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#1
10-15-2003, 12:02 PM
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1990 GMC Sierra, 350, 5.7 liter fuel injection problems
Hi,
The fuel injectors on my 1990 GMC Sierra 5.7 liter are spraying wide open while trying to start. My spark plugs are continuously fouling out. I have replaced the O2 sensor on the manifold, but that is it. Can anyone help me diagnose this problem with the EFI? Or suggest the most probable cause. Thanks, Rick 
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#2
10-16-2003, 08:54 AM
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Re: 1990 GMC Sierra, 350, 5.7 liter fuel injection problems
The injectors should pulse.
If you remove the wiring connector for the top of the injectors and spin the engine over does fuel still come out? If it does than the injectors are leaking. Check the resistance of the coolant sensor should be about 3400 ohms at 70 degrees and will go higher as the temperature drops...if the resistance is high that means the sensor is reading a colder temperature..so you may have a coolant sensor that is reading incorrectly causing the ECM to think that you are in a "cold start" and is pouring on the fuel . 210 degrees = 185 ohms 160 degrees = 450 ohms 0 degrees = 25000 ohms
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#3
10-17-2003, 09:37 AM
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When you say wide open, do you mean that they are just open or that they seem to operate at a wide pulse? Wide open, (not pulsing), means that, for some reason, the computer is not pulsing the ground, meaning that either the computer hasd a problem or that the wiring is gounded, causing the ECM to lose control of the injectors. If the pulse width is excessive, it is possible for the sensors to be telling the ECM that the air pressure is very high, the coolant temp is very low, or some type of signal is telling the ECM to operate at a wide pulse. It is also p[ossible for the ignition to be weak, allowing the plugs to foul before the engine lights. The involved components include the plugs, wires, cap and rotor, etc. When the engine os overnight cold, the scanner should shoiw the coolant and the air temp to be very close. The baro, (MAP), should show air pressure, something close to 4.5 volts. I have frequently seen the computer set its own value for air pressure, in complete disagreement with the MAP signal, and flooding the engine as a result. I would check carefully the following, in order: the ignition then sensors, then suspect the computer. Ray
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