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My Beater wont start. Technical advice welcome.

ManBearPig

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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
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Kinjirra

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Hook a fuel pressure reader to the Schrader valve. If it doesn't meet factory spec while the key is on then its most likely the fuel pressure regulator. A lot of the older cars have them separate from the fuel pump if I remember right but I'm not sure.
 

ahl395

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Did you check for spark? If you have fuel and air, you probably have no spark (or improperly timed spark).

Easy way to check for spark. Remove one of the spark plug wires, stick a screw driver into it so it touches the electrical connector inside, and hold the screwdriver shaft near something grounded (engine block or any bare metal). If there's spark, you'll see it jump from the screwdriver to the metal. Wear gloves and only hold the insulated part of the screwdriver so you dont get shocked. Don't worry though, if you do it only stings for a minute, ive grabbed the wrong part of the screwdriver plenty of times :lol: But still at your own risk.

If no spark, you may have a problem with your ignition coil/distributor or a bad spark plug wire.

If you have spark (and your car doesn't have a distributor) you may have a bad camshaft or crankshaft position sensor, which tell the ECU/PCM when to fire the spark. A distributor's timing can't really be off unless it was installed improperly.

Back to the fuel topic... Although I've never troubleshooted quite like your steps, if your saying the pump works when powered manually but not when hooked up to the car, your fuel pump control module or "driver" may be bad. I've seen several people replace fuel pumps only to find the module was bad, this may not apply to all cars though. I would also recommend "renting" a fuel pressure gauge from Autozone so you can rule that out and have actual numbers instead of guessing, especially if you have an easy access Shraeder valve on your fuel rail. They loan tools out for free at Autozone. As mentioned above the fuel pressure regulator could be the issue too if applicable.

It's possible your PCM is bad, but it's pretty unlikely. I would bet on the other things first. PCM is always the very last possibility.
 

Tommy V

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Don't think it's spark as he said it will.try to.start with starter fluid.I would check all your power and ground wires,especially for the pcm.Also see if u can run a koeo test to.see what codes are in the pcm.That would be a good start.Also what a bout the fuel.filter???
 

Ebm

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.

Did you check for spark? If you have fuel and air, you probably have no spark (or improperly timed spark).

Easy way to check for spark. Remove one of the spark plug wires, stick a screw driver into it so it touches the electrical connector inside, and hold the screwdriver shaft near something grounded (engine block or any bare metal). If there's spark, you'll see it jump from the screwdriver to the metal. Wear gloves and only hold the insulated part of the screwdriver so you dont get shocked. Don't worry though, if you do it only stings for a minute, ive grabbed the wrong part of the screwdriver plenty of times :lol: But still at your own risk.

If no spark, you may have a problem with your ignition coil/distributor or a bad spark plug wire.

If you have spark (and your car doesn't have a distributor) you may have a bad camshaft or crankshaft position sensor, which tell the ECU/PCM when to fire the spark. A distributor's timing can't really be off unless it was installed improperly.

Back to the fuel topic... Although I've never troubleshooted quite like your steps, if your saying the pump works when powered manually but not when hooked up to the car, your fuel pump control module or "driver" may be bad. I've seen several people replace fuel pumps only to find the module was bad, this may not apply to all cars though. I would also recommend "renting" a fuel pressure gauge from Autozone so you can rule that out and have actual numbers instead of guessing, especially if you have an easy access Shraeder valve on your fuel rail. They loan tools out for free at Autozone. As mentioned above the fuel pressure regulator could be the issue too if applicable.

It's possible your PCM is bad, but it's pretty unlikely. I would bet on the other things first. PCM is always the very last possibility.
+1 to CKPS. I just had a similar problem with my '96 XJ with the 4.0 in it. The crankshaft position sensor wasn't working right, plus it was an aftermarket unit. Certain older vehicles hate aftermarket parts. Anything electrical for my XJ I'll hopefully be able to get Mopar. Might be a similar issue for your Ranger Danger.
 

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cdq85

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holy f lol I am literally going through the exact same problem right now. And I do mean exact. 97 ranger with 4.0. replaced fuel pump first, still nothing. found the PCM fuse is blown and then replaced it. the truck fired right up then blew the fuse again. paid one of my technicians to look around and after digging around he figured the pcm itself is shorting out. i ordered a pcm for 160 bucks from autozone and am currently waiting for it to arrive. i'll keep you posted.
 

cdq85

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Well, update on mine just in the off chance that it helps you too. The PCM in my car ended up being ok. Chased around everything looking for a short in the wiring. Ended up being the steel fuel line coming up under the intake manifold ruptured and was spitting gas onto a connection. The fuel must have ate away at the wire and exposed it which I guess was shorting everything. Have to source that fuel line and fittings but Ford no longer makes it and every junkyard around here says that was very common for the 4.0 motor and people snatched those up quick. So gotta fab a line up. Perfect.
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