Hello all so the same 1990 4runner I have been working on now for about a month seems to be getting closer and closer to a finish, I think I have this one last problem to overcome. I am popping a check engine light and the code is for both a Rich mixture, and a Lean mixture. I just finished adjusting the TPS via 4crawlers web site, by the way I found a way to cheat. I have a 90deg phillips driver that is just the right length to get at the pesky adjustment screws. Also another note that I am guessing could be the issue I had the engine harness wire for the O2 sensor sitting on top of the exhaust for a short while, but long enough to melt the wire casing. To ensure that there wouldnt be any issues I spliced in all new wire, including the signal wire with the mesh sheilding on it. I ended up pigtailing the mesh sheilding and splicing a 12 gauge wire betweent the two mesh ends as well. So I guess my true question here is could an issue with the signal from the O2 sensor be giving me both a rich and lean mix signal? If I did screw up in splicing in new wires what do I need to do to fix it? Is there any way to check the 02 sensor to ensure that it is not the issue before worrying about a bad engine harness peice. Thanks all

 

shouldn't the 90 have a 4 wire O2 sensor? I know my 91 has two of them...
anyhow, the code is just a generic O2 sensor failure and means that at one time or another (or still) the feedback to the ECU from the O2 sensor has caused the ECU to repeatedly compensate for a lean or rich mixture.

Have you tried clearing the code and seeing if it returns? (I'm guessing you have but had to ask.)

 

Yea I have tried, well tried as in I have disconnected the battery, and then within about an hour of run time it comes back.

 

Post the code number.

 

If my memory serves me correctly it is #25 and #26 on a 22re.

 

Both codes came back the last time your CEL came on (after the last time you reset the codes)? Or were these the two codes that were stored the first time you checked?

 

I had that problem, I also had a pretty drastic power loss over time and my truck sounded like a diesel.

Turns out the dealership didn't tighten my spark plugs down all the way and they worked themselves out enough to let combustion gasses through the threads.

 

Just checked the codes. The codes are 25 and 26. I bought the truck about a month ago with a blown head gasket, and as such I dont know if it was poping these codes before I fixed the head gasket. I have recently put on a brand new head, changed the head gasket, all of the timing components, the rear seal, clutch, and have just recently set the TPS adjustment correctly. I will certainly check the sparkplugs to make certain they are in there good. The #25 and #26 were the codes it was popping before I adjusted the TPS. I disconnected the battery after adjusting the TPS and let it set for a few minutes. I then started it up and it drove significantly better with the TPS adjusted, but then the check engine light came back on after driving for about an hour. I checked the codes and it came back with the same #25 and #26. Is there some code clear function other than diconnecting the battery I should be doing? Thanks all.

 

Checked the spark plugs and they apear to be in well. What should I try next?

 

A Factory Service Manual has an O2 sensor testing procedure. Basically you get the engine hot and then run @ 2500 RPM with a volt meter plugged into the sensor test port and watch for at least 8 swigns from near 0 volts to about 1 volt in a 10 second period.

 

Yeah, a sensor that is going bad may either fail to switch or switch very slowly, causing the ECU to log both lean and rich codes. When he O2 was toast in my truck it caused low- and part-throttle stumbling, but no CEL until it was really far gone.