Richard’s Law of Accelerated Entropy

The first place the guy went after he bought his truck was to his cell phone provider. At that point, Richard’s Law of Accelerated Entropy took over.

Vehicle: 2000 Ranger

Powertrain: 2.5L I4

Mileage: 108

Symptom: No-start, Power locks inoperative

Immediate Deterioration

            Everybody knows that if you park a brand-new car in the woods and leave it there it’ll begin to deteriorate.  If you go back two years later, even if the engine will spin over, it probably won’t start.  Two years later, the battery will certainly be dead.  It may have one or more flat tires.  This is an example of the Second Law of Thermodynamics, or  “The Law of Increasing Entropy.” 

This brings us to what I call “Richard’s Law of Accelerated Entropy.”  In trying to improve their cars, some owners will immediately shave thousands of dollars off the trade-in value of the vehicle.  We’ve all seen it. Somebody (usually a guy) will buy a brand-new car or pickup and take it to have the exhaust ripped off from the catalysts back so they can have mufflers installed that make it sound like uncle Burt’s ’57 Chevy. 

Or they’ll have the factory radio yanked out of the dash and some gung-ho audio system installer will make mincemeat of the wiring in the process juicing up the guy’s sound system so he can rattle windows in any neighborhood he’s driving through.  What about the folks that butcher the suspension to lower the belly of the ride and install those tiny little tires that make the car ride like a jersey wagon and render it impossible to drive the vehicle onto the front-end alignment lift?

      In the case of this 2000 Ranger, however, the modifications were meant to be minor. On the surface, it looked as if the cell phone installer did an exemplary job of mounting the phone, and he was no dummy.  He had put phones in Rangers before, and never had a problem.  This time, however, when he tried to start the truck and back it out of the shop he wound up having to call a tow truck.

No Fuel Pressure… Why?

            When Ryan, my helper, found the Ranger on the service lot, it was unstartable.  The engine spun but wouldn’t fire.  A moment later he found that it had spark, but no fuel pressure. After a quick check of the fuses, he found a blown 20-amp fuse in the Power Distribution Center (PDC) under the hood.

Replacing the fuse, Ryan found that switching the key to “run” popped the fuse like a tiny flashbulb. When I got out there, I didn’t hear the fuel pump hum when I turned on the key.  That was good, because it’s better to have a dead short that’s dead all the time instead of a come-and-go problem that drives us all batty and keeps coming back every few weeks.

Overview

The Powertrain Control Module (PCM) on the Ranger energizes the primary side of the fuel pump relay when the ignition is switched to “RUN”, closing the relay’s secondary contacts and powering up the pump for only a couple of seconds unless the engine is spinning. 

The fact that it blew the fuse after we switched the key on was a sure indication that the short was between the fuel pump relay and the pump itself.  Occasionally, the fuel pump itself can be shorted, and this was a new truck, so it wasn’t beyond the realm of reason to think the pump might be the source of the problem.

I had Ryan feel of the relays while I switched the truck on, so we could see which relay was the fuel pump relay.  He claimed to have discovered the relay that clicked on, then off when the key was switched on, then unplugged it, and we checked by installing another fuse to see if the short was still there. We found that nothing had changed. It blew the fuse immediately. 

I had Ryan to operate the key and found that he had fingered the wrong relay.  I popped the relay Ryan had pulled back in place (I ultimately found out that I had put that relay in the wrong place, but I’ll talk about that later) and pulled the fuel pump relay.  The short was gone. We pushed the shiny new truck into the service bay.

“Ryan,” I said, “go pull up a schematic of the 2000 Ranger Engine Controls.”

Following the Map

A quick study of the schematic showed that the blown fuse had been feeding the secondary side of the fuel pump relay, which explained why it only popped when the key was switched on. Connecting the test light alligator clip to the positive side of the battery, I gently wedged the probe on the test light into the relay terminal feeding the pump, so as not to distort the terminal, but so the light would stand up and be easily visible. Even if there was no short, this should light the test light bulb because of the continuity through the pump motor brushes to ground.

I opened the passenger’s door and rapped the inertia switch with the heel of my pocketknife. The button on the switch popped up and the test light went out, so the short had to be between the inertia switch and the pump.  The map showed us that our circuit went through C309, a handy 40-pin connector Ford put in the floor pan on this particular model.  The connector was quite easily accessible from underneath.  Resetting the inertia switch, I had Ryan roll under there on a creeper and disconnect the big floor pan connector.  Our test light stayed on, indicating that the short was between the inertia switch and the point of exit from the cab to the fuel tank, which was connector C309.

Locating the Short

When I found the point where the harness disappeared under the carpet, it lined up perfectly with the place beside the console where the phone installer had drilled his holes (see photo).  It would have been wise to look here first.  Removing the console and pulling the carpet back, I saw a nasty hole in the metal of the transmission tunnel.  That screw had missed the harness, as had one other screw, but the third screw went straight through the center of the harness and the sharp sheet metal threads managed to saw their way into the wire leading to the fuel pump.

Very little actual damage was done to the wire, but enough contact with body ground was made to overshoot what the 20-amp fuse could carry.  Repairing the wire and reinstalling the console, I remounted the phone holder in a more innocuous fashion, this time avoiding wire harnesses with the screws.

Door Lock Problems

            The service writer had originally printed the repair order with the no-start complaint, then added a handwritten addendum about the door locks being inoperative also.  When I tried the power locks, they wouldn’t operate with the key fobs or the door panel buttons. 

The door lock actuators in the doors are operated by relays in a panel above the driver’s right foot. The common terminal on each relay feeds the both wires on each actuator with a ground when the relays are at rest.  Energizing one relay will switch the common terminal on that relay from ground to B+, which runs the door lock actuator in one direction, while energizing the other relay reverses the polarity to the motor, reversing the motor’s movement.  

This is an old method of controlling DC motors that has been around for a very long time in automotive applications. According to the wiring schematic, fuse 3 in the battery junction box and fuse 20 in the fuse panel under the dash were both responsible for powering up pins on the Remote Keyless Entry Module RKE or RAP, as Ford calls it), which was located behind the passenger’s side kick panel.  Checking with my low impedance test light, I switched on the key and found a good 12 volts at pins 12 and 20 on the RKE module. 

Moving my test light alligator clip to B+, I found that good ground signals were delivered to the proper relay coils (unlock is pin 11, lock is pin 22 at the module) when the RKE fob was operated on lock and unlock, but the lock and unlock relays weren’t responding.  My schematic showed the positive side of each relay coil was supposed to be “hot at all times”, but when I moved the test light’s gator clip back to ground and checked at pins 11 and 22, I found no power coming through the coils to the module.  (If the relays aren’t energized, the 12 volts feeding them should light a high-impedance test light through the wire leading to control pins 11 and 22. 

A low-impedance light will actually close the relay’s primary windings like a short to ground.)  The wire map for the RKE gave no indication of where the “hot at all times” power was supposed to come from.

            Moving from the RKE wiring map to the Power Door Locks map, I found that instrument panel fuse 18 was supposed to deliver power to the “Hot at all times” side of the door lock relay coils.

“AHA!,” I said.

It only took a second or two to move back to the instrument panel fuse block and find that fuse 18 was mysteriously missing.  I felt like a dummy, having gone the long way around to find that somebody at the cell phone place had apparently snatched a fuse. 

Generally speaking (not always), when something doesn’t work and you see and empty fuse position that has both terminals, it’s smart to pop a fuse in there and see what happens.  I got burned back in 1984 on an inoperative cruise control this way.  I installed the proper size fuse in position 18 and the door locks came alive.  I was kicking myself. I should have found that problem quicker than I did, but now I was done. Or so I thought…

Another Job Well Done… Almost!

As I was parking the truck back on the service lot, I found more problems.  When I punched the “lock” button on the fob twice to lock the doors and chirp the horn, the park lights flashed but I heard no horn.  I was beginning to get a little irritated.  Every time I thought I was done with this heap, it would show me a new problem that demanded attention. 

I unlocked the truck again and tried to blow the horn by pushing on the airbag (incidentally, this seems like a dangerous arrangement to me; most folks are prone to get on the horn button right before they crash…), but the horn was unresponsive. I had no junction box diagram with me, but I remembered that relay swapping business when Ryan and I first checked the truck, and I eyeballed the position of the relays in the junction box under the hood. 

My own Law of Accelerated Entropy was nipping at my heels. 

There were some empty relay sockets for optional equipment that was absent, so it had been easy to plug the relay Ryan had removed back into the wrong spot.  I pulled the relay I thought I had installed in the wrong place when Ryan misidentified the fuel pump relay, and plugged it into the horn relay position. 

The horn started working then, but when I checked the rest of the stuff, the wipers had gone dead.  This was really beginning to annoy me. It took me about five minutes playing “musical relays” to figure out which sockets were supposed to be vacant and which ones were supposed to have relays in them.

“Those cell phone guys have this truck so fouled up nobody can fix it!” I muttered.

All’s Well that Ends Well

            It was humorous how that relay business humbled me as I was patting myself on the back for finding the cell phone installer’s goof.  Those of us who have been pulling steel and chasing sparks for a while can make some funny mistakes.  I’d like to hear your stories, if you have time to e-mail them.