I think my car is running too cold. Suggestions? Might be the O2 sensor, help?

[TERRA Operative]

How else could it be running uber rich?
According to my testing (which may or may not be correct) the ECU seems to be thinking the engine is running lean.

[thechuckster]

what do the spark plugs look like? (checking for uber carbon coating)? or rear bumper coated in soot? or can you borrow/loan a Wideband sensor and attach it to the zorst? I wouldn't go diagnosing an AFR issue by replacing sensors.

fuel smell not coming from the vent line (to charcoal canister) from tank? Or from around filler seal around inlet (my MA61 used to get fuel smell inside until I realized the seal between filler pipe and body work was missing).

Heating element in the sensor should be powered up 100% when IGN is on. As the thing heats up, the resistance of the heater increases and current draw drops - a simple self-regulating thing. The ECU doesn't control the O2 heater element in any smart fashion.

And don't forget gauge temp sensor is unrelated to the ECU temp sensor. Toyota seemed quite willing to change gauge sensor specs as models progressed, but by in large, the ECU temp sensors use the same specs. Once dashes went 100% digital, then you start to see gauge temp data coming from the ECU.

Have you checked continuity from ECU temp sensor to ECU (easy to do, disconnect plug on sensor, ECU should throw a code, plug back in, code should go away). The autoshop PDFs should have a temp/resistance curve for common temp sensors so you can check whether it's producing the right data.

[dnegative]

Coolant temp sensor
IAT sensor
TPS
AFM issue
ECU fault
Injector fault
FPR fucked

Take your pick
My 4AGE ran with no O2 sensor running stupidly rich due to cams on factory ECU and it didnt run any colder.

[4th surf]

I will go with an O2 issue here. Too lean=runs hotter, too rich=cooler.

I'd find the original O2 sensor if you still have it and note the part number off of it (Toyota are pretty good like this and stamp the part number on the sensor). Then perhaps contact AFI (australian fuel injection) or Automotive Service Solutions who will be able to cross it over to a Bosch one at half the price of genuine (about $158 from memory for 1UZ main and sub O2s each). You can't use a generic O2 as you've found out as they quite simply will not "talk" to the ECU which then in turn goes into a "default" or "limp" mode, runs the engine richer (thus cooler) with the intention there being to enable you to carefully drive to a place of repair. Half the time they don't even bring up the engine check lamp (yet do log a code) but just run like the "Choke" is stuck on.

Also most EFI Toyotas are as stock run slightly lean as a compromise between power, economy and emissions hence why the stock engines do get up and sing with simple mods such as exhaust and injector upgrades

[TERRA Operative]

ECU has had the caps replaced, AFM is working ok, as is intake air temp sensor, and the TPS is working and calibrated. Injectors are freshly cleaned and tested too.
I could stick a Sard FPR on to test if it comes to that, but it's a bit of a pain.

The cold running is now a non issue, as I've mentioned previously.


As I mentioned in my last post, the O2 sensor is reading way lean during normal driving, hence my leaning towards that being the problem.
Tomorrow I'll test the sensors back at the ECU plugs to check I have continuity and see if that shows anything up. The ECU isn't throwing codes during normal operation though.


The symptoms you mention 4th surf sound like what my engine is doing. The part number for my O2 sensor is 89465‑19495 so I'll contact those places and see what they want for an equivalent. I'm getting a price from Toyota (I get trade price) so we'll have a laugh when they get back to me....
I just don't think the O2 sensor is heating up, as it starts reading ok once I give the engine a bit of a thrash, but then reads lean once I return to cruising. The sensor sits way back behind the firewall, so there's quite a way for the exhaust to cool down.

I'll pull it out again tomorrow and grab the IR thermometer from work to see if I can get it to heat up when connected to the battery.

[4th surf]

Coolant temp sensor

ECU fault

These two are also quite likely esp the ECU which is more common than what you think. Why? the caps inside are only rated to 1000hrs of use at their specified voltages so think around 100000km, then they start to leak which in turn causes the tracks on the motherboard to degrade, you'd most likely notice this as a bit of power loss or in the case of an auto loss of O/D and lockup functions. A rebuild isn't too expensive ($2-300) and usually money well spent.

I'd check for codes and if all clear put a master gauge across it at operating temp and see what it says. Above 80C you're fine, below you have a problem. Also remember this about the stock gauges.. They work on the "I'm ok, I'm ok,I'm ok... Oh SH!T IT'S Too LATE!!" way of things. As a result I apply a simple rule of thumb... 1/3 to 1/2 way up then no worries, below or above then start looking for a problem

[TERRA Operative]

Yeah, I know aaalll about the capacitor issue (they are actually counterfeit capacitors that were used, long story of corporate espionage gone wrong there), and have fixed dozens of Toyota ECU's over the years... I tend to use Rubycon ZL and YXF series capacitor when I do a swap.

I'll rip the stereo out tomorrow to get easy access to the ECU plugs and see what my Fluke says.

[thechuckster]

you can check if your ECU expects to see the later Titanium Dioxide (narrow band, resistance varies) sensor: it will have two dedicated pins for the O2 sensor (OX and OX+). With ECU on, you will see 1v at OX. The other pin (OX+) will have resistance between itself and ECU ground (The ECU compares OX+ signal with an internal reference voltage).

The sensor element heats up to ~400C but only in the tip area. You'd know if it was the more accurate wideband units as they get even hotter at the tip and body gets way too hot to touch. Will take well over a minute to warm up.

The more common type of sensor may have 1 or 2 dedicated pins. One will be a sensor earth and it will be common (zero ohms) to other sensor earths (as found in the TPS or CLT or AIT or AFM).

If it's like other engines of the same vintage, it will have a heated narrowband sensor.

Some quick google searching says it is a plain-old 4-wire sensor, you should have one HT pin at the ECU (the other part of the heater circuit coming from an IGN-switched source). The differences are the plug where it hooks into the engine loom (mid '90s V6 petrol Hilux apparently is a direct swap), lead length and the mounting flange.

The fact that your jaycar A/F kit worked (and I'm presuming you had it monitor a 0-1V range?) says that it is the garden-variety O2 sensor that's spitting out a voltage based on exhaust gas contents.

[TERRA Operative]

On the ECU it has the following Pins:

HT - switched to ground for the heater
OX - Sensor input I guess (also goes to the diagnostic connector).
OXL1 - to the other side of the sensor.

I definitely have a narrowband sensor, just gotta try to get it to send the right signals to the ECU and hope the ECU can read it.

[jdm86gtz]

Looks a good bit lower than mine anyway. My oem thermostat is I think 3 years old now. If I think of it I'll take a picture tomorrow.
Does your fan operate like normal? Did you stick a thermostat into the radiator to measure temperature?

On my AE111 it had a low temp thermostat and wouldn't get warm enough to close the ISCV completely after I fitted oem thermostat it idles as it should.

[TERRA Operative]

Ok, I did some tests.

The O2 sensor heats up when directly connected to a power supply. It stabilises at about half an amp, and the metal shroud got to about 92 degrees, so the element inside would be somewhat hotter. It seems the O2 sensor itself is ok.
I then hooked it up to the car and measured the current again. It seems the ECU is pulsing the current when the ignition is turned on. I was reading a peak of 0.6 amps, on and off.

I'm about to check the wiring and other sensors now, I'll see if I can find anything that's not right.

[TERRA Operative]

Ok, all the wiring from the ECU to the sensors, and the sensors themselves check out ok. (IAT, WT, TPS, AFM, O2).

Toyota want $287.50 for the O2 sensor, trade price. Hmmm, I won't be buying from there on a whim...
I'm chasing up the leads from 4th surf, but I'm at a loss as to why it runs so rich. Next step is some hard core diagnostics on the ECU, unless there's something stupidly obvious I'm missing???


Oh, Here are the radiator temps just after driving, just for the sake of it. I used an IR thermometer, so it was hard to get a good reading due to the emissivity of the shiny alloy radiator.

Top of radiator - 75 degrees.
Bottom hose to engine - 62 degrees.

The actual water temp inside the rad will probably be a little more than that. I'll try sticking my meter on the ECU water temp sensor to see what it says tomorrow. I CBF right now as I just did a Houdini to swap the busted voltage regulator on the alternator while it was still fitted to the engine, under the intake manifold, on the firewall side of the engine. I'll let you figure out how it's done...

[jdm86gtz]

This is just after driving for about 20mins outside temp probably 5-7 degrees Celcius.
Do you know how much gas the A/C system in these Levins take?

[TERRA Operative]

A little warmer than mine although I have a brand new everything and upgraded radiator.
Mine heats up nice and quick too, and is rock stable once at temp.


AC gas will be the same as any other AE101 Corolla.

[jdm86gtz]

The alloy rad shouldn't make too much difference as the thermostat controls the temperature. I have a Koyo in my AE86 and it doesn't run cooler than the original single core rad.