Fuel pump relay?

Tiny
NUKESDADDY16
  • MEMBER
  • 1999 FORD F-150
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 175,000 MILES
I am only getting 6.89 volts to the fuel pump after changing the pump itself all the fuses the fuel pump relay as well as ECM relay and the ignition module. I have also had the anti theft checked to ensure it is not the problem and it was not. I put a brand new battery in and still crank with no start. Where am I losing voltage and why am I not getting power to my pump? Help please God bless
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Wednesday, October 10th, 2018 AT 4:29 PM

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Tiny
CARADIODOC
  • EXPERT
There is a number of things we have to consider before starting the diagnosis. First, if you were measuring that 6 volts at the fuel pump's connector with it unplugged, that may be confusing the real cause of the problem. This would be similar to standing on a garden hose and blocking ninety nine percent of it. You would still see full pressure at the nozzle, as long as it was closed. No water is flowing, so no pressure is dropped across your foot. Voltage is electrical pressure. With the connector unplugged, no current is flowing, so no electrical pressure, (voltage), is dropped across some undesirable resistance in the circuit. This would suggest everything in the circuit is turning on properly, but there is a high-resistance connection or break in that circuit. To avoid this confusion, voltage readings should be taken with everything plugged in. Some connectors make that very difficult, but most have rubber seals around the individual wires where you can slide the voltmeter's or test light's probe in. Test lights are more accurate too for this type of problem because they draw current from the circuit. A voltmeter will give a false 12 volt reading when there is a high-resistance break that is preventing the needed current flow. Voltmeters confuse the issue because you have to interpret the reading. We are looking for 0.0 volts or 12.0 volts. Which do you have? 6.89 volts is neither. With the test light, you are much more likely to find something or nothing. The only way to get a bright light is for the circuit to have no breaks or high-resistance connections.

The second potential clinker is that feed wire to the pump is tied to the Engine Computer. The computer turns the fuel pump relay on, then the 12 volts that gets switched on goes to the pump, and it goes to the computer to verify it got turned on. Often the computer will send out a small voltage, then watch the resulting current flow, to verify the integrity of the circuit. Once the fuel pump relay gets turned on, the 12 volts that shows up makes that little signal voltage from the computer irrelevant. You could have a relay that is not turning on, meaning you would have 0.0 volts at the pump, but the 6 volts you are seeing is coming from the computer.

The biggest issue is you must find 0 volts at the fuel pump when the engine is not rotating, (cranking or running). That is the safety feature on all cars with electric fuel pumps. If a fuel line got ruptured in a crash, the pump would dump raw fuel onto the ground, creating a serious fire hazard. Instead, the engine cannot run with no fuel pressure, so it stalls. Once stalled, no signal pulses show up from the crankshaft position sensor or the camshaft position sensor. It is the lack of those pulses that tell the computer to turn the fuel pump relay off. What this means for you is other than for one second when you turn on the ignition switch, the fuel pump will not get 12 volts until you are cranking the engine. In fact, that one second can provide a clue. If you can hear the hum of the pump for one second when you turn on the ignition switch, that entire circuit is working, and there is no point in diagnosing anything in it. Often you cannot hear the pump over the noisy chime.

One more important point is did you check for spark? Too many people get hung up on the first thing they find missing, and forget to check for additional symptoms. Check for that first. If you do have spark, we will need to find where the voltage is being lost in the fuel pump circuit. It is not practical to have a helper crank the engine while you poke around in the circuit. Instead, remove the fuel pump relay, then gently insert a jumper wire between terminals 30 and 87 in the socket. A small stretched-out paper clip works well. Be careful to not use anything fat enough to stretch those terminals. That will cause intermittent problems in the future.

The ignition switch does not need to be on for this. The jumper will energize the circuit, and the fuel pump should be running. If it is, this entire part of the circuit is okay. If it is not running, now is the time to work your way through the circuit with the test light.
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Wednesday, October 10th, 2018 AT 5:58 PM
Tiny
NWILLEY
  • MEMBER
  • 1999 FORD F-150
  • 6 CYL
  • 4WD
  • MANUAL
  • 78,000 MILES
My truck does not start when it is hot outside - especially if parked in the sun.
If it is cool out (60's) it start fine and runs great. If it's in the 80's and parked in the shade it will start fine - if moved into the sun it will not start. If its 100 out it won't start no matter what.
I found that when the ignition is turned to on (engine is not running) and its hot out there is no buzz from the fuel pump. If its cool there is a buzz.
So I check the voltage at the plug on the frame rail by the fuel tank. When it will start it shots up to 12 or 13 volts. When it won't it only goes up to 7 or 8 volts.
Next I thought maybe it was the fuel pump relay. In the fuse box under the hood there were several relays that looked the same. I took the one for air suspension, which I don't have, and switched it with the fuel pump relay. This did not change anything.
I have tried starter fluid when it will not start and it runs briefly and dies.
One other thing I have done is sprayed the truck with water when it won't start. If its parked in the sun and in the seventies this will cool it down enough to start. If its any warmer this will not work. As you can probably tell I have been trying to figure this out for a long time. What should I try next?
Thank You in advance!
-Neil
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
JACK42
  • EXPERT
First be sure you have 12 volts a the relay feeds, if you only have 8 in it may only give 8 out. If ok, test the continuity (ohms) of the wire from the fuel pump relay to the inertia switch(under right side of dash) then test the same out to thepump right at the tank unit. You have a bad connection somewhere that is losing contact when it expands due to heat/load
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
NWILLEY
  • MEMBER
Thanks Jack, I tested everything and confirmed there are 12 volts at the relay feed. When the ignition is on there's 6.5 volts at the fuel tank and 6.5 at the inertia switch whether it starts or not. When the truck does start, at those spots the volts jump to the 12-13 range when the ignition is *initially* turned on. On the other hand, when its hot out and won't start, the volts only jump to the 7-8 range.
So my question is, what makes the voltage jump up to 12-13 when the ignition is turned to on? It seems like this is where the problem is.

The continuity is good in the areas you talked about. I tested the green wire from the fuel relay to the inertia switch and it passed. I then tested from the green wire at the relay to the red wire at the tank and this passed. So the green wire from the relay to the inertia switch is good and the red wire from the inertia switch to the tank is good. There are 3 other wires at the relay and I'm not sure how to test these. I can see that 2 go to fuses but then I'm not sure were they go from there? Other wires I'm not sure about are the 3 at the tank plug (Black, small yellow and small blue/white) and the one small gray/orange wire at the inertia switch.

What do you think I should try next?
Thank very much for your time Jack!
-Neil
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
JACK42
  • EXPERT
When itis only giving out 7-8 test the feed to be sure itis staying at 12 during this time. Also test relay power and ground and trigger to see what voltages are where and the resistance to ground at the relay when it is messing up
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
NWILLEY
  • MEMBER
Thanks again Jack,
Today it was around 100 degrees so all the tests I did tonight were with it not starting. At the feed there were 12 volts. At the relay power there are also 12 volts. At the trigger when the ignition is on there are 12 volts. And at the ground with the ignition on there are also 12 volts. I want to test the resistance to ground but I don't know how to do it -- can you describe how to test for this?

I had it parked in the shade and it started fine. Pulled out into the sun and it was 90 degrees out. Left it idling for 1.5 hrs and the temp went up to 100 during that time but it never stalled. I shut it off, waited a few seconds, and it wouldn't start. Not sure if these details would help diagnose.

Thanks again,
Neil
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
JACK42
  • EXPERT
Those are with it not starting? So it has 12 in but how much out to the pump when it wont start? Find the ground wire and use a meter on "ohms" setting. One lead plugged into the ground the other to the chassis or other known good ground to measure the resistance in the circuit
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
NWILLEY
  • MEMBER
Thank You Jack,
I think we are on to something! First to answer your questions: Those readings were with it not starting. Going out to the pump its 6.7 volts.

I checked the ground wire tonight and nothing happens it does not zero out. Just to make sure I was doing it correctly I tried it on another relay and this one did zero out. Next I spliced into the ground wire just below the relay and then grounded that wire to the motor. Resistance at the relay ground plug was then good. I turned the ignition on and the fuel pump came on but did not shut off like it should?

Where Does the ground wire go, and how do I figure out where the problem is?

Thank You for your time!
-Neil
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
NWILLEY
  • MEMBER
Hi Jack,
Well now that its cool enough, I went back out and the truck would start. So I re-tested everything and what I am assuming is the ground performs the same way when it starts. Now I'm not sure there is a problem with the ground.

The wire on the fuel relay that I think is the ground is kind of a blue color w/ an orange stripe.
On all the other relays the ground wire is black and when I check the resistance they zero out. The fuel relay ground doesn't do anything on the gauge when I test the resistance, whether it starts or not.
When the ignition is on - the power in on the fuel relay shows 12 volts, power out shows 0 volts, the trigger shows 12 volts and the forth wire which I think is the ground also shows 12 volts. This is whether it will start or not.
On the other relays the grounds show 0 volts.

I am now lost again!
-Neil
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
JACK42
  • EXPERT
According to my wiring diagram there are 2 lt blue/orange wires. One of them comes from fuse #10 and should be hot all the time, the other is the trigger from the PCM to turn the pump on.
Ther red wire is fed from the batt junction box"fuse 18" and should also be 12 volts.
The dark green/ yellow wire is fuel pump monitor, also for the PCM so it see the pump on or off. The PCM power relay feeds thefuse block that supplies the 12 volts, check for 12 volts at fuse 18 and the othrs in the same fuse block. The wire you grounded sounds like the trigger from the PCM that is why it wouldnt shut the pump off
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
NWILLEY
  • MEMBER
Hi Jack,
Fuse 18 and the others in that block show 12 volts. With the ignition on the green/yellow power out wire at the fuel pump relay reads zero volts. Whether the truck starts or not.
I was telling you the power out reads 6 or 7 volts, but that is only when I break the circuit somewhere such as unplugging it at the fuel pump. When its all connected it reads zero. Is that normal?
When the truck is not starting, and I initially turn the ignition on I get 3, 4, 5, up to 6 volts at the green/yellow wire at the relay. It then falls back to zero.
When it will start the green/yellow wire jumps to 11 or 12 volts and then goes back to zero. With the truck running the power out reads 13 or 14 volts.
Thanks for the help
-Neil
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
JACK42
  • EXPERT
Did the relay you tried have the same number of pins where the connector goes? According to my diagram that is the monitor wire(PCM) as well as the feed to the inertia switch(Fuel Pump), so if it isnt giving out a full 12 I would think the relay is the issue if all other feeds are in spec. Have you tried jumping terminal 30 (Power) to 87 (fuel pump) with a fused jumper wire when it is hot to see if it will start?This will basically by-pass the relay
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
SCHREPLOCK
  • MEMBER
Following this thread as I am experiencing a very similar situation with my 01 SprCrw 5.4 4x4, and I see a similar situation with the voltage at the fuel pump harness, key on 12 volts, second later 6-7, however I'm not getting the cold/hot issue, my truck just wont stay running period.

What I'd like to know is if it is possible that the CamShaft Position Sensor or crankshaft postion sensor could be bad and possibly telling the fuel pump to shut off immediatley.

I have no DTC's to indicate this is the probelm, yet if you turn the key on/off/on etc. The engine seems to get gas for a second then dies. I was getting ready to drop the tank and install a new pump, yet after finding this thread I may have to rethink it.
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
NWILLEY
  • MEMBER
Hello Jack,
Yes the relay has the same number of pins as the one I took out. They all have the extra (87a) in the middle that does not go to anything.
I tried jumping 30 (power) to 87 (fuel pump). When I hooked it up the fuel pump came on and stayed on. So I tried to start it but it still wouldn't run. With it jumped I tried testing the power at the pump and it was reading 12 volts.
Then just to make sure it would fire I spayed a little starting fluid in the intake and it did fire. I then tried this while jumping the relay and it fired but wouldn't start.
Does the PCM tell the relay to send power to the pump? If so I feel like this might be where the problem is?

Thanks again Jack,
-Neil
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
JACK42
  • EXPERT
Try your tester relay in place of the EEC relay. If it isnt getting any injector pulse it could be the PCM or possibly the relay that turns it on
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
NWILLEY
  • MEMBER
Hello Jack,
I am not sure which is the EEC relay, could this also be referred to as the PCM relay. I know I have had it in other vehicles but can't seem to locate it on this one or in any of the books I have on it?

I tested the resistance on the 2 wires that run from the fuel relay to the PCM (blue/orange & Green/yellow), and found they where both good.

The PCM relay seems to be working properly it has 12 volts at the power in, power out, and trigger. The ground is also good.
Thank you!
-Neil
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
JACK42
  • EXPERT
Yes, that is the PCM relay, Send me your email and I will shoot you all of the wiring diagrams for this truck so you can see what is tied into the fuel pump circuit
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
NWILLEY
  • MEMBER
Hello Jack,
I know it has been a while, but my truck still will not start when its hot outside. Thank you for the wiring diagram, I tested a bunch of wires. The latest thing I have noticed is that when it won't start the anti theft light blinks quickly, when it does start it shuts off. From what I have read it sounds like the PATS system shuts down the fuel system when its not cleared. Do you have any suggestions, is this something I am go to have to go to the dealer for? Could the heat affect the PATS module?
Thank you for your help.
-Neil
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
JACK42
  • EXPERT
Yes, I guess it would be possible for heat to affect the module. You will need the dealer or a shop with the software capable of programming the module
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Tuesday, September 8th, 2020 AT 12:36 PM (Merged)
Tiny
USMCRETIRED50
  • MEMBER
  • 1999 FORD F-150
  • V8
  • 2WD
  • AUTOMATIC
  • 98,000 MILES
I turn the power on and I went to the fuel pump, to check the power and found no power to the wires. The fuse is good and the relay is good too. And check the safey switch to and is good too.
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Tuesday, September 8th, 2020 AT 12:37 PM (Merged)

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