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Have been working on 2000 Mercury Cougar 2.5L V6 Auto w/ Return-less fuel system when cold ambient weather car will crank but not start. If car sits for several days or if it warms up (over 40F) car usually starts. Ignition Has good Spark, put in new plugs and wires. Good Cam and crank sensors.
Replaced fuel pump and fuel rail pressure sensor. Fuel Pump Primes but no pressure builds unless I cycle key on 5-10x. When car happens to start it shows steady 40+psi. but Fuel pressure ALWAYS drops to zero as soon as car is turned off (true if crank no start and when it runs). On warm days when car starts it is running really rich (LT Fuel trims -20+). Before diving into electronics I thought I was getting stuck open injector. I verified injectors are good, no leaks and all fire as expected when rail pressure is > 30psi
Electrical Check:
Fuel rail Pressure transducer Sensor - 5V ref is good, ground is good, signal line voltage is 1.2V when connector unplugged. When connector plugged in signal voltage goes to 0.48V (gnd and 5V ref still good)
At Fuel Pump Driver Module: (comparing values to Scanner danner video): Inertia Switch voltage supply is good 12V, Grounds are good.
The issue are 2 signal wires values I believe. Pin 1 (Ground/Switched) - KOEO (0V) Cranking (2.7v) when turn key off goes up to 3.3V then to 0v. Video shows it should go to 5v. Pin 7(Voltage , Ignition switch in start or run (not overload protected), switched) - expected square wave 0-5V, getting square wave 0.4 - 2.3 volts)
I am new to most of this but learning from videos and forum. Trying to understand these signal voltage as they seem low as compared to all videos where they show 5v ref and 5v signal when unplugged and 3.5v or so when connector plugged in.
Hoping for some guidance. I only have forscan, fuel gauge and voltmeter for diagnostic tools.
Thanks
Nathan
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