427_Roadster

I've seen a few topics about carbon buildup on exhaust tips, and one of the causes that usually comes up is your car is running too rich. This is probably a stupid question, but how is that possible? Shouldn't the computer be using it's sensors to adjust the fuel/air mixture so it's dead on? If the Vette is running rich, wouldn't that indicate a problem with the computer? :confused:

DsC5

good question, I'm curious also. :confused:

iceburgh

Many people in here will tell you that these cars run rich from the factory...I got an adjustable fuel pressure gauge to help with this problem.
Factory setting was set at 62lbs. :eek: at idle I backed this off to 46lbs. I have no black build up at all now and dyno tuning shows that this is a much better fuel curve at 48.
IMO GM set this high for insurance on the warrenty so that you will not lean out and go boom

RHILL

You also want to make sure you have no intake leaks,keep a clean air filter and replace your O2 sensor when needed. :cheers:

Mike Mercury

Yes, but that is assuming the O2 sensors are still calibrated; clean; and giving accurate results.

Like Rhill said; there are many small problems that can make a computer controlled engine run rich/lean. And don't forget that during WOT, the PCM stops looking at the O2 sensors.

427_Roadster

Hey Iceburgh, did a better fuel curve also translate into better numbers on the dyno?

MattG

It is very realistic for an LS1 engine to run either rich or lean... At PART THROTTLE your computer does do its best to get your car running at the perfect air/fuel mixture for reliability, drivability and fuel economy, which is 14.7 to 1... The PCM uses the readings from its 02 sensors to decide how rich/lean the engine is running, and then makes corrections in the Fuel Trims to add or subtract the apropriate amount of fuel to get the engine to run at its desired a/f ratio.. When you put your foot to the floor, your car goes into a Fuel Enrichment Mode where it richens up the air/fuel mixture entering the engine in order to keep the engine safe, and produce more power. The amount of extra fuel that is added into the engine when the car enters Fuel Enrichment mode is based only on RPM and it does not use any feedback from the 02 sensors to figure out whether it is rich or lean.. This is where you need a wide-band 02-sensor dyno and a tuning tool such as ls1edit to correctly setup your fuel enrichment mode settings.

I hope this helps out a bit..

MattG

46?? Are you sure you arent thinking 56?? 46 is way too low of fuel pressure for our cars, even under extreme load at WOT.

iceburgh

Matt,
I know this sounds crazy and there was no way I wanted to go that low but the tuner I had with me showed me what he was talking about and at idle it was between 46 and 48...He was talking chinese to me but I saw the results on the print out.
I did bump thisup to 56 when I hooked up nitrous to be safe but ???
You guys know a heck of bunch more than me all I can show is what he showed on my car.