Muffler delete equals Rich condition
 

I did some searching and I was not able to find a similar thread so here goes.

I went ahead and removed the muffler to save some weight and get some good noise. Ever since then I've been running extremely rich. I would say about 280 miles per tank of fuel (I used to average 310 to 340). So I did some research and I tried the "Idle Air Volume learning" procedure but to be honest I am sure I screwed it up:

2003-2011 Nissan 350Z - 370Z Idle Air Volume Learning Procedure | Nissanhelp.com

I can further prove this rich condition due to the fact that I had a dyno on the same day of the muffler delete and the shop tech told me I was running extremely rich.

Dyno:

http://i786.photobucket.com/albums/y...y/IMG_2544.jpg

Notice the TON of torque...I must have a v8 for like 1 whole second...LMAO!! :roflpuke2:

http://i786.photobucket.com/albums/y...y/IMG_2545.jpg

So my question is am I forced to get a tune? or is there another reset procedure I can run? Did I do the above mentioned procedure wrong? Etc?

EDIT: note that the pull showing the most power is with the filters removed.

how can a muffler delete possibly cause a rich condition? it must be something else that has caused this. allowing air to more easily flow out of your cylinders cannot cause a rich condition.

someone else chime in if im missing something here

I was confused about that one as well so let me add to the story:

When I originally picked up the car (used) I got a check engine light a few days later. Nissan (its still has factory warrantee) indicated that the car was "flashed tuned" by the previous owner. They went ahead and reflashed the ECU with the stock tune (so they say) and the check engine light went away.

I am not sure but could it be that after market tune is still hanging around causing some drama? The only thing is it was reflashed a long time ago. Why would it all of a sudden happen now after thousands of miles driven. In my opinion the exhaust is the most likely suspect. :shakes head:

Why not put back on the exhaust and check your A/F again? Since you have a '09 it could be you have (had) a Cobb AP tune. You might want to see if you can pick one up used for cheap so you can check. It would also allow you to monitor your A/F. There are other devices that allow you to monitor the stock O2 sensors, I have a Dashhawk on my '09.

Muffler delete and air intake filter delete won't cause this. Bad O2 sensor sounds more probable or some other problem causing the fuel management system to dump more fuel through the injectors than is actually required.

Right but a bad O2 censor would throw a code correct? Which in turn would trigger the CEL. Since Nissan reflashed the ECU I doubt I have a phantom flash so I am at a loss. :shakes head:

There was welding involved so I dont want any more invasive changes made. What I may end up doing is going to autozone and getting the codes checked. Either way I'll prob take it to Nissan on Friday.

Yes, in an ideal world a code would be triggered. Welcome to reality.

A bad O2 sensor doesn't throws a code. It took a long time before I figured out I had a bad sensor. Cipher helped me track it down. And yes, it ran pig rich.

I also did a Cain and muffler delete and buddy was behind me o. Freeway. When I down shifted and matted it he said it puffed out black smoke (rich) makes me wonder.... what was hour end result???

Bad gas... pulls out timing and adds fuel when it determines ping. Put some Shell or BP in the tank, then go back on the Dyno.

Please re-read the original post...I implied multiple fill ups but to be more clear...I have filled the tank more than a dozen times since then and the bad mileage is still an issue.

I had my brother (A master ASC cert mechanic) look at it and he had software to look at the O2 sensors and he noticed 3 out of the 4 exhaust sensors were reading pig rich (I.E. wide open) the moment the accelorator is pressed. I am surprised the car has not flooded. I am going to ask the dealer to reflash the ECU. :shakes head:

Another idea: what if the knock sensor is loose? Would that not cause the ECU to dump more fuel since its getting a false knock?

Sounds like bad O2 sensor dude. Just went through this with my headers. My one plug was slightly cracked so the wires werent making a complete connection on the one sensor. I was getting 10-12 city and 15-17 highway....pulled the plug and now I'm at 18 city and 28 highway. Plug for you is easy to replace anyone 2011 and up will be a bitch. They use different plugs and the dealerships can't even order them...having one specially made :/

what did you replace the muffler with?

two pipes...just the canister...the cats and resonators are untouched.

Basically two 2 ft pipes were welded in its place and my old stock tips were welded onto the new pipes.

Question/Opinion: I know how dealers can be so I want to see if you all agree with me...Should I wait to bring the car to Nissan and just put my Fast Intensions (not ordered yet) exhaust on? I have a feeling they might bitch about the welding.

They may give you a hard time even with the FI. If the dealer is to try to find the reason why you are running rich (which has to do with the info from the intake and various exhaust sensors) they may say, well you have an aftermarket exhaust which may be causing your condition. As you may already know, running rich is bad for your car. Fouls the plugs, bad for your CAT and of course really poor fuel economy.

The irony is if it were that simple I would be happy but my brother checked the sensors with this tool and they are ok. I have an extended warrantee untill 100k miles so I am all set in that regard. It's the not knowing that is killing me.

OP are you sure you didn't get the case of "my car is louder so my foot got heavier"? Theoretically a muffler delete really shouldn't have any plan in a/f ratios but I'd like to see what the outcome of this really is. I highly doubt it relates to the muffler delete

Maybe put the stocker back on and see if the mpg goes back?

i have done a muffler delete and tb bypass's.that was my first mods and when i bought the car,the computer said i was getting 18.5 miles to the gallon.after delete and bypasses,i havnt seen under 20.

I just did the muffler delete last week and had the tips custom welded back on and sometimes usually when I am getting on it I can smell gas. I mentioned it to my buddy and he said it means its running rich. I asked the shop before hand if it could have any negative impact and they said no it will just change the sound. So if it is causing a rich condition (which would suck...) then I will go have the muffler put back on.

I just got a tune this past weekend, and after several discussions with various people of varying knowledge, I believe that the car runs rich regardless. Has anyone ever seen a stock 370Z that isn't running rich? With an 11:1 compression, it's likely Nissan just being cautious. They have to run it even richer to account for uncaring drivers who use regular gas.

I amfully stock except for intakes (which, if anything, should make it leaner) and my tuner said I was running extremely rich.

Let me revise this and say it doesn't bluntly say your O2 sensor is messed up when you look it up. It was a ver common P0300 code and maybe something else that did nothing to help track it down. Data logging was the only way I saw it.

After installing my FI exhaust my gas mileage went back to normal.

It's your o2 sensor. Happened to my Z also

so you fixed it? What was it?

If your muffler delete was rattling, then yes, the knock sensors could have picked up vibrations.

Im not sure how loud it was, but if you car was crazy loud, then the knock sensors can pick up on that in general.

any updates?

Still running with stock gas mileage when I installed the FI exhaust. I honestly cannot give you a definitive answer as to why it ran rich with the muffler delete but perhaps the knock sensor theory has some merit? I don't think so but perhaps.

Shortly after the FI install I also installed the Takeda intake. The only change was a HP increase. Mileage while cruising on the highway is more or less the same. I have 15k + miles with both mods without any issues. So I consider the issue resolved.