QuestionThis is my son's car. He is a college student with little money so we try to keep things low priced and simple.Car just returned from Florida to NY and made it! Upon returning home we changed oil and filter ourselves to save some money. Right after doin this the car began to run extremely rich. Almost looked like coal dust coming out of exhaust. Mileage went from about 22 to 14 on the highway. Just before oil change son took car into a local muffler shop where they welded a short piece of pipe between cat. converter and muffler wher it previously had only been clamped together. Car seems to idle a bit rough. Read some of your earlier posts and attempted to get to the EGR and test and free it up, but didn't seem to make any difference.
Codes I am getting are 12,32,33,51. I looked these up on another web site and 51 really stands out to me. What do you think? Also I should mention that just before returning to NY from Fla. based on your advice to other readers I sent my son to a local junk yard where he bought a ATC control for his crazy ATC system that hasn't worked since being in the heat of FL. and it solved his problem just in time to take the trip home in comfort instead of with high heat blowing on him and baking him. Thanks for that tid bit of info. Await your reply. Thanks a lot.
AnswerHi Bruce,
The powertrain controller may be responding to a false lean mixture from one of the two oxygen sensors and enriching the mixture on the injectors for that set of cylinders. That assumes that you are visually "reading" the exhaust correctly, of course. But also note that the egr if sticking open could be causing a true lean mixture during idle and deceleration and very poor burning of the mixture so you need to check that too.
So I would suggest measuring the signal voltages to find out if an oxygen sensor is flaky. The sensors are mounted on the right and left exhaust manifolds. Because you may not want to invest in two sensors (I think they run around $80, but check that out) I would try measuring the signal voltage on each sensor before removing it to find which one is inaccurate. The right sensor's signal wire is tan/white on the engine side of the 4-wire connector and the reference ground wire is black/light blue. You could take very fine pins and probe thru the insulation of those two wires and see whether the voltage is about 0.5V which is normal, or 0.1V which says the mixture is lean. The left sensor's signal wire is black/dark green and it too should be read across to the black/light blue wire. This should be done with the engine running and warmed up so that the sensors are heated. Whichever one has a reading near 0.1V is the one that is presumably faulty. If you find it easier to probe the wires at the power traincontroller on the right side frame rail the right sensor signal is on pin 49, the left sensor signal is on pin 41, and the ground it on pin 4, all with the wire colors as given above. Once you find which sensor is bad, use some penetrating oil on it threads and let it sit for a few hours to loosen it up. Then remove and replace the sensor, tightening to about the same torque at a spark plug. Be careful to not damage the wires at the tip of the sensor. If both sensors are showing lean then that would indicate a need to look more closely at the egr, because the odds of both sensor failing together are fairly low.
If for any reason you believe that the mixture might be way lean rather than rich, check that the egr is closed when the engine is idling, look for an intake manifold leak, or measure the fuel pressure to see if it is too low, any of which would cause a true lean mixture.
The 33 is probably not involved in the mixture issue. But note that the 32 is, if the egr is for example sticking open which would cause a true lean mixture and bad idle which might be so far off as to look like black soot. So lever the valve stem in and out against spring pressure in one direction and make sure that it closes tightly at idle. Then run the engine and see if the valve stem moves when you rev it. Examine the vacuum lines for any breaks.
Is there anything that might have been disturbed when you did the maintenance is another thing to consider?
Please let me know what you find out.
Roland
