Odd Long Cranking Issue
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5th Wheeling
Joined: Aug 2020
Posts: 44
Likes: 2
From: OK
Odd Long Cranking Issue
I'm having an issue on my '94 F150, 351. When I first go to start the truck in the morning, I have to crank it for what I'd say is a long time (4-5 seconds) before it starts. For the rest of the day it will start right up immediately. I just happened to figure out recently that if I go turn the key on, wait for the fuel pump to stop, then turn it back off, and then go to actually start it within an hour or so, it fires right up. I've also tried cycling the fuel pump two or three times and then trying to start, but that doesn't do the trick. Would you think fuel pressure regulator, fuel pump, or something else? Side note, I've replaced all vacuum lines, air charge sensor, water temp sensor (the one that actually talks to the computer), TPS, EGR valve, plugs, wires, cap, rotor, coil. I didn't do all that for this issue, but this issue has persisted through all of that. Also replaced leaking capacitors on the ECM.
Fleet Mechanic
Joined: Aug 2015
Posts: 1,835
Likes: 363
From: Candy Mountain
It sounds like the fuel pressure is bleeding off overnight, but it should build back up very quickly when the pump comes on. You can put a gauge on it to see what is going on at the rail.
How old is the fuel filter?
How old is the fuel filter?
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5th Wheeling
Joined: Aug 2020
Posts: 44
Likes: 2
From: OK
Okay, ran a pressure test today. At first I thought I had gotten a bad gauge. I connected it, turned the key on, and no pressure reading. Zero. Yet, I could hear the pump and have been driving the truck, so obviously it's working. I finally just started the truck, and pressure built to 34 psi within a few seconds. Then tested with the regulator vac line off and plugged and 44 psi. Okay, we're right on the money on both counts when the truck is running. Shut the truck down, bled the gauge, turned the key back on, no pressure again. This time I decided to cycle the key several times. After about 3 cycles, I read around 20 psi. Side note, I was of the understanding that revving the engine should produce a pressure increase. I didn't see hardly any change when revving. Is that an issue? I'm also puzzled about something else. When I purged the gauge the first few times, I got VERY varnished fuel out (and the gauge was very clean and dry before I started. After the first few purges, fuel was nice and clean. Anybody have thoughts? I'm puzzled all the way around. Quick note too, no fuel leaking out of the vac line on the regulator.
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
You should get at leat 35 PSI on the first key cycle from Off to Run. Since you also observed very little pressure increase when blipping the throttle could be a weak fuel pump. Does the truck have two tanks?
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5th Wheeling
Joined: Aug 2020
Posts: 44
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From: OK
It does have two tanks, but the rear pump has been dead since before I got the truck. So you're thinking weak pump even though I'm getting 44 psi with the engine running with the regulator unplugged?
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Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
Under load, not idle, the pump may not be able to supply enough fuel. On the other hand the regulator may be holding things back. It is a simple and relatively cheap item to replace for testing purposes. I would do a FPR change before going into the fuel system. The 1990 and later gas engine F-Series trucks have a high pressure pump assembly in each tank. Each of these assemblies, Fuel Delivery Module (FDM), have a high pressure check valve and a shuttle valve to prevent flow into the unselected tank. These valves are known to leak which bleeds off fuel pressure to the unused tank. If the rear tank is getting mysteriously filled you have a bad valve in the rear tank.
It is an overly complicated system so that's why I suggest to start with the easy and less expensive parts first.
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5th Wheeling
Joined: Aug 2020
Posts: 44
Likes: 2
From: OK
Ok. I'll check the rear tank first. I siphoned it down as close to empty as I could right after I got the truck, so if it has a significant amount of fuel in it, it will definitely indicate a problem. Any thoughts on the varnished fuel coming out of the rail during testing? It was probably the first couple of tablespoons and then clear. I would have thought the fuel rail would always be getting fresh fuel circulated? EDIT: Checked the rear tank. It's dry.
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5th Wheeling
Joined: Aug 2020
Posts: 44
Likes: 2
From: OK
Ok, so after testing and observation, I really think the pump is fine, but the internal check valve has failed. 3 primes in the morning reliably starts the truck right up with no hesitation, and there's never any evident fuel starvation when driving. Did some poking around, and came up with what seems to be a direct fit Ford part that could solve this: Ford Check Valve If I have my info correct, this part was originally produced for a recall on '93 models to correct crossflow issues from one tank to the other, and would have been installed on the return line. Could I just turn it around and plug it into the output side of the fuel filter and accomplish my goal? Seems like a pretty easy solution unless I'm missing something.
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