I searched and I couldn't find any other threads that have the symptom of the non existent CEL. Ever since I changed out my exhaust and header to the Megan and the fuel line that rotted through,my car has been running a bit rough on take off. It bogs down under load in 1st and 2nd gear. Once I push the clutch back in and rev it good it's fine. It's usually when I start cold too. I've also noticed my car is running a bit rich. My bumper is covered in carbon and I'm getting roughly 30mpg. The thing that puzzles me is my car isn't throwing a CEL. I know damn well that my CEL bulb still works.

I'm wondering if its the o2 sensors or the fuel filter......... My dad can't figure it out either.

It's a 97 LX 5 speed with an EX exhaust conversion.

 

Take the spark plugs out and inspect them. If one is black and the others OK, likely a bad fuel injector on that cylinder. Also get a gauge and test your fuel pressure. Is the vacuum line on the back of the fuel regulator hooked up properly?

 

The spark plugs should be fine because I changed all of them, the wires ,the cap and rotor out back in the spring. Although when I did change them one of them was fouled.... The problems I'm having now only started up though after i changed out my exhaust back in june. I'll have to check the vacuum line....didn't think about that.

 

You're missing my point. Looking at the plugs now will tell you if it's one cylinder running rich or all 4. If you had one fouled plug before you probably do again, need to identify which one and concentrate on finding what is wrong with that cylinder. Finding it is one cylinder rules out a lot of stuff, since all the sensors and stuff outside the engine tend to affect all 4 equally.

You don't have to replace them with new ones, they will clean themselves up unless so badly fouled that they short out.

 

Bringing it back from the dead... I had my dad check the spark plugs and he said they looked fine, one was slightly discolored, but nothing major. I tried a bit of fuel injector cleaner and it still ran rough. I still can't figure out what it's running rich but not throwing a CEL.... I think it's somehow tied into the fact that I had to have one of the fuel lines replaced because it rotted through.... Could that have something to do with it? :-/ I'd check out my manual (which is on a disk) but my disk drive in my computer is dead.

 

Fix this problem as soon as possible as it may destroy your cat.

You just replaced the exhaust system, so the engine may be running rich due to an exhaust leak around or upstream of the primary O2 sensor.

Another possibility is that the primary O2 sensor is deteriorated to the point of having low performance but not enough to throw a CEL.

 

Thanks Ron! :-)

 

Ok, just looked at the plugs again. Looks like cylinder 3 is the problem. The plug was more discolored than it was last time. Looks like its a bad injector?

 

In addition to checking the fuel injector, also check whether plug 3 has bright blue spark. If not, you may have a bad corresponding plug wire or corrosion of the distributor cap point corresponding to plug 3.

 

the spring I did a tune-up. Changed out the plugs,wires,cap and rotor. If the plug wire's coroded already I'll be pissed since they're new NGK's. Yet I will check that for good measure. I really appreciate you helping me out!