Thread: cooling sensor help!!!!!

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When the engine is started cold, the ECM mode is open loop. This uses preset parameters to set injector pulse width, idle air, and ignition advance. The engine will run fine, but uses more fuel, and it will not make max horsepower.

Once the engine warms up, it goes into closed loop. At that point, it takes input from the various sensors, TPS, MAF, O2, temp sensor, oil pressure, knock sensor, ect., and uses that to calculate injector pulse width, Idle air, and ignition advance. This is closed loop. It will make more horsepower, and increase the fuel mileage.

The sensors for the most part operate on resistance. The computer supplies the sensor with a set voltage, and samples the return voltage, and uses the difference to make the calculations. If the return voltage is the same as supplied voltage, it reads that as a malfunction, and holds it in open loop.

When the early installers started retrofitting EFI engines, many of them just wired them for open loop to make them work with stock PROMs in non stock applications. One way to do this was to remove the temp sensor, and twist the wires together. It wasn't right, but it worked.

If you are happy with the way it runs, just leave it. But if you want all that you can get you will probably have to rework the harness for the right pin outs, and replace the PROM, or go to an aftermarket harness.

Originally Posted by enjenjo

The sensors for the most part operate on resistance. The computer supplies the sensor with a set voltage, and samples the return voltage, and uses the difference to make the calculations. If the return voltage is the same as supplied voltage, it reads that as a malfunction, and holds it in open When the early installers started retrofitting EFI engines, many of them just wired them for open loop to make them work with stock PROMs in non stock applications. One way to do this was to remove the temp sensor, and twist the wires together. It wasn't right, but it worked.

If you are happy with the way it runs, just leave it. But if you want all that you can get you will probably have to rework the harness for the right pin outs, and replace the PROM, or go to an aftermarket harness.

Sorry for jumping in here,but if the wires are twisted together will the engine not run rich? (I was thinking of doing this on my old plow truck) Thanks!

Originally Posted by Oldmanb

Sorry for jumping in here,but if the wires are twisted together will the engine not run rich? (I was thinking of doing this on my old plow truck) Thanks!

i think we are both backwards .. the first paragraph of post # 8 says during cold start the ECM mode is open loop .. meaning current is not flowing .. causing cold run situation .. close the loop ( tie the wires together ) and it runs in warmed up mode .. that sound logical .. i quit being a mechanic when cars went computor but im still a hotrodder

Originally Posted by Oldmanb

Sorry for jumping in here,but if the wires are twisted together will the engine not run rich? (I was thinking of doing this on my old plow truck) Thanks!

Yes it will make it run rich. I would not advise wiring it that way permanently on your truck.

Originally Posted by enjenjo

Yes it will make it run rich. I would not advise wiring it that way permanently on your truck.

Thanks! I think you helped a lot of folks out with this one!

After a little research this is what i found in a chevy fuel inj. mod book:



CTS - or cooling temp sensor-- a resistor known as neg. temp coefficient thermistor. This type of resistor responds dramatically to temp.

At 40) degrees F - the resistance is 100,700 ohms

At 212) degrees F- the resistance is around 200 ohms

***** it also says the IDEAL TEMP IS 185 ohm at 212) degrees F*******

The CTS replaces the choke like on a carbed car

When the ECM sees high volts from the CTS sensor it increses the pulse with to the fuel injectors

When the engine is cold the wire carring the 5 volt reference will have 4 to 5 volt reference. As the engine warms up the volts will drop

A old Track Trick is installing a 640 ohm resistor across the terminals of the wiring/ with it disconnected to the sensor will trick the ecm to believe the temp is 145) degrees F and you may gain some power.

It will make the ECM respond by enriching the mixture /air-fuel plus advance the timing--
It also says the prolonged use may cause severe over heating because the ECM wont know to turn the fans on

:

Originally Posted by enjenjo

If you are happy with the way it runs, just leave it. But if you want all that you can get you will probably have to rework the harness for the right pin outs, and replace the PROM, or go to an aftermarket harness.

40Chevy,
It sounds to me like enjenjo knows the specifics here, and he warns that if you want to wire in your coolant sensor you will probably need to rework your harness for the right pin outs, replace the PROM or go to an aftermarket harness. Someone probably took the easy open loop mode in the past, and now you either leave it alone, or dive in and do it right.