Clogged catalytic converter??
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Joined: Sep 2000
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Clogged catalytic converter??
Hello. My 1985 gets a big 8 mpg. The carb is new and I have done a full tuneup, oxygen sensor also, no improvement. Is there a simple way to check to see if the converter is clogged?? HELP!!!!
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Senior User
Joined: Sep 2000
Posts: 162
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From: Castine, ME
Clogged catalytic converter??
yes, there is a backpressure test:
1. you will need to attach a vacuum guage to a source of manifold vacuum and a tach will be helpful.
2. warm engine to operating temp. and shut it off
3. Restart engine and look at vacuum guage. Vacuum should be 16 in Hg on a well tuned engine. (a good way to verify you tune up was complete)
4. let the engine idle for 4-5 min while watching the guage...vacuum should hold reasonably steady
5. increase engine to 2000 rpms and hold for not more than 60 sec. At the end of 1 min, the guage should hold high vacuum wihout any additional throttle to maintain 2000 rpm. If vacuum dropped significantly or if considerable throttle was needed to hold rpm, the converter is suspect. if you want, to verify the results, disconnect the exhaust pipe from the manifold and repeat test...if the vacuum holds steady...its the cats.
Thats the test i performed on my vehicle...I learned it from a mechanic friend a year ago. hope that helps. Also, restrictive cats usually cause some performance issues. Do you notice less power or signifigant hesitation on a warmed up engine, while a cold engine runs excellent?
Captain Tim Bland
1986 F150 2WD LWB
300 I6 1bbl
3.08 geared 9"
three speed w/od
1. you will need to attach a vacuum guage to a source of manifold vacuum and a tach will be helpful.
2. warm engine to operating temp. and shut it off
3. Restart engine and look at vacuum guage. Vacuum should be 16 in Hg on a well tuned engine. (a good way to verify you tune up was complete)
4. let the engine idle for 4-5 min while watching the guage...vacuum should hold reasonably steady
5. increase engine to 2000 rpms and hold for not more than 60 sec. At the end of 1 min, the guage should hold high vacuum wihout any additional throttle to maintain 2000 rpm. If vacuum dropped significantly or if considerable throttle was needed to hold rpm, the converter is suspect. if you want, to verify the results, disconnect the exhaust pipe from the manifold and repeat test...if the vacuum holds steady...its the cats.
Thats the test i performed on my vehicle...I learned it from a mechanic friend a year ago. hope that helps. Also, restrictive cats usually cause some performance issues. Do you notice less power or signifigant hesitation on a warmed up engine, while a cold engine runs excellent?
Captain Tim Bland
1986 F150 2WD LWB
300 I6 1bbl
3.08 geared 9"
three speed w/od
Junior User
Joined: Sep 2000
Posts: 73
Likes: 0
Clogged catalytic converter??
Hello. I don't notice a difference between when the engine is cold or warmed up, both run strong and idle smooth. The exhaust dosen't smell bad either. I dont have a vacuum guage so I was hopeing there was an easier way to check.
One person told me let the truck warm up then put my foot over the tailpipe and the exhaust should blow my foot off. Never heard of that one. Greg.
One person told me let the truck warm up then put my foot over the tailpipe and the exhaust should blow my foot off. Never heard of that one. Greg.
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