My 98 EX (Canadian) has been having some stumbling/sputtering problems that only seem to occur at highway speeds after the car has warmed up. When it happens, it feels like the enginee is starving for gas. It'll sputter for 5-10 seconds, then jump back to life, then sputter again a few seconds later. It only seems to act up on the highway, around town it feels fine. The only code present is a P0420. I replaced the fuel filter and that didn't help. I swapped the coil and igniter with ones from a junkyard and that didn't help either. The spark plugs are less than a month old. The cap and rotor are about a year old. The oxygen sensor was replaced a week ago. I'm leaning towards a fuel pump issue. I had a 96 2.4 Stratus that did something similar and in that case, it turned out the fuel pump was bad. Do any of you think my Civic's fuel pump could be the cause of the problem?

 

...anyone?

 

fuel pump is a cause of it, but my car just had the same problem 2 days ago, it only did it when it warmed up, turned out it was my 4 month old rotor cap.

 

try a different gas

 

I got my Ultragauge today and hooked it up, then did a little cruising to see what it could tell me. I noticed that when the car starts doing those little sputtering episodes, the short term fuel trim goes way negative, almost to -30 and the oxygen sensor voltage goes to 1.275. I guess what that tells me is that for whatever reason the car suddenly senses it's running way lean and needs to massively enrichen the mixture. The only reason I can think of for why it goes massively lean all at once is that fuel flow is reduced by a large amount, like by a failing fuel pump...at least that's the only thing that makes sense to me. I'm going to order a cheap fuel pump off eBay and install it when it comes it and see if it fixes the problem

 

How about a bad fuel injector?