94 Z, sometimes starts with no ses light, sometimes cranks forever then once running i have an session light. Sometimes it runs great for 20 minutes, other times it falls on its face, coughs, backfires then runs fine, but with an ses light on. It is slightly down on power with the ses on, and throttle response is kind of laggy. I'm having a hard time believing my opti is on its way out the door already with only 6000 miles on this one. This will be my third one in as many years! I tried avoiding blaming the o2 sensor but I think this time it actually may be the o2 sensor. Oh, and the exhaust smells extremely rich. Any thoughts or ideas would be greatly appreciated! Thank you in advance.

 

Did you replace the wiring harness on the Opti? It's also a common failure and often overlooked.
My '93 acted like that when the alternator was going bad so it's another possibility,could even be a bad battery connection.
Might want to check the fuel pressure,could be the pump is going south or as simple as a plugged filter.
What brand Opti did you get? GM Performance is the only one I'd use.
Good luck getting it sorted out.

 

Check for bad wiring in the under hood harnesses. Had a somewhat similiar prob on my 94 3.4l bird when TPS wires were shorting each other.

Get an ALDL OBD1 connector (got mines from Red Devil River for ~$60) to pull codes.
Get the ALDLdroid app($19.99) to pull any codes if you have the obd1 system.
You may have to find the .adx files if its not already in there (should be "A273-LT1-1994-1995
-9600" in the data stream file under settings)

Good luck

 

First step is to find what codes are tripping the SES light. Then you can start to track down. It can be as simple as an exhaust leak before or immediately after the O2 sensor, which would show excess O2 in the exhaust so the computer would compensate by adding more fuel (that it doesn't really need), wash, rinse, repeat. Check your plugs, they can tell you a lot about how the engine is running and where in particular a problem may be at. There are so many things that can cause what you're describing. Find out the what codes it is throwing before you start throwing parts at it.

 

You not using those cheap Opti's ? I have been told the Chinese version commonly failed after 1-2 years. Many don't make it 6 months.

 

find out what the codes are. had a icm give me problems that was like what your seeing, also could be many things that a code would better let you know where to start.