I have a 95 LT1 with an auto trans. The problem all of a sudden happened one day. It runs like it should in open loop, just fine, but when it runs in closed loop it runs like crap. At idle in closed loop, it smells really really rich, like your eyes water and you can smell gas in the car. Driving it, it won't maintain a constant speed, just keeps running slower (like it is way way too rich), then the SES light comes on and it goes into open loop, then it runs fine. It'll stay in open loop for a while, then the light will go off, and go back into closed loop, then run like crap again. This is a cycle, it'll stay in open loop for a while, then go back to closed looop. I looked at the code it gave me, it's right bank rich; which makes sense.

How this happened: I was going to school one day and got sick of going really slow behind some people. I floored it two separate times. It ran like it was supposed to then. The next time I started it and drove into town for lunch it started acting funny and has done it since.

Help me please diagnose this. Is it a stuck injector, faulty oxygen sensor, or fuel pressure regulator maybe? I'm an airplane mechanic by trade so I am not afraid to delve into technical things.

 

Sounds like bad O2's as the PCM is reliant upon them in closed loop to maintain the A/F ratio. If they are fouled it will default and run it rich and throw the SES light your seeing.

 

That was my initial thought too. Can I get by with cleaning them, or should I get a new one? I don't want to buy a new one and not have it fix the problem, I know those things are expensive. I am trying to get into tuning too, and I am pretty sure I'm supposed to have a wideband for that. What's a good suggestion for brands of wideband o2's?

 

You'll find a lot of posts here about the O2's and cleaning as it usually does not work. Get it scanned first and let us know what codes your throwing so we can see if it is indeed the 02's. FYI - you have 2 O2's (one pass and one driver side) both are before the cat. As to wideband do a seach as there is lots of posts on this subject.

 

my driver side 02 was bad and it didn't throw a code. you could tell it was bad by the low mv ranges it was hitting compared to the passenger side.

 

I don't think I want to get a wideband after all. Next time I am with the car I'll see what codes it has, also I know how to check if the sensors are bad by the voltage they produce. I can check that too when I get a chance.

 

bad o2, if you floor it and it runs good , thats because in closed loop the computer dosent use the o2s only under wot , therefore looks like your problem. dont clean them , buy new ones.

 

change the o2's

 

On good O2s you will see a constant variation between 100-900mv. Most bad ones will have a more limited range or will get stuck around a certain reading, they will also not fluctuate correctly but tend to read the same thing over a long period.

 

It's ok now, the problem seemed to correct itself. I let it sit for a couple weeks because I had tests at school, went to fix it, but the problem never recurred. I bought an 02, but haven't had to use it yet.

Strange I know.

 

Did you ever pull your o2 readings, Right now I am working on sorta the same issue.

In open loop The left is sitting at like 5oo-6oo mv and has a injector fault and the right side is at like 3oo-4oo mv with no fault . Take it out at at wot I have power but it is hoping in and out of closed loop like its scared of it.

Once mine hits closed loop it riches out and both jump to like 6oo-7oo and the car starts sputtering