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The fuel pump does not run. Less than 7 volts to fuel pump?

Tiny
CUNNINGHAM587
  • MEMBER
  • 2003 FORD F-150
  • 4.2L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 277,000 MILES
No fuel pressure at fuel rail. The fuel pump does not run. Less than 7 volts to fuel pump (battery voltage 12.4). Jumped terminal 87 to 30 and read battery voltage at connector to fuel pump. I bench tested the PCM relay and fuel pump relay. Relays are okay. Checked terminals for PCM relay at relay base with my logic probe. Signal at all terminals. I checked the terminals for fuel pump relay with my logic probe. I found no signal at relay terminal #85. It seems I am losing ground somewhere. I have not traced the wire from terminal 85 at relay base back toward the PCM. I a very basic wiring diagram from a Chilton manual that only shows the general layout with no specific details. I plan to check from fuel pump relay terminal 85 to PCM I(hopefully today, weather permitting) I would appreciate any helpful advise.
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Sunday, March 15th, 2020 AT 10:50 AM

24 Replies

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

Pin 85 goes to the PCM and the PCM provides ground to the control side of the relay to energize it to close the power side of the relay to allow current to flow to the fuel pump. The wire going from pin 85 would not be the problem. The problem is going to be in the wires going from pins 30 and 87. There is excessive resistance somewhere in this part of the circuit. The best way to find this is with the voltage drop method. In the diagrams down below I have included the engine management wiring diagrams for your vehicle as well as a guide explaining how to find excessive resistance in an automotive circuit using the voltage drop method and a diagram of a typical 4 pin relay for you for reference. Please go through these guides and get back to us with what you find out.

Thanks,
Alex
2CarPros
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
I agree that this sounds like the PCM is not grounding the relay but have you checked for a crank sensor signal to the PCM? If you don't have this signal the PCM will not signal the grounding of the relay.

Let me know and we can go from there. Thanks
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
BMDOUBLE
  • MECHANIC
  • 1,139 POSTS
Here's my version of a quick test. Let me know if you need more help!
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
CUNNINGHAM587
  • MEMBER
  • 11 POSTS
Hello,
I want to first start thanks to the replies. With what’s happening in the country and with poor weekend weather I have not had much time to check everything necessary. I did have a small window of time between thunderstorms to check a couple things. I tried bmdoubles quick test by jumping 87 to C145 (if C145 is the left connector block in the photo) I ran a jumper wire from 87 to pk/blk wire I relay side of connection. Voltage still low (+- 9v) at pump connector. I then jumped from 87 at relay terminal directly to pink and black wire to fuel pump. No luck. I checked for signal to the crank sensor as KASEKENNY1 suggested and had 0 voltage. No voltage when key cycled on and nothing during cranking. It started to rain heavily not allowing me to check anything else include the suggested voltage drop test (s).. I should have seen battery voltage at the Crankshaft sensor correct?
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
So it appears you have what is called a non floating inductive crank sensor. Non floating means it is grounded and voltage is applied to one side of the sensor and the signal return is the other side which is what the PCM uses to determine engine position.

The picture that you provided, is that of how you tested for voltage on the CKP sensor? I just can't tell if you used a safety pin through the wire or something else.

If so, which wire are you on?
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
CUNNINGHAM587
  • MEMBER
  • 11 POSTS
I did not check voltage for the crank sensor there. I checked directly at the connector to the sensor with a volt meter. There was no voltage key on or cranking. The photo was to show what I thought was connector C145. Sadly yes that’s a safety pin(I couldn’t find my wire piercing probes ). Probably not the best method but nobody locally sells these on Sunday. I jumped terminal 87 at the fuel pump relay base to the pink and black wire at C145. I then jumped the same green yellow wire at terminal 87 directly to the pink and black wire at fuel pump. I am a mechanical hydraulic technician. It has been a while since I worked in the automotive industry and electrical systems were certainly not my strengths. Forgive any of my ignorance.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
KASEKENNY
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No problem. A safety pin works just make sure you cover those punctures with nail polish so you don't have a corrosion issue later.

As for the crank sensor, clearly we need voltage on that sensor so I would just double check for voltage while cranking on both wires if you didn't do that already. If you have a lab scope then lets check the pattern. I attached a known good pattern of it running and then one while cranking. Being a hydraulic tech you may have access to this so if you do, let me know and we can go down that route if you need help with it.

The first attachment talks about the possible causes of not having a signal back to the ECM. I would suggest removing the sensor and checking for debris or anything that may be between the sensor and the tone wheel causing no signal.

Then I attached a test that we need to do for the crank sensor itself. This will run you through all possible wiring issues, sensor, or PCM itself.

Let us know if you have questions and what the results are. Thanks
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
BMDOUBLE
  • MECHANIC
  • 1,139 POSTS
Woah nelly! So if you have low voltage at the pump, then we need to either trace that power circuit or run a new wire from the relay to the pump. The crank sensor will produce a low voltage a/c signal more than.3v but less than 1.0v. If your tachometer is registering while cranking the engine, the crank signal is good, just saving you some time chasing your tail. Do you live in the northern states? (Rust belt).
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
CUNNINGHAM587
  • MEMBER
  • 11 POSTS
Hello,

I will have hopefully have some time tomorrow to continue on the 03 F150. Should I see battery voltage (DC) to crank sensor when key is turned on and a/c voltage when cranking? Last week when checking for voltage I did look for any debris at the pulse wheel and it was clean/clear. I did check voltage when cranking and not cranking. I do not have access to a lab shop anymore. To answer BMDOUBLE is do not live in the rust belt. I live in southeast Texas.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
BMDOUBLE
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There will not be any battery voltage at the sensor at any time, only an alternating zero to one volt signal. If you have a scan tool that has the capability of seeing pids/sensor data, you could select the rpm data and verify that it is registering rpm's, this is the easiest way to verify crank signal other than looking at the rpm gauge on the dash.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
CUNNINGHAM587
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Good morning,

I did check the crank sensor with my scan tool. I do have signal.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
KASEKENNY
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Sorry for the delay. Good idea with checking for RPM signal. I didn't even think to ask if you had a scan tool.

Let's circle back and answer bmdouble's question/statement -

"So if you have low voltage at the pump, then we need to either trace that power circuit or run a new wire from the relay to the pump."

From what I am seeing, I suspect we have high resistance in this circuit. Have you unhooked it from both ends and just measured resistance (ohms) on this wire alone? You should only have about a half ohm of resistance on just the wire.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
CUNNINGHAM587
  • MEMBER
  • 11 POSTS
I followed the harness from the fuel pump, along the frame, to the connection under the air filter housing. I checked the resistance on the pink and black wire from the fuel pump connector to the connector under air box. This measured.1 ohms. Measured pink and black wire at connector under air filter housing to connector at expansion tank. This reading was also.1 ohms. Followed the harness from this point to the connection at left fender/firewall area (C145?) I measured the pink and black wire and also read.1 ohms. I ran out of time to follow from the firewall to the interior (not sure where it leads to). I did check voltages at the relay base again. Battery voltage at this time was 12.4V.

PCM relay terminal 30= 12.4V; terminal 87=12.4V; terminal
86= 11.2v with key cycled on, 9.5 cranking.

Fuel pump relay:
Terminal 30=12.4v.
#87=11.65v key cycled on. 10.1v cranking
#86= 12.17v with key on (10.3v when cranking)
Read 10.6v at pink/black wire to inertia switch (back probed)
11.1v at green/yellow wire at inertia switch. (Back probed).
I should have some more time this weekend to continue. Thank you guys for all the assistance.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Clearly we are losing voltage somewhere. Have we checked the basics and load tested the battery?

https://www.2carpros.com/articles/car-battery-load-test

If the battery can't carry a load then it will drop in voltage when a load is put to it.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
CUNNINGHAM587
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  • 11 POSTS
Yes. The battery is new (approximately 2 weeks old). It has been load tested since purchase.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
KASEKENNY
  • MECHANIC
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Okay. Then based on your previous information, the PCM relay you are getting 9.5 volts on pin 86. That is what feeds the coil. I understand that you will not start but try unplugging the coil and then cranking the engine and taking all the same measurements.

Based on this, have we confirmed that this a fuel issue and not a spark issue? Try using starter fluid with everything hooked up and see if it starts. If not, pull a plug and connect the plug wire and hold it against the block then crank the engine to see if you have spark.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
CUNNINGHAM587
  • MEMBER
  • 11 POSTS
There is zero fuel pressure at the rail (Schrader valve). Not even a dribble of fuel. I did check for spark in the beginning. Then I checked for fuel pressure at the rail and there wasn’t any. I will check again (spark)as you instructed to be sure. I’m thinking it might be a good idea to check the positive cable to battery. I have not checked that yet.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
KASEKENNY
  • MECHANIC
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Okay. Sounds like a good plan.

No fuel at rail is pretty clearly a fuel issue. I would just start with spraying fuel in the intake with everything hooked up and see if it fires. If it does then you know the ignition side is fine and able to fire. Could still be the coil shorted but if it is able to fire the engine then we can assume it is okay but it is worth unplugging and trying the measurements again while cranking.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
CUNNINGHAM587
  • MEMBER
  • 11 POSTS
Voltage drop on cable shows okay. Checked ignition visually okay. Sprayed fuel in intake and engine fired. Spark is still good. I ran a jumper from terminal 87 at fuel pump relay to pump (pink/black wire) and engine attempted to start for a brief second. Cycled key and cranked again with jumper in place. No results. I ran out of time for today.
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Wednesday, January 20th, 2021 AT 10:11 AM
Tiny
KASEKENNY
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Based on that, I suspect the pump has failed. I scanned back through this and I don't see where it was replaced. Did I miss that or have we not done the fuel pump?
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Wednesday, January 20th, 2021 AT 10:11 AM

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