1988 F-150 4.9L 4X4 manual transmission.
Today the truck began having a hard time starting, it acted like a dead battery. I have confirmed that the battery is good. I then removed the ground cable to reset the computer, while removing it, I noticed that it was sparking. I take it that a spark on the ground cable means that somewhere a hot wire is going to ground. I also noticed that with the ground cable removed, my check engine light was on, but it won't come on like it is suppost to with the battery hooked up. I thought that it was odd to have a light on without the battery hooked up. I then began to look for the source of the short. Here is what I found.

On the always hot side of the solenoid, there are 4 connections. one from the battery and 3 others. I removed all but the main battery and then looked for a spark on the ground wire. It wasn't there. so I started connecting the others one at a time till I caused a spark. I found out that one of the connectors was causing it. I have no idea what is on this line nor do I know where it goes. This is where I need help.

all i can tell you is that on that connector there are two wires molded together with fuseable lings on both of them. one wire is yellow and is thicker than all the others, the other wire is black w/brown stripe. On the mold is stamped P2. and the fuseable links are stamped p27 on one and p28 on the other. Also sometimes when I touch this wire set to the battery voltage, I will hear a relay click. the relay is located inside a harness that is bolted onto the back of the air filter housing. any ideas what this is or does??

while there, I though I would try to run an eec test. I have done this several times before, this time it did not work. so I definately know there is a serious electrical problem somewhere.

Any ideas?? cause I am at a loss.
Thanks

 

There are several questions here, I will start with the starting. It can be several things, bad cables or connections (ground and hot) or the starter. Do the cables get hot or does a connection get hot?

If the spark is a small one when you touch the cable to the battery it is more than likely OK and I would not worry about it too much. After all, the EEC uses a small amount of power to keep its memory alive, this is why you should not unhook the battery unless necessary.

The relay should not click unless you left the key in the on position. You have two relays there behind the air cleaner, one is the EEC Power Relay and the other is the Fuel Pump Relay. If they click with key off when you touch the cable to the battery you have a problem and it needs to be addressed. If it clicks and the other wires (fuse links) are not hooked up then you have shorted wires.

As far as the fuse link wires the Black/Orange wire goes to the EEC pin #1 (spark?) and to the EEC Power Relay Power Contact. The Yellow wire goes to the Fuel Pump Relay Power Contact.

As far as Lights that come on without the battery hooked up I think I will let somebody else answer that one. The engine was not running when you removed the cable was it?

 

alright that helps a little. at least now I know what some of the parts are that I am dealing with. as far as the other questions; all the connections are good and no wire or connector gets hot. The spark is a fairly large one and it is occuring when I touch the ground cable to the engine body.(if the engine body has voltage to it there has to be a short somewhere. right?) the relay clicks with the key off (the key is laying in the seat) and it occurs when I touch the wires to the positive battery lead(where it stays hooked up). so according to Subford's post. this is a problem.
could the relay itself be the problem? can you test them or buy new ones?

 

I think I might know the answer to the question about the light being on with the ground cable disconnected. Look at the ground cable and the - of the battery closely. Do you have a smaller ground wire branching off the - cable, going to a ground to the inner fender or radiator support? Some of these trucks did, and this provided a ground for the computer as well as some of the sheetmetal. You should also have a smaller ground going from somewhere on the engine to the firewall sheetmetal.

You could go ahead and do the official battery drain test. Your spark test is a clue that something is drawing current, but it's not a very good indicator. Get a testlight and hook it up like the picture below. If it lights up bright, then you do have a battery drain.



Here's a diagram that may be of some help. If you do have a drain, I would get a small battery charger and hook it up every night to keep the battery up till you get it figured out. This will also confirm this is the cause starting problem if it cranks better with the charger on it overnight.

http://www.autozone.com/images/cds/g...3d800a3a47.gif

 

Do the Fuel Pumps start running when you hook up the battery with the key off?

 

ok I got the starting issue taken care of. it turned out to be a totally unrelated issue with the starter. as for the electrical issue it is still there. when I start the engine it can barely idle.

I have tried the battery drain test and it is ok. in fact, it has set for about a week while I was out of town and the battery still had 12.52 volts in it.

when I connect the wires, the fuel pumps do not turn on. when I turn the key to the on position they do pump momentarly like they are designed to do.

 

Ok. So the only problem you have now is the engine doesn't run very well? Is this all the time, or only when it's cold? And it's only at idle? It runs ok down the road?

 

ok got a chance to drive it yesterday. it runns really rough when cold. it barelly idles, and when i give it a little gas it will hesitate and miss. once it warms up, the problem minimizes. it almost runs normal. almost, but not quiet.

so far I have cheked the resitance of both the air charge and the coolant temp sensor. they are both well within specs.

I'm really starting to wonder now what is wrong lol.

 

Did you try pulling the codes?

 

yes I did try pulling the codes, and I am unable to. the eec will not respond. I have pulled the codes several times before, but now it will not let me. As soon as I attemp to do a KOEO test, the system looses all voltage. but as soon as I turn the key back off, I get voltage again. (this is reverse of what it is suppost to be.) There is still a short in the system somewhere. I am begining to wonder if something in the eec system has failed and/or is causing the short.

my manual does not cover the eec component very well at all and i have very little experience wit them, so I am kinda at a loss in terms of what to look for or what to check.

 

Franklin2 left you a link above to the schematic of your system, did you look at it?

Sounds like you have a poor connection or bad ground and not a short.

Make sure the small black wire is hooked up at the Battery NEG (-) Terminal.

Check that all of the fuse link wires at the Battery side of the Starter Relay are making good connection.

Make sure your Batteries Neg. cable is grounded good to the Engine and the body is grounded.

 

Here's some other options to try to retrieve codes.