Fuel pump electrical?

ATOMICDR

MEMBER
1990 FORD F-250
5.0L
V8
4WD
AUTOMATIC
126,000 MILES

Had a mechanic install a new fuel pump and rear gas tank in my truck. Had low voltage to the pump, figured that out (fusible link issue). Along the way to diagnosing that issue managed to knock out the ignition (turn the key on but no lights, no juice to the starter). Figured that out. Now engine turns over and have fuel pressure at the rail but seems the injectors are not opening. He believes it may be another electrical issue. He needs a better schematic to find the connection between the ignition and the injectors.

NOTE: prior to the fuel pump going out the truck ran fine. The battery is fully charged and there's plenty of fuel in the tank and the fuel selector switch is working properly.

Anybody else ever run into this scenario before? Thanks a 3/4 ton for any helpful advice.

7 Replies

JACOBANDNICKOLAS

MECHANIC
109,253 POSTS

Hi,

I attached the wiring schematic I have, below. As far as this issue is concerned, these don't all happen by replacing the pump. Do you hear the pump operate when you first turn on the key? I ask because the fuel pump relay gets power from the same location as the injectors.

Let me know. Based on everything you mentioned, we may have an issue or a damaged ECM. To me, it sounds like something was shorted and caused a few different failures.

Let me know if the pic helps.

Take care,

joe

See pic below.

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Saturday, May 25th, 2024 AT 7:39 PM

ATOMICDR

MEMBER
40 POSTS

Thanks for getting back to me so quickly. The schematic helps. New info: I erred when I stated that the fuel pump was working when the key was on. Apparently he (my mechanic) had already run a bypass wire from some other source of power located behind the kick panel on the passenger side directly to the fuel pump wiring. That's when he determined that the pump was working. He now needs to make power to the pump and injectors from the ignition. Does that make any sense? I hope I described the problem adequately.

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Tuesday, May 28th, 2024 AT 6:19 AM

JACOBANDNICKOLAS

MECHANIC
109,253 POSTS

Hi,

Yes, that does make sense. However, before we jump the gun, tell him to switch the EEC relay with a different one having the same part number. If this relay fails, you will lose spark and fuel.

I attached a pic below showing its location. Also, have him check to see if there is spark to the plugs. If there is no spark, this is my first suspect. If there is spark, see if the inertia switch needs reset. See pic 2.

I noted that there are fusible links that may have failed as well. See pic 3. He can remove the fuel pump or eec relays and check if there is power to them as well. If there is, have him also check if the inertia switch has power. In pic 3, I highlighted how the primary side of the fuel pump relay gets power from the EEC.

Let me know what you find.

Joe

See pics below.

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Tuesday, May 28th, 2024 AT 7:39 PM

ATOMICDR

MEMBER
40 POSTS

Hey guys,
Sorry for the delay in getting back to you. My mechanic has been on hiatus from my truck issue for a while. Here is what I now know. He believed he may have crushed the wiring harness between the frame and the fuel tank. He checked that out but made no comment on his findings. We have power to the ignition. Turn the key, engine turns over. All dash lights function properly. He says he has proper voltage to the pump. He appreciated your wiring diagrams. One side issue; the wires and colors of the truck harness do not match the pump harness. He's tried various configurations and believes he has it right. With the key off, I turn to the "on" position. No sound of the pump working, don't feel any vibration from it working. Any ideas?
I have a question myself. Do the Fords of that era also have like GM an oil pressure sensor that can prevent the vehicle from starting? Just curious.

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Tuesday, June 18th, 2024 AT 2:11 PM

JACOBANDNICKOLAS

MECHANIC
109,253 POSTS

Hi,

No to the oil pressure switch. However, when you first turn the key to the on position, the pump should prime. If he has both power to the pump and a ground, it should work unless the pump itself is bad.

Also, the pump should have a connector that is already wired properly. I'm not sure why he would need to change that.

Confirm power and ground. If you have both, the pump or whatever he has done to the wiring is the likely issue.

Let me know if there is anything else I can do to help.

Take care,

Joe