ArkBird96

Ok so my LS1 in my formula (mods in sig), is being . I posted this in the transmission section earlier because I though it was a transmission issue. It clearly is not.

Basically what is happening is, sometimes the engine won't rev when under load up above a certain RPM. Usually above about 2500 or so. I am throwing the P0420 code, so I changed the driver's side rear O2 sensor. That didn't fix either the code or the problem.

I was cruising on the freeway at about 70 the other day on cruise control and going up a hill, I could feel it bogging down, even in overdrive.

I should also say that this is an intermittent problem, and sometimes it bogs down worse than other times.

Also, I noticed that it seems to be worse when the gas gauge is at around 1/4.

Does this sound like a bad cat or something in the fuel system? WTF is going on here ?

Zerokube

iTrader: (4)

Maybe plugs and wires might help a bit if you havent already done it. Also clean the maf really good.

ArkBird96

OK. I will look into that. Is that as much of a PITA as I think it is?

Isn't the MAF out of the equation when it is in closed loop except at WOT? It isn't just a problem at WOT when it happens, it is an issue when you give it any throttle, like enough to make it downshift. Make sense? I'm confused here.

LS6427

iTrader: (2)

Yup

If you replaced that 02 sensor and you didn't at least clear the code...then you need to check into the electrical a little deeper. Might be a burnt or frayed wire beyond the plug. A bad or failed 02 sensor will cause your issues.

.

bboyferal

iTrader: (9)

Yeah, if it didn't clear the code, I wouldn't worry about digging into other issues, focusing on the O2 sensor code still occuring instead.

ArkBird96

OK. Now I'm really confused. Do the O2 sensors AFTER the cat mess with parameters in the computer or are they just to determine if the cat is working or not? That's the one I replaced. If memory serves (and I could be wrong) the 2 sensors before the cat determine how the engine runs. I have also heard that P0420 usually means the cat is bad. I may replace the cat this weekend.

Searching4Sierra

iTrader: (27)

maybe you have a clogged cat, thats all the rear sensors are really there for. Like when people get LTs and run w/o cats they just have the rear o2s tuned out.

wssix99

iTrader: (5)

Correct.

Your driveability issue is similar to a dirty MAF (it looks like you are running a K&N - so the $5 investment in MAF cleaner is definitely a good one) but busted CAT could be creating excess back pressure in the exhaust and causing your issue.

Please post back and tell us what happens after the CAT swap.

ArkBird96

OK. I will take a look at the MAF also. Is there a write-up on how to clean it? When I bought the car, it did have a K&N filter, but one of the first things I did when I got it was !K&N. I've seen what those things do and I don't like them. I should be swapping the cat this weekend and I'll let you know what is up. I will also double check and make sure that the code it is throwing is indeed P0420 and not something else. Thanks for your help!

Zerokube

iTrader: (4)

just go to any auto-parts store and buy the can of maf cleaner. should be around $5 bucks. take it off and spray it down and let it dry, if you want you can take a q-tip and clean the little sensors

Searching4Sierra

iTrader: (27)

The MAF will be much easier to deal with than the cat, so hopefully that solves the problem

ArkBird96

How long can I expect replacing the cats to take? It looks simple enough if I just get bolt-in replacements from Magnaflow or whatever the local Summit store sells.

Also, I need to take the MAF off the throttle body in order to clean it, right? I have an idea I don't want that stuff in my intake manifold.

wssix99

iTrader: (5)

Working with pipes always takes longer than you plan for! With a lift and good tools, it should take a matter of minutes. On ramps with hand tools, it will take hours. Regardless, you'll want to give yourself some cushion and don't get in to the job if you need to go somewhere.

Right. The cleaner won't hurt anything in your manifold. Its a special type of non-residue electrical cleaner and evaporates completely. You will want to take the MAF completely out so you can get the spray closer to the elements and get better cleaning.

biggb1783

I would suggest pulling the post - (i meant PRE) - cat o2 sensors and see if the bogging gets better. P0420 is a ctatlyst in efficincy code and usually means the cat or cats are not doing their job. easy fix - replace or remove the cats and either space the o2 sensore out of the pipe with some spark plug non foulers or have the post cat o2's tuned out.

wssix99

iTrader: (5)

Blocking out the sensors will just get rid of the code. My understanding is that they do nothing for the car other than to report on the state of the CATs. The forward sensors are the ones that do the grunt work on fuel mixtures.

ArkBird96

bumping for update.

I cleaned my MAF yesterday. It smoothed out my idle a bit, but that's it. Boy was it dirty!. Do you guys think I could run a can of Seafoam through the fuel tank?