p0300 pissing me off

[BOSS]

mine yukon is misfiring and sputtering like crazy during the first start of the day but after it warms up its fine the rest of the day. i changed the plugs and wires, feul pressure regulator, had a fuel pump failure and changed it, and a few days ago it threw the p0420 code. if it was the cat wouldnt it make a loud "rattle can" noise. i have used the rubber mallet to bang on the cat to see if it rattles but i got nothing.

IF you really want to test the cats efficiency, go to a state inspection place and pay them to test the exhaust with their equipment they use to test pre96 vehicles.

Chances are good that both of you have clogged cats.

B

 

[lilsolo68]

thats the thing with me, im spending more time checking out the forums to see what others have done right because i dont have alot of money to do it wrong. not saying that what your suggesting is wrong but since ive been laid off i dont have alot of funds to do the expensive troubleshooting. how much would they typically charge for that?

 

[BOSS]

thats the thing with me, im spending more time checking out the forums to see what others have done right because i dont have alot of money to do it wrong. not saying that what your suggesting is wrong but since ive been laid off i dont have alot of funds to do the expensive troubleshooting. how much would they typically charge for that?

Ah well it would be better if you had true duals to test it at a shop, and the fact that you were laid off puts it into a different perspective. Have you done all the free stuff like clean the TB, MAF etc?

Well free to do but you have to have the MAF cleaner and TB cleaner...or use brake cleaner
B

 

[lilsolo68]

yeah i clean it every so often.

 

[Chucktown Mako]

Anybody think it may be an EGR valve?

I have a problem on my '96 K3500. It sputters like crazy on hot restarts and doesn't go away until I come to complete stop and go again. Then it's fine again. I can't figure it out and that damn EGR valve keeps coming back into my mind.

They definitely are not cheap, so I am reluctant to drop $170 on a guess.

 

[amaz]

First - My driver side rear O2 sensor started to make rattling sound at cold starts. I changed it and the noises were gone. Drove it for a week and my truck started to run like shit and gave P0300-P0308 (misfire and 1-8cyl misfire). After a while I found the problem in ECM ground point at passenger side cylinder head near firewall (pics: http://www.kadotus.org/hoe/G103/ ). After I fixed that connection, truck run well. Few days after that I got P0420. Replaced also driver side front O2 sensor and have driven after that ~500ml without CEL coming on...

 

[hassoun]

BOSS, i have true Dual exhaust. i am replacing the cats next week anyway. Amaz, i'll be checking my ECM's ground wire in few mins and will report back!

 

[Caliptix]

Did you ever find out what the problem is?

 

[BOSS]

BTW I seafoam'd a p0300 away a few weeks ago....

http://www.tahoeyukonforum.com/forum/showthread.php?t=15400


B

 

[Caliptix]

Don't think that will help this. My truck is an '03 tahoe z71 flex fuel. Recently when i try and get into traffic, right around 3800-4000rpm, it sounds like some predetonation in the cylinders. The CEL starts to flash about 8 times and then turns off. It took awhile before a code was thrown, a P0300. I cleared the code.

I replaced the sparks, wires, air filter, changed the oil and oil filter, flushed the tranny, changed the Fuel Pressure Regulator(this is how i found out its a flex fuel).

After that it threw a P0430 code, making me think it could be the o2's or maybe the cats. Problem is I had the dealer replace both cats before I bought. I am narrowing downt he problem, but im not sure what it is yet.

My guess right now, is either a leak in the intake gasket, clogged fuel injectors, or a vacuum leak somewhere.