3SGE running rich :(

[korban]

Ok, this seems to be a rather weird problem.

My gen1 NA will blow fuel smoke at about 5000rpm on a cold day, but on a warm day it seems to run fine.

After unplugging the ECU (to reset it) and plugging it back in, the car ran SUPER rich, blowing huge clouds of fuel smoke from 3000rpm, I had to granny it until the ECU sorted itself out (20min+ of driving).

Ive checked the air intake temp sensor, and its working fine. The next thing i'd suspect is the o2 sensor, but I can't find where it's located?

Any help or ideas would be appreciated.

PS. Through all of this I have not got a CEL at all.

[mr220v]

I'd try a coolant temp sensor next.

[Enthalpy]

The O2 sensor appears to be working okay. You are running incredibly rich in open-loop. Coolant temp sensor is something to try if your idle speed is above ~1000 RPM when warm. Air temp sensor is another likely candidate. How did you verify its operation? Your MAP sensor might be bad or have a leaky vacuum hose.

[korban]

Originally Posted by Enthalpy

Coolant temp sensor is something to try if your idle speed is above ~1000 RPM when warm. Air temp sensor is another likely candidate. How did you verify its operation?

I removed it, measured the resistance, and then heated it to see the resistance drop from 2k ohm, to about 1.5k ohm.

Where do I find the coolant temp sensor?

Thanks

[Enthalpy]

The coolant temp sensor is usually on the water neck of most cars, which is the pipe coming out of the motor going to the radiator. They typically have 3 or 4 tees on it that go to things like the heater core and the filler cap.

[korban]

Ok, I didn't have the right tools to remove and test the coolant sensor, but I measured it's resistance in place and it was 580ohms (after a short drive) seems normal to me, i'll test it again once the car's cooled down.

[korban]

My car has no O2 sensor, so it won't run open or closed loop lambda. So I figured it must be fuel adjusting on something else. So I put the car on the dyno and ran it at 3000rpm for a while to warm up, and checked all the sensor outputs. Turns out the engine was barely getting upto 70degC (158 fahrenheit). Therefore the car is still adding warmup enrichment, which will be higher at the higher rpm.

This pretty much outlines the thermostat as the problem. So i've replaced it and now the car gets to the proper temperature. Haven't driven it enough yet to know if it's fixed the problem yet though.

[Enthalpy]

LOL!! I didn't know you were missing a sensor! Of course your ECU will fail rich.

Fix your O2 sensor.

[korban]

I was under the impression that not all NA's had o2 sensors. There's no hole in my exhaust system for one, and no wiring for it on the harness.

I've had the car for years, this problem has only been for the last few months.

[Enthalpy]

Well, if that's the case, then it's a first. I have yet to see any fuel injected system without an O2 sensor. It's easy to impliment.

Even the latter carb systems had O2 sensors with closed-loop control.

Sometimes, the bung will be quite a bit downstream of the motor.

[korban]

Well replacing the thermostat has fixed the rich problem, now it's just fuel smoke... Most likely my rings i think, but that's a different problem.

Enthalpy, my apologies, was under my car today, and found the o2 sensor, it was hiding behind a heatshield, above the rear cross member.

I was talking to a tuning friend, who said that there are efi cars without o2 sensors, the usual indication if it should have one though is if it has a catalytic converter, mine doesn't .... but it used to.

[Enthalpy]

Perhaps the REALLY early Bosch Jetronic stuff with the variable flapper and constant-on injectors didn't have a closed-loop system, but that was in the very early 80s.

Anything 1990+ will DEFINITELY have closed-loop systems.

[Weasy2k]

they have an o2 sensor...lol cant believe its not in there! Should be on the exhaust manifold uptop...