OK all, I haven't been working on the truck much this summer, been short ont time and funds.... LOL The story of my life. What I have done is this. I wanted to be sure that I had not damaged anything when I hooked all my wiring back up, and the relay wires were pretty atrocious so I pulled all my harnesses and checked the wires. I saudered everything that was broke/cut (I found 2 wires that were broken) then put everything back together nice and tight and everything repaired. I then checked that everything is working, Lights horn, Turn Signals, Heater, Radio etc.. Pretty much everthting electrical ssems OK. BUT I get no fuel pumps. The truck turns over well, just no gas. When I check my relays (Fuel Pump Relay & EEC) all the power seems correct EXCEPT the Green tan line from the EEC. When I check this with my multimeter it just cycles numbers. When I turn the ignition switch on the numbers just speed up, but I get no power out to (brown wire) that goes to the Inertia Swirtch. It sounds to me like the EEC Computer is bad, ( I just bought a new one, but it may have got shorted) Is there anyway to determine for sure? I am thinking about running a hot wire to my fuel pumps to see if the truck will start if it gets fuel. Any ideas?

 

Does the fuel pump relay pick for one second when you turn the key to run and then drop back out?

 

Whwn you say pick do you mean activate?
Here is what I have..
Constant power, (yellow) on EEC and Fuel Pump Relay,
Ingnition Power when switch turned on (wHITE/Blue Stripe)
Power from Fuel Pump relay to EEC relay (Red)
NO Power out on Brown line (to inertia switch)
How can I test my eec to sii if it is grounding the Low circuit?

 

Ground the fuel pump test port on the eec-iv test connector. Turn the switch on and see if pump runs. If it does then the PCM or the wire going to it from the fuel pump relay for the fuel pump has a problem. All The PCM does is ground that wire when it sees the engine turning over and it runs for 2 secs when the switch is first turned on. I have seen the driver in the PCM go bad. I have ran the fuel pump with a toggle switch to ground until I could find a replacement PCM.

 

Thanks SUBFORD, I will try it tomorrow. just to be sure, when you say ground, you mean run a ground wire to the test port, right

 

Yes the common term for the relay closing or changing state with persons working with relays is that the relay is picked.
I did work with relay logic for many years as an electronic tech.
Saying activate may not mean that the contact in the relay is in the state you want it in.

Grounding the self-test pin #6 by either shorting it to pin #2 or grounding it to the engine block or brake line and turning on the key should pick the fuel pump relay and put power on the wire going to the selected fuel pump.



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OK, When I jump the EEC test as you show, I do get power out on my Brown line from the relay to the inertia switch. I then went to check the inertia switch because I did not hear the pumps running, and the wires were very hot...(starting to smoke) so I killed the power. I have already replaced those wires once, the Brown wire leaves the FPRelay and goes through the round connector in the firewall, the line leaving the inertia switch goes back out through that round connector to the wire harness to the pumps. I don't think it connects to anything else (EEC) once it leaves the inertia switch. So I am not sure why there is so much power on the line to the inertia switch. I checked voltage, I am getting 11.75 (the battery is a little low) leaving the relay to the Inertia Switch, The line in the interior going to the Inertia switch is showing 11.75, There is no power at the pump, so I think when I hooked the Outgoing line back up in the firewall connector, i put it in the wrong location. I can cut that out and run it directly out to the harness going to the pumps, BUT there is no power coming out of the Relay unless I jump the tester (as you showed) so I am thinking the computer is dead/shot. What do you think?

 

If you get power out of the fuel pump relay by grounding pin #6 and not for one second when you turn on the key then either the computer is bad or it does not have a ground (pins 40 & 60) or no power on its power pins (1, 37 & 57).

Not sure what year you are working on so I will not post a wiring diagram.

 

Yes, Without jumping the Tester I get nothing out of my relay....I tried several beacuse I wan't sure if my relay was bad or not. As soon as I jumpered the tester I got power out. The truck is an 89 F150 Custom, 4.9L EFI Now that I know it isn't grounding, then that meane it is eaither the Wire going to the computer, or the computer itself, Correct? Is there a way to test to determine which it is? I have tried to find a PIN-OUT digram for the computer (and the firewall connecton as well) but I can't find one, I have been told if I buy the shop manual they have them there.....

 

No it is not in the shop manual, I have the 1989 Ford shop manual.
You would have buy the big fold out 1989 f-series diagrams to get the pin-out for the big round fire wall pin.
If anyone has one they do not seem willing to post it or share it.

As far as the computer goes this one is for a 1990 7.5L but pin #22 is in the same place and you can get the other end at pin #6 of the self-test plug.

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You need to figure out where your short is in the line from the FP relay to the inertia switch to the pump. It is pretty easy to by pass the inetria switch for testing purposes. An ohm meter should tell you what is going on. Disconnect the pump and test the circuit.

 

Ok, thanks a lot for the Pin out! That does help, (and is impossible to find). But I guess the "Million $$ Question" Is how can I test it? I am pulling the line leaving the inertia switch to the pumps today, beacause the Line coming from the Fuel Pump Realy is getting exactly the same voltage at the inertia switch as it has when it leaves the relay. Which leads me to believe that the line exiting the Inertia switch is pulling in power from somewhere. (As I said I replaced it in the Connector, and I may have put it in the wrong location) I don't think I did, but I cannot imagne why the lines at the inertia switch get so hot with 11.75 coming in on one line. I didn't get any power on the other line, BUT I don't think I checked it with the tester Jumped and key on. I need to verify that. Does it matter which wire connects to which side of the Inertia switch? I know it matters everywhere else, the Inertia switch could be the issue but I haven't checked it, not sure how I could.

I did run a wire directly from the battery to the pump to see if I could get anything, but the Pumps did not work, I just got spark at the battery. I have checked both the ground and hot wire going to the pump and neither have power right now.

Once I get the power down to the Inertia Switch, and then the Pump, Most of the problem is fixed. BUT how can I test my computer to see if it is the problem or the wire between it and the relay is the problem? If I can verify the wire to the relay is good, then that pretty much brings it to the computer. (RIGHT?)

By the way, thanks for all the help guys! I had thought about switching over to a Carb, but I guess I am kinda stubborn. I would REALLY like to keep this as original as possible, and I guess, kinda win the battle and fix the issue... I guess learn a little more along he way as well. One thing I'm going to do is take a class on reading wiring digrams, and understanding what my Multi Meter is telling me. I know the basics, but I think this would be so much easier if I were "Fluent" in Electrical diagrams, and Multi Meters... Thanks Again....

 

Sounds like you have a short to ground in the wire running from the inertia switch to the pumps or a short in the pump motor.

I would remove the wire leaving the inertia switch and going to the pumps.
Unplug the computer and ground pin #22 at the computer plug. Turn on the key and if you have power at inertia switch if so you will know the relay and the wiring under the hood are OK.
If OK turn off the key and plug the computer back in. Now check to see if you have power at the inertia switch for one second each time you turn on the key. If so the computer is working OK as far as the fuel pumps are concerned.

Now turn the key off and disconnect the wiring at non running fuel pump. Put the wire back on the inertia switch. Ground pin #6 at the self-test plug and turn on the key. Do you have power a the fuel pump plug. If so remove the pump and bench test it. If it does not run and you get a big spark replace the pump and install the replacement pump.

 

Here is a start on reading Electrical diagrams.

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OK, I unplugged the Computer and grounded PIN 22, as soon as I turned the Key I heard the RELAY "Click" So I pretty much knew that was the issue BUT I checked voltage coming into the Inertia Switch and it was 11.68, (which is what the battery is putting out right now) when I reconnected the computer, the Relay did not click/trip and I had no voltage at the inertia switch.... So I believe I have identified problem # 1, I will check the FUel pump later this week, I need to leave he house now, but I will pull that computer and try my old one one time before I order another new computer. I am just glad that I now know my harness is good. It was in good shape when I got it except for the Relays which had all been cut up....Now that they are repaired, everything seems to be working well but I need to get the computer working and then hopefully I will be on the road. I am very pleased about this! I know it may cost me a little money, but figuring out the probelm really makes me glad! I would like to have it on the road this fall, and now that may be possible. Thanks fr the help. I will let you know what i Figure out on the pump.