a backpressure gauge. A friend had same problem and could hardly pull it up on a trailer. However, I had a bad fuel pump that gave similar results. Good luck finding your problem.
 
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Backpressure gauge at 02 sensor as stated by NHGuy. Should be around 1.5-3psi @3000 RPM if I recall. If it is more, your CAT is blocked.
 
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MolaKule

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Originally Posted By: Falken
Backpressure gauge at 02 sensor as stated by NHGuy. Should be around 1.5-3psi @3000 RPM if I recall. If it is more, your CAT is blocked.
Do you mean the differential pressure from input to [email protected]?
 
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I'm guessing he means 1.5 to 3 psi as measured upstream of the cat, not differential. It varies by make, but the ones I've seen have been driven until it's a major problem. Typically I'd see 6+ psi. We'd usually whack the throttle real quick and watch the gauge. Once we had one that would barely start and pull itself. We suspected a plugged cat so we pulled the O2 and fitted our gauge then started the engine and gave the throttle a good hard whack. There was so much back pressure that it blew the hose off the fitting and ruined the gauge. It was stuck buried well beyond the 15psi the gauge read to!
 
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If you can redline the engine in any of the higher gears you can assume the exhaust is working correctly. Easy, if potentially illegal test.
 
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Originally Posted By: wally6934
Originally Posted By: NHGUY
Put a vacuum gauge in the 02 sensor port.
I am looking for the spec for pressure and the RPM to check it at.
My guess is you won't find it... Using the o2 port would be a useless effort, even if converter isn't plugged there will be exhaust pressure at that point due to muffler and remaining exhaust system...
 
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