QuestionQUESTION: Problem: No fuel. Not getting ground from PCM to fuel pump relay, A8 any idea what components inputs to PCM control this function? Perhaps you know a place I might download a fuel pump circuit flow diagram for same. Thanks
ANSWER: the PCM provides the ground to the coil side straight wire from the PDC to the PCM.
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QUESTION: I think we may to rethink this one just a little bit... You have 12 VDC being applied from Fuse Block to A10, if there was a ground applied to pin A8 then the relay would be energized all the time key is in run position. Without a ground being applied to A8 there is no current running through relay resistor to set up voltage drop across relay resistor so, no energizing relay... Besides, C10 of PCM is labeled "Fuel Pump Relay Control" the only way it can control energizing relay is by applying a ground to the relay. My question is what criteria must be met by sensor inputs into PDC to forward bias the fuel pump relay control circuit thus providing the ground to PDC A8 to energize relay? I can apply ground to A8 and relay energizes but, still have no fuel pressure for some reason.
I am betting that what ever input signals forward bias fuel pump relay control also forward biases auto shut down relay or what ever Chrysler calls a "roll over" relay thus shutting off fuel pump in case of accident/roll over but, that is only a guess (would make sense) you see I am a GM certified mechanic, use to work Computer Command Control and drive ability problems... State board Certified Electronic Technician don't know anything about jeeps but, a car is a car only don't have dealership service manuals for this one... Not trying to be argumentative or a pain, just need to know what inputs control "fuel pump relay control" signal. thanks DJ
AnswerA10 is 12v from ign switch
A6 12 all the time
A7 output to fuel pump
A10 ground signal from pcm
The pcm is the whole thing it has it own internal grounds that it makes this is how it controls alot of the functions with low side drivers.
When u turn on the key for 1-2 seconds the PCM will turn things on to primp it up When cranking things stay on aka the fuel pump relay control.
Check for the 2 powers with key on and get a second person to check for the ground when u are cranking or just turn the key on for a second.
"Besides, C10 of PCM is labeled "Fuel Pump Relay Control" the only way it can control energizing relay is by applying a ground to the relay"
this is what I answered the first time
