coolant temperature sensor issue or not

[67malibu]

'88 K1500 350 with the Holley 670cfm TBI. Last year this truck started intermittently running rich to the point of stalling while at idle. I replaced the coolant temperature sensor and it ran fine, for a while. After a few months the same issue returned during cold weather but seemed to resolve this spring when things turned warm. Now the engine is really running rich all the time. I checked the CTS and got 2400 Ohms cold and 270 Ohms hot which isn't far form what I found as to be in spec. If I disconnect the CTS the truck runs better (idles up some) and does not appear to be running as rich but still not right. There are no codes in the computer and the O2 sensor was also replaced not that long ago. Any ideas?

[MT-2500]

Originally Posted by 67malibu

'88 K1500 350 with the Holley 670cfm TBI. Last year this truck started intermittently running rich to the point of stalling while at idle. I replaced the coolant temperature sensor and it ran fine, for a while. After a few months the same issue returned during cold weather but seemed to resolve this spring when things turned warm. Now the engine is really running rich all the time. I checked the CTS and got 2400 Ohms cold and 270 Ohms hot which isn't far form what I found as to be in spec. If I disconnect the CTS the truck runs better (idles up some) and does not appear to be running as rich but still not right. There are no codes in the computer and the O2 sensor was also replaced not that long ago. Any ideas?

You need to get it on a engine capable scanner and see if engine and air tempt sensors are reading correct.
Also check wiring and ground on stat housing and engine coolant sensor and make sure air intake tempt sensor is hooked up if it has one.

[j cAT]

Originally Posted by 67malibu

'88 K1500 350 with the Holley 670cfm TBI. Last year this truck started intermittently running rich to the point of stalling while at idle. I replaced the coolant temperature sensor and it ran fine, for a while. After a few months the same issue returned during cold weather but seemed to resolve this spring when things turned warm. Now the engine is really running rich all the time. I checked the CTS and got 2400 Ohms cold and 270 Ohms hot which isn't far form what I found as to be in spec. If I disconnect the CTS the truck runs better (idles up some) and does not appear to be running as rich but still not right. There are no codes in the computer and the O2 sensor was also replaced not that long ago. Any ideas?

you should rather than replacing the sensor and guessing at its being the cause measure the resistance of the sensor. I would first remove the connector and insure the pins are good not green damaged . then with the engine cold measure the resistance of this sensor and record the temperature. then I would run the engine until its hot and record the engine temp then measure the resistance . now you use the temperature chart to determine if the sensor is in proper cal. range.

new may mean wrong sensor also for this vehicle .

[jdl]

Just curious, can you communicate with computer? You should have at least got a code 12?

Can you tell if the system is going into closed loop? Is that TBI set-up factory? Just my opinion, I leave the factory set-up, alone.

[67malibu]

I answered most of the questions in the original post. I measured CTS voltage and got values within 10% of specs (the one I replaced last year gave resistance reading way out of spec - yes I test parts when possible before replacing.) The TBI is not stock, it is the 670cfm Holley aftermarket. I put that one on about 10 years ago due to the stock one being worn out (220K miles.) The new TBI had operated flawlessly for a good 8 years before this issue began. There computer communicates fine and is clear of codes. This is an '88, no air temperature sensor. When I get time I will do what I was going to and run some new wires around.

[j cAT]

Originally Posted by 67malibu

I answered most of the questions in the original post. I measured CTS voltage and got values within 10% of specs (the one I replaced last year gave resistance reading way out of spec - yes I test parts when possible before replacing.) The TBI is not stock, it is the 670cfm Holley aftermarket. I put that one on about 10 years ago due to the stock one being worn out (220K miles.) The new TBI had operated flawlessly for a good 8 years before this issue began. There computer communicates fine and is clear of codes. This is an '88, no air temperature sensor. When I get time I will do what I was going to and run some new wires around.

cannot comment on cold resistance no temp, on normal engine temp this should read 170-200 ohms. in the hot weather should be closer to 170 ohms.

when the sensor resistance is higher than spec, the engine will be fed more fuel. the injector open time will be longer.

you could also have EGR issues . EGR opening too much and or not closing properly. this would lower engine temp and cause rich conditions.