Need Help- Truck Cranks but will not Start
#1
Need Help- Truck Cranks but will not Start
Truck is a 94 4.0 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.
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
#2
Join Date: Jun 2013
Location: Carlsbad Springs Ontario
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Hello, in order for an engine to start you require: correctly timed spark; correct air fuel mixture: that is, correct fuel pressure at the rail, and properly pulsing fuel injector solenoids. There are other obvious things: cranking, correct valve timing etc. So my suggestion is, think simple first and troubleshoot carefully. Also do not forget fuel quality, that is, is there water in the fuel? I did have a problem with water in the fuel once. It is rare, but possible.
#3
RF Veteran
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The 5-8volts is from computers monitor circuit, no amps just volts, it monitors if fuel pump is getting power.
Fuel pump Relay's coil gets 12volt with key on, Computer Ground coil to close relay and pass 12voltt to the inertia switch and fuel pump
So yes if fuel pump relay is not being Grounded by computer then there is a problem with computer OR that ground wire, from computer to fuel pump relay.
pin 22 on computer is the Ground for fuel pump relay
Pin lay pouts here: Ford EEC-IV
If engine starts by manually adding gasoline or ?? but dies after then it has spark at the right time and it has enough compression, so yes, fuel is the issue.
If you "hot wire" fuel pump and still have a no start then first check that fuel injectors have 12volts with key on, they all get 12volts on a Red wire that runs from one injector to the next.
Computer Grounds injector to open it
If injectors have 12volts then yes, probably computer is bad
Fuel pump Relay's coil gets 12volt with key on, Computer Ground coil to close relay and pass 12voltt to the inertia switch and fuel pump
So yes if fuel pump relay is not being Grounded by computer then there is a problem with computer OR that ground wire, from computer to fuel pump relay.
pin 22 on computer is the Ground for fuel pump relay
Pin lay pouts here: Ford EEC-IV
If engine starts by manually adding gasoline or ?? but dies after then it has spark at the right time and it has enough compression, so yes, fuel is the issue.
If you "hot wire" fuel pump and still have a no start then first check that fuel injectors have 12volts with key on, they all get 12volts on a Red wire that runs from one injector to the next.
Computer Grounds injector to open it
If injectors have 12volts then yes, probably computer is bad
#4
Join Date: Jun 2013
Location: Carlsbad Springs Ontario
Posts: 39
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Hello 'ManBearPig'
Good suggestion about the ground.
This past summer a friend had a similar problem with a recent model E-350 Ford work van. It turned out to be a corroded ground strap to the frame.
It took us a while to figure this out because the voltage checks did not make sense due to the missing ground. I even used an oscilloscope for troubleshooting. There was a braided ground in the wiring to the pump that was good so we did not check frame ground, but that is what the problem was.
Good suggestion about the ground.
This past summer a friend had a similar problem with a recent model E-350 Ford work van. It turned out to be a corroded ground strap to the frame.
It took us a while to figure this out because the voltage checks did not make sense due to the missing ground. I even used an oscilloscope for troubleshooting. There was a braided ground in the wiring to the pump that was good so we did not check frame ground, but that is what the problem was.
#5
#6
RF Veteran
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Hi Ron, I’ve got the same issues and have gone through the same troubleshooting procedures. Where can I test for 12 volts to the injectors? Also, where is the ground connection I should check? I’ve got the schematic but it doesn’t show the injector electrical wiring.
Thanks,
Rick
Thanks,
Rick
Ground volt meter and test either wire on a plugged in injector with key on.
Both wires should have 12v, most fuel injectors are low OHMs, 15ohms or so.
This means voltage passes thru them with very little resistance, so there would be 12v on both wires
A fuel injector is a Solenoid, so electrically just a coil of wire inside, if one wire has 12v and the other wire no or low volts then that injectors is bad, wire inside is damaged.
Most fuel injection is sequential, after 1994 on Rangers, so besides the Red wire there will be a different colored wire at each injector going back to the computer(PCM)
PCM Grounds that wire to open the fuel injector for a few milliseconds.
Injectors get 12v with key on but are not Grounded so stay closed, when Crank sensor or Cam sensor starts to sends Pulses to the PCM it starts Grounding the injectors to open them.
You can't "see" these Ground pulses with a volt meter, they happen too fast.
There is a tool called a Noid Light that attaches to injector and its wires, it will flash when injector gets Ground Pulse.
You can also use a smaller hose, like a vacuum line, as a stethoscope, place it against the injector and crank engine with key on, you can disconnect coil for a no start, and listen to each injector, it will "tick" when it opens and closes.
Or listen to each injector with engine idling, should be a steady tick, tick, tick
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