running rich

vanhal · 12-18-2005, 06:48 PM

on my brother's 1995 chevy 5.7 with a tbi. it seems to run rich when it is cold out like freezing temp but after running for 5 to 10 min. seems ok
any one know why ??? thank you ............pete

wojeepster · 12-20-2005, 05:02 PM

check temp sender for the ecu (not the one for the gage) This has a large effect how rich the computer sets the engine. Check engine grounds and ground wires around ecu. Measure the ohms of the sensor at different temperatures to see if is ok. It is a reverse cofficient thermistor which means it will have higher resistance when cold and a lower resistance when it warms up. Bad connections add resistance and make the computer think it is much colder than it actually is so it richens up the mixture. Hope this helps.

You will have to check a manual for the values at different temperatures. You can also measure the voltage with it connected up and running. Teflon tape can act as an insulator and screw you up if the sensor does not have a ground wire. I am not familiar with your particlular fuel injection system, just fuel inj systems in general so this is general information not more specific.

12-18-2005, 06:48 PM	#1
vanhal Senior Member Join Date: Mar 2005 Location: ontario, canada Posts: 102	running rich on my brother's 1995 chevy 5.7 with a tbi. it seems to run rich when it is cold out like freezing temp but after running for 5 to 10 min. seems ok any one know why ??? thank you ............pete __________________ I am gm all the way ....... black 98 Z71 3 door short box 5.7

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12-20-2005, 05:02 PM	#2
wojeepster Senior Member Join Date: Nov 2005 Posts: 92	check temp sender for the ecu (not the one for the gage) This has a large effect how rich the computer sets the engine. Check engine grounds and ground wires around ecu. Measure the ohms of the sensor at different temperatures to see if is ok. It is a reverse cofficient thermistor which means it will have higher resistance when cold and a lower resistance when it warms up. Bad connections add resistance and make the computer think it is much colder than it actually is so it richens up the mixture. Hope this helps. You will have to check a manual for the values at different temperatures. You can also measure the voltage with it connected up and running. Teflon tape can act as an insulator and screw you up if the sensor does not have a ground wire. I am not familiar with your particlular fuel injection system, just fuel inj systems in general so this is general information not more specific.