I've got a 98 Honda Civic EX (Canadian model, D16Y7 engine) that's been having some sputtering problems only when at highway speeds, it runs just fine as long as I don't take it on the highway. 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? The only codes present are P1457 and P0420.

 

Start by replacing the fuel filter.

Any CEL codes?

 

Just a thought, but how's your distributor? If the fuel doesn't properly ignite, it's a possibility that's what the O2 sensors are detecting. I was suddenly running rich and had many seizures while driving on the expressways. When Vtec would engage, past 6K rpm the exhaust would get progressively dark. Possibly signifying it was running rich. Being that I don't shift past 4K often, I thought it was normal...until the expressway failures. I thought it was everything from the TB to the O2 sensors, but it was an 18 year old distributor. Never an issue since. And the dark exhaust fumes while in Vtec are completely gone.

 

The fuel filter is about a week old. Only codes showing are P0420 and a P1457. Not sure about the distributor, but I did swap the coil and igniter with ones from a junkyard car with about 100,000 kms less than my car and it didn't change anything.