94 vette oxygen sensor
Thread Starter
Intermediate
Joined: Aug 2005
Posts: 37
Likes: 0
From: Colorado Springs Colorado
94 vette oxygen sensor
Help! Over the past 10 months I have installed 2 new oxygen senors in front of the Cat on the passenger side and about to do a third.The car will be running good (although rich), start to run and idle rough. Then will set the service engine soon light and goes into the limp home mode and runs smooth. Both exhaust pipes indicate and extremely rich condition with daily driving. This is confusing. The gas mileage has dropped off by 4-5 mpg also. My code reader says that the sensor believes the engine to be in a lean condition. The driver side sensor indicates that all is normal. Any suggestions as to what could cause the rich condition to start with? Why does the right oxygen sensor think it's a lean condition and cause more fuel to be added and finally, when it goes into limp home mode it will run like it was before the lite came on. I am getting ready to add headers and new cats and I need to resolve this problem before I add more to the mix. Any help, suggestions, prayers or lighting of candles would be greatly appreciated.
Dray
Dray
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Do 5 Hail Mary's... all will be fine. 
From what I can figure, you may have the makings of an injector problem... Which makes me wonder if the ECM is 100% right.
I would also check the harness to the O2... make sure it's not cut or shorting to ground.
Check the injectors. There is this thing called a "fiddle light" that will flicker as the injector is fired. If the light is off, then the injector isn't firing, if it's on all the time, then it's stuck open.
Check spark, too. Make sure your coil is getting and giving as it should. One of the forum members, JetJocky93, had a problem with where the ignition driver connected up to the harness. The connector itself was bad. Sucky, eh?
You really need a copy of the Helm Factory Service Manual, www.helminc.com.
Keep us posted.
From what I can figure, you may have the makings of an injector problem... Which makes me wonder if the ECM is 100% right.
I would also check the harness to the O2... make sure it's not cut or shorting to ground.
Check the injectors. There is this thing called a "fiddle light" that will flicker as the injector is fired. If the light is off, then the injector isn't firing, if it's on all the time, then it's stuck open.
Check spark, too. Make sure your coil is getting and giving as it should. One of the forum members, JetJocky93, had a problem with where the ignition driver connected up to the harness. The connector itself was bad. Sucky, eh?
You really need a copy of the Helm Factory Service Manual, www.helminc.com.
Keep us posted.
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Also make sure that you do not have any exhaust leaks on that right bank. If you do then raw o2 gets sucked into the exhaust stream and the sensor will see it as a lean condition and the PCM will fuel for it. Any mis-fires will also cause the same problem. A mis-fire means raw unburned o2 injected into the exhaust stream.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
It sounds as though it is spending most of the time in the limp home mode. Every now and then it comes out of the limp home mode and runs really crappy. Instead of throwing parts at it, why don't you fix it? O2 sensors don't "wear out" at the rate of 3 per year. Because the code says "O2 sensor" doesn't mean that the sensor is bad. It means that the ECM (or whatever it is in a '94) received a reading FROM the O2 that is "out of range". A bad O2 CAN cause a code, but it is just as possible that the info sent to the ECM that set the code was TRUE information, from a fully functioning O2, with a cause, yet to be determined. DON'T shoot the messenger (the O2). Get out your FSM and follow the trouble shooting charts to track down the CAUSE of the problem, and FIX it.
RACE ON!!!
RACE ON!!!
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Originally Posted by bogus
Check the injectors. There is this thing called a "fiddle light" that will
flicker as the injector is fired. If the light is off, then the injector isn't
firing, if it's on all the time, then it's stuck open.
flicker as the injector is fired. If the light is off, then the injector isn't
firing, if it's on all the time, then it's stuck open.
A poor boy stethoscope (screwdriver or something like a piece of
wooden dowel) can work for this, too. Place the tip on the injectors
and listen for sound.
.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Also, make sure the header check valve is good - remove and make sure you can only blow air through it the direction of the header. And/or crimp the air pump hoses at the headers and if the problem goes away, it's pumping air to the headers when it shouldn't be. Have either of these situations and the O2 senses a lean condition which causes the ECM to fatten up the mix and it ends up too rich.
Racer
Joined: Mar 2002
Posts: 430
Likes: 1
From: Beavercreek OH
Cruise-In III Veteran
Originally Posted by Dray
Help! Over the past 10 months I have installed 2 new oxygen senors in front of the Cat on the passenger side and about to do a third.The car will be running good (although rich), start to run and idle rough. Then will set the service engine soon light and goes into the limp home mode and runs smooth. Both exhaust pipes indicate and extremely rich condition with daily driving. This is confusing. The gas mileage has dropped off by 4-5 mpg also. My code reader says that the sensor believes the engine to be in a lean condition. The driver side sensor indicates that all is normal. Any suggestions as to what could cause the rich condition to start with? Why does the right oxygen sensor think it's a lean condition and cause more fuel to be added and finally, when it goes into limp home mode it will run like it was before the lite came on. I am getting ready to add headers and new cats and I need to resolve this problem before I add more to the mix. Any help, suggestions, prayers or lighting of candles would be greatly appreciated.
Dray
Dray
