2003 Ford Expedition Fuel Pump Relay (R303) Damaged

[mggmgm1]

@Martynka I am still not understanding how I determine if the fuel pump is drawing too much current? How would I check the current it is drawing if the R303 relay is damaged? The fuel pump does work perfect when I bypass the R303 so I know it is the R303 that was damaged. Also, this is the second R303 relay that is damaged which is a 30 A relay and it was damaged within 5 days after working perfectly.

 

[mggmgm1]

@whtbronco I did isolate the issue to R303 two different times.

1. The first time, the R303 relay was visually melted.
2. I installed a 30 A R303 relay and it worked perfectly for 5 days. Then all of a sudden the Expedition stalled. I bypassed the R303 relay and the Expedition starts perfectly.

Do you have any idea of how to identify the root cause of what damaged the original R303 fuse and then the newly installed one after 5 days of working perfectly?

You suggested installing an external relay but if the root cause is not fixed, I believe even the external one will be damaged.

It might be the fuel pump drawing too much current but how would I check that?

 

[whtbronco]

You've may have a fuel pump drawing too much power for the 15amp relay to handle, motors can draw more power as they age/wear. Or there may be an intermittent short in a wire.

This video should help with how to test for current draw. You won't need an external power source, the battery in your truck will work. https://youtu.be/c9KNAIjoEYs

 

[mggmgm1]

The relay was actually a 30 amp relay and not a 15 amp relay and it was damaged in 5 days.

 

[whtbronco]

Then you have a rather serious problem if a 30amp relay didn't hold up. Test the current draw from the fuel pump. Also test and inspect the wiring for potential issues.

Another idea would be to visually inspect the circuit board the relay is soldered to. I say this because the electrical runs in it can connect over time. Or you could have messed it up while repairing it the first time, like I did. I mistakenly grabbed plumbing flux and after a little while the acid in the plumbing flux ate up the board causing an internal short.

 

[Martynka]

I am still not understanding how I determine if the fuel pump is drawing too much current?

Like this:

How to use multimeter to measure current amperes #shorts

#shorts #electrical #plc Please Subscribe to PLC Tutorials for more Videos and TutorialsPLC Programming Tutorials for beginners

www.youtube.com

but use 20A multimetr.

The relay was actually a 30 amp relay and not a 15 amp relay and it was damaged in 5 days.

We don't know how your pump works before you measure it.

Then you have a rather serious problem if a 30amp relay didn't hold up. Test the current draw from the fuel pump. Also test and inspect the wiring for potential issues.

Correct

 

[mggmgm1]

When I use a multimeter what numbers are normal and what numbers are abnormal?

 

[Martynka]

It should be few amps at idlle, but better to check it when driving because current draw is changed by temp and fuel flow.

 

[mggmgm1]

So I should be looking at amps and nothing else?

 

[Martynka]

So I should be looking at amps and nothing else?

yes. only higher amps can burn relay. High amper means:
- hard working pump
- electrical short circuit

 

[mggmgm1]

Thank you so much for that information. I suppose if the relay is burned, I can bypass it and just accelerate it to measure the amps and higher rpms since I can't drive it like that. Do you think that would work?

 

[Martynka]

Yes, you can measure it with bypass.

 

[mggmgm1]

Do you know how many amps are within normal range?

 

[whtbronco]

The stock relay is 15amp so I'd want to see no higher than 15 or 16amps. The newer relays are 20amp which helps prevent the relay from being at the design threshold of the 15amp.

 

[mggmgm1]

@whtbronco thank you very much for the amps considered to be in the normal range.

 

[mggmgm1]

@whtbronco I replaced the melted R303 relay and my Expedition worked for a couple days and then it failed again, my Expedition was not getting fuel. This second time I replaced the R303 relay and the fuel pump and my Expedition worked for a few months perfectly but it failed on me again, any ideas what might cause my Expedition to fail even with a new relay and new fuel pump?

 

[whtbronco]

The factory 15amp relay can barely handle the power consumption when new. As our trucks age the wiring has more resistance, grounds don't make contact as well, the fuel pump motor draws more power as it wears. You'll need to look into those to isolate the issue. Or install a 20amp relay either internal or external to the central junction box.

This thread has some info on the replacing the relay with internal or external relay. If I do it again I'll make it external since it's then super quick and easy to swap it out if needed.

Another fuse box replacement ....

Had the same problem with the same solution. Glad it all worked out for you.

www.expeditionforum.com

 

[mggmgm1]

Thank you so much for the advice, I really appreciate it! I will try the external relay.

 

[CertusExpo]

I’ve been putting off attempting the external relay modification for years. I’ve been using a jumper to power the fuel pump for years. My Expedition has been sitting unused for just over 2 years. I’m returning to the office and need to get Bonnie road worthy once again. There are several things I’ll be changing, upgrading, adding, etc.
This is the first one I’m doing and then swapping out all her fluids. I plan on documenting everything in a post.

For this project, I’ve decided on a relay with a built-in fuse. And that fuse will be replaced with a mini circuit breaker. I’m also going to replace the color coded pigtails with silicone shielded wire for the flexibility.

@whtbronco I’m also wondering. Those of you that used an external relay, how did you anchor it to take the strain off the soldered ends?

 

[CertusExpo]

Here's the circuit board relay connection points once you get the old fuel pump micro relay out of the way.

Did you end up using 87a?