Another freaking cht question?, Sorry lost all text on previous post Options

[sholman5]

73 1.7 Low cold start idle.Basically MPS holds vacuum. Pin 8-10 reads 359 ohms, pins 7-15 102 ohms. Fuel pressure 29. AAR opens and close properly. Idle air, if I screw it closed engine will stall. Checked cht 82 degrees 1764, warmed up car and read cht hot 1659. Is this a short in the cht. Would it be sending ecu a signal that it is running rich and lean it out. If I turn the ecu knob 2 or 3 clicks the idle smooths out,, but increases the idle speed.I'm pulling my hair out.

Thnx Chris

[BeatNavy]

First off that "hot" CHT value is not good (I assume by "hot" you mean running for at least a couple of minutes or more). I'm surprised the car would even idle with a resistance that high. It would be running pig rich. If you reduce air with idle bypass screw with a rich condition you end up with an even richer condition and probably stalling.

Also, just to be clear, the ECU doesn't "sense" a rich or lean condition. It's not a closed-loop system like modern FI. It's simply designed to provide more fuel (through longer injector pulses) when the engine is cold/cool based CHT resistance.

This is from someone else's thread, and even though your CHT (xxx-03, IIRC) isn't on the chart, it should behave similarly.

(IMG:http://www.914world.com/bbs2/uploads/post-5956-1610819580.jpg)

Could be a bad CHT or a break in the wiring harness. You should trace the connection from the sensor all the way to the ECU to make sure there are no breaks. If none, I'd remove it, test it out of the car, and replace it as needed.

You didn't mention which way you turned the ECU knob (CW or CCW). It has a relatively minor effect that's not going to overcome a bad CHT, but out of curiosity which way did you turn it?

[sholman5]

Car ran for at least 15 mins. ECU knob turn CW to enrichen. According to @pbanders " An open which would be 0 and car would not start. A short, the ECU interprets a shorted sensor as a signal to lean the mixture (about 30% leaner). The car will start and run, but have poor driveability." According to the cht chart, my start up ohms fall in line at the 82 degree temp at 1764 ohms. Hot should be around 200, mine is 1659. Would this be a short in the cht? Either way I will replace the cht.

[BeatNavy]

Car ran for at least 15 mins. ECU knob turn CW to enrichen. According to @pbanders " An open which would be 0 and car would not start. A short, the ECU interprets a shorted sensor as a signal to lean the mixture (about 30% leaner). The car will start and run, but have poor driveability." According to the cht chart, my start up ohms fall in line at the 82 degree temp at 1764 ohms. Hot should be around 200, mine is 1659. Would this be a short in the cht? Either way I will replace the cht.

No, this is not a short in the CHT. Your CHT reading hot is way too high which the ECU will interpret as a cold engine and dump more fuel in (when you don't want it). That reading is more of an open circuit.

A short would be like the CHT connector, or somewhere along the wiring harness between the ECU, touching the engine block or something else connected to ground. Like if you had a nick in the wire covering and it was leaning against the case, or if the CHT spade connector was doing the same thing. That provides a short to ground which the ECU will interpret as a hot engine requiring the least amount of fuel.

How are you checking the CHT reading? Unplug the CHT from the wiring harness, then check resistance from CHT spade connector to ground (e.g., negative battery terminal).

[sholman5]

Disconnected from the wiring harness. Ground to battery terminal. Thanks for your input @beatnavy . I ordered a new CHT, will change it. Hopefully that will help.

Thanks Chris