94 z28 ran off road over a culvert a few months back.That knocked a hole in the exhaust right where the y pipe comes into one,but back up the passenger side pipe a few inches.Car ran ok for a few miles then it started running rich ,real rich.The hole was on the passenger side pipe but the plugs on the right side were all black not the pass side.Anyway I got the hole patched changed the plugs and it still ran rich.So I replaced the 02 but nothing changed.Changed the MAF,coil and ICM.Changed the opti out for a dyna spark and toke off the AIR pump.Now in the mornings you have to open the throttle wide open for it to crank and then it runs super rough and rich untill it warms up.It wasnt doing that before the opti change but my water pump had started leaking after it hit the culvert and water got all over the opti.So it was time for a change,the old opti would barely turn by hand so I think the bearing was freezing up.It also has a high idle now that wasnt there befor the opti and AIR removal.Some mornings it will fire right up and seem to run not so rough.But the gas mileage has went from around 20mpg down to 10mpg since the hole in the pipe.I had the codes ran and it said the left bank 02 was reading a lean condition(it only has one 02 sensor) and it had a code for the AIR pump.Why is the pcm reading lean but the car is running rich?Could there be a vacuum leak somewhere?It has 21" of vac and it is steady.Could it have a cracked head somehow from the impact?Sometimes it runs smooth and sometimes it runs like stomped ****,at full throttle it seems to still have the same power before the hole which it ran 13.8 stock.I am completly lost right now dont know were to turn next.I have a donor car for parts but its an m6 and the z28 is an a4 so I cant change out the PCMs to see if the lick it toke damaged the PCM.Can anyone give me any ideas,any help is very much appreciated. Also I checked the fuel pressure and it was fine but after about 20 minutes it drops around 15psi with the motor turned off.So I dont know weather it has a leaking injector but I dont think that would make the PCM think its running rich.

 

It sounds like it has an exhaust leak somewear before the o2 on the rich side. Can you hear it ticking?

 

No doesnt seem to have any leaks,but could a very small leak cause it to run so bad?

 

Anymore answers?

 

Not sure about this, but I would think that if you are getting a lean condition reading at the o2 then the PCM would try to richen up the mixture to compensate. My C5 was getting a lean reading and it turned out my cats were clogged and my o2 sensors were bad, I just changed the midpipe and o2 sensors and it ran like new. If your cats are clogged it would cause an incorrect reading at the o2 anyways. Maybe the cat was damaged during the accident. I also noticed that when I changed the midpipe and the o2's my mpg went from 24 hwy to about 31 hwy. The lean reading could also be only at startup. I know on the LS1 you can have a condition only at startup and the check engine light will remain on for 10 key cycles or so many miles even if the problem is no longer present. Hopefully this helps you out some.

 

It did crush the cat during the hit.But I gutted it soon after.

 

If you ripped a hole in your exhaust you could have damaged the wiring to your O2 sensors. You should have 2 oxygen sensors, check the wiring to both and if the wiring is ok try replacing the other one. If the ECM thinks it's lean it will add fuel to try to get it back to normal.

 

My 94 only has one 02.Its on the passenger side on the y.

 

Is there a doctor ,or priest,in the house?

 

How does it only have 1 o2 sensor?

 

I think obd1's all had one single 02,but I'm not sure.Both of my lt1's have only one 02.A 94z28 and a 95 ta.

 

you should have one in your drivers side manifold also