240sx fault code 13 help

Have a 1990 240sx SOHC. 138,000 miles. Car peridodically is hard to start or will not start when hot. Today it left my son strandd for a few hours. The temp gage only goes up to about 1 or 2 more hash marks past the middle hash mark on occassion, but 99% of the time it stays in the middle of temp gage. Today I did the ECU check (after it failed to start ) and it gave me a 13 code which is temperature control...I can't see how its running hot, as the overflow resivoir is at the normal range, so nothing boiled over, and gauge never got into the high area, but I still get a fault code 13.

Is there anything else I can check or look for that may cause these problems. I used the troubleshooting logic tree off the 240sx . org website.

This car has the air conditioning disconnected. Today after the heating problem code I got, I hotwired the air conditioning aux radiator cooling fan to see if a bit of additional cooling air flow may help, but the temp gauge still remains in the mid portion. Any ideas of advice accepted.

Water pump seems to be flowing, not a very strong flow, but it will cause the water tpo flow out the top if you rev the motor with the cap off. The block has been flushed with chemical, and new coolant installed.

Thanks

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Code 13 is not overheating. It's means the ECU is getting a resistance reading from the temperature sensor which is outside of the acceptable range.

1: Temperature sensor faulty - unplug and check resistance, 300ohms hot 176F, 2.5Kohms cold 68F (both approx). It's the one with two wires on the connector, the other temp sensor has one wire and goes to the dash gauge. 2: Wiring fault between sensor and ECU. Check connector to sensor is clean and properly connected before checking loom between sensor and ECU plug.

With code 13 active ECU will assume engine is cold when starting, then as soon as it is running it assumes it is hot. This causes problems on cold starts as the engine will not get enough fuel while warming up. It causes hot start problems as too much fuel is delivered when cranking. When cold apply a bit of throttle to keep revs up until warm. When hot floor throttle as though flooded. If it's the sensor

2 cheap resistors can be used to fool it. Stick a 2.5Kohm one in the connector for cold start and warm up, after it is warm stop and put a 300ohm one in. With a resistor in place of sensor you should be able to clear the code and it should not return. If it's a wiring fault the code will return.

Sounds about right.

Has the rad been cleaned? Check rad is warm all over after a 15 min run. If not warm and has a cold patch at mid point inline with rad cap, tie a piece of wire to a hacksaw blade and probe a few water tubes, if you pull up mud from one then they all have mud in them. Only way to shift it, is to take header tanks off and scrape it out.

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