moondance

Which o2 sensors control the fuel at all? Is it the back two or the front two? I have a 1997 z28. It seems when its warm it runs really rough so I was wondering if those are causing it which two it would be. Also if I unplugged them what exactly would happen after the engine was warm? I get crappy MPG atm. I believe around 11-12 city with no hwy driving. Thanks in advance.

rat93

iTrader: (2)

the front 2

moondance

What happens if they are unplugged once the engine is warmed and the computer tries to turn them on?

Z28_LT1

iTrader: (2)

Front o2 are the ones that control that. I think it should run how it is when its cold. If not then u may have other problems.

EDIT: oh and ur SES light will come on after a while.

moondance

Will it help or hurt MPG with them unplugged

RamAir95TA

iTrader: (2)

Without the O2s plugged in, the PCM will have no way of determining whether or not the combusted fuel mixture is rich or lean.

moondance

I think its rich after its warmed up. I think thats why my MPG really sucks and why after warm the car runs rough at idle. I could be wrong but it seems to be from there since it runs better when the engine is cold compared to hot.

RamAir95TA

iTrader: (2)

Are your O2s already unplugged? If so, plug them back in.

Running rough when the car is warmed up is a tell-tale sign of the ICM (ignition control module) becoming heat-soaked.

moondance

no they are not unplugged now. would the ICM doing that cause crappy MPG too?

RamAir95TA

iTrader: (2)

A bad ICM can cause a host of problems including bad MPG.

Unfortunately, there's alot of other things that can affect MPG as well.

VF1000R

PCM goes into open loop and goes full rich to protect the engine if the O2's are unplugged.

Front 2 do the work, but don't unplug the rear two, or as above happens.

RamAir95TA

iTrader: (2)

Unplugging the rear two won't affect the fuel trim at all - it will just set an SES light.

moondance

I dont get a running rich fault although I use to from time to time. It just runs rougher after hot and I get 11-12 MPG city.

gregrob

iTrader: (8)

How many miles on the car? If over 60 change them. They should be part of your preventive maintenance. Use only AC Delco / Delphi..

Clean your maf sensor and inspect for signs of damage.

Do the ICM cooling mod.

Tuneup if it hasnt been done.

If those things dont fix your mpg and rough running problems you can keep looking but they are all good things to do anyway.

moondance

109k miles on the car. How do you do the cooling mod or even check to see if the ICM is bad to begin with?

transamws6_97

iTrader: (5)

to do the mod to keep the icm cooler you place a nut on each stud between the head and the icm bracket to keep it cooler. Simple mod that takes 5 minutes

moondance

Being that I have the optispark would it being heat soaked cause it to run rough and maybe rich after the car is hot?

VF1000R

Should not have anything to do with it. Other problems would pop up.