Author Topic: If the Ultragauge suddenly shows massive negative short term fuel trim...  (Read 7820 times)

Offline Infinitrium

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I've got a 98 Honda Civic that's been having some sputtering problems only when at highway speeds, and I  just got my Ultragauge today so I hooked it up then did a little cruising to see what it could tell me. I notice that when my car starts sputtering, the short term  fuel trim goes way negative, -29.7 and the oxygen sensor voltage pegs at 1.275 and stays there until the sputtering stops. I guess that means the ECM has detected an overly rich condition and is trying to subtract fuel, but what would suddenly make the ECM think it's too rich? I think I may have a fuel pump that is close to failing, so I was thinking that maybe during the times when the car is sputtering, the fuel flow is drastically reduced and the ECM catches this and tried to get the engine to run rich to compensate for the lean condition. Does this sound like what could be happening?

Offline bamzippow

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How good are yer plugs?  Spark plug wires?  Coil condition?  Throttle position sensor?  Cam/crankshaft sensor?  Coolant temp sensor?  Vacuum lines?