Exhaust/Air Flow issues

[Shadow1189]

I have a 1998 Eclipse GSX. I just recently purchased a Megan Racing Downpipe and cat back exhaust. After installing this I noticed my exhuast tip was filled with black dust and when hitting the gas hard there was black fumes coming out the exhuast. I was told this was probably an fuel to air ratio problem, that I was burning more gas the I should be. Is there any thing I could do to fix this problem or would I need advice from a mechanic shop?

 

[Splitpi]

Get a logger to find out if indeed that is the case. You still have the rear O2 installed or is it simulated? If you removed it and didn't compensate you could be throwing the ECU off. Either install it or get a simulator for it. See if that fixes it.

Measure the fuel ratio and see if its rich or lean. May need a new front O2 sensor as well.

 

[chico904]

The downpipe you got I am assuming got rid of the cat, so you will definitely be running richer. As stated above what did you do with the O2 sensor?

 

[Shadow1189]

I uninstalled the o2 sensor when changing over, then i just reinstalled it after I put the pipes on. And how exactly do i check fuel ratio on my car?

 

[talonz27]

you need a wideband sensor for you to check your air fuel ratio. do not buy a cheapo narrow band sensor.

http://www.dsmtuners.com/forums/showthread.php?t=261006

 

[Splitpi]

I uninstalled the o2 sensor when changing over, then i just reinstalled it after I put the pipes on. And how exactly do i check fuel ratio on my car?

By reinstall do you mean that you cut a hole into the exhaust, welded an O2 bung to it and then screwed the rear O2 into place and connected all the lines... or do you mean you simply reconnected the rear O2 without having it acuallty in the exhaust?

 

[talonz27]

give us a list of mods you have done besides the exhaust. just putting some exhaust on your car shouldnt make it runs bad. and how many miles are on your engine/turbo?

 

[Shadow1189]

My car has 50k miles. The megan racing cat back already had a threaded o2 senser slot, so i just plugged it into that. Besides the exhaust I have a dejon tool intake pipe and K&N air filter.

 

[spyderturbo007]

You still have the rear O2 installed or is it simulated? If you removed it and didn't compensate you could be throwing the ECU off.

The rear O2 sensor has nothing to do with fuel delivery. It is only there to verify catalyst efficiency. Please don't post about things that you aren't sure of.

If your only mods are an UICP, K&N and the exhaust, the ECU will compensate for the additional air mass. Did this just start after installing the exhaust? Have you checked for shaft play in the turbo?

 

[Splitpi]

The rear O2 sensor has nothing to do with fuel delivery. It is only there to verify catalyst efficiency. Please don't post about things that you aren't sure of.

I was walking him through a list of potential problems and trying to get definitive answers back. Also you may want to read up on O2 sensor behaviour in the shop manual and its debug methods and trouble trees.

Next I would have had him check the front, then his fuel pressure (pressure regulator), etc...

You shouldn't be so quick to judge my motives.

 

[spyderturbo007]

How is a bad rear O2 sensor going to cause driveablility problems??

You said that the rear O2 sensor, if bad, could be causing problems with the ECU fuel delivery adjustments. That is 100% wrong and complete misinformation.

 

[Splitpi]

How is a bad rear O2 sensor going to cause driveablility problems??

You said that the rear O2 sensor, if bad, could be causing problems with the ECU fuel delivery adjustments. That is 100% wrong and complete misinformation.

Once again, I will have you take that up with the shop manual trouble trees.

Per his statements the only change was the exhaust and elimination of the cat which means nothing prior of the front O2 sensor changed. Hence I was starting from the back and working forward.

Secondly, ODBII systems richen the fuel during its diagnosis of faulty Rear O2 sensors as it is part of the feedback loop for A/F ratios. Whether it is the rear O2 sensor or not remains to be seen as we are still trying to diagnose what all he has done to the car.

 

[chico904]

If your only mods are an UICP, K&N and the exhaust, the ECU will compensate for the additional air mass.

The car will still run richer due to the simple fact that there is no cat there now to help get rid of unused fuel.

 

[spyderturbo007]

The car will still run richer due to the simple fact that there is no cat there now to help get rid of unused fuel.

No, it's not going to run richer. The ECU will still shoot for it's pre-programmed AFR of 9.5:1. It will seem like it is running richer because the cat isn't there to deal with the unburnt fuel, but the car isn't going to run any richer than it was before.

 

[spyderturbo007]

Once again, I will have you take that up with the shop manual trouble trees.

So I see that you are once again avoiding my question.

Secondly, ODBII systems richen the fuel during its diagnosis of faulty Rear O2 sensors as it is part of the feedback loop for A/F ratios. Whether it is the rear O2 sensor or not remains to be seen as we are still trying to diagnose what all he has done to the car.

Huh? The ECU uses feedback from the FRONT O2 sensor during idle and light cruise. It doesn't give a crap about what is going on after the cat.

 

[chico904]

No, it's not going to run richer. The ECU will still shoot for it's pre-programmed AFR of 9.5:1. It will seem like it is running richer because the cat isn't there to deal with the unburnt fuel, but the car isn't going to run any richer than it was before.

Sorry, I meant you will have more black soot in your tailpipe without a cat than with one.

 

[PieEyedPiper]

I don't see anything erroneous about SplitPi's post.
The rear 02 sensor does not affect fuel trims, but it might "throw off" the ECU (throw a code). Considering it was handled/uninstalled/reinstalled etc it is reasonable to investigate.

Nobody freak out because the help is being overly thorough.

If the Op's 02 sensors etc are all in check I would chalk this one up to a brand new exhaust. They do smoke and get "black dust" build up when they're being "broken in".

 

[Splitpi]

So I see that you are once again avoiding my question.

Listen, I gave my reason asking the question to the orginal poster. Its even in the trouble tree sections of the Mitsu shop manuals so if you have a problem with it then write Mitsu and tell them your problem with their diagnostic methods and how they don't know what they are doing. I am just trying to talk the OP through this problem to figure what he has/has not done.

Huh? The ECU uses feedback from the FRONT O2 sensor during idle and light cruise. It doesn't give a crap about what is going on after the cat.

Incorrect. The rear O2 is indeed to diagnose the efficiency of the cat. But it also is a second basis for the ECU make judgement on rich/lean inorder keep the cat at an efficient state. As it looks at the transition of the two to make its calculations for fuel adding/withdrawling from the front O2's calculation to figure out the amount of extra O2 in the cat or lack their off for catalyst. Otherwise, it would have absolultely no usefulness other than to set a light that the O2 sensor isn't working. Its intended to allow the ECU to regulate the Cats efficiency based upon varying A/F since it has sampled pre and post cat A/F. Are you going to continue to argue this, or get back to trying to help the OP. I dont mean to sound like a prick about this...