Having some issues ( 3 ).

1) Charging circuit not working properly. Alternator checked out fine, but not charging battery properly. Checked wiring - seems to be ok. Green wire w red stripe - not energized with key on - goes to alternator.

2) Fuel pump circuit not working (no signal back to fuel pumps). Power to fuses, power to relays (not sure if signal getting past relays properly). NO signal to kick panel switch (forgot what it's called) trips when vehicle in accident.

3) My "check engine light" does not illuminate on dash when key turned to on position and cannot retrieve any engine codes. I wonder if computer is fried ? Sometimes grounds can produce problems, not sure if this relates to this one.

4) Could problems # 1 and # 2 be caused by # 3, or are they truly independent circuits ?

Some short background, I was driving on highway when charging normally went down to about 9 amps, drove the truck until it quit, then had it towed home. At that point was able to start and move it (with a jump). Then lost fuel pump pressure, then noticed the check engine light problem.

Any direction appreciated. Happy new years ...

 

Sorry guys, forgot to mention 1994 F150 5.0 litre 4 wd.

 

I would suggest that you start out checking your grounds and battery cables. You probably have a ground strap that goes to the engine. Check that for sure. Also, check fuses.

I'm guessing that something in the wiring let go while you were driving. It may have gotten worse.

Your computer gets its power through a relay( and probably a fuse). The fuel pump will not work if that circuit is out.

The autozone website probably has an engine wiring diagram. It would be a good reference.

 

Id even try the relays,If the check engine light is not on when u turn key to run, theres no computer power and When i had a corroded wire goin into my eec relay the fuel pump did not run and the check engine lite was off.

 

Thanks guys for your responses so far. I also have a 92, only difference is that truck has a manual trans - but there are some differences in fuseboxes as well. Anyways, is there a way to test this diode ? I exchanged it with the other trucks, no change. Also the relays, is each one different ? Or are they all the same (and interchangeable) ?? According to the (internal wiring) diagram on the side of each one and the ford part # s on the top, they are all the same. I did test for incoming power up to each of the relays (with them removed) and noticed the power coming in could be in different pins (from 1 relay to another). Also one relay had 2 wires hot coming in. Does any of this sound unusual ? Also, how would I test these relays ?

Thanks again for your help.

 

I'm not great with auto electrical, but I usually manage to stumble my way thru it. I know that if the greenwire with red stripe is not hot, your alternator will not charge at all. I THINK the green with red strip wire going to the alternator should be hot with the key on, irregardless of a bad computer or faulty ground. Is it possible your ignition switch is not working correctly? The alternator circuit runs thru the instrument panel. Have you had this apart or swapped recently? Maybe bad connection on the panel?
I test the relays by holding them in my hand while an assistant turns the ignition on and off. If they click they are working.
Good luck Frank

 

Frank:

Anything is possible. Until yesterday haven't had dash apart, but checked and changed 2 non working bulbs (to rule out that problem). Guess it's possible that I have an ignition switch problem. What I still do not know is - the total circuit for this wire. Perhaps I need a professional tech manual showing all the wiring ? Autozone and Chiltons doesn't give a complete picture ... Maybe the computer get's a signal from the switch as well ?

 

Frank:

Regarding a relay, how do you hold it in your hand and check it ? Needs to have power to it in order to work - perhaps a jumper wire to the proper energized leg ?

 

I just leave the relays connected and turn the ignition off and on.
Mine are mounted on the drivers side inner fender next to the air filter box. They slide up into a black plastic sort of box. I just side them out and they have a few inches of wire that allows me to hold on to them. This doesn't check the connections going to the fuel pump, but it does check the incoming connections and the function of the relay. If the fuel pump relay clicks the other relay, and wiring for the computer is ok. Actually when you turn the key to on, the fuel pump relay and the other relay both should click , then 2 seconds later the fuel pump relay clicks again when the computer turns the pump off.
Good Luck
Frank

 

"Maybe the computer get's a signal from the switch as well ?"

Do you mean from the ignition switch? It does get a signal from the ignition switch.
That is why I ask about the ignition switch, seems to me every problem you described runs thru that switch. The ignition switch is adjustable. You can loosen the two bolts and slide it up or down the steering column to get it adjusted right.
I hope I am not pointing you in the wrong direction. It could be a bad ground or corroded connection, but I can't think of where the computer, fuel pump, and alternator all share a ground or connection except the ignition.
Frank ps I warned you I tend to stumble thru my electrical problems.

 

Alrighty Frank, mine are fixed in a holder, but I do have one of those stethoscopes, perhaps I could check for clicking in that manner. I just cleaned a couple of frame to body ground straps, no luck yet, couldn't find an engine to frame or engine to body ground strap. That seems odd. Seems that the only ground is between engine and battery which grounds to body by a small wire.

Does anybody have a 94 with the 302 and familiar with an engine to body/frame ground strap ? Where should it be ?

Thanks

 

Frank:

Thanks for your help. I will try adjusting ignition switch tomorrow. Looks like we posted the last responses about the same time.

 

Do you have a dmm, digital multi meter? The diode is a one way device. A meter set to diode scale will forward bias the diode with .7 volts. The meter will display the voltage drop accross the diode. Now reverse the leads and the meter should read open circuit. If not the diode is bad. Diodes are used on the armature of the relay to keep it from back feeding into the rest of the electrical circuits. The best way to test a relay is to set your dmm to either volts or ohms scale and check for voltage drops or impedance readings as according to a Helms manual. The relays on outputs of the computer are driven by the pcm or eec ports so they do not overload the ports of the pcm. Was this helpful?

 

Can you get a schematic of the electrical wiring? Regarding your question, voltage is not consistent accross relays, that is becuase some are probably outputs and others may be inputs. Without a diagram I am dead in the water. My truck has similar problems, no codes, but floods the motor. I am replacing the pcm, $100 at Auto zone.

 

Just a note what I found - a faulty wire behind the instrument cluster - going to the gauge and a corroded wire UNDER one of the relay's - fuel pump circuit. The bad news - after fixed turned it in on a clunker deal. However, this is for the benefit of other folks. I still have a 92 - similar truck except a 5 speed ....