My friend got a SES light the other night after we did a bunch of work on his car, a 90 IROC L98 with SLP cam, catback, and few other small mods. We got rid of all the air injection junk, smog pump, punched cats out, new plugs(one heat range hotter), manifold gaskets, and new o2 sensor. The car ran awesome, better than it has in along time. It was running perfect until he checked the code with his code scanner, it got a code 13. When he tried to start the car up after pulling the code, it would not idle, and was running really bad. Tried unhooking the battery, but nothing. What would cause this all of a sudden?

 

Code 13 means a steady lean signal from the O2... Maybe you have a defective O2 sensor, or the wire from it burned up on the exhaust pipe. Thats what it sounds like to me anyways. Unplug it and see if it will idle then.

 

Brand new o2 as of the other night. Would any of the things we did cause a lean condition? So just unplug the o2 sensor?

 

Not that I can think of. 2 possibilities are either a, you really are running lean, or b, the O2 is saying you're running lean but you might not be.

I'm just saying to unplug the O2 and see if some of the problems disappear. If they do, then you know your problems are more than likely caused by a faulty O2 giving bad readings.

Also, does it run bad on a cold engine? If it runs good cold, then it very well might be the O2 or other emissions components...since the computer doesn't use the O2 until it warms up and starts running closed loop.

 

double check that o2 sensor. Before you go to all the trouble here in these steps, hook the scan tool up and see what the O2 sensors mv readings are.

If you want the steps to troubleshoot a code 13, here goes:

Start engine and run at 2000 RPM for 2 minutes. let it idle and install a jumper on the ALDL with the engine running. Does the check engine light flash on and off slowly?

If yes: The problem is intermittant, no repair needed at the time.

If no: connect a high impedance voltmeter to the O2 signal wire (on the ECM side of the plug, not the O2 Sensor Side). With the engine off, ignition switch on, disconnect the O2 sensor, and ground the ECM O2 input wire (purple wire). does the voltmeter read close to zero or zero?

If no: The purple wire has an open circuit. Find and repair.

If yes: Connect the voltmeter to the purple wire where it would be normally connected to the O2 sensor, If the reading is :

between .3 and .6 volts : The ECM is defective. Replace it

Over .6 Volts: The ECM ground wire for the O2 sensor (usually tan) CKT 413, or its connection to the ECM has an open circuit.

Under .3 volts: check for an open circuit in the purple wire to the o2 sensor, CKT 412 for a connection at the ECM. If wire and connection are both good then replace the ECM.

There you have it, hopefully you can get something figured out.