TBI 350 Running Rich

[95 Tahoe]

Not real reliable.


The computer is in lean-command, trying to get the actual air-fuel mixture to the desired 14.7:1. IF the O2 sensor is showing the expected swing between low- and high-voltage, the mixture is "correct", averaging neither rich nor lean.


.4 mV and 800 mV? Or 400mV and 800mV?

400 to 800 mV would indeed be "rich". I don't think I've ever seen an O2 sensor go down as far as .4 mV, but a swing from very low to very high voltage is normal for a properly-functioning O2 sensor.


Let us know how that goes.

For the record, the "right-side injector" does not feed only the "right bank". Both injectors feed two cylinders on each bank--the two outer cylinders on one bank, the two inner cylinders on the other bank.

One injector feeds 1, 7 (outer left bank) and 4, 6 (inner right bank).
The other injector feeds 2, 8 (outer right bank) and 3, 5 (inner left bank).

Therefore, a TBI with only one O2 sensor, is still sensing the fuel output of both injectors.




Good catch on the EGR.

It's not commanding a lean condition. It's in lean-command, trying to get to a CORRECT air-fuel ratio. Lean-command is reducing the "expected" amount of fuel according to the base programming because for some reason the base programming would be too rich on your engine. For example, excessive fuel pressure. The O2 sensor (if it's working properly) is the best way to determine rich/lean, and yours seems to be showing a proper air-fuel ratio once the fuel trims are in lean-command.

What is your fuel pressure?

Thanks for the detailed reply. The lowest value on the 02 sensor was around .4MV from watching the graph. It goes very high to very low. I haven't checked the fuel pressure yet. I plan to do this over the weekend since I will probably need to take a bath in gasoline to do this if I do it at the fuel filter location.

 

[95 Tahoe]

Just a follow up if anyone has the same problems. I've read a ton of these threads recently and they all fizzle out without a conclusion. The EGR solenoid cleaned up most the problems that I thought was coming from running rich. I don't have the soot accumulating on the exhaust now.