weird idle

[white99tahoe]

so heres the deal. i noticed when the wife and i returned from supper earlier, that the tahoe, when put in park, had a very low almost rough idle. just replaced plugs, wires, distributor cap, and rotor last week. the fuel pump and filter were replaced several months back. we just recently picked this tahoe up from my aunt, which i know they didnt do anything else to it. any ideas? ran a bottle of the BG 44k through it when we first got it bout 2 weeks ago. reckon i should try some seafoam, or are yall believers in that stuff? ive never used it myself, but have always been curious bout it. ive seen videos where it clears up a motor pretty good. any ideas would be great.
oh, also, sometimes, when we go to start it, when it finally fires, its like there isnt much behind it. kinda hard to explain. right after the tune up, i started it over and over, and it would fire great. now, sometimes, its like it hesitates. the starter has no issue, or battery doesnt seem to not have the cranking power. im just not sure on it.

 

[lesterl]

Check the fuel pressure...... Check for fuel pressure bleedoff...... Could be a leaky injector/ FPR or a possible bad fuel pump? I would change the filter again....

 

[white99tahoe]

Ok, so first, this has been doing this for yrs, so I'm figuring it's not the pump, possibly filter as well. The pump was recently replaced due to it taking a dump when my aunt was driving down the highway.
Next, what will be my best way to check my fuel pressure? I have a gauge setup to read it on the duramax, but never really dealt with a gas motor fuel system.
Thanks again

 

[lesterl]

Fuel pressure guage gets hooked to back side of intake on drivers side there is a schrader port.

If you used an aftermarket pump it has probably taken a dump on ya again... I only use OEM pumps in GM products....

 

[white99tahoe]

ok, so its finally throwing a code, P0420 catalyst system efficiency below threshold (bank 1).
so im figuring this exhaust, motor to catS, is factory? yep, 2 cats. dual all the way back to muffler, dual in, dual out. some crappy muffler thats rusting through.
ive been thinking bout going with a whole new exhaust already, now this has me wondering if i shouldnt just replace the WHOLE setup, from front to back. any ideas? best place to start? should i try to find it all and install myself, or take to professional? if pro, then where? i live in san antonio, tx. thanks ahead of time for anybody who has awesome ideas on this.

 

[lesterl]

Just installing 2 new cats on my Sierra.... $50/ each from amazon.com Might check the live data and see if b1s2 is not holding steady (cat is non functional).

 

[white99tahoe]

well i got to talking to a guy who is more saavy with this stuff than me. actually hes an engineer. suggested changing upstream O2 sensors first. i said ok. so i go to oreillys and autozone to compare prices, and they ask a question that i have no clue of the answer. now dont laugh when i say this, but how do i know if i have the 4l60 or 4l80 tranny? apparently there will be 2 different parts.
then the guy at autozone says i should replace all 4 instead of just the upstream 2, cause then it might mess up the other 2. wtf?!? how does that make any sense at all??

 

[lesterl]

You have a 3/4 ton? 1/2 ton usually has a 4l60e. Tahoe AFAIK is 1/2 ton.

UPSTREAM sensors are all that are needed. Downstream on GMT400 ONLY monitors how good the cats are AFAIK.

 

[white99tahoe]

nope, just 1/2 ton 2 door tahoe. i looked it up and found it says its the 4l60e, but thought i would double check.
yeah, my guy told me to try the upstream O2 sensors first, then if still problems, go ahead with the cats. it all seems to be rusting out, so i will probably end up just buying a whole kit to replace it all. im sure it will be pricey, but damn, this is irritating.
the truck is my wifes dd. we went to walmart earlier, and i heard a clinking sound when we hit speed bumps. i looked underneath, and just as i suspected. stabilizer bar end link on passengers side is wore out and loose. looks like my next project as well.
i appreciate the input.

 

[lesterl]

Get the heavy duty endlinks, they are a bit beefier....

 

[white99tahoe]

I'm pretty sure i did, or at least thats what they told me at advance auto parts. $30 each side i believe.
i replaced both upstream O2 sensors, truck seems to run a bit smoother, and start easier.

 

[lesterl]

Ouch, methinks the only set me back $10 each side when I did mine from autozone...

 

[white99tahoe]

well these bastards better hold for the remainder of the life of the truck.
so back to original reason for posting. i cleared code long before the O2 sensors were installed. didn't notice a difference in the way it starts or runs. driving it tonight, SES light came back on. haven't had a chance to plug in scanner yet, but I'm sure its the same as before. i have found the complete cat section, after manifold, before cat back, for $300-400 by walker. then i will go ahead and get a decent cat back set up. ideas?
I'm sure some of you think i may be crazy, or not too smart with this, and i apologize. i haven't owned a gasoline truck in a very long time. i deal with my 2006 sierra 6.6l all the time.

 

[lesterl]

I keep getting a p0141 for my drivers post cat sensor, I dont really give a $hit about it tho.... it does nothing for the runability of the engine in this body style.....

 

[adam74]

wheres a good place to get the hd end links from lester? I also need to replace both of mine.

 

[lesterl]

I picked mine up at autozone, but they are just beefier bolts, I suspect if you want some real killer ones you would need to get online like lmctruck or something.....

 

[white99tahoe]

well, got the cat section of exhaust swapped out. truck definitely runs better. thinking bout going ahead and getting the catback section with muffler changed out. the only real kit i have found, that won't cost my paycheck, is flowmaster, but still $389. anybody know a muffler shop in or around the san antonio area that will do a quality job on the exhaust, and still cheaper than a new kit? this crap on there now, just bothers me. muffler is rusting and rotting out. figure i would get it all swapped out, and get rid of the crappy rigged up duals out the back. I'm sure there is a reason why none of the big companies have a dual exhaust set up for a 2 door tahoe. but the mom and pop shop that did this, made it work. not a fan of the exhaust coming out the back.

 

[adam74]

did you replace the cat yourself? how hard was that to do?

 

[white99tahoe]

yeah, it was relatively easy. i purchased the flowmaster kit 2010023 from amazon, $312 plus tax. the worst part was getting the nuts off the back side of the flanges where the 'cat back' section would start. its a 9/16" head vs the 15mm i thought fit it right. got the front flanges broke loose, dropped it down, pulled it out. it is best if you jack up the front of the vehicle so tires are about 3" off the ground. i set up jack stands to keep it propped up. new section, is 2 pieces, with a clamp to connect them. slipped new section in, connected all flanges, tightened, then tightened clamp. install O2 sensors back, all done. also, if you want to prevent a burning smell, get a rag or something with dawn soapy water, wash off new pipe. there is an oily substance on it, I'm guess to keep it kinda protected. otherwise, you will smell the burning of it, and it kinda stinks.

 

[adam74]

oh ok you bought a kit that goes from the manifolds. gotcha. yeah protective coating to keep it from rusting kinda like they do brake rotors.
Ive been having trouble getting mine to pass emissions and its getting narrowed down to my cat. good thing is its only one on a 95 so almost half the price. didnt know they sold this as a kit.