'92 3FE Hard Start / CEL (1 Viewer)

[FJ80Duo]

My LC has always fired right up. But starting last week, it became very hard to start - cranks a long time, then barely runs until it warms up, then runs pretty much normal. Except that the check engine light comes on and off occasionally while I'm driving without noticeable loss of power. Infrequently, it will hesitate/die from stop at warm idle. Afterwards, I changed fuel filter, distributor cap & rotor, liked the look of the plugs. No change. Diagnostic codes are 22 & 28. The water temperature sensor wire looks fine and the O2 sensors were replaced earlier this year (old were factory, so no big surprise). Ideas / next action? fuel pressure at the cold start injector?

 

[jonheld]

The water temperature sensor wire looks fine

Are your eyeballs properly calibrated to read resistance?
Have you gone through the test procedure as stated on page FI-37 of the FSM?

 

[FJ80Duo]

Are your eyeballs properly calibrated to read resistance?
Have you gone through the test procedure as stated on page FI-37 of the FSM?

80 ohms at 90F. FI-37 is for the ECU. Are you thinking that's the problem?

 

[jonheld]

80 ohms at 90F. FI-37 is for the ECU. Are you thinking that's the problem?

80 ohms @90F?
Should be closer to 2K ohms according to the chart on page FI-77.

Hard starting could be multiple things, the simplest being an overdue tuneup.
What is the condition of the plugs/cap/rotor?
Water temp sensor could definitely cause hard starts and poor fuel mileage.
I would also inspect the intake hose from the air filter to the throttle body. Any unmetered air entering through cracks can cause all sorts of issues.
The top half of the motor wants to be air tight.

 

[FJ80Duo]

Thanks. That's why I just replaced the distributor cap & rotor and fuel filter (Toyota branded). Plugs are still great, so I left them. My '92 FSM shows the water temp sensor check on FI-41 & the O2 sensor on FI-48.
But I see what you're saying about the diagnostic procedures from the CEL codes. I'll do that as soon as I can figure out how to access the back of the ECU ports with my meter. The harness makes it so it always points towards the firewall or windshield. Hopefully, it doesn't require pulling the dash.
The bad behavior started abruptly for no apparent reason. No recent work done. I'm skeptical of a temperature sensor wire making it hard to start, but willing to follow the procedure.

 

[jonheld]

I'm skeptical of a temperature sensor wire making it hard to start, but willing to follow the procedure.

It has been documented and your sensor is reading out of spec.
This is 1986 technology, first gen EFI. There's really no magic here. If the ECU is getting false information, it's not going to supply the correct amount of fuel for the situation.

 

[huminajumina]

also there are 3 temp senders on the Thermostat housing, are you checking the correct one for the cold start switch? I was having the same issue and found mine was broken, I also removed and cleaned the cold start injector while I was at it.

Wanted - 3FE Cold Start Injector Time Switch - https://forum.ih8mud.com/threads/3fe-cold-start-injector-time-switch.943944/

 

[FJ80Duo]

Thanks. The one I was I checking is the one you called the "Cold Start Injector Time Switch".
I have a spare, but it also reads 80 ohms at room temperature, same as the one JH above recommends replacing.

 

[jonheld]

Thanks. The one I was I checking is the one you called the "Cold Start Injector Time Switch".
I have a spare, but it also reads 80 ohms at room temperature, same as the one JH above recommends replacing.

No.
The cold start injector time switch is the cold start injector time switch.
The water temp sensor is the water temp sensor.
The water temp sender is the water temp sender.
The water temp switch is the water temp switch.

They are 4 different items with 4 different functions.
You were talking about the water temp sensor. That is the one that sends water temp info to the ECU for fuel trim.
The cold start injector time switch fires the cold start injector based on water temp for rich cold starts.
The water temp sender feeds the dash gauge.
The water temp switch throws a VSV for the fuel pressure regulator.

You need to be specific about what you're talking about.

 

[FJ80Duo]

OK. New temperature switch cleared it right up.
Getting the old one out was way more involved than I had planned on, but that was the issue.

 

[jonheld]

OK. New temperature switch cleared it right up.
Getting the old one out was way more involved than I had planned on, but that was the issue.

And once again, please be specific regarding what you replaced so that others can reference your posts.

 

[FJ80Duo]

And once again, please be specific regarding what you replaced so that others can reference your posts.

This is a reasonable request as there are so many things plugged into the thermostat housing / water outlet.
For diagnostic code 22, the Water Temperature Sensor, part number 89433-20010, was the culprit. The original and the replacement had green plastic, but I don't know that you can count on that. Here are the pertinent FSM pages:

Theoretically, I should have been able to check the resistance at the ECU. However, because due to the orientation of the ECU and how short the harness was, I was unable to get my VOM probes in there. Likewise, I couldn't get a direct reading at the sensor with all the stuff in the way. So I pulled the thermostat housing ("outlet"). Once I removed the sensor, the resistance measurement showed around 800k ohms, instead of the 2000 or so that it should have. I guess the computer thought, "Oh, it's 10,000 degrees below zero. I can adjust for that."
I don't know why the Toyota factory service manual doesn't have a diagram like the one from Jon Held:

I made a copy and stuck in the cooling section of my FSM (which I also did for the belt layout).