Check engine light???

[SpoolingMr2]

I am currently running just the downpipe for my exhaust. I was driving around all day with no problems until BAMM... check engine light. The car is still running strong but i am wondering why this would just all of the sudden come on ?? I was thinkin o2 censor or possibly its reading an exhaust leak?? If anyone could help me out it would be appreciated.
thanks

[drazhartd]

Drive around for another day and see if the CEL turns itself off.


That's what happened with my headers.

The CEL will randomly turn on, then turn off.

I believe it has something to do with the change in airflow.

[JekylandHyde]

If you get the check engine light to come on, you should check the codes. Whatever code you tripped is stored in the ECU and finding out what it is, is really simple to do.

On the engine bay/trunk firewall there is a little grey box that says DIAGNOSTICS on top of it. It is on the passenger side of the car and it is only 1"x2" or so.

Pop open that little box.
Inside the roof of the box is a little diagram.
Use that to locate the pins for
E1 and TE1
You need to jumped those two ... a paper clip unbent works fine (or a small piece of wire).
Just stick each end into each of those ports.

Chances are good those ports look gunky and it does not feel like you are really pushing into anything ... but this will work ~ I promise

If you did it right, when you turn the key on (you do not have to start the car) ... the check engine light will start flashing in code.

It is possible that you will have stored more than one code!
It will keep cycling thorugh them.

Watch the flashes and learn the pace. 5 flashes, small pause, 2 flashes, long pause, 5 flashes, short pause, 2 flashes, long pause, etc ...

That would be one code and it is code 52. The long pause is the break between flashes. The short pause is the break between digits.

Code 52 is the knock sensor ... it is one of the most common codes to get.

[SpoolingMr2]

So when i find out what it is what do i do?? just reset the ecu each time this happens?

[JekylandHyde]

The code will tell you what is wrong.
You need to address THAT issue.
Just resetting the codes isn't going to make the problem go away.

[SpoolingMr2]

Ok but my issue is if its the knock sensor or possibly the 02 sensor why would i want to replace it when its just most likely doing this becasue im running straight down pipe. When i had my exhaust system on i never got any check engine lights. so im guessing when i put my aftermarket exhaust system on that everything will be ok becasue it will be getting back pressure again. But i dunno i check the codes and see what pops up. Thanks again Jekyl

[JekylandHyde]

If you happen to get the code for "knock" ... this issue is not a "broken knock sensor." That is the result.

Cause and affect. You need to resolve the CAUSE and fix the AFFECT.

If you did indeed break the knock sensor, you are going to have to solve why you are detonating. The sensor is there to protect your engine. Withit broken you are not having protection and if you knocked loud enough to break the sensor .. chances are you are in a position to knock hard enough to break the engine.

[SpoolingMr2]

Would this be happening becasue i am running 15psi ?? because i took the boost vac line and corked it. i have my boostcontroller set at 15psi. i will check it asap. i hope its just running a code becasue there is no back pressure if it a busted knock sensor im gunna be pissed.Also shouldnt you hear the engine pinging and knocking?Also another thing is the only time the check engine light comes on is when im in 5th gear right around 2500 rpms. Let me know what your think jekyl and then ill get to the codes after i get back from a family gathering. Thanks you have been a ton of help

[JekylandHyde]

There is no "back pressure" code.
The computer can only store codes from thing's in monitors and there is nothing that monitor's back pressure. I ran Hyde for 3 years with no exhaust (just 3" of pipe).

I can't tell you "why" you are getting a code until we know what code it is.

When the check engine light comes on has nothing to do with it at this point ... you already had a code stored so they light will come on randomly or just stay lit.

It is not ypical to "hear" pinging or knocking in our engines since the knock sensor adjusts timing/fuel to stop it as soon as it starts to sense knock (when it is not audible yet).

Yes, increasing boost increases your chance of knock. More or less anything you do to increase horsepower will increase your chances of knock(detonation).