So I've been dealing with a CEL on the 1-4 since last fall. Was throwing a 4112 (phase sensor) and 4121 (Cat ECU) Replaced the phase sensor last time it was decent weather and took her out for a drive. Drove great. Except for the fact when I stopped for gas I realized I didn't hook the darn new phase sensor up. So I did. Gassed up took her out and bam... CEL 1-4 and a stutter in 1st - 2nd gear. Nudged her home and parked her. Leap forward to tonight. Checked all my connections and pulled the phase sensor again just to make sure I actually put the sensor in there. I did. Cleared all the codes.Disconnected battery for 1/2 hour and then reconnected battery and fired her up. Took her out.. ran great... until the last ten minutes... sputtered at a light and the CEL 1-4 bank lit up for a second, stutter and then it was fine. Took her home. Pulled the codes and have a 4121 code now as well as a rough idle and a solid CEL 1-4. I have replaced the CAM sensors as well with the KIA versions. I don't have CATs either. I'm kinda stuck. Would prefer not to tow her to a repair shop if it's just something stupid I've missed. Any help would be appreciated. For now, I've cleared all the codes again and disconnected the battery and going to let her sit overnight. sigh.. first time she's ever really given me a problem in the 4 years I've owned her..
Yep obd2.. damn thing keeps hitting in the codes even when disconnected Sent from my SM-G930P using Tapatalk
What did you do to the Thermal Couple Control Unit? Did you remove it? Did you disconnect the Thermo Couple but left the TCU in place? Is 4121 the only code you have?
I thought ifyou pulled it out it will throw codes. You need to trick it using a circuit. Some on here have done it. Can you describe in detail exactly what you have done. You should have originally had 2 cats on main exhaust with two o2 sensors on each and 1 thermocouple on each. On bypass you should have two cats with no o2 sensors and 1 thrmocouple. O2 sensor wires run back to main motronic and all three thermocouples wires end up at the thermocouple control units. There is three of these.
taz355 has the correct question.... Can you describe in detail exactly what you have done.. The stutter is interesting. Spark plugs,and leads can also cause stuttering.. Every misfire puts unburnt fuel into the exhaust path. This will cause codes to pop up since the exhaust temp system is actually not easily fooled.
Yep.. Ernie posted that if you pull the Thermo ECU it will still store a code but not throw the light. So on my test pipes I do have o2 sensors (one per side) and then right near the end of the exhaust pipe I have the Thermo ECU probe (one per side) which goes back to the thermo ECU tucked up near the shock/spring. The only code it's throwing is the 4121. I'm thinking of swapping the T-ECU's side to side and see if the code follows the T-ECU. But last night was the first time I had a solid CEL 1-4 so that is what is throwing me. Thanks for the help... it's all appreciated.
an Update: so I swapped the T-ECU's side to side hoping the CEL would follow to the 5-8 bank. Nope. Stayed on the 1-4 bank. Same minor blip in the engine, CEL, then the code 4121. Maybe a bad T-ECU probe? Maybe 02 sensor on that side? I did just replace that side initially hoping it would be that? or worse.. bad ECU or wiring somewhere?
David you have a 348 and its Obd1 i believe. Because of this ernie or someone else understands it better than I do. My mistake I thought you had a 1996 355 or later.
Just a guess but swap your motronic from side to side. I believe you have two. And also swap the o2 sensor. Maybe the o2 sensor first. I think logically once you swap the right component it has to change the sides giving the code.
When i had the major done..it did the same thing until i replaced both o2 sensors. I'm going to swap the o2 side to side and see of that follows. Will update after i do that. Sent from my SM-G930P using Tapatalk
Good idea. If needed, and there is room, you can add a spark plug non fouler to the O2 sensor to back it out and reduce exposure to the exhaust stream. Works great on my high flow cat and 2.3 inch full stainless exhaust on the Miata.
Found 2 new O2 sensors in stock. Installed them. Same result. 4121 on the 1-4. Even swapped the t-ecu again..same result. Can i simply unplug the Main ECU's and swap them side to side? At this point its the only thing i haven't tried. Any other ideas from the brotherhood? Sent from my SM-G930P using Tapatalk
Update: Getting closer. So its not the main ECUs. Swapped them side to side and still got a 4121 on the 1-4 bank. It throws that code no matter if the t-ecu is hooked up or not. So what is between that t-ecu and the main ECU? Could it be short in that wiring causing it? What about a fuse in the footwell? I saw a post about that. What about the panel near the strut tower? Something in there causing the issue? Really looking for some help here. Thanks. Sent from my SM-G930P using Tapatalk
David, You need to tell us what you have done with the TCU. Did you install the cat bypass, and still connect up the Thermal Coupler and the TCU ? Did you install the cat bypass and remove the TCU as well as the thermal couple, and just left the 4 pin connector hanging? Did you do something else? Your car is the 1993 348, and I believe that is Bosch 2.5, OBD 1 (not OBD2), right? M
Ok let me try..will add some photos too. Btw. This was all working until recently. Straight pipes with o2 sensors in them. They connect up under the oil filter. The TCU connects to the exhaust pipe rear of the o2 sensors. They are actually a 6 pin connector. I have disconnected the tcu but left in the o2. Have'nt tried disconnecting everything... And yep odb1..flashing lights and all... really have a hang of clearing the codes now. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
OK, same set up I have, except that I remove the TC and the TCU. And even then I still get the 4121, which I promptly reset and I ignore because there is no CAT to be hot. If it comes back, I might try shorting the analog output pin to ground and see where that leads. Two of those 6 pins must be analog out and GRD.
I get the 4121 on the 5-8 bank too but it doesnt cause the drop in rpm. Heres some more info - right before the CEL the car is idling a little over 1200 ..it stumbles, drops to 1000 the the CEL lights. Then idle returns then CEL goes out. I know ernie posted that you will still get the 4121 stored but it wont light the cel. That's how the 5-8 bank is acting but not the 1-4. Its like its ignoring reality. How do i short those pins? Sent from my SM-G930P using Tapatalk
Another thought... how about gas? I did put stabil in the tank before she sat for the winter. Could it be that? Grasping here Sent from my SM-G930P using Tapatalk
Cant do the old o2 sensors. Could redo the phase sensor and the RPM sensors. Thought about them. Sent from my SM-G930P using Tapatalk
I wouldn't waste time taking out the new parts just installed and put back the old ones. Since they didn't change anything, the problem is not in them. Ignore the code number (for the time being) and check all connectors on bank 1-4 - MAF, TPS, Ignition Module etc. Sometimes just pulling out and plugging in again (a few times) a connector can clear a bad contact. Possibly there is a corroded contact somewhere after the winter hibernation.
You did not specifically say about the RPM sensor, but I assumed you replaced them with Kia sensors? What about the phase sensor? Stock or something other? As for which 2 pins, I am reading from a fuzzy schematic. 6 GRD 5 SD light 4 Fused 12V 3 To ECU 2 GRD 1 Switched 12V So the two pins to short together are: pin 2 and pin 3.
