CEL light after ecu reset

[gacklez]

Hey fellas, sorry if this question has been asked before. I'm on my phone. Okay soo I got my 03 s2k a few months ago and it had been running with an almost squished exhaust pipe. I figured that out when I was putting my HKS hi power on. I decided to randomly reset the ecu today to see if it made any difference. I removed the 7.5A backup fuse after the engine was warm. Left it for 2 minutes and then put it back in and started the car. I let it idle for like 10 minutes. The CEL came on and started blinking for 30 seconds and then just stayed lit. I turned it off and turned the ignition back on without starting. I turned it off and then cranked it again, the car runs perfect and it's never been lit before and I'm a litttle worried. It just stays on now. I always click the fuel cap 3 times or more. I've ran fuel cleaner through before. I took it to autozone and the fatty said my 1 and 3 cyls are misfiring and that there is some "random misfire code" appearing. Any ideas? Is this normal? I'm about to go on a road trip so was already going to replace plugs and another oil change maybe.

Thanks fellas,
Jason

[griffon]

Was your O2 sensor also damaged?

[repiv]

Where was the exhaust "squished"?
Misfires, especially "random" ones are very hard to resolve. You have misfire code for cyl 1 and 3, so I suggest you take those coilpacks and put them in the 2 and 4 positions and see if the code follows to those cylinders. While you're at it, check the plugs to make sure they all are gapped properly and look "normal". If in doubt, get new OEM plugs and check the gap and put them in, reset the ECU by pulling the BACK UP fuse again. So long as the CEL doesn't blink, put it through 2 or 3 driving cycles and see what happens. If the light continues, you may be looking at diagnosing fuel injector problems, ECU problems, fuel pressure problems. How's your fuel? You're using premium, right? From a brand name gas station?

PS. No need to leave the fuse out for so long. 30 seconds is good enough. Make sure the key is full OFF when you do it.

PPS. You let it idle for 10 minutes. At what point did the CEL light come on? Why did you idle it for so long? Typically, idling for that long is unusual but shouldn't create a problem unless the car has something else going on, in which case, lengthy idling may bring those issues to the forefront. Now, you say you "idled" the car. Does this mean you just let it run on its own and NOT touch the throttle? Some people consider holding their foot on the gas pedal with slightly elevated rpm is "idling". It is NOT and this alone can create problems of its own.

[sdosmil77]

chek your o2. mite not b source of prob but it was mine. the cat broke inside and shifted bak towards car inside and burned the tip of o2 off. no runnin different tho

[gacklez]

I let it idle for probably 5 or 6 minutes actually. By idling I mean I didn't touch anything and it was idling steady around 900 rpms or 1k. Ty for the responses, how long should I let it idle after I reset?

[gacklez]

Also, it was like... 1/2 of the flowing capability of the pipe was squished on the stock exhaust right above that little metal bar that bolts from one side of the rear suspension/brake assembly area-- (the one you have to take off to remove the stock exhaust) It looked like the previous owner ran over something and it squished that bar into the pipe really hard,

[repiv]

I let it idle for probably 5 or 6 minutes actually. By idling I mean I didn't touch anything and it was idling steady around 900 rpms or 1k. Ty for the responses, how long should I let it idle after I reset?
You don't have to let it idle at all. Just drive it or not drive it. I'm not sure where you got the idea for idling it after an ECU reset. It doesn't do anything one way or the other. Running it at above 3000 rpm in neutral for 3 minutes is a diagnostic tool for very specific problems and has nothing to do with resetting the ECU. In fact, idling for a long time or running above 3000 rpm for more than 3 minutes creates a whole other set of issues that need to be dealt with.


This kind of constriction would hamper performance to some degree. However, the removal of such a constriction and bringing the exhaust flow back to normal should not affect the running of the engine in a way that would bring about a CEL. The ECU may have learned to run the engine with the restriction and when you removed the restriction, it may have eventually learned to deal with that. One thing that concerns me is that when you removed the damage exhaust and put on the HKS, something may have gotten damaged during the process, like the O2 sensor in the cat or even the O2 sensor in the header (if you messed with it for some reason). The CEL may have triggered anyway regardless of you resetting the ECU.

The random resetting of the ECU is not something that is recommended. What this does is put the ECU back to default settings, requiring it to completely re-learn the specific running conditions dictated by your driving environment. This may compound with other things that coincide with the exhaust work.

[gacklez]

Bleh. I just replaced the plugs. It's running fine, everything seems great but the check engine light popped on again. The only thing I can think of that changed is after I installed the HKS, I can smell my exhaust a little. I don't believe I damaged the sensors because before I reset the ecu today the CEL had never displayed before.

[repiv]

Bleh. I just replaced the plugs. It's running fine, everything seems great but the check engine light popped on again. The only thing I can think of that changed is after I installed the HKS, I can smell my exhaust a little. I don't believe I damaged the sensors because before I reset the ecu today the CEL had never displayed before.
This doesn't mean the CEL can't come on now. Something has happened. It may be pure coincidence or it may be related to what's been done to the car.
What did you replace the plugs with and did you check the gap and did you screw them in with the right torque? I made a suggestion in my first reply. Give it a try or not.

[gacklez]

I replaced them with bosch platinum iridium fusions, They have a preset gap. The car runs absolutely perfect right now.. even better than before the light appeared.. it's just there.. and annoying. Thanks so much for your help man.. Can it really be misfiring and I not even notice it like that? When my wife's 4.0 xlt ranger misfired it seriously went crazy, my car doesn't jerk or behave like it's misfiring imo.. I don't know why his odbii would tell me that though.

[repiv]

I replaced them with bosch platinum iridium fusions, They have a preset gap. The car runs absolutely perfect right now.. even better than before the light appeared.. it's just there.. and annoying. Thanks so much for your help man.. Can it really be misfiring and I not even notice it like that? When my wife's 4.0 xlt ranger misfired it seriously went crazy, my car doesn't jerk or behave like it's misfiring imo.. I don't know why his odbii would tell me that though.
If it's running fine, keep monitoring the CEL. Pull the code now and then to see if anything's changed. Yes, you can have a CEL and the car will run "OK" ................ for now. But who knows what kind of damage can be going on that you don't know about.
BTW, Bosche plugs have been known to not work well in an S2000 engine. Same goes for iridium plugs. In almost all FI engines, they produce a high rpm miss and in NA engines, they have been known to begin to miss after a while. The only example where they seem to work is in a car with a Mugen ECU. Also, you cannot depend on any sparkplug having the correct gap out of the box. There is no such thing as a "preset" gap. Things can happen during manufacture and during shipping. ALWAYS confirm gap before installing a plug.
It's your car and it's your choice to run with a CEL but the smart money is on getting it resolved. This car has been known to run really well when you lean it out a bit, at least till you burn something up. One of the reasons this engine throws a misfire code is because of a very lean condition.

[gacklez]

Okay.. So the CEL was coming on for misfiring of 1+2 and multi random misfires. When I changed the spark plugs to the bosch I had it checked again and it was just reading the 1st cyl misfire. I replaced them with cheaper champion plugs and adjusted the gap myself, reset the ecu and it's gone. Thanks for all of the help man, I appreciate it. I'm going to get the oem ones when I get the time.

[repiv]

Good to hear. If only all random misfires were that easy. The OEM platinum plugs are the plugs of choice. Don't forget to check the gap before you put them in.