Can a weak fuel pump really cause misfire?

[avacado11]

Genuine Ford or aftermarket fuel module?

Leaky injector, bad sensors, bad coil(s), or electrical glitch are worth troubleshooting. Get that fuel PSI prior to replacing pump. Otherwise, it becomes a shotgun repair.

Dorman aftermarket. I caught myself real quick. Already threw on a new EVAP purge valve($30) and a new battery($120). Purge valve was leaking slightly, battery wouldn’t hold 12v overnight so I guess it was money that had to be spent anyways.

After finding that leaving the key in the on position helped, and pulling the fuel line and putting the key on resulted in a drop of fuel coming out I had a feeling it is the fuel pump.

Anyways, I’ve got the tank strap bolts broken loose so all I need to do is drop the tank tomorrow and change it out. Not too hard, just have no motivation due to the cold weather. I will check the wiring above the tank while I’m at it.

 

[brianl703]

After finding that leaving the key in the on position helped, and pulling the fuel line and putting the key on resulted in a drop of fuel coming out I had a feeling it is the fuel pump.

You should get a steady stream of fuel, not a drop.

 

[avacado11]

Then how do you verify the fuel pressure sensor is accurate? You can't tee in between the supply line and the fuel rail? Might need some adapters but hard to believe there isn't a way.

I believe the ECU pulls data from the injectors, pump, and I’m almost certain there’s a sensor built into the fuel line right by the pump that reads pressure.

Seems like an oversight from ford to assume their fuel pressure sensor will never fail. But it is what it is. Kinda mad I didn’t find out about forscan earlier. I thought it was dealer only software.

 

[brianl703]

I believe the ECU pulls data from the injectors, pump, and I’m almost certain there’s a sensor built into the fuel line right by the pump that reads pressure.

The fuel pressure sensor is often located on the fuel rail on top of the intake manifold. At least on the 2004 Crown Vic, it's a 3-wire device.

 

[wtd]

I checked fuse 27, it has a new fuse with no issues but is still at the original location. I will install the relocation kit once the weather gets nicer.

Do the female receptacles down inside the fuse box for fuse 27 look like they have started to melt or get hot? Even though the fuse is new, if the wiring inside the fuse box is compromised, you could still have higher resistance on the fuel pump circuit.

 

[wtd]

Dorman aftermarket. I caught myself real quick. Already threw on a new EVAP purge valve($30) and a new battery($120). Purge valve was leaking slightly, battery wouldn’t hold 12v overnight so I guess it was money that had to be spent anyways.

After finding that leaving the key in the on position helped, and pulling the fuel line and putting the key on resulted in a drop of fuel coming out I had a feeling it is the fuel pump.

Anyways, I’ve got the tank strap bolts broken loose so all I need to do is drop the tank tomorrow and change it out. Not too hard, just have no motivation due to the cold weather. I will check the wiring above the tank while I’m at it.

I would not use anything Dorman for electrical parts. Most are complete junk. That could be part of your problem.

 

[Lubener]

C'mon man.... automotive forums are full of owners dumping wheelbarrows of parts into a vehicle then starting a thread on cel's or running issues.

I'd make sure all your 'software' is up to date. Means a trip down to a dealer, or Ford competent shop, to verify any ecu tsb updates for errors, drivability concerns.... If none, since its a pickup, take it down to the local chinesium parts store and load the bed up.

Genuine Ford or aftermarket fuel module?

Leaky injector, bad sensors, bad coil(s), or electrical glitch are worth troubleshooting. Get that fuel PSI prior to replacing pump. Otherwise, it becomes a shotgun repair.

After being eight years old, it's unlikely having an old version of firmware is going to cause an issue after all this time has elapsed. I wouldn't waste the money at a dealer for a firmware flash for this problem and hoping it solves something. That's guessing and the dealer isn't going to guarantee anything... He needs to verify a proper level of energy is being delivered to the pump then troubleshoot this logically before tearing into it.

 

[avacado11]

New fuel pump is in. Installed the tank, hooked everything up. Truck starts perfectly now. The back flow valve spring was completely gone on the old pump(also a Delphi unit, not OEM). Went to attach the filler neck and the hose busted. No way to reach the tank side of the hose so the tanks coming out again tomorrow.

But atleast the long crank issue is fixed, I am familiar with dropping the tank. It shouldn’t take too long.

 

[avacado11]

I take my last post back. After I got everything situated the truck ran great for 1 night. No misfire shake. No long crank. Nothing. Ran good as new. The next morning it immediately went to a long crank again. So after some toying around there is still something wrong with the fuel system.

It isn't holding pressure after a cold soak. Despite the new fuel pump, I pulled the fuel line at the engine rail, put it into a plastic bottle, cycled the key to the on position. It blew out gasoline at 60psi for a split second, full force, then stopped. Nothing else. Not a constant stream, not even a trickle of gasoline. It will do this every time you cycle the key to the on position but will not keep the pressure constant. There is no pressure sensor or anything of that sort - just 1 single unit built into the fuel pump.

At this point I suspect it has to do with the electrical system thats powering the fuel pump, possibly a bad relay or wiring. Fuel pump driver module is a new Dorman unit. I know not all new parts are good parts so theres that, I need to jump the fuel pump module to see if thats the issue, and test for voltage at the fuel pump fuse and at the fuel pump module at the back of the vehicle. Fuel pump is obviously new so it's highly unlikely to be it.

If be ok with toying around with it a little more except its -14 degree windchill and of course it only breaks when its super cold.

 

[michaelluscher]

It did on my xB
Meh power progressed to lean codes and stupid high fuel trims, progressed to hard starting/vapor lock, then eventually wouldn't run
If you're suspecting it's a fuel issue, make a thorough test of pressure, ability to hold pressure, and flow
I would've saved myself a lot of time
Had to learn somehow 🤷‍♂️

Edit: you lost me at the Dorman t brand fuel pump driver module
Have you checked powers and grounds to said FPDM?
FORScan is your friend when it comes to full data access and bi directional control

 

[350Rocket]

I take my last post back. After I got everything situated the truck ran great for 1 night. No misfire shake. No long crank. Nothing. Ran good as new. The next morning it immediately went to a long crank again. So after some toying around there is still something wrong with the fuel system.

It isn't holding pressure after a cold soak. Despite the new fuel pump, I pulled the fuel line at the engine rail, put it into a plastic bottle, cycled the key to the on position. It blew out gasoline at 60psi for a split second, full force, then stopped. Nothing else. Not a constant stream, not even a trickle of gasoline. It will do this every time you cycle the key to the on position but will not keep the pressure constant. There is no pressure sensor or anything of that sort - just 1 single unit built into the fuel pump.

At this point I suspect it has to do with the electrical system thats powering the fuel pump, possibly a bad relay or wiring. Fuel pump driver module is a new Dorman unit. I know not all new parts are good parts so theres that, I need to jump the fuel pump module to see if thats the issue, and test for voltage at the fuel pump fuse and at the fuel pump module at the back of the vehicle. Fuel pump is obviously new so it's highly unlikely to be it.

If be ok with toying around with it a little more except its -14 degree windchill and of course it only breaks when its super cold.

I would want to confirm that is a reasonable way to test fuel pressure. I suspect it's shutting down for safety when it detects no load on the fuel system. If it actually had no fuel right after it would likely start briefly and then die as opposed to having a long crank. It could be unrelated to the fuel system.

 

[another Todd]

Has you fuel mileage dropped recently? If you are smelling raw fuel out of the exhaust during your long crank, it is either getting too much fuel (doubtful on a cold engine) or your problem is elsewhere. I would be looking at ignition system.

 

[avacado11]

It did on my xB
Meh power progressed to lean codes and stupid high fuel trims, progressed to hard starting/vapor lock, then eventually wouldn't run
If you're suspecting it's a fuel issue, make a thorough test of pressure, ability to hold pressure, and flow
I would've saved myself a lot of time
Had to learn somehow 🤷‍♂️

Edit: you lost me at the Dorman t brand fuel pump driver module
Have you checked powers and grounds to said FPDM?
FORScan is your friend when it comes to full data access and bi directional control

I purchased forscan lite for my phone. Fuel pressure is showing anywhere from 59-60psi but nothings coming out. Not getting any fuel trim data as it’s not starting at all. Basically useless for me right now. MAF was showing 2.84 g/s despite not even cranking key. My friend has an ‘11 F150 5.0 and I was comparing data with his. His MAF showed 0 g/s until the key is turned. So, logically I replaced the MAF sensor thinking it’s not reading correctly. No luck. His fuel pressure was also showing 59-60psi.

Pulled the fuse box to inspect wiring and install a factory TSB for fuel pump fuse relocator - all is good. Haven’t tested voltage running to the pump yet but I’ll have to drop the tank to get to that connector. I ended up bypassing the FPDM and still had no luck even seeing fuel pressure come out of the tank. Swapped both new dorman and old OEM FPDM with no difference

since it’s too cold to be doing anything outside I decided to tear apart my old fuel pump(also a Delphi unit) to see how it works. Submerged the pump in water. Turns out, when I send 12v power directly to the pump it whirrs but nothing comes out of the output hose on the pump. The pump currently in the truck is also a Delphi unit. Since it’s Christmas Eve I decided to run to Autozone to pick up a spare fuel pump so I have one on hand tomorrow incase I find out it’s a pump issue(it also is a Delphi, all they have in stock). I hope this $300 pump is good.

At this point I highly suspect the pump is dead(I’ll test voltage to the connector first). I purchased it off Rock Auto. Funny part is, they retail for about $180 on their site right now. I only paid $48 2 weeks ago and it was pretty late at night. Possibly system error? No clue. But the Delphi pump(same part #) I got from Autozone is fully wrapped up in the box. My pump from Rock Auto was not packaged the same way despite being the same part. I almost feel like the Rock Auto one is a fake Delphi or was at minimum defective, tested, and resold.

Regardless, when that rock auto pump originally went into the truck it held fuel pressure overnight. I had to drop the tank a second time to get the filler neck back on and when I popped the fuel line off it sprayed gas everywhere. It doesn’t do it anymore.

 

[avacado11]

Has you fuel mileage dropped recently? If you are smelling raw fuel out of the exhaust during your long crank, it is either getting too much fuel (doubtful on a cold engine) or your problem is elsewhere. I would be looking at ignition system.

My fuel economy actually got better with the new pump in, til it failed a day and a half later.

My coil packs are original Ford. The plugs had been replaced sometime prior with Autolite double platinums but were not gapped correctly(0.044 when spec is 0.048-0.054). I replaced the plugs with another set of Autolite double platinum and gapped all to 0.049.

When I originally noticed it not holding fuel pressure again I assumed it had to be a bad injector(s) that was leaking overnight. But the fact that when you turn the key nothing comes out - I’m highly suspicious that it’s simply a defective pump. I was thinking maybe some dust/dirt got sucked into it but upon tearing apart my old pump the filter on these is pretty robust. Nothing but gasoline can get through it.

 

[avacado11]

I would want to confirm that is a reasonable way to test fuel pressure. I suspect it's shutting down for safety when it detects no load on the fuel system. If it actually had no fuel right after it would likely start briefly and then die as opposed to having a long crank. It could be unrelated to the fuel system.

Correct, there may be some sort of safeguard built into it to cut pressure if it detects no load. Sucks that Ford switched to a non-return fuel system. Everything has to be read through the ECM.

But, if that was the case wouldn’t the line still be pressurized if I cycle the key with the line hooked up, then popped it off? I mean when I cycle the key then pop the line, nothing comes out.

 

[brianl703]

But, if that was the case wouldn’t the line still be pressurized if I cycle the key with the line hooked up, then popped it off? I mean when I cycle the key then pop the line, nothing comes out.

On older Ford vehicles turning the key on turns the fuel pump on for 2 seconds. On my 2004 Crown Vic with it's jammed fuel pump (it was physically locked up and would not turn), this caused the dome light to noticeably dim for 2 seconds due to the current it was pulling. (This 2004 Crown Vic is a returnless fuel system with the FPDM).

So if you unhook the fuel line, and your newer Ford still does the 2-second fuel pump, you should get about 2 seconds of fuel coming out of it when you turn the key on. You should also be able to hear the fuel pump running for those 2 seconds.

 

[avacado11]

On older Ford vehicles turning the key on turns the fuel pump on for 2 seconds. On my 2004 Crown Vic with it's jammed fuel pump (it was physically locked up and would not turn), this caused the dome light to noticeably dim for 2 seconds due to the current it was pulling. (This 2004 Crown Vic is a returnless fuel system with the FPDM).

So if you unhook the fuel line, and your newer Ford still does the 2-second fuel pump, you should get about 2 seconds of fuel coming out of it when you turn the key on. You should also be able to hear the fuel pump running for those 2 seconds.

The 2 second theory sounds reasonable. I had someone cycle the key and I watched the line. There was a flood of gasoline after a couple of cycles for but it was nowhere near 60psi like what the pump is supposed to do. And you could cycle it right after and nothing comes out. It’s only pumping intermittently, which could possibly be the time out for the pump, but who knows. I know ford changed a lot with the 5.0 engines. The fuel system is a completely different design from the 4.6/5.4. No return line, or pressure regulator. ECM reads parameters and will adjust pressure accordingly.

I’m going to drop the tank tomorrow and see if running 12v directly to the pump will make fuel come out.

 

[michaelluscher]

The 2 second theory sounds reasonable. I had someone cycle the key and I watched the line. There was a flood of gasoline after a couple of cycles for but it was nowhere near 60psi like what the pump is supposed to do. And you could cycle it right after and nothing comes out. It’s only pumping intermittently, which could possibly be the time out for the pump, but who knows. I know ford changed a lot with the 5.0 engines. The fuel system is a completely different design from the 4.6/5.4. No return line, or pressure regulator. ECM reads parameters and will adjust pressure accordingly.

I’m going to drop the tank tomorrow and see if running 12v directly to the pump will make fuel come out.

FORScan (on a laptop) can bi directionally control things

Might be a little easier for you if the relay/wiring is hard to access

 

[brianl703]

I’m going to drop the tank tomorrow and see if running 12v directly to the pump will make fuel come out.

You should be able to apply 12V to the pump at the FPDM connector. If you have the wiring diagram for the vehicle, it should show you what terminals on the FPDM connector have the 12V to the FPDM from the fuel pump relay under the hood and what terminals go to the fuel pump in the tank. If the FPDM connector has the round terminals 14AWG solid wire (like from Romex cable) is just the right diameter to fit in them.

 

[wtd]

You said that you bypassed the FPDM but did you also try bypassing the fuel pump relay? If you don't have a wiring diagram, I would get a few days access of Alldata so that you can look at diagrams and see what the theory of operation is for the fuel system. A wiring diagram will also see if there are any connectors that are in between the FPDM or fuel pump relay that you can access to check for power and grounds before you drop the tank. Do you know if the FPDM or the fuel pump relay is last in line before going to the tank?