Blown90hatcH

DC 4-1 header....stock cat...new O2 sensors....Throwing code 45. The O2 sensors are in the correct location. Dead cat? The plugs are really sooty and black from richness. Stock ECu. Tanabe cat back. Thanks for your help. I dont know why it is running so rich.

Jason

EE_Chris

Look at it from this point of view: Your ECU uses the O2 input to trim injector pulse width to meet the strict emmisions of OBD-II. Over time, as things age, the ECU needs to be able to compensate for things, such as a clogged fuel filter for instance. Well, the ECU does this with parameters called Short Term and Long Term Fuel Trim.

The way it basically works is this: Your ECU has pre-programmed maps for injecotr PW. If the actual injector pulse width is off from this 'set' value, the STFT begins to change such that its value is the difference between the actual PW and the 'set' PW. Now, as STFT begins to change (and it has a range of +/- 20%), and STAYS changed at some value, it begins to move the LTFT value towards the STFT value so that the STFT value starts to head back down to 0%.

Example: Your O2 is indicating a rich condition. So your ECU begins to lean out the injector PW while updating the STFT value. The O2 is still indicating a rich condition for some reason. The ECU sees this, wants to correct it by leaning it out and thus updating the STFT value even more. As this continues, and STFT is still decreasing (remember, it goes the opposite way of what the O2 is indicating), over time it will begin to decrease the LTFT value. Now, the ECU is happy because it sees the O2 responding the way it should and saying "emmisions are great", meanwhile, it still has that stored value of LTFT.

Well, over time, if the the LTFT value exceeds its range (+/- 20%), the ECU throws a fuel system code.

So, just a recap: The ECU throws this code as a result of not being able to bring the mix back into an acceptable range to meet emmisions as indicated by the LTFT value.

I don't think your Catalytic Converter is dead, thats what the 2nd O2 is there for, to monitor its health.

You need to check some sensor inputs. Your MAP sensor has a big effect on injector PW. Just a little change here could cause your problems. This voltage should be at about .95V at idle. If just a little higher (which could be cuased by a lumpy cam for instance, as this cam will decrease available vaccum at idle) than it should be, it could be cuasing your problem.
ECT sensor perhaps could be stuck at a voltage that is telling the ECU that its still cold, thus richening up the mix.

Have you tried resetting the ECU lately? With this code, if its still 'going' to be there, it should return in a day or two (or rather, after a couple drive cycles).