I'm sure you guys with o/r pipe notice that raw fuel smell when your car is idling, is there any negative effect this may have on the engine? I dont want to get a tune yet until I get my T/B and plenum installed.

 

Welcome to the world of no cats! That odor is the smell of pullutants leaving your exhaust system that are not being scavenged by the cats since they are not there. I asuume that is what you have noticed and it is normal.

 

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But by not havings cats it's not causing the engine to run richer at all?

 

In theory it shouldnt, because you havent made it pump more fuel, it just doesnt get captured by the cats.

 

I think this whole rich vs lean debate will go on for years with newer cars.

As a general rule, most intake and exhaust mods tend to cause some leaning of the a/f and not a rich condition. The only mods that I can think of that will make the car run rich is Long Tube Headers and larger fuel injectors when the MAF is not calibrated for them.

Here is a basic lesson on how the closed-loop fuel system works:

The Mustang's computer is coded with different fuel trims depending on operating conditions. These conditions are based on such things such as engine temperature. For example, when the motor is cold, the car will run rich...on purpose.

The 02 sensors (there are four I believe) are constantly being monitored. The forward bank which is just before the cats is critical to the function of the car. The 02 sensors read the a/f and send a voltage signal that is interpreted by the ECU. The ECU then determines if more or less fuel needs to be added. It is really A LOT more complicated than that, but this is a real simple explanation. As a result, the car is able to compensate quite a bit for the typical bolt-on mods.

Messing with the Mass Air Flow Meter (MAF) can really screw things up big time. If not done right, you can ruin an engine. The ECU gets important data from the MAF.

I guess what I am trying to convinve you of is that the odor that you detect is the result of not having cats and is not from a rich condition. HOWEVER, the car could be running rich also, but not because of not having cats.

 

what about a throtle body and plenum upgrade? would the computer be able to compensate from the extra air the engine is ingesting? I still have the stock MAF That I dont plan on touching. I'm kinda hesitant to do the T/B and plenum upgrade right now without a tune, that it might cause a very lean condition. Thanks for the info.

 

I think that if you had a complete exhaust (stock headers), CAI, TB, and Plenum upgrades you will run leaner than stock but should be just fine for an n/a application. The Mustangs come a little rich from the factory and you can lean then up about 20% or so (maybe more) w/o a problem. This little bit of leaning will actually improve hp and fuel economy.

This is how my car is modified plus a chip. I have not had it on a dyno, but I did have a C&L MAF Kit at one time and was running too lean. As soon as the weather warmed up, I was getting missfire codes. I had a Ford Tech put it on the computer and the fuel injectors were trying to compensate by 30% (the max) and it was still running so lean that I was having missfires. Removing the MAF Kit and returning to stock, corrected the problem.

I have plans to have my car dynoed in October as I need to have my nitrous application checked out. I will be sure to post my numbers.

 

Great info as always man. Thanks for clearing some of that up for me.