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V6 catalytic converter causes blown head gasket

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Old 06-20-2011, 10:08 AM
Join Date: Mar 2010
Location: Greensboro, NC
Vehicle: 2003 Ford F-150
Posts: 95
V6 catalytic converter causes blown head gasket

Okay, everyone, here's something you need to watch out for. My '99 4.2 blew a head gasket, let water into the right front cylinder, and bent a rod when I tried to start it.
I rebuilt the engine, and it ran like a top for about 3,000 miles. One day, I went to start the engine after it was hot and had been doing some shopping, and it made bad noises again. The same head gasket had blown again! Fortunately, it didn't bend a rod this time.
Turns out the right side catalytic converter was clogged. It caused excessive back pressure, and that caused the head gasket to blow.
If your truck has high miles on it (mine has about 270K), be aware of this and watch out for it!
To check it out, take out the O2 sensors on both sides, put pressure gauges (15psi) in each hole, and start it up. At idle, you should see little, if any, back pressure. Rev the engine - both sides should go up the same, and shouldn't go over 3psi. If you see more than that, replace the converter. It's a PITA, but it'll save you some real grief down the line!
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Old 06-20-2011, 04:39 PM
glc glc is offline
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Join Date: Dec 2006
Location: Joplin MO
Vehicle: 2003 Ford F150
Posts: 31,301
Muffler shops have infrared testers that can detect clogged cats without having to pull anything apart.
2003 F-150 XL RCSB 2wd 4.2 M5OD 3.55 LS
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