Can I hook fuel pump up direct? Permanently? | Ford Explorer Forums - Serious Explorations

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Can I hook fuel pump up direct? Permanently?

Malchi

Well-Known Member
Joined
August 6, 2010
Messages
103
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1
City, State
Ontario, California
Year, Model & Trim Level
'91 X 4x4
Ok, here's my scenario.

91 Explorer has been having trouble with fuel pump not working. Usually if I keep trying it will work after a bit. Finally just quit altogether. I just replaced fuel pump (cut hole under seat method worked absolutely wonderful!) since I know fuel gauge was out and it seemed the check valve was bad as well. After replaced fuel pump, truck started right up and worked great for a week, maybe.

Then it started having same trouble again. Yesterday it just quit altogether. Parked it for a bit and when I came back it would not start. So, after researching on this forum, I found to check for 12v at pump, only getting just a little under 8v. Checked at inertia switch, only about 8v going to switch.

PCM I assume?

Anyhow, in my distress of needing to get truck home I decided to pull a fuse out of fuse panel ( chose one that only works with key on) , took a piece of wire, put a spade on end of it and plugged that into the fuse panel, then cut the wire coming from the inertia switch and spliced wire into it. Then, when I turned on the key, fuel pump came on as well. Truck started right up. Drove it home and when I turned off key, pump turned off. But, I unplugged it just in case. :)

So, my question is this. First, any idea what the problem is? ECM? Or what? Also, can I just hook this up permanently? Or, at least till I find the problem and fix it? I need this as my daily driver for work.

Any help would be greatly appreciated.
 



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Mine is hooked to a toggle switch, sometimes it works without using the switch most of the time it doesn't.
 






The problem could be with the fuel pump relay. The connections where it plugs in ould be corroded, or, the relay itself could be turning off due to a bad coil inside it.

If this check out pul the ecm , remove the cover and look for bad solder joints on the PCM.
 






The problem could be with the fuel pump relay. The connections where it plugs in ould be corroded, or, the relay itself could be turning off due to a bad coil inside it.


The relay is clicking. I always assumed that meant it is working. Am I wrong here?

If this check out pul the ecm , remove the cover and look for bad solder joints on the PCM.

Ok, I will look for that.

Thanks, Turdle.
 






It may be clicking, but the internal contacts could be bad, or, the coil might fail under heat in which case the contacts will open. Just because a relay or solenoid clicks or moves, does not always mean it is functioning correctly.
 






It may be clicking, but the internal contacts could be bad, or, the coil might fail under heat in which case the contacts will open. Just because a relay or solenoid clicks or moves, does not always mean it is functioning correctly.

I didn't know that. Thanks again.
 






Of course, the reason why the circuit is designed the way that it is, is to prevent the pump from running in an engine off condition. Otherwise, a leaking injector could fill the engine with raw gas. That's pretty much if and when the key is in the on position but the engine is not running. Maybe you turn the key to on to roll down a window or something.
 






I wouldn't hard wire the pump to always be on. You'll burn it up, especially idling in traffic. I haven't looked at the relay in a while but I believe it is a double throw, and the low current coil probably doesn't need much more than 8V to activate (or less). Make sure the contacts are good, and check that ECM, but I'm willing to bet it's the relay.
 






I wouldn't hard wire the pump to always be on. You'll burn it up, especially idling in traffic.

So you are saying that the system is designed to shut the pump off at times even when engine is running? That's what I was wondering.

I will check the relay as soon as I get opportunity. Hopefully Monday evening I can get a chance to do that. I am assuming I just check to make sure one of the wires has 12v only when the relay should be activated?
 






Yes exactly. The pump shuts off when the pressure has reached a certain point and will turn back on when it falls below a different point. This is essentially done to reduce the duty cycle on the pump. It has 1 speed, on, but you don't use the same amount of full in idle as you do cruising down the freeway, or accelerating. I might be wrong but I believe some high end cars (probably Benz) has a multi speed pump so that accelerating when you use the most fuel it runs at one speed and then cruising it runs at a different speed.
 






Ok, I know it's been a while, but I have been too busy to look into this and so it still doesn't work.

Today i checked the Relay. There are 4 wires coming from the relay. One is a ground, and the other is a constant 12V. The other 2, a red one and an orange/black one. Both of these two are dead with Key Off, but get 12V with Key On.

I assume this means my Relay is good. So, with that said, I checked again at the connector for the Inertia switch and with Key On I only have about 6V, also at the Fuel Pump I only have about 6V.

I assume that the next step is the ECM. So, I will try to locate that and take a look at it.

Anyone got any other ideas at this point?
 






Yes exactly. The pump shuts off when the pressure has reached a certain point and will turn back on when it falls below a different point. This is essentially done to reduce the duty cycle on the pump. It has 1 speed, on, but you don't use the same amount of full in idle as you do cruising down the freeway, or accelerating. I might be wrong but I believe some high end cars (probably Benz) has a multi speed pump so that accelerating when you use the most fuel it runs at one speed and then cruising it runs at a different speed.

I'm afraid I have to disagree. The fuel pump does run full time so long as the computer determines the engine is running. You can verify this in a couple of ways. First, the fuel pump relay does not cycle, it stays on. You can put your finger on the relay and verify this. If you look at an actual pump, there is no pressure sensing mechanism. In fact, there is no fuel pressure sensor anywhere on the system. It depends on the fuel pressure regulator to bleed off anything over 30 psi.
 






Ok, I know it's been a while, but I have been too busy to look into this and so it still doesn't work.

Today i checked the Relay. There are 4 wires coming from the relay. One is a ground, and the other is a constant 12V. The other 2, a red one and an orange/black one. Both of these two are dead with Key Off, but get 12V with Key On.

I assume this means my Relay is good. So, with that said, I checked again at the connector for the Inertia switch and with Key On I only have about 6V, also at the Fuel Pump I only have about 6V.

I assume that the next step is the ECM. So, I will try to locate that and take a look at it.

Anyone got any other ideas at this point?

Are you doing this with the engine off? The ECM only energizes the pump for about a second, once you turn the key to ON. You can jump a contact from the diagnostic connector to ground, and then turn the key ON to make the pump run while the engine is not running. Then, you can test voltages as you have done.
 






Are you doing this with the engine off? The ECM only energizes the pump for about a second, once you turn the key to ON. You can jump a contact from the diagnostic connector to ground, and then turn the key ON to make the pump run while the engine is not running. Then, you can test voltages as you have done.

I was testing it with my Wife turning the key on and off for me.

Do you happen to know what contact to ground for this to work?

Also, I just pulled the ECM out and removed the cover and everything looks great, inside and out. Connector looks great. I can see no problems at all with the ECM.
 






ok, I found the wire. It's the light blue/orange wire on the diagnostic connector. I grounded it out, and everything is the same. I am actually fluctuating from 6-8V.
 


















Subscribing,
I always thought the pump ran continuously, I decided that after I had a wierd pump noise going on whenever the engine was running. Anyway it always seemed to be on whenever I listened for it, but I always wondered if it ever did shutdown.
 






Ok, went to the local pick-a-part and grabbed a relay. Popped it in, hooked up the wiring back to the way it is supposed to be, and she cranked up and ran just fine. For about 2 miles. Then, sitting at a traffic light she died and would not start till I hooked the fuel pump back up to my jimmy rig switch.

So, either the relay was bad already, or I have a problem that is blowing relays. Any more suggestions? I figure, at $5/pop, I'll just run to the local pick-a-part again tomorrow and grab another relay and try it. If it does the same thing, then I have a problem. No?
 



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i had the same problem on my ranger it happend to be an electrical problem so what i did was just run wires from the fuel pump to the switch and battery and worked just fine after that..
 






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