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5.0 EFI Problem ~ Need some help

Sbolt19

Bronco Guru
Joined
Nov 8, 2005
Messages
1,098
Loc.
Colorado Springs
My Bronco was running fine until I brought the other one home :cry:

Well, the problem literally jumped up. I came home for lunch last thursday, running great, went to go back to work and she wouldn't start. After a weekend of trouble shooting, I am at a loss. At first, I thought that it was the fuel pump that went out. I have a lifetime warranty pump, so I took it back and that didn't fix the problem. It seems that there #1 isn't power getting to the pump. I traced out the wire, and ran it back to a relay. Thought the relay was bad and it seemed that was where the problem was, replaced that, no go again. So the wires in the relay are as follows..1 to fuel pump, 1 to a fuesable link on the battery side of the starter solenoid, 1 hangs free with nothing attached & 1 going into the EEC. I thought the relay was bad because I could hot wire the pump directly to the hot side of the solenoid and you can hear the pump. Well, when I do that, theroetically, it should start. All it does is just cranks and cranks. Step on the gas to give it a little and it kicks over and dies before the starter stops spinning.

I am not an EFI guru by any means, so I am pretty much at a loss and don't know which way to turn. What else could be going wrong and what should I look at before I take it to someone who knows what they are doing?
 

justinoshea

Contributor
Sr. Member
Joined
Feb 16, 2007
Messages
479
Loc.
Gilbert, AZ
A fuel flow test can be done by disconnecting the return line. Run the pump for 10 seconds by grounding the FP pin on the EEC test harness. Capture the fuel in a measuring cup. do the math, is it even close to the pump rating?
do you have a fuel pressure gauge? the return flow rating should be done with the fuel rails at operating pressure (35-40lbs)

stepping on the gas while cranking doesn't dump in fuel like a carb. Holding the pedal at WOT during cranking will 'choke' the engine and shut off fuel to the injectors.

Also check that the ignition and 'puter have power when the key is on, not just when cranking.
 
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Sbolt19

Sbolt19

Bronco Guru
Joined
Nov 8, 2005
Messages
1,098
Loc.
Colorado Springs
Fuel pressure is fine. That was the first thing I checked. I had a similar problem a couple of months ago and it acted almost identical to this and it was the fuel pump. That's why I thought it was the FP again, but I was wrong. Everything has power when the ignition is in the on position.
 

Ryan

Sr. Member
Joined
Aug 29, 2003
Messages
739
Loc.
Lansing, MI
Thought the relay was bad and it seemed that was where the problem was, replaced that, no go again. So the wires in the relay are as follows..1 to fuel pump, 1 to a fuesable link on the battery side of the starter solenoid, 1 hangs free with nothing attached & 1 going into the EEC.
Only 3 wires hooked up? Sound like the wire harness is screwed up near the relays
 
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Sbolt19

Sbolt19

Bronco Guru
Joined
Nov 8, 2005
Messages
1,098
Loc.
Colorado Springs
That is the way it has always been. I have had the EFI on it for about 5 years now and this is the first major problem I have ever had.
 

AZMike

Full Member
Joined
Feb 4, 2005
Messages
292
Loc.
Flagstaff
I've got a not-so easily seen fuse in the wiring harness under my hood that occasionally blows and disables the fuel system. In fact, it just happened to me on Saturday. You might want to double check that you don't have the same problem.
 

SaddleUp

Bronco Guru
Joined
May 23, 2004
Messages
9,655
Loc.
Vancouver, WA
As Ryan indicated 3 wires at the relay is a problem. There need to be 4 in order for it to be useful. 2 of them are to energize the circuit and the other 2 are to connect the circuit. On the side that energizes the circuit one will probably be from the battery and one from the ecm (The ecm provides the ground). On the other two one will be from the battery and one will go to the fuel pump. From the description it appears to be missing one of the hot wires. Probably jumped together at that point. Is it possible that the wire that is hanging free was jumped over to the other hot wire and just pulled loose?
 
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Sbolt19

Sbolt19

Bronco Guru
Joined
Nov 8, 2005
Messages
1,098
Loc.
Colorado Springs
As Ryan indicated 3 wires at the relay is a problem. There need to be 4 in order for it to be useful. 2 of them are to energize the circuit and the other 2 are to connect the circuit. On the side that energizes the circuit one will probably be from the battery and one from the ecm (The ecm provides the ground). On the other two one will be from the battery and one will go to the fuel pump. From the description it appears to be missing one of the hot wires. Probably jumped together at that point. Is it possible that the wire that is hanging free was jumped over to the other hot wire and just pulled loose?

No, like I said, I traced them out, and the one that is hangning is and has always done just that. There are two connectors where relays or another harness connection would have been on the donor car close to that area, but that is the way it has always been. There is also no other loose connections hanging right there that maybe should be connected. I have looked at this wiring harness hundreds of times before and there was never another connection at that loose end. Just so you guys know, I am not the one who installed the EFI on here, I had it done for me and have slowly been learning it. I am taking it into an auto electric shop tomorrow, it is my DD, so I gotta get 'er fixed. I will let ya'll know what the final problem was.
 
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