2002 GMC Sierra 1500 downhill after cleaning K&N Filter (now needs cats)

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Old 02-08-13, 06:12 AM
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2002 GMC Sierra 1500 downhill after cleaning K&N Filter (now needs cats)

2002 Sierra Denali AWD Quadrasteer about 143,000 Votec 6.0 engine U.
After installing my first boiler (see previous posts) my truck died on me. Truck was averaging about 12.8 mpg city and highway for the last three months. Its rated from the factory at 14 city/ 17 highway from the factory.

About a year ago I cleaned the MAF and throttle body using the proper cleaners.

Anyway, did a routine cleaning of the K&N Air Filter and let it dry out pretty good. Sprayed the filter with oil and reinstalled it.

Drove it around on very short trip...no problem.

Drove it to work next day. No problem.

Same day at work, ran an errand at lunch time it started missing heavily and "Service Engine Soon" light came on. Backed off it and eased it back to work. Very short trip.

Drove home, tried cleaning MAF and throttle body. MAF appeared to be not to dirty. Throttle body was okay since I cleaned it a year ago. Still missing.

Took it up the street to autozone to get the codes checked next morning. I was throwing random mis-fire (no specific cylinder), MAF sensor error code (no cat codes). Getting concerned because a steep drop in performance. On the way there it starts missing heavily under a load, now on my way to my mechanic. Fuel gauge was going from 1/4 tank to empty and bouncing back. Started thinking I had a bad fuel pump.

After doing some 02 sensor checks, my mechanic says I need cats because they are clogged. He removed the 02 sensor and it ran a bit better. Also need a tuneup and I'm leaking air because of the back pressure. Cost to repair $2800.00 (this includes tuneup, OEM cats, fixing a leaky exhaust or intake). He checked wiring, pump and it was okay.

I've ordered a MAF sensor and brought the truck home. I'm a little skeptical of my mechanics diagnosis because he said I needed cats on my wife car because of a service engine soon light. I found a loose battery cable and the error went away and never came back.

Not saying it wouldn't benefit from new cats. Right now I have no power when warmed up.

My questions are;

1. I will cautiously try replacing the MAF sensor.

2. If I need cats for sure, should I go with aftermarket or OEM cats? I see rockauto sells Eastern Cats.

3. I should do a full tune up also, which includes plugs, wires, air filter (dumping k&n), gas filter, pvc...am I missing anything else.

4. Air leaks...guess that needs to be repaired also.
 
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Old 02-08-13, 06:20 AM
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Catalytic convertors last a long time although vehicles that burn oil will shorten their life. Loss of power is one of the signs of a plugged cat. I'd get a second opinion before I spent the money.
 
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Old 02-08-13, 06:26 AM
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My engine does burn oil. I have to keeping an eye on it. This is something I may do myself. Depending on how hard or far I drive the truck, maybe a 1 quart once every two week or month.
 
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Old 02-08-13, 06:36 AM
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It might be too corroded to unbolt but if you removed the cats and made a quick trip around the block - that would verify if it's plugged and causing the loss of power. I've heard of some folks drilling a hole in a plugged cat to relieve the back pressure but...........
 
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Old 02-08-13, 06:43 AM
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lol...I will keep drilling a hole in the cat in mind.
 
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Old 02-08-13, 08:10 AM
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I was talking to a co worker and he put after market cats on his car. Needed to make some modifications to his 2002 Maxima, firewall. Make a long story short he says his car sounds like a truck. Maybe less of a problem though with a truck.
 
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Old 02-08-13, 02:30 PM
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I think I would get a second opinion. You should have 2 upstream and 2 downstream sensors. If the cats are clogged, the 2 downstream sensors should be throwing codes because they are after the cats.

I just reread your post. You mentioned replacing the intake gaskets. If the intake is leaking it could very well be your problem.
 
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Old 02-09-13, 08:38 PM
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jpr28056 leaking intake will burn out the cats?
How about leaking exhaust manifold gasket (manifold to head)?

My cats are clogged. started her up with the two upstream exhaust sensor removed. Truck seamed to run better just as the mechanic said.

Do the exhaust manifolds go bad themselves? Just concerned about damaging the new cats. I want to be as thorough as possible.

I started breaking down the truck already. Got everything loose so far as far as front pipes and 02 sens
 
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