Whats Wrong With My Yukon?

[mcnaught82]

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.

[n8ball2013]

timing maybe? Bad distributor etc

[mcnaught82]

Its a 2003, so it doesnt have a distributor, it has 8 individual coils for each spark plug.

[jmitch]

check ya gas cap, pvc valve, pull ya plugs out see what they look like, MAF sensor and air filter see it they r clean. thats all the inexpensive stuff to check first b4 u go to the shop and let them rob u lol Hope u Get back rollin soon

[EricM9104]

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.

When you have a bad O2 sensor, the engine will generally run a bit rich soo... Have you replaced the O2 sensors yet??

[G_Fresh]

Ticking can be alot of things. When my engine made that noise, we thought it was the tensioner, then the timing cover. None of those, so brought it to a shop and it was the crank shaft. Hopefully that's not your case!

[Chris D]

When you use the brakes does the RPM of the engine drop or does it stall out? Also, have you noticed any oil spots after the truck sites overnight, or anywhere you park? And the engine light flashing is probably caused by the engine misfiring.

As long as the motor is running, it shouldn't be spark plugs. When the truck is out of drive, does it rev to a high RPM like it should or does it only go up annd stop before hitting the rev limiter?

[mcnaught82]

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.

[meade916]

did you try cleaning your throttle body? Also your throttle sensor on the side of the throttle body might be bad too.

[roscoe1129]

sounds alot like your cats are bad.