Intermittent MCU functionality
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7th Gear
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Intermittent MCU functionality
Newbie here, thanks in advance for efforts expended contemplating my problem.
1994 F350 gas guzzler. It refused to start, and symptoms (unwillingness to provide OBD codes and fuel pump which would not shut off) led me to remove the MCU, on which I replaced the electrolytics and a resistor in series with the 10uF electrolytic. After replacing the MCU, there was no change in behavior. I tightened the connector bolt a bit more and MCU was working again, providing codes, turning off fuel pump, and allowing the engine to purr. I came back the next day, and failure mode. I wiggled wires, fuses, relays, etc. with key on to listen for fuel pump to shut off, no luck. I took a phone call, and while I was gone 5 minutes and came back, the fuel pump was off, it started right up, provided codes (EGR problem no surprise). I’ve checked grounds and voltage always above 12 volts. This has cycled between working and non working mode now several times, I’m stumped.
Any ideas as to what might be causing this mysterious intermittency?
1994 F350 gas guzzler. It refused to start, and symptoms (unwillingness to provide OBD codes and fuel pump which would not shut off) led me to remove the MCU, on which I replaced the electrolytics and a resistor in series with the 10uF electrolytic. After replacing the MCU, there was no change in behavior. I tightened the connector bolt a bit more and MCU was working again, providing codes, turning off fuel pump, and allowing the engine to purr. I came back the next day, and failure mode. I wiggled wires, fuses, relays, etc. with key on to listen for fuel pump to shut off, no luck. I took a phone call, and while I was gone 5 minutes and came back, the fuel pump was off, it started right up, provided codes (EGR problem no surprise). I’ve checked grounds and voltage always above 12 volts. This has cycled between working and non working mode now several times, I’m stumped.
Any ideas as to what might be causing this mysterious intermittency?
Logistics Pro
Joined: Nov 2013
Posts: 3,928
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From: Mojave, Ca
Newbie here, thanks in advance for efforts expended contemplating my problem.
1994 F350 gas guzzler. It refused to start, and symptoms (unwillingness to provide OBD codes and fuel pump which would not shut off) led me to remove the MCU, on which I replaced the electrolytics and a resistor in series with the 10uF electrolytic. After replacing the MCU, there was no change in behavior. I tightened the connector bolt a bit more and MCU was working again, providing codes, turning off fuel pump, and allowing the engine to purr. I came back the next day, and failure mode. I wiggled wires, fuses, relays, etc. with key on to listen for fuel pump to shut off, no luck. I took a phone call, and while I was gone 5 minutes and came back, the fuel pump was off, it started right up, provided codes (EGR problem no surprise). I’ve checked grounds and voltage always above 12 volts. This has cycled between working and non working mode now several times, I’m stumped.
Any ideas as to what might be causing this mysterious intermittency?
1994 F350 gas guzzler. It refused to start, and symptoms (unwillingness to provide OBD codes and fuel pump which would not shut off) led me to remove the MCU, on which I replaced the electrolytics and a resistor in series with the 10uF electrolytic. After replacing the MCU, there was no change in behavior. I tightened the connector bolt a bit more and MCU was working again, providing codes, turning off fuel pump, and allowing the engine to purr. I came back the next day, and failure mode. I wiggled wires, fuses, relays, etc. with key on to listen for fuel pump to shut off, no luck. I took a phone call, and while I was gone 5 minutes and came back, the fuel pump was off, it started right up, provided codes (EGR problem no surprise). I’ve checked grounds and voltage always above 12 volts. This has cycled between working and non working mode now several times, I’m stumped.
Any ideas as to what might be causing this mysterious intermittency?
Fleet Owner
Joined: Oct 2005
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