EEC Fuse blowing with KOEO

[Fiddlehead]

I am helping a friend troubleshoot and fix his 1994 Ford Explorer XLT w/ 4.0L, A/T, 2WD. He had the motor replaced about a year before having this problem. Then 6 months before the problem, he had the fuel pump replaced. He suddenly began having problems starting the engine and then it quit starting completely. He bought another car and set this one on the curb for a year before I got involved. The first time I looked at the Explorer, I opened up the hood and started checking fuses and found the 30A, EEC fuse blown. I pulled the 30A fuse from power locks slot and put it into the EEC slot. It started right up. After a couple of days of driving it intermittently, it quit while he was driving it. We pushed it a couple of blocks home, where it still sits. We have replaced the fuse several times where it quickly blows with the key off, most of the time, but sometimes we have to turn the key on. Weird! I pulled the EEC relay and tested it with a DVOM. It checks good, but I haven't manually applied power to it and checked it. I do feel it click when the key is turned on. After having read a lot on this and other forums, I decided to perform continuity test on the wiring from the EEC plug.

Today, I disconnected the battery and the unplugged the EEC. Below are the results both with the EEC relay, Fuel pump relay and the AC WOT cutoff relay (all 3) in and (all 3) out. I used the pin 60 as the ground (black lead on the DVOM) and checked for a short to ground at each pin with the red lead. I have listed only those pins that showed a short to ground.

With Relays In – 3, 6, 8, 9, 10, 12, 15, 16, 17, 20, 21, 30, 33, 35, 37, 39, 40, 51, 53, 57, 58, 59,
With Relays Out – 2, 6, 8, 9, 10, 16, 17, 20, 30,

After examining a wiring diagram that I found tonight on this site, I know that those listed below are grounds and can be eliminated from the list of possible shorts; 6, 16, 20, 40,

I don't understand why I picked up a short on 2 after pulling the relays.

I also tested for shorts to ground at the EEC data link under the hood. This was done without the relays in their sockets. I found that there was a 31 ohm reading on the pink/Lt. Grn wire which is shown to be pin 17 on the wiring diagram.

I am still scratching my head and trying to figure out what the data is telling me. I have checked for melted and worn wires in the engine compartment, but I cannot consider it thorough enough to eliminate the wiring. I have not been under the car yet.

I have had considerable experience with electronics and wiring since I was in my teens, but this one has got me. Any help with this would be greatly appreciated.

In His service,

Fiddlehead

 

[2stroke]

The thing that comes to mind to me is that it takes a lot to blow those 30 amp fuses. I don't think you are going to draw 30 amps from a frayed wire, but It could happen. To me it sounds like a potential faulty wiring job, possibly a result of the fuel pump. Did he do it himself, or by a shop? Whole sending unit, or just the pump? One thing that would not make any sense would be to un plug and re plug the fuel cut off switch under the passenger dash. I couldn't tell you why that would fix anything, but I laugh at the number of times doing this has fixed problems for me. I'll take a look at a wiring diagram tomorrow and see if I can help. While I am not a pro, I am currently going to school for this kind of thing.

 

[the_don]

take a peak at the harness inside the drivers side frame rail just under the fire wall to make sure it has not come loose and melted/rubbing against the exuast pipe.

 

[BrooklynBay]

Check for melted O2 wiring on exhaust pipes. Sometimes the internal wiring harness in the transmission could short against the case or the pan.

 

[FR-425]

You may want to start buy pulling the power distribution block and having a look at the bottom side.

 

[Fiddlehead]

Thanks for all of the help. Yesterday, I did the following:
I got under the the car and looked for shorted/melted wiring. I examined the harness under the drivers side all the way from above the exhaust to the plug for the fuel tank/pump/sending unit. I looked good at the temp sensor wiring & plugs on the exhaust. I also looked around on top of the engine again and under the battery compartment and again under the power distribution/relay box. I have not found on wire that was melted or frayed or broken. The harness in the frame still had the orignal wrapping and an orange color on the ends. Kinda strange for a vehicle this old, but for someone who never takes a car off of the pavement, I guess that's possible. I also did some testing on the wiring of the MAF and TPS and on the AC plugs to check for cross shorting in the harness. Nothing. I then took each of the relays in the distribution box and put power to the coils and tested for continuity across the contacts. Everything worked as it should and there was no bleeding of voltage across from the coil to the open and closed contacts. I checked the Diodes in the distribution box and got 5.5 - 5.8 M ohms forward and zero backward.

I know that he had the fuel pump was changed and that the fuel gauge had stopped working before the change and is still not working. So I don't believe that the sending unit was changed but just the pump. That being said, I have not checked the fuel gauge fuse in the interior fuse panel yet, but will next time I work on the car. I will also make a note to unplug/replug the fuel switch under the dash.

Thanks again for any and all of the help

 

[Turdle]

Just an idea for giggles

Disconnect the fuel pump connector near the tank. Then try a new fuse, turn it on and off several times trying to blow it again.

 

[the_don]

im starting to wonder if you have a bad capacitor in the ecm. and the fuel gauge could be the anti-slosh module in the cluster.

 

[Turdle]

im starting to wonder if you have a bad capacitor in the ecm. and the fuel gauge could be the anti-slosh module in the cluster.

^^ 2nd the ECM

 

[Fiddlehead]

Thanks guys. I will be doing some more continuity testing tomorrow and I will check the fuel pump unit - short idea and the fuel cluster under the dash by unplugging it and checking for shorts and then put the relays in and a fuse. Its cool here to be standing in the cold, but i sure would like to solve this mystery.

 

[larrydd999]

My vote is for a wire grounding out while the vehicle is in motion. My wife had a vehicle when we first married (35+ years ago) that periodically quit when she made a left turn. It was always the same fuse and due to a wire in a harness that had rubbed through its insulation and grounded on the chassis. It was very difficult to find because it only happened under the one condition and only occasionally.