03 Tahoe Z71 - P0300...

[nritzell]

Hi everyone, almost a year ago I got a p0300 random missfire, light started flashing as I was going down the freeway, turned off and never had an issue since, until on Monday, I was driving on the freeway and went to pass someone and accelerated, at about 3k-3.5k rpm it started flashing, engine started making a pinging noise and seemed sluggish and hesitant to shift, i left off and drove normal, no issues. Tuesday I take my truck to the shop, they did maintenance, new plugs, wires, cleaned throttle body, cleaned fuel system, new fuel filter and air filter, I pick the truck up, they said they went and drove it on the highway and tryed to re create the issue, didnt come back. I get in, drive down the road and at about 2k rpm it starts flashing again, hesitant as it was before, no more pinging though... at this point im not really sure what to do so i wanted to see if anyone else has had similiar issues to this before i just started throwing money at it.... one thing i read on another forum is to get my crank re learned in the computer?? also on monday this all started after I put gas in at walmart... not sure if that has anything to do with it, but worth noting.


Thanks.

 

[Scottydoggs]

how many miles you got on her? really sounds like clogged cats.

flashing cel means a catastrophic even its occurring, most of the time its due to needing a tune up real bad, or clogged cats.

clogged cats will make it feel like its down on power for sure.

 

[nritzell]

how many miles you got on her? really sounds like clogged cats.

flashing cel means a catastrophic even its occurring, most of the time its due to needing a tune up real bad, or clogged cats.

clogged cats will make it feel like its down on power for sure.

Scotty, I have 195,000 miles, I'm also throwing a code for P0420.. Would it be a cat even if power seems fine at lower rpm, normal acceleration, just under more of a load it seems to be bogging?

Thanks.

 

[Chubbs]

There are methods of diagnosing faulty catalytic converters. You can search the Internet for answers but it's fairly simple and quick to deduce. If 1 or both of them are not glowing red @ engine operating temp, I believe there is a critical or specified temperature at which the determination can be made that the unit is faulty or operating under proper conditions.

Factory authorized facilities or dealership service departments have dedicated tools for diagnosing cat-converter faults but from what I've read, there are layman techniques as well such as temp or internal rattling. Def worth pursuing as a DIY

Scan tools are used to measure functionality on a technical level, which could also be of value but I believe the above exercises would be utilized first, in a case such as yours.

Are those the only 2 codes? When did you last scan it and were both codes simultaneous or 1 here, 1 there?

 

[Scottydoggs]

Scotty, I have 195,000 miles, I'm also throwing a code for P0420.. Would it be a cat even if power seems fine at lower rpm, normal acceleration, just under more of a load it seems to be bogging?

Thanks.

po420 is a cat code https://www.p0420.com/

with those higher miles, sounds just like a bad cat or two. the cats can clog, or they break up and clog the exhaust pipe. hit a bump pieces move and clear the exit of the cat again.

like chubbs said, you can use a temp gun to read pre and post cat temps. or drive it hard at night, pull over and see if the cat or cats are glowing red, if you see it glowing red you now know that cats are clogged up.

 

[Walkercraig01]

does it do it on hot days or does that matter

 

[nritzell]

does it do it on hot days or does that matter

It just started this week and it has been pretty hot, previous time months ago it was cold..


I took it to another shop they checked cats, they said they were still good, we checked the fuel system and all numbers were good...

Now it is missing at lower RPMs, I had to drive home on side streets doing no more than 30 mph as it was missing at that or higher, I pulled over turned it off and back on and could get up to 45.. at this point Im leaning to think maybe its the crank sensor or camshaft sensor... motor does make a noise when WOT currently so maybe something timing related??

 

[Doubeleive]

just a thing to possibly check is the MAF sensor, try cleaning it or pick up a used one from the junkyard there usually only about $25-30 used, a can of maf cleaner spray is only a few bucks as well, I have had lean cat codes come up before, cleaned the maf and it went away, may not be the case here but just one thing to check that's easy and not costly. I would be hesitant to blame it on the crank/camshaft sensor.

 

[nritzell]

just a thing to possibly check is the MAF sensor, try cleaning it or pick up a used one from the junkyard there usually only about $25-30 used, a can of maf cleaner spray is only a few bucks as well, I have had lean cat codes come up before, cleaned the maf and it went away, may not be the case here but just one thing to check that's easy and not costly. I would be hesitant to blame it on the crank/camshaft sensor.

also, cat code hasnt come back, only the p0300 has.

 

[Doubeleive]

also, cat code hasnt come back, only the p0300 has.

I was recently having p0300 come up on a 04, changed the intake gasket, plugs, wires coils, knock sensors, was still running like crap, shifting weird, changed the maf out, smoothed right out shifted correctly again, the maf code had come up right after doing everything else but I am sure it was getting bad before it threw the code, that stupid sensor does all kinds of weird stuff when they get bad.