Tahoe Lack of Power Stumbles on Acceleration when Cold..

[stikky_p]

Hey guys.. I'm new to the forum and a 4th time Tahoe owner.. Unfortunatly I've never had this issue.. Hopefully you guys can help..

For starters it usually only happens "noticibly" when the vehicle is cold and has been sitting for hours or overnight. I start it, put it in gear, press the gas and it goes but stumbles and seems like a drastic loss in power. It does not rev up in terms of a slipping transmission. After driving a couple blocks it seems to clear up and be driveable.. During normal conditions it also has a lack of power.. I do have an engine light on but i've had it checked numerous times and its the evap sensor.. I'll fix that later..

I had a family friend look at it who happens to be a GM transmission tech at our local dealer and his first thoughts were not transmission but a clogged Cat.. He recomended i purchase a heat temp gun (29.99) and test the back and front of each CAT Converter.. I didn that.. the rear or the CATs were hotter then the front which is normal from what i understand.. A increase in Temp in the front would mean a restricted system causing pressure.. He then thought possibly dounle checking with a Pressure gauge but I haven't got that far..

None the less I'm looking for other alternatives. I don't want to book it into the shop and pay $109hr for someone to tell me something silly.. Im getting no codes and not to familiar with this 2000+ stuff.. Can anyone offer suggestions..?

 

[2005yukonxl]

clogged cats usually set some codes based on the o2 sensor readings. have u had the codes checked? most exhaust places can check for cat flow as well...usually for free. u may have a chronic evap code but i bet u have others as well now... check your codes if u have a scanner or run to auto zone and let them do it for free...then come back with that info and we can help....

 

[stikky_p]

clogged cats usually set some codes based on the o2 sensor readings. have u had the codes checked? most exhaust places can check for cat flow as well...usually for free. u may have a chronic evap code but i bet u have others as well now... check your codes if u have a scanner or run to auto zone and let them do it for free...then come back with that info and we can help....

Fortunatly I have a code reader handy.. The codes are

P0446 Evap Emmission system vent control circut
P0453 Evap Emmission system pressure sensor/switch high input

Same codes I had before that refers to the Canister or switch issue.. No new codes were thrown..

 

[2005yukonxl]

well crap. that doesnt help any.

you can do this- take out the forward 02 sensor, ahead of the cat, and then cold start it. if its a clogged or partially clogged cat that will create enough of an exhaust leak to see if thats the issue. it will throw a code if you drive it that way of course or if it idles long enough to not get any readings but seems u can reset them since u have a reader. i eliminated a stupidly annoying drivablitly issue that way with a dodge neon i built for my bro in law.

 

[Thumper8302]

clean ur throttle body man.. ive owned my yukon xl for a lil over a year and a half.. 2001 with over 240,000 on the clock... give it a good clean and since u have to take the intake tube off u might as well clean ur mass airflow sensor as well... make sure u get cleaner specifically for the mass air flow sensor.... i had the same issue as u on this and it cleared it up.. havent had an issue with this in over a year

 

[stikky_p]

well crap. that doesnt help any.

you can do this- take out the forward 02 sensor, ahead of the cat, and then cold start it. if its a clogged or partially clogged cat that will create enough of an exhaust leak to see if thats the issue. it will throw a code if you drive it that way of course or if it idles long enough to not get any readings but seems u can reset them since u have a reader. i eliminated a stupidly annoying drivablitly issue that way with a dodge neon i built for my bro in law.

Didn't seem like it helped.. Im going to try the throttle body cleaning tonight and give you an update tomorrow.. I'd like to make sure it isn't a transmission issue before i spend the $$ on 22" shoes for her.. here's hoping she gets new shoes

 

[fire730]

I had a similiar problem on my 98 5.7 Vortec.

Mine ended up being a cracked head so it would leak coolant into 2 of the cylinders when it would sit for a while. After a minute of driving and the coolant in the cylinder cleared it ran fine.

Im sure you heads arent cracked since they are aluminum but it could be a head gasket leak. Has the truck ever been overheated or does it use any coolant?

Just throwing out ideas. I would kinda rule out the cats cause you would most likely get a P0420 code for catalyst inefficiency. I really dont think it has anything to do with the tranny.

How many miles on it?

 

[stikky_p]

It's got 202000kms. I haven't noticed any coolant issues or fluid issues at all.. Although this is one vehicle that I haven't checked the plugs, cap, rotor or fuel filter.

 

[fire730]

Well I would definitely start with plugs, wires , and FF. If they haven't been changed recently.

 

[stikky_p]

Well I would definitely start with plugs, wires , and FF. If they haven't been changed recently.

You have a good point. I'll start there and I guess if that's not my fix at least I'm confident it's been tuned up. I'll spray the intake too while I'm in there. I've already cleaned the maf but noticed no change. I'll post pics for an update.