open downpipe/running too lean
 

ever since i started running a 3 inch mpx open downpipe my check engine light came on..now when i try an start the car sometimes it turns over an over then fires up an feels like it wants too shut off for a few seconds, is that because the o2 sensor is reading wrong?

if so im prob gunna run a turndown about 30 inches back if that will fix the problem or not.

helpp thanks

Please don't make multiple threads on the same issue in different sections, one will do, I left this one here as you will probably see the best results in this specific forum.

As for the downpipe, did you get the code checked? I would assume that the code is simply a cat deficiency code since you no longer have one. The 02 sensor in the downpipe only measures emissions, so changing the downpipe won't really affect AFRs, nowhere near enough to throw a code at least. AFTER getting the code read, try disconnecting the battery for 15 min to clear the code out, and see if your issue goes away at all. Get the code read at an autozone for free.

i still have a cat on the downpipe..modern performance makes a downpipe with or without a cat, and i already did the autozone thing and the code came back a few days later the code had something too do with the fumes an heat messing with the sensor because its so close too the opening.. i dont think the cars getting enough gas also because of the whole reading the codes wrong which is why i think its running too lean. i ordered a 32 inch pipe extension with a turndown that im gunna bolt onto the downpipe, do you think that might fix the problem?

the problem with the open pipe is that the sensor location is so close to the opening the air coming out of the 3" during standard cruise or idle has no velocity to prevent the natural air surrounding it from mixing withing the back section of the open downpipe thus giving false read to the sensor and making your mil light come on. the fix would be to lengthen the distance of 02 position from the pipe exit be either relocation or lengthening the pipe. i believe turndowns only have minor affect on flow but i have not seein their effects on this issue so i cannot say whether or not it will be of any significance to your problem

You need to get the code read, write it down and put it up here... Until the code is know, anything is really just speculation.

I ran open downpipe while my exhaust was being built and never had a problem where it would run to lean

i went too a muffler shop today..there gunna run a 3 inch side exit in front of my rear drivers side tire..its gunna have a few bends in it an be a good bit of pipe so im thinking that might do the trick an make the cel go away..paintballer78 do u got a side exit? i just seen that..how is it?

run open turbo.

MPx's catted downpipe will throw a code. The only catted downpipe which reliably will not throw codes is Hahn.

Jannetty makes a side exit exhaust that you can buy ..... might be something to look at.

2008-2009 Turbo Cobalt SS 3" Side Exit Exhaust

Read the code. It's not because the DP is open.

Yep........ Agreed. The car doesn't care about anything cat -back.

Is there a reason your running an open downpipe? Doesn't the car start to smell like exhaust on the inside?

the down pipe ending under the firewall causes a cell bcause it is too short during idle and cruise to push enough velocity of exhaust to keep the atmospheric air from reaching the 02 sensor thus making a false read, so yes it is currently the dp it should go away with the extension hes getting.

Even if it does see outside air it's only the #2 o2 sensor...... it shouldnt cause any issues with the car running lean or rich...... it would only be able to set a Cat efficiency code.

No it won't. MPx catted downpipe will throw codes.

im throwing a few different codes all having to do with air and exhaust and a catylyst code, so once i get the side exit hopefully i only throw the catylyst code since its a mpx dopwnpipe

run open turbo am i talking to a brick wall or something?

No,
Just noone wants to take advice from an burned out,crack head,philly steak eating loser

Dude, you need to run to autozone or something and get the number for every code you are throwing... There is no sense in spending money on your car "hoping" it will fix the problem... There are some very knowledgeable people on here that have experience with their cars, and they can help you out if you give them the right info..... tell us your codes!

or scann them with hpt and the catalyst code needs to be disabled with hpt to run open header or you will stay in catalyst failure mode(limp)

If he has HPT... I think he said earlier that he had the codes read at an auto parts store... but he didn't put up what they were... I asked for codes in like the 4th post but he still hasn't posted any.

oh well i got money too blow ;) and im good now anyway just put the exhaust on an its only throwing an oxygen sensor code..so once i get tuned soon ill be good, anyone recomend some tunes other then trifecta?

Horrible mentality to have... better to know what needs to be fixed and get it done right... as to your other question... HP tuners is a better option.

is zzp any good? i saw that they had like a package for sale, camshaft,head, and a tune.