1UZ main O2 sensor issues

[J-min]

Hi all, I've been lurking here for a while but have not posted.

I have come across a 1UZ swapped cressida (someone elses unfinished project) and I'm trying to get over the issues that it has.


Currently it has main O2 sensor codes (21,28). I have briefly checked the connections, everything looks good- the wires are physically AT the ecu plugs, and it has brand new sensors. Motor/harness/ecu etc is a 1990 LS400 unit. I can't find a downloadable FSM so I don't know what the required testing values are.....


The o2 sensors themselves pass their specific tests- but I am not sure if they are getting voltage or if the heater is coming on? Does anyone know what the input and output values are, and how/where I can check to see if the wiring itself is at fault?


Has anyone else come across this issue, and having it not be the O2s that were the problem? Thanks!

 

[J-min]

Thought I'd update this since it got no attention. The previous owner had cut the heater element power wires for the main O2s, during his swap. I sent them 12V and the o2 code is now gone. The car, however, still ran very rich.

I cleaned the MAF and checked my ECT sensor- it was reading -20 deg C (lol) so I changed that as well. Car still runs rich:

around 14.5 afr when cold cold, warm up to around 12-13 AFR and hits 10s and 11s under WOT.


Its a stock 1990 ls400 motor, with an aluminum intake pipe, cone filter, and 3" single exhaust. No other engine codes so far, just runs real rich. But very driveable.

I checked all my plugs to see if an injector was fouled/sticking, but all the plugs were an even shade of richly brown.

 

[J-min]

No one?

Does anyone know if the Ls400 runs differently between being in park/neutral and being "in gear" i.e the gear indicator telling the ECU its in drive? Someone told me it runs better when its in drive and the engine has two maps. Also, my car doesnt seem to go into closed loop

 

[George_R]

Disconnect the battery for 5 minutes, put it back and turn ignition on.

If the codes immediately appear, then it's heater circuit (HT1R/HT1L is negative from ECU, +B is positive power for each heater). Each heater should be some 16 Ohms of resistance.

If the codes appear after a while, then it's 02S not working, or fuel mixture has gross offset from normal value due to some other failure.

ECU sees if its in gear based on STA/NSW pins (0V @ NSW when in park) and D,3,2,L,R pins (exact list depends on prod.year).

Get a diagram for UCF10/SC400/LS400 of the same year and see what's missing

 

[J-min]

No more o2 codes, fixed that issue. I'm still wondering if there is any difference in running condition between park and drive gears. Also, would the air intake temp sensor have a great effect on richness? As much as the coolant temp sensor?

I checked voltage between nsw wire and e1, said I had around 9v which leads me to think the ecu is seei g thag the car is "in gear", all of the plugs from the trans have been cut off and terminated by the previous owner.. ugg

Does anyone have any baseline afr values for a stock ls400? Ive heard they run rich as is, I'm just now sure how rich, rich really is.

Motor and ecu are '89 or '90.

 

[Sudsy]

Have you checked that the cold start injector isn't staying on or faulty and leaking. Just something else to look at

 

[Subjug4tor]

My sc4 has a similar issue. When first started, and for about 20 mins of driving, all is good, afrs around 14.7 while cruising. Then at some point, after the car is good and hot, it starts running rich. Afrs drop to 12 or so, and it idles around 10.5-11, and is around 10-11 at full throttle too. After the car cools off it's fine again, until I drive it for another half hour or so. Never happens on short drives (under 20 miles). I've replaced the maf, o2 sensors are only a couple years old, and the car still drives fine. I'm stumped.

 

[J-min]

Yah..my car DRIVES fine. Just poor gas mileage and probably a slight decrease in overall horsepower output. Its more of a nuisance than an actual ISSUE. I'll take out the cold start injector and see if it changes anything. The last time i had the throttle body off, the inside of the intake smelled quite gassy and had a oily/gassy film all over it. Not normal considering it was cleaned about 1000 KM ago.

 

[Subjug4tor]

Just an update- I replaced both sensors (they were universal Bosch sensors, only a couple years old) with new Densos and the problem is gone entirely.