Hello everyone, I recently bought a 1994 Camaro Z28 Convertible with 101,000 miles which had been garage kept and driven 4,000 miles in the past 8 years. I removed and replaced the spark plugs, plug wires, fuel filter, air filter and performed an oil and filter change but it's running rich at all times and the SES light comes on about 30 seconds after engine start. I bought a scanner from autoxray and did not get any codes however running in monitoring mode I noticed that both oxygen sensors initially start at 440 mV and once the engine is warm there are very rapid fluctuations between 90mV and 700 mV, the ECM is runing in closed loop. Is this normal or are the oxygen sensors the cause of the problem? I couldn't find any information on this in the Factory manuals that I purchased. Also my oil pressure at idle starts at 40 and drops to 20 when warm, I am using 10W30 with 1 quart of Rislone, is this oil pressure normal? Reading some of the posts I think I'm going to go ahead and change the oil and filter again and switch to synthetic. Any insight any of you guys can give me will be appreciated, thanks.

 

I don't know how true it is but I've heard you dont want to use sythetic on a high mileage car that hasn't already been using sythetic. Like I said, I don't know this to be true, thats just what I've heard.

 

Thanks for the info, I'm open for suggestions.

 

check and see if theres a aftermarket chip add on. some of em tell the computer the moter is cold all the time so it runs rich. i use 10w30 synthetic in the lt1 i have now. no additives. dont use fram. oil pressure u have is ok. could be better could be worse. pretty sure the sensors are supposed to flux way up and down just dont know numbers. lol. sorry.

 

The fluctuations sound right. The scanner you picked up probably isn't going to work since 94 has OBDI codes and an OBDII port. There are directions in the sticky at the top of this section on how to flash out the codes. Just because the O2's are fluctuating doesn't mean the computer is in fact in closed loop mode. I would recommend flashing the codes and see if that gives us some more insight.

 

Thanks for replying. The port is OBD1 so I was able to scan for codes and the only one was in the history section dealing with the EGR system which has been disconnected. The ECM is operating on an open loop rather than the closed loop as stated before. All of the sensors monitored when the engine was running were in the normal range except that one oxygen sensor registered from about 90mV to 600 mV while the other registered from about 120 mV to around 700 mV. Like I said before, the SES light comes on about 30 seconds after the engine starts when it starts to warm up. Any ideas?

 

sticky or stuck injector. bad spark plug or wire.

 

One other area to check would be your coolant temp sensor for the computer. Your scanner said that the system is in closed loop but that may not be accurate info. Hopefully your scanner will give you a temp. value and you can compare that to your intake air temp value with the key on before and after a cold start. They should be close in temp reading. A defective coolant temp sensor could give the wrong info telling ecu that the engine is cold and thus adding more fuel. Your O2 sensors wouldn't flucuate if the sensor was always bad but sometimes scanner info isn't "instant" and you could be missing info when you need it. Anyway, good luck with your problem and hopefully you will be out burning tires soon.

 

Thanks for the suggestion. I had both water temp. sensors replaced and the difference in the temp. value between the intake air temp sensor and water sensor was 4 degrees. I monitored the running engine again and one of the oxygen sensors was consistently in the 200-300 mV range while the other moved between 400-700 mV so it looks like it's the oxygen sensors. I'm going to make sure that there isn't an exhaust leak that is influencing the low sensor reading before I replace them.