Fuel Problem

monteSS872000 · April 11, 2010

I've got a 1993 GMT400 k1500 with a 5.7l. Hooked up scanner to the DLC and found everything was in spec except PCM was telling injectors to spray to much fuel. tried switching PCM's but have the same result. Any ideas what might be goin on or what i can do to make good use outta the extra fuel. lol. any help would be greatly appreciated...

rodram · April 12, 2010

I've got a 1993 GMT400 k1500 with a 5.7l. Hooked up scanner to the DLC and found everything was in spec except PCM was telling injectors to spray to much fuel. tried switching PCM's but have the same result. Any ideas what might be goin on or what i can do to make good use outta the extra fuel. lol. any help would be greatly appreciated...

this might be an issue with your Coolant Temperature Sensor (CTS) ... located at the top front of your engine right beside the thermostat housing ... this is independent of another sensor used to send a signal to the temperature gage on your dash...

the CTS monitors coolant temperature and sends a voltage signal to the PCM to regulate the fuel mix.... these usually fail so that the emgine will start OK... but as the engine warms up the injectors keep sending too much fuel ...

you could test the sensor by checking the resistance across the two pins using the resistance-temperature cross reference below using an ohm-meter ... or just replace the sensor ... it is a cheap part and simple to remove and replace.

Coolant sensor approximate resistance specifications:

177 ohms @ 212 deg. F. or 100 deg. C.

467 ohms @ 158 deg. F. or 70 deg. C.

1459 ohms @ 104 deg. F. or 40 deg. C.

5670 ohms @ 50 deg. F. or 10 deg. C.

16180 ohms @ 14 deg. F. or -10 deg. C.

52700 ohms @ -22 deg. F. or -30 deg. C.

100700 ohms @ -40 deg. F. or - 40 deg. C.

the CTS does not need to be exactly as on this chart... but as you can see, as the engine warms the resistance should drop dramatically

monteSS872000 · April 12, 2010

That's another thing, this truck will not warm up, If i am sitting in McDonalds drive thru it will get to about 160 but other than that the warmest i can get her is around 135, I've replaced the thermostat twice now both with a 195 to have the same results. even tried sticking cardboard in front of radiator. Nothing... wasn't sure if that might be it as well, but i will check the ECT sensor, thank you.

rodram · April 12, 2010

That's another thing, this truck will not warm up, If i am sitting in McDonalds drive thru it will get to about 160 but other than that the warmest i can get her is around 135, I've replaced the thermostat twice now both with a 195 to have the same results. even tried sticking cardboard in front of radiator. Nothing... wasn't sure if that might be it as well, but i will check the ECT sensor, thank you.

... the sensor for your dash temperature gage is on the drivers side of the block down somewhere around the level of the spark plugs ... this could be out of whack giving you low readings ... if you have a new 195 thermostat in the truck it should work properly, unless it is just stuck wide open for some reason....