Hi guys, I recently finished my 350 conversion into my 89 formula from a 305 tpi. I upgraded to L98 22lbs injectors and an 89 formula 350 chip. I have been doing a lot of reading on code 13s and closed loop parameters. Let me list my mods, vortec heads and tpi intake, lt4 production cam, edelbrock headers and y pipe, no cats or egr. I run a 180 stat with the secondary fan on a separate thermostat that keep it running around 190 degrees. Car idles smooth, has great acceleration, runs good overall. While cruising at constant speeds I get an occasional code 13 for 30 seconds or so. The code doesn’t bother me, but I think it might be linked to my motor never getting into closed loop. I’ve seen a lot of people go to heated O2 sensors, or better grounds to rid themselves of the code 13. Is that code 13 possibly related to my motor never getting into closed loop? I have also heard that not running an egr causes an occasional 13. The code really doesn’t bother me, but not going into closed loop does. The crappy auto-xray never gives me a reading of over 500mv. I have read that closed loop requires over 600mv from the 02 sensor. Do you think a heated 02 sensor is the answer, am I going in the wrong direction? I really don’t think running a lower stat is my problem either, because my motor stays at 190, or higher. It is a new bosch 02 sensor; single wire. Are there any ways I can test my ground on the o2?

 

Something really has to be screw with the o2 sensor (ie not connected) for the ecm to throw a code. That code 13 means that the computer isn't seeing enough activity (voltage and crosscounts) from the 02 sensor to go into closed loop operation. The ecm expects it to function within a given period of time or it will set this code. This can be caused by a few things such as bad connections/grounds, a defective 02 sensor (even bad 02 sensors will read enough for the computer so this probably isn't the case), or the oxygen sensor not ever reaching operating temperature, thus not showing very much activity. This is prone to happen on cars with headers, more so and specifically with long tube headers where the 02 sensor is located much farther down. Its not that much a problem with cars with shorty headers. I have a heated o2 sensor on my gta and i have hooker supercomp shorties and i've disconnected the heater element wires and ran the car and it still went into closed loop just fine. You mentioned you did a conversion to tpi. Make sure the oxygen sensor wire didn't get damaged or knocked loose at either end (harness connector to ecm or o2 sensor). make sure the pins (for the 02 sensor wire) at both ends are not corroded . Pull the oxygen sensor and inspect the threads for excessive corrosion or anything else that might insulate it from ground as well. The "default" voltage the ecm sees is about 450 mv, so this sure sounds like the case.

Just my .02

 

Thanks for the reply. I am running shorty headers, but I have seem a few complaints from guys on the board with shortys. The car was originally a tpi, i just swithed motors. I should have cleared that up before. Being new headers and o2 sensor i dont think it is corrosion. If it did have a bad wire or connection though, would it just occasionally throw a code, or all the time? Will this code 13 only always prevent closed loop, or just when it is acting up?

 

The threads in the headers might not be corroded but the threads on the old 02 sensor might be or there could be something else insulating it (possibly lubricant?). Again its also possible that the wire or the connectors on the harness got damaged during the process of removal and installation of engine and associated equipment (like the ecm at the other end). an easy way to test this is to get under your dash and remove the ecm. Now looking at the big harness connector from which you just disconnected the ecm, find the pin for o2 sensor wire and do a continuity test between that point and the actual connector the for 02 sensor at the other end. As long as the computer is detecting that fault (code 13) your will not go into closed loop and run rich. If its an intermittent code it could be the oxygen slipping in and out of operating temperature.

 

interesting i was popping the same codes at times. now i am just getting a false code sometimes. it will pop on the freeway and i will check it and nothing. i have manifolds though.

 

I pulled out the 02 sensor which looks almost new still. I started the car with it out...and it ran just the same! My scanner gave me the same volatages I was getting when it was in there...right around 400. Should it do this....I didnt even get a ses light either???? Could me ecm be bad...or is this what happens in open loop?

 

Your computer is not connected to the O2 sensor. It could be one of a few reasons. As was stated before, the wire may not be connected somewhere in the harness, or the threads of the O2 sensor may have a non-conductive coating on them, or the O2 circuit in the computer may be bad. I would unplug the wiring harness from the computer and the O2 sensor and test for continuity. If that checks OK, then try another O2 sensor and make sure not to use any sealant or antiseize on the threads. If that still doesn't work, then it's the computer. You can get a reman computer at a local autoparts store for under $100. I had the same problem and it was the computer that was the culprit.

To test for closed loop operation, use a jumper wire to connect the A and B terminals of the ALDL connector under the dash while the engine is running. With the engine at operating temperature, and running at around 2000rpm(to keep the O2 sensor hot), the check engine light should blink once per second if it is in closed loop. If it is in open loop, it will blink 2.5 times per second. That is a quick way to test for open and closed loop without waiting for code 13 to appear. And to answer your question, it is not an intermittant problem even though the check engine light only comes on during highway cruising. The computer can only determine that there is a problem in that area when no other variables are changing(i.e throttle position, airflow, rpm, etc.), otherwise it just tries to compensate by giving it more fuel and retarding the timing.

 

Thanks for all the advice. I got it fixed tonight. I was tracing wire all the way back to ecm. I was about ready to replace the ecm when I found the 02 wire pin in the ecm wasnt seated properly. I attatched it firmly back into the harness, and was getting an 02 signal in no time. I had bought a heated 02 also, but the single wire heats up very fast in the shorty headers. No codes after a lot of driving tonight!