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mcnaught82

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Posts posted by mcnaught82

  1. I 2nd this

    Just had an 03 silverdao with a 5.3 in the shop wednesday with missfire codes and a cat efficiency issue, damn thing had no power at all. pulled the exhaust loose on one side and she ran like a striped ass ape.

    Being you have 02 sensors b4 and after the cat, throw a back pressure gauge on it and get some readings, anything over 2psi of back pressure and yer screwed. and be sure to check them with the rpms raised up as well, not just at idle. If ya dont have access to the tool, just drop the exhaust off one side.

    Aftermarket cat assembly aught to run you bout $750. A dealer part would be prefered due to some aftermarket cats not burning correctly and setting codes after replacement but when i called the dealer they were out of stock in all the warehouses in the midwest and were on back order.

    Good luck man

    I thought about doing that, disconnecting the exhaust from the headers and see what happens? How much does a back pressure gauge cost?

  2. I haven't changed the O2 sensors yet but I am going to, I am going to clean the MAF because a couple month ago my Yukon through a code, I cant remember which one basically saying that the MAF wasn't reading correctly, that there was more air entering the motor and the MAF wasn't detecting the extra air. No there isn't a leak between the MAF and T/B. It doesn't leak oil at all. Chris D, the engine can still run and have a few bad spark plugs as long all of them aren't bad. I haven't tried REV my motor to the max while in park, since I don't want to risk damaging the motor more in case there is a small head problem. I do rev the motor to about 2000 RPM and when I let go of the gas it will drop down and almost stall out but than jump back up to normal and start idling like shit again. Right before it fucked up really bad I did floor it from a stop because I noticed my yukon felt a little weak in power and it didn't want to go fast at all. Basically it felt like a 6 cylinder instead of a V8 in my yukon.

  3. Last week I started up my yukon and I heard a light tapping coming from the heads. So I checked the oil and it was barely even reading on the dip stick, and I still had 1500 miles till my next oil change, No my yukon was not smoking or anything indicating that there was oil burning. So I went down to the shop to get my oil changed and my engine light poped on so they scanned it for me and it came back with a P0420. which means ether the cat is plugged or my O2 sensor might be faulty. So this weekend I went to San Jose which is almost 200 miles round trip and I noticed my yukon was lacking power. On the way home it barely wanted to go over the mountain I had it floored and it was barely doing 30 MPH, so when I finally got to the next truck stop at the top I pulled over and noticed my yukon was idling really rough kinda like it was mis firing. I checked my oil and it was still full. I started down the hill and while I was accelerating my engine light started flashing, and I could only do about 30 MPH all the way home. When I would come to a stop and try to accelerate my yukon wanted to barely move and I heard alot of knocking in the motor. I though maybe my heads were damaged. I get home and I put it in park and I rev the motor and the knocking is gone, but as soon as I put it in drive and accelerate the knocking comes back.

    Could the problem be my cats are plugged and the back pressure from that being pushed back into the motor caused me to damage my spark plugs? Also when I start up my yukon right away I smell gas really bad, like the exhaust is blowing back into my engine bay. I checked my oil when I got home and it is still full. I know my head gaskets arent blown because the radiator fluid is still perfect and not oily and my oil doesnt look milky ether.

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