So here is the delima..I have a 96 cav 2.2, cai, 2.25"exhaust(no cat, 18" res, flowmaster 40).

2 days ago the car started running like I had a real big cam in it(lopey idle) and started using alot of gas. Some black smoke like it is running real rich, so I pull a plug and its black. In my experience this leads to an o2 sensor, so I get 2 new o2s and change them to no avail. So I start to think what is gonna happen if I un plug the manifold o2, the thing runs the same with it un-plugged or plugged in, what gives? You guys ever have anything remotely close to this happen with your cars? Any insight will be greatly appreciated, thanks guys.

get a cat


Ill make a sig someday

What is the cat gonna clear up? I for got to mention that I did change the plugs as well.

MAF sensor. It doesn't know how much air it is getting and is dumping fuel. Swap with someone that has a known good one... will also need to do plugs since they are probably fouled.


1995 Cavalier 2.2 Liter Auto With 64k Miles

MAF? Ok so call me a newb but isnt the maf supposed to be in the intake tract before the tb? If so my cavi came from the factory with maf delete

You guys think I might be having some PCM probs if I can diconnect the o2 and the car still runs the same? Plus, does any one know what the o2 shold read(ohms) so I can check it? Thanks again for the info guys.

The rear O2 sensor has a heater on it, the heater circuit should have resistance, but I don't remember how much. As for the actual sensors themselves, try this:

Testing and Inspection

Diagnose the Fuel Control Oxygen Sensors (O2S) for the following conditions:

@ CAT:
Slow Response
Response Time (time to switch R/L or L/R)
Inactive Signal (output steady at bias voltage - approximately 450 mV )
Signal Fixed High
Signal Fixed Low
Diagnose the Catalyst Monitor Heated Oxygen Sensors (HO2S) for the following functions:

Rear:
Heater Performance (time to activity on cold start)
Signal fixed low during steady state conditions or power enrichment (hard acceleration when a rich mixture should be indicated)
Signal fixed high during steady state conditions or decel fuel mode (deceleration when a lean mixture should be indicated)
Inactive Sensor (output steady at approximately 438 mV ) heater circuit should read some resistance.

the cat on mine ispunched, no cat will not cause this problem, the problem may be a MAP sensor (our cars dont have a MAF sensor...) or maybe a bad F/P regulator

Check vacuum lines, it may be as simple as a cracked hose.

.


John Wilken
2002 Cavalier
2.2 Vin code 4
Auto

have you replaced the PCV valve? the old LN2's dont have that many vacuum hoses that would cause that, also the fouled plugs indicate more than the rough idle does. there are no MAF sensors on the newer cavs, so thats not a problem. the MAP sensor can do this, so besides something simple like O2 sensors and a PCV valve, thats the next place to look. a bad cat doesnt cause fouled plugs to my knowlege. he is running rich and using lots of gas, so thats a fuel problem of some kind. the FPR might be bad, but i would try the sensor and the PCV valve first. if it hasnt thrown a check engine light though, i kinda doubt the o2 sensors and the MAP sensor are to blame....he shoulda got a check engine light....check on the hose leading to the PCV valve on top of the valve cover and on the hose leading to the FPR, the fuel pressure regulater may be to blame. it can be screwed up and make your car run rich without throwing a code.

Does the car start as normal? When you pulled the plugs were they soaked? I had a similar problem, turned out to be bad coil pack(s).

there aint a maf but there is an iat and i think after 95 there aint a pcv valve on the 2.2's or is that the egr? ok ill shut up...

Nothing to add here, other than '96s have a PCV valve AND EGR. A bad PCV wouldn't foul plugs, only make for a poor performing engine. Still, nice idea to check it.