Infinitrium

My 98 Civic 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?

lazlong

P0420- Catalyst system efficiency below threshold

If you already replaced the O2 sensor then you need a new catalytic converter. If you need to pass emissions I recommend you bite the bullet and go with OEM. You can get a universal cat (way cheaper), and it may pass emissions this year but, it won't pass next year. If you don't have to meet emissions standards you can also go with a high-flow cat or straight pipe.

There are several online dealers like this that you can get a much better price on OEM: http://www.hondapartscheap.com/southbay/jsp/home.jsp

Infinitrium

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?

lazlong

Sensor 1 (primary) or sensor 2 (secondary)? But, to answer your question, yes, it's running lean if it spikes that way. It's running rich if it spikes toward .5V.

EDIT: Are you sure it's 1.275V, not 0.1275V? After some research it should read somewhere around 0.2-0.7V

Infinitrium

Yup, senson 1 bank 1 shows 1.275 volts when the car starts sputtering. Otherwise, when the car runs normally, the sensor's voltage is in the normal range.

lazlong

Something is causing it to run very rich. Test the fuel regulator and test the injectors to see if one is sticking open.

Infinitrium

How do I test the pressure regulator or injectors? I swapped the regulator with another used one but it made no change.

Infinitrium

New development! Maybe this problem is related to a malfunctioning oxygen sensor? It seems that with the new, non-OEM oxygen sensor either unplugged completely or replaced with the one that came with the car when I bought it (which had the bad heater circuit), the sputtering at highway speeds disappears completely. I was on the highway this afternoon for about 45 minutes at around 72 mph and it never hiccuped once. With the new, non-OEM sensor, it would have acted up within the first 5-10 minutes. Here's the thing about the non-OEM sensor, the website I bought it from said it wasn't the proper one for my car (it was for a 99 Civic w/ D16Y7) but it seemed to plug into the connector and it fit into the manifold so I figured it would be ok. So far, the car feels like it's running ok with the old O2 sensor, fuel mileage is a bit lower though since it can't get into closed loop which was the reason I bought the non-OEM sensor in the first place. I think I will leave the old sensor in place for a while longer to see if there's any change.

lazlong

Yeah, the O2 sensors are made for specific engines. Usually Hondas are finicky about O2 sensors anyways. Save up for an OEM one.

Infinitrium

I gave the Honda dealer in town a call to see how much an oxygen sensor for my car is. 300 bucks. No lie.

lazlong

Yeah, sorry about that. If you go to one of the online dealers it's still $240. Like here: http://www.hondapartscheap.com/southbay/jsp/home.jsp

Infinitrium

How about a Denso part? I found a Denso exact fit oxygen sensor on eBay for $48 shipped.

lazlong

Denso is the manufacturer for OEM. I think it would be worth a try. I would confirm it with someone else like Gearbox first tho.

JackedByJack

have u tried any junk yards in the are or maybe even craigslist?