Cold Starts Lean, Warm Up Enrichment Issue

[3p141592654]

I'm a bit confused. Your last paragraph seems to say that the coolant sensor is working fine. It should drop down in voltage as the engine heats up to operating temp just as you describe. The initial reading of 4.97V at THW is not correct though and suggested an open circuit. Something is not consistent here.

The HT current is monitored by the ECU, and an open or short should trigger a code 21. Your symptoms sound a lot like a O2 sensor problem, and no heater current when cold will delay the switch to closed loop. Have you stuck an ammeter in series with HT and actually measured HT current? The ECU switches it on an off according to operating conditions. I forget the details but can look it up.

 

[suprajim54]

I agree that the 4.97 volts didn't seem right, but when I started the car, voltage dropped. I'm going to go back and check my work. I'm thinking maybe in all my testing, the plug wasn't reconnected to the sensor.

As far as the heater signal, I will check the current and see what I find. Does the TCCS use the THW signal as one of the triggers for the O2 Sensor heater?

I have 3 ECU's 1 JDM and 2 USDM. One of the USDM's throws a Code 21 and always has since I bought the car. I replaced the sensor but still had the code. When I switched USDM ECU's it went away and never came back. Same with the JDM one, no 21. I guess its possible that one is "correct" and the other 2 have issues.

 

[jetjock]

I agree that the 4.97 volts didn't seem right,...

It's not right. If it were a code 22 would have been set. There more in your posts that doesn't make sense and much of it implies a misunderstanding of how the EFI system actually works. Not that I'd be blaming it anyway. Most people are overly quick to do so when it's usually not at fault.

 

[suprajim54]

I took a couple minutes just to check THW and got 1.3 volts. I unplugged the sensor and got 4.97v and code 22. I must have had the plug connected when I checked last time. When I have time this weekend, I'm going to check current in the heater signal and try to figure out why it doesn't seem to be working. My earlier posts were done while I was using a piece of junk meter. I've since picked up a better one and going to go recheck the results I got last time.

I agree that I have much to learn about the EFI system. The issue with it running good and bad with only the turn of the key leads me to believe there's something EFI/ECU related. I could just leave it be and accept that I just have to warm up the car and restart it every time, but I'm trying to fix the problem and learn along the way. I really appreciate the help and feedback from all of you guys.

 

[suprajim54]

So I went back through all my work and all the wiring seemed to check out, acccording to the TSRM and TEWD. I still could not get the HT circuit working and normal AFR's unless I turned the car off and back on. According to the TEWD, the AFM is one of the input signals for the HT circuit. I found a clean looking 1UZ AFM at the junkyard for $50. I put it in and fired the car up. While it was still a little lean, it seemed to be running better. I went ahead and bumped up the FP with vacuum attached to about 36 PSI. Now, it's idling right around 14.7, and O2 sensor will cross count after it warms up without requiring a restart. VF is 2.2 volts until WOT when it goes to 0 and AFR's are around 10.0. I put about 200 miles on the car over the weekend without any issues. I will leave it alone for awhile until I feel confident it's fixed. Afterward, I can tweak the FP and re-install the SAFC. It seems that my AFM was bad or going bad, although not throwing a code. I'll update if the symptoms return, but so far it seems like its fixed. Thanks again to the Supramania community for the help and suggestions.

 

[Mr. Joe]

Sorry to be that guy that brings back the thread from the dead but have you noticed any similar issues since you replaced the afm? My car has almost the exact same symptoms you described and replacing the afm didn't work for me, so I guess what I'm really after is how you found the input signals for HT from the wiring diagram.