ManBearPig
Well-Known Member
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Truck is a 94 Ranger. 4.0 v6 5-speed 2wd. Has 220k miles. Ive had the truck for 2 years and have put about 40k miles on it, never had an issue. I just joined a Ranger forum but it doesn't look to be very active. Theres some smart folks on here so I figured it wouldn't hurt to post here, too
About a month ago I drove the truck to work and it would not start in the afternoon. I made some minor diagnostic efforts and determined more work was needed than what I wanted to perform in the parking garage, so I trailered the truck home and it has been sitting several weeks as I haven't had time or motivation to mess with it. I started working on it today and cannot figure out whats wrong. Below is what the truck is doing and what I've tried:
Truck has a fresh, fully charged battery. Will crank over plenty fast but makes zero effort to start. I have visually inspected and given a quick spray of the MAF. It is clean and not damaged. Ive checked every fuse both under the dash and in the fuse box under the hood. Swapped PCM and fuel pump relays. I haven't tested actual fuel pressure but noticed that after even significant amounts of cranking, there is barely a dribble of fuel when the Schrader valve on the fuel rail is depressed. I can get the truck to kinda-sorta stumble to run for 2-3 seconds if starting fluid is sprayed into the throttle body. I also noticed that I do not hear the fuel pump prime when the key is cycled. I made sure the inertia switch is not tripped.
At this point I was certain I needed a fuel pump so I went and bought one. Swapped it in and got nothing. No change at all. I then had the idea of bench testing the old fuel pump and noticed the pump will run if connected to a 12v power source. I then checked voltage at the connector going to the pump (I realize these steps should have been taken before buying a new pump, but oh well).I get 5.5v-5.6v at the connector any time the key is on. I have had a helper cycle the key while I watched voltage and I never get a full 12v, even for the first 2 seconds after the key is cycled.
At this point, just to rule anything else out, I hooked the pump to a 12v battery and tried to start the truck. Nothing. Even with the pump audibly running in a full tank of fuel it will not start. Again I can get it to cough and sputter a bit if starting fluid is sprayed into the TB but I cannot get anything resembling a healthy idle. At this point I get what looks to be a significant spray from the Schrader valve on the fuel rail. To verify pressure, I also disconnected the engine side of the filter and cycled the pump manually. I get a nice, healthy flow of fuel, so I'm confident I'm getting fuel to the rail. I realize this is not an accurate way to gauge fuel pressure but I don't have a gauge and I'm pretty sure fuel delivery is not the problem (when the pump is hooked to an alternate 12v source).
So I have two issues, and here are the cliff notes:
First, the known good fuel pump will not turn on and is only getting 5.5v when the key is cycled and when the truck is cranking.
Second, even when connecting the pump to an alternate 12v source the truck will not start even with what appears to be adequate fuel pressure.
Is it reasonable that the PCM may have gone bad? It would seem that somehow it is not turning the fuel pump on, nor is it firing the injectors. I cant think of anything else but I welcome any suggestions from here
Thanks
About a month ago I drove the truck to work and it would not start in the afternoon. I made some minor diagnostic efforts and determined more work was needed than what I wanted to perform in the parking garage, so I trailered the truck home and it has been sitting several weeks as I haven't had time or motivation to mess with it. I started working on it today and cannot figure out whats wrong. Below is what the truck is doing and what I've tried:
Truck has a fresh, fully charged battery. Will crank over plenty fast but makes zero effort to start. I have visually inspected and given a quick spray of the MAF. It is clean and not damaged. Ive checked every fuse both under the dash and in the fuse box under the hood. Swapped PCM and fuel pump relays. I haven't tested actual fuel pressure but noticed that after even significant amounts of cranking, there is barely a dribble of fuel when the Schrader valve on the fuel rail is depressed. I can get the truck to kinda-sorta stumble to run for 2-3 seconds if starting fluid is sprayed into the throttle body. I also noticed that I do not hear the fuel pump prime when the key is cycled. I made sure the inertia switch is not tripped.
At this point I was certain I needed a fuel pump so I went and bought one. Swapped it in and got nothing. No change at all. I then had the idea of bench testing the old fuel pump and noticed the pump will run if connected to a 12v power source. I then checked voltage at the connector going to the pump (I realize these steps should have been taken before buying a new pump, but oh well).I get 5.5v-5.6v at the connector any time the key is on. I have had a helper cycle the key while I watched voltage and I never get a full 12v, even for the first 2 seconds after the key is cycled.
At this point, just to rule anything else out, I hooked the pump to a 12v battery and tried to start the truck. Nothing. Even with the pump audibly running in a full tank of fuel it will not start. Again I can get it to cough and sputter a bit if starting fluid is sprayed into the TB but I cannot get anything resembling a healthy idle. At this point I get what looks to be a significant spray from the Schrader valve on the fuel rail. To verify pressure, I also disconnected the engine side of the filter and cycled the pump manually. I get a nice, healthy flow of fuel, so I'm confident I'm getting fuel to the rail. I realize this is not an accurate way to gauge fuel pressure but I don't have a gauge and I'm pretty sure fuel delivery is not the problem (when the pump is hooked to an alternate 12v source).
So I have two issues, and here are the cliff notes:
First, the known good fuel pump will not turn on and is only getting 5.5v when the key is cycled and when the truck is cranking.
Second, even when connecting the pump to an alternate 12v source the truck will not start even with what appears to be adequate fuel pressure.
Is it reasonable that the PCM may have gone bad? It would seem that somehow it is not turning the fuel pump on, nor is it firing the injectors. I cant think of anything else but I welcome any suggestions from here
Thanks
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