Totally in the weeds with my 04 LX

[Chevyguy]

No end in sight really out of ideas now

All the stuff I tried so far listed here

http://www.crownvic.net/ubbthreads/ubbthreads.php?ubb=showflat&Number=2628411#Post2628411

So anyways I have a car randomly shutting down the PCM and the fuel pump, shutting off the CEL and ALT lights, not setting any fuel pressure codes or erasing any codes or setting the not ready code.

Thought the PCM or the PATS were bad so PCM swapped to a 04 P-71, The car ran for over 3 weeks with no problems then died 2 weeks ago then died for 1 minute and re-started fine.

Ignition switch replaced and wire harness inspected and it still stalls. The car can quickly stall and restart while the key is still on all the way to shutting down and the CEL will not come back on for over 15 minutes.

Tried replacing the PCM diode and the car still dies but was stuttering in/out but the CEL was coming on when it was not running or stalling. Did notice the Speedo was dropping down too, like the engine was just shutting off. After a bunch of this the PCM finally would shut down, as in the CEL shuts down when the Key is in the ON/run position. In this mode the CEL and Alt light wont' come on, the car will crank but won't start and the fuel pump for sure is not turning on but this requires a signal from the PCM IIRC.

So what else could be wrong? It must be trying to fry the PCM, so when it shuts down it's been overloaded?

I did confirm there is power at the PCM relay and there is power at BOTH sides of the PCM diode??? I desperately need the 2004 wiring diagram to hunt this down.

HELLLLLLLLLLLLLLLLLLLPPPPPPPPP PPPPP

[Rockettman]

Try this:
http://www.mercurymarauder.net/forums/showthread.php?t=83507

(courtesy of "the birdman".)

[stevesoasis]

Not sure if this will help u but i had a very simular problem with my 05 p71. The car would just sudenly die while driving, didnt throw any codes at all. Eventually we tracked the problem to the wiring behind the front bumper cover on the passenger side. Turns out that at some point the car must have hit something in that spot and the wiring was damaged. All they did to fix the wiring was wrap some electrical tape around the busted up wires and than put a new front bumper cover on. The electrical tape eventually became loose and the exposed wires began to corrode and short out from time to time. Hope this info might lead you in the right direction, good luck!

[Chevyguy]

Thanks for the wiring diagram info, I will download the entire mess soon.

As for the wiring shorts, I checked out that whole mess EXCEPT for the run along the radiator support. All those wires looked perfect and the car looks like it never hit anywhing and I would have had to pull apart the bumper cover to get in there to see anything.

All the wires from the PCM that go through the power dist box go through there. So maybe a closer look is needed

[Chevyguy]

Whatever it is the car is now stuck 200 feet from it's normal parking spot. Either both my PCM's are toast or whatever was shorting has now blown out the circuit.

I will be metering the harness tomorrow AM to track down the dead circuit, the PCM and fuel pump still are not turning on hours later.

[Chevyguy]

PCM is still dead, car won't come alive. This should be good news as the intermittent problem is now permanent.

Ok fixed my faulty DVM kept flaking out as the batt contacts were loose

I also made a test light out of a spare trailer light. Test light confirms proper voltage flow the DVM can give false readings of potential with no current flow.

So my previous voltage tests were wrong, I have 12 V at the PCM diode and this will iluminate the test light. Pulling the diode makes all the relays click when the key is on.

Head to the PCM harness connector
bl


Test light iluminates (tLI) on pins 55 KAM unswitched circuit 554 YE/BK

TLI on 71 and 97 both fed by the PCM diode and relay ckt 361 red

Also checked the brake light switch power, 92 ckt 569 also TLI

Checked grounds all near 0 ohms

Pin 3 ckt 570
Pin 24 ckt 570
Pin 25 ckt 57
Pin 57 ckt 570

Pin 76 ckt 570
Pin 103 ckt 570

Still no sign of life in the PCM, no fuel pump start

did check ckt 16 which powers the PCM diode at a COP I see 12 v but it wont illuminate the light

I did try the old PCM breifly before so I still don't think the PCM is actually toast, but I will try again anyways.

So now what!!???

PCM has switched power and constant power and all the grounds work.

Short in fuel pump or some other connected sensor etc??

[Michael]

Are you saying when you turn the key to the run position none of the dash lights come on and the car is dead?

The car still cranks but not fire off?

Or is it doing both of these things intermitently?

I don't want to over simplify the problem but the first thing I do when the car stops running even if it sputters or hesitates and dies is to yank the intake tube off and shoot some starting fluid down the throttle blades.

[Chevyguy]

Some of the lights come on, but the Check engine and Alternator lights don't come on, nor does the fuel pump.

[TFB]

PCM is still dead, car won't come alive. This should be good news as the intermittent problem is now permanent.

Ok fixed my faulty DVM kept flaking out as the batt contacts were loose

I also made a test light out of a spare trailer light. Test light confirms proper voltage flow the DVM can give false readings of potential with no current flow.

So my previous voltage tests were wrong, I have 12 V at the PCM diode and this will iluminate the test light. Pulling the diode makes all the relays click when the key is on.

Head to the PCM harness connector
bl


Test light iluminates (tLI) on pins 55 KAM unswitched circuit 554 YE/BK

TLI on 71 and 97 both fed by the PCM diode and relay ckt 361 red

Also checked the brake light switch power, 92 ckt 569 also TLI

Checked grounds all near 0 ohms

Pin 3 ckt 570
Pin 24 ckt 570
Pin 25 ckt 57
Pin 57 ckt 570

Pin 76 ckt 570
Pin 103 ckt 570

Still no sign of life in the PCM, no fuel pump start

did check ckt 16 which powers the PCM diode at a COP I see 12 v but it wont illuminate the light

I did try the old PCM breifly before so I still don't think the PCM is actually toast, but I will try again anyways.

So now what!!???

PCM has switched power and constant power and all the grounds work.

Short in fuel pump or some other connected sensor etc??

Ahh some useful info... The COPs are supplied voltage from the same fuse as the PCM diode, if there is no voltage to light the test lamp on ckt 16 at COPs you have a open or corroded connection in the harness between the fuse and COPs... Check S117, C1026 & S103... Interesting thing is I don't see how that would kill the CEL & F/P... Possibly the PCM isn't happy with voltage on the COPs drivers inside the PCM...

The Alt light out is likely because the PCM isn't turning on, it controls the charge indicator...

[Michael]

If the car is not running at the moment, shoot some starting fluid in the motor, and crank it over, I'm curious if it will run for a few moments. It will rule out the the circuit running the coil packs.