89 toyota p/u V6 mystery problem

[toyota2]

the truck runs poorly when its cold and stalls out easily, but when it warms up it runs fine. I replaced the O2 sensor, pcv valve, reset the timing but nothing seems to work and its been like this for about 6 months

[Airjer_]

Maybe check the coolant temp sensor resistance when its cold. At 70 degrees it should be roughly 2,000 to 3,000 ohms. Higher if colder, lower if hotter. I think you can check it at the DLC1 connector but can't remember for sure.

[toyota2]

thanks for the information. I looked up what the coolant temperature sensor controls and it sounds like its the culperate. the only problem is that i cant figure out whare its at on the motor. I havent been able to find it in the book.

[auto89]

Originally Posted by toyota2

the only problem is that i cant figure out whare its at on the motor. I havent been able to find it in the book.

It's near the firewall, behind the air plenum (the silver air intake which covers the top of the engine), on the driver's side of the air plenum.

There's 3 things screwed into the top of the engine block there. The temp sensor is in the middle, directly below a water hose entering the firewall. The thing to the left side of it (toward the passenger side) is the "cold start time switch." (I'm not sure what the thing on the right is.).

I went and looked at mine again. Just follow the driver's-side edge of the air plenum all the way back to the firewall. You'll see a couple of wires connected to a hex fitting screwed into the top of the engine block. That's it. Coolant hoses are above it. But you can see it at an angle, underneath the hoses. There's a smaller sensor screwed in lower, and 3 inches to the right (driver's side) of it. And, a sensor about the same size, to the left. Like I said, it's the one in the middle, directly below a hose entering the firewall.

I changed mine 4-5 years ago. It wasn't too hard to get to. It was just hard to initially locate.

EDIT: made some corrections, that there are 3 sensors, not 2.

[toyota2]

i replaced the coolant temperature sensor and it wasent the problem. im wondering how to check the fuel pressur on this truck. a couple of people have said it might be the fuel pressure regulator. but i dont know how to check it and i cant find it in the book.

[auto89]

Originally Posted by toyota2

. a couple of people have said it might be the fuel pressure regulator. but i dont know how to check it and i cant find it in the book.

The two times my pressure regulator needed replacement, it was very noticeable (fuel odor from the front of the truck, and hard to start after it had set for 30-60 minutes and let the fuel pressure bleed off, requiring a lot of cranking to rebuild the pressure).

Once it leaked into the vacuum line going to the space-saucer shaped plastic diaphram at the passenger-front corner of the engine. That thing needed to be replaced, and I had to use a small drill bit to unclog the metal vacuum line which had been carrying fuel.

The next time it leaked out of the crimped top cap. I used some Lucas fuel treatment and that seemed to swell some rubber inside the regulator. It hasn't leaked for 4-5 months now.

I don't know much about testing the fuel pressure. If it starts easily after sitting 1-2 hours, I believe the pressure is adequate (just because I've seen what it's like when the pressure is inadequate). If you can floor it when it's warm and it isn't starved for gas, then I think it has adequate pressure/volume.

You can disconnect the fuel line from the cold-start injector on the passenger side of the air plenum, and see if it has pressure. Do that immediately after starting the engine and building pressure. And, do it 5-6 hours after stopping the engine (to see if it maintained similar pressure).

Do you see smoke from the exhaust when you start the engine after it's sat for a few hours (and it's hard to start)? If so, I would suspect a bad cold-start injector. But, when I had that problem, it ran fine when cold. It was just hard to get it started. It smoked when it started because it was burning off all the gas that bled into the air plenum while the vehicle sat for hours.

There's another sensor to the left of the temprature sensor. It's called a cold-start time sensor (or something like that). It seemed to be similar to the temperature sensor (it was in contact with the coolant), but controlled the time that the cold-start injector dumps gas into the air plenum. (I'm just guessing. I remember seeing it and making that conclusion after reading a little about it.). Maybe that could be the problem? Causing the injector to enrich the fuel too much, even after the engine's started?

There's also a fuel-pressure dampner screwed into the rear end of the fuel rail, passenger side, beneath the air plenum. I had one of those go out. It was like the fuel pressure regulator. I could smell gas after the truck was parked for awhile (even driving). And, it was hard to start when cold because the pressure had bled down.

Your problem sounds different. You didn't mention hard starting. Just "stalls when cold."

Mark