21 ranger Low fuel pressure and misfire

[SimonSaucy]

Hi friends was out driving with my teardrop trailer today. When out of nowhere after stopping, my truck started misfiring horribly. And shutting off and throwing codes. Eventually, the truck was not shifting properly and not maintaining power. Had to get it towed home….

A few few notes I’ve only had the truck for about a month. It has 140 K. So far the transmission has been great lol

I have noticed a lingering low fuel pressure code. And the fuel pressure it’s asking for is definitely lower than what it is getting. But I’ve noticed the duty cycle of the pump is normals

The unfortunate fact is, I just drove the car off the tow truck and it started up perfectly no issues and drove into the garage.

Wondering if anyone else has run into this issue. I’m thinking it’s a fuel pump issue. This truck was used a lot in construction.

seems like the issues only happening when the truck is at operating temperature in the hot Vegas sun.. I put 87 in it BTW

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[airline tech]

Before you condemn the LP Fuel Pump - Get an actual (Gauge) on the system to verify that the pressure reading is accurate.

Note: A Pressure difference of 15 PSI (is within acceptable limits) - Gauge to PID
The TAP in - = The HP Fuel Pump Feed (QD)

Ref: Normal Readings (Approximate) @ Hot Idle

LP Pump Press - Actual / Desired - 69 PSI
LP -Low Press Voltage (Sensor) - 2.80 volts
LP Pump - Duty Cycle - 25%

Fuel Pump Module - Duty Cycle - 40%

Fuel Rail Pressure Actual / Desired - 229 PSI - this will vary depending on load

The Fuel Low Press (Sensor) is what gives you the LP Fuel Pump (PID)

Being that you are stating its more noted (Heat Related) - (?) is it from pump heat or bad connection heat

I would pull (inspect & clean) the related connectors

1. The Fuel Pump Module Connector - it's the module mounted just above the spare tire
2. C410 & C408

You do not have access to the top of the tank - so you cannot reach the Fuel Pump Connector or the Low-Pressure sensor connector

C410 and C408 are known to have corroded connections (moisture intrusion)

For Reference:

Top of tank ref

At 140K - it does appear to be the pump itself, but it may be a good idea to either verify with an actual gauge and or replace the (Low Press) sensor along with the pump - which I think comes with the tube - reason is to avoid pulling the tank again (if it's the sensor) - this is my reasoning for the gauge test - Verify the Press Reading is accurate

 

[Grandaccess]

Before you condemn the LP Fuel Pump - Get an actual (Gauge) on the system to verify that the pressure reading is accurate.

Note: A Pressure difference of 15 PSI (is within acceptable limits) - Gauge to PID
The TAP in - = The HP Fuel Pump Feed (QD)

Ref: Normal Readings (Approximate) @ Hot Idle

LP Pump Press - Actual / Desired - 69 PSI
LP -Low Press Voltage (Sensor) - 2.80 volts
LP Pump - Duty Cycle - 25%

Fuel Pump Module - Duty Cycle - 40%

Fuel Rail Pressure Actual / Desired - 229 PSI - this will vary depending on load

The Fuel Low Press (Sensor) is what gives you the LP Fuel Pump (PID)

Being that you are stating its more noted (Heat Related) - (?) is it from pump heat or bad connection heat

I would pull (inspect & clean) the related connectors

1. The Fuel Pump Module Connector - it's the module mounted just above the spare tire
2. C410 & C408

You do not have access to the top of the tank - so you cannot reach the Fuel Pump Connector or the Low-Pressure sensor connector

C410 and C408 are known to have corroded connections (moisture intrusion)

For Reference:

Top of tank ref

At 140K - it does appear to be the pump itself, but it may be a good idea to either verify with an actual gauge and or replace the (Low Press) sensor along with the pump - which I think comes with the tube - reason is to avoid pulling the tank again (if it's the sensor) - this is my reasoning for the gauge test - Verify the Press Reading is accurate

This is why we cant have nice things when all we really need is a fuel gauge and a hose to get the damn gas a few feet, but we get something that looks like it fell off a Starlink rocket

 

[SimonSaucy]

Before you condemn the LP Fuel Pump - Get an actual (Gauge) on the system to verify that the pressure reading is accurate.

Note: A Pressure difference of 15 PSI (is within acceptable limits) - Gauge to PID
The TAP in - = The HP Fuel Pump Feed (QD)

Ref: Normal Readings (Approximate) @ Hot Idle

LP Pump Press - Actual / Desired - 69 PSI
LP -Low Press Voltage (Sensor) - 2.80 volts
LP Pump - Duty Cycle - 25%

Fuel Pump Module - Duty Cycle - 40%

Fuel Rail Pressure Actual / Desired - 229 PSI - this will vary depending on load

The Fuel Low Press (Sensor) is what gives you the LP Fuel Pump (PID)

Being that you are stating its more noted (Heat Related) - (?) is it from pump heat or bad connection heat

I would pull (inspect & clean) the related connectors

1. The Fuel Pump Module Connector - it's the module mounted just above the spare tire
2. C410 & C408

You do not have access to the top of the tank - so you cannot reach the Fuel Pump Connector or the Low-Pressure sensor connector

C410 and C408 are known to have corroded connections (moisture intrusion)

For Reference:

Top of tank ref

At 140K - it does appear to be the pump itself, but it may be a good idea to either verify with an actual gauge and or replace the (Low Press) sensor along with the pump - which I think comes with the tube - reason is to avoid pulling the tank again (if it's the sensor) - this is my reasoning for the gauge test - Verify the Press Reading is accurate

Holy cow man!! Thank you so much! Running those tests on it right now so should have an update shortly!
Simon

 

[TJC]

Changing the intank fuel pumps is a royal pain. I think pulling the bed is easier than dropping the tank. I actually considered cutting an access hole in the bed of my 4G Ranger when I replaced my dying fuel pump. But I figured the truck will probably outlast me.

 

[SimonSaucy]

So just ran the truck up a long hill, few things that stood out after getting the truck up to temps the fuel pump is constantly oscillating in pressure… it’s not maintaining one constant pressure.

As well as after climbing this mountain pass and then letting it sit for a bit and revving it, the pressures are about 100 K PA below desired. On the low side….
But ofc no misfire or other codes now

I’m heavily leaning towards the fuel pump being the issue. Just with that lingering code before I have these issues. Some lingering occasional misfire is at idle.

 

[21rangerCactus]

Changing the intank fuel pumps is a royal pain. I think pulling the bed is easier than dropping the tank. I actually considered cutting an access hole in the bed of my 4G Ranger when I replaced my dying fuel pump. But I figured the truck will probably outlast me.

I did that on my 4th gen Fbody. Lifted the carpet in the hatchback area. Made a nice clean cut and pulled the pump right out. Then I sanded the edges smooth, painted it, glued a piece of sheet metal over the hole, and replaced the carpet.

1hr vs a few hrs dropping the tank.

 

[DukeCanBuildit]

Changing the intank fuel pumps is a royal pain. I think pulling the bed is easier than dropping the tank. I actually considered cutting an access hole in the bed of my 4G Ranger when I replaced my dying fuel pump. But I figured the truck will probably outlast me.

Yeah, why wouldn’t they build an access panel into the bed?

 

[dtech]

The saabs I owned had an access panel under the rear seat, on the 1986 the oem fuel pump was still good at 250k miles, but on a 9-5 the pump died a bit over 100k. If one had an osco scope you could see the signs of a pump on the way out.

 

[TJC]

The saabs I owned had an access panel under the rear seat, on the 1986 the oem fuel pump was still good at 250k miles, but on a 9-5 the pump died a bit over 100k. If one had an osco scope you could see the signs of a pump on the way out.

My 2005 Ranger simply exhibited signs of low fuel pressure. I started noticing it would take longer to start. I then noticed that if I cycled the key 3x without going all the way to the starter, it would fire up immediately. It was really more about the pressure valve in the pump assembly than the motor.

I figured if I had to remove the pump assembly to replace the pressure valve that I might as well replace the entire unit. I had 175K miles on the truck and it was 18 years old.

 

[airline tech]

The Duty Cycle - is maxed out - in an attempt to reach desired

So that leaves - Weak Pump (most likely) or Dirty Ground (as a possible)

G403 - General Location
Note: These location diagrams (are) only general locations and are not always 100% (exact location)

Example: From another member - note that G403 may be the (Some Ground) listed here
A verification would be disconnected C410 and this ground and (meter it) for verification

So, while it appears to be the pump - since it's not a simple R&R, it may be a good idea to just verify you have a good ground circuit - before actually committing to replacement
So, this would be C410 and this ground point G403
and C410 - Closely Inspect Pin #2 for corrosion

Noting that - The Pump (Itself) - Routes to the (Pump Module) - then routes to ground and ties in the (Shielded Ground) for the harness - these are the only 2 things on G403

Granted - it does have high milage and the pump may be just weak and worn out as the most likely issue.

 

[SimonSaucy]

For anyone who finds this thread. YOU CANNOT PULL THE BED AND GET ACCESS so uhh anything else I should do while the bed is off?

 

[DukeCanBuildit]

That’s a tough break. Post photos of what it looks like so folks can see what’s in the way, what’s accessible, etc. It might help them with locating connectors, wire harness routing, or other items they might be troubleshooting.

 

[TJC]

For anyone who finds this thread. YOU CANNOT PULL THE BED AND GET ACCESS so uhh anything else I should do while the bed is off?

I am sorry for recommending it. Seems Ford broke all the old rules when they built the 5G Ranger. I pulled the bed on my 4G and it was easy access.

While its off you can access and inspect your driveshaft, maybe lube the slip joint.

I would appreciate pictures while the bed is off the truck to see whats in the way.

 

[SimonSaucy]

Hahaha it’s not ur fault mate! Other forms side it could be done that way LOL!!’ But yes I will be sure to post lots and lots of photos! I will document the process.

Does anyone happen to have the FMS? I wanna see if there is a access panel inside as it seams possible but I dont!

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