So, nobody has EVER fixed their speedometer.

[SJBikesaws]

98 Expedition 5.4 EB

My wife was driving it a few weeks ago, and the speedo shot up to 100 mph, then flat lined. Followed by bad shifting. Stuck my ODB2 scanner on it and I am reading P0500 only.

Hunted through ALL relays, and ALL fuses. All I did was fix the power socket to the rear, I guess my kids can charge their Ipods now.

Changed the VSS sensor.

No change.

Changed the ABS sensor.

No change.

Pulled the transfer case apart, the gear was good.

chased the harness looking for grounds and bad connectors, none found.

Jacked the vehicle up, ran it in gear at various speeds and was able to get signal from both sensors all the way to the black and white wire in the back of the cluster, so I figured a bad speedo head. Changed it out.

NO CHANGE!!!!

I am in a dry climate, the car hasn't been wet for a while so I am doubting I got the GEM wet. I have no other symptoms that would indicate the GEM???

I keep seeing issues like this all over forums (Truck and Expedition) WITH NO RESOLVE. Whats the deal, the speedometer dies and you junk the vehicle out????

Any body EVER find the problem with theirs???? ANY Feedback?


I have been through every other "normal" Expedition problem so far in the few years I have owned this POS (air suspension to real spring swap, bad COP's, blown a spark plug out the third back passenger side, rotted vacume fitting, changed the heater core and blend door, etc.). But this one has me stumped, I'm am sick of tossing money at a problem that I cant get rid of.

I am a heavy equipment mechanic, I run through this kind of crap for a living but I'm am stumped on this one. Of course, when its your own vehicle, Murphy strikes.

 

[1stGeExpedition]

Here's one...

http://m.ford-trucks.com/forums/showthread.php?t=1143832&styleid=20

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[SJBikesaws]

Well, I haven't gave up. Went back and chased wire again yesterday. Pretty much the entire path of the of the ground (pink and orange) and the analog AC signal (grey and black). After some phone calls with a friend that was a dealer mechanic and the Expedition guy when this thing hit the road, and a few hours hunting the path through my On Demand 5 digital manuals, everything points to the PCM. So, that will be the next hunk of cash thrown at it.


And YES, I will leave a full report here so the next guy knows what to look for and where to go (something the internet has REALLY lacked so far).

 

[gteater97]

I work on diesels everyday and im just tired of messing with this thing....I dropped mine off at a shop in town so I will know something tomorrow.

 

[stamp11127]

Before changing the pcm I would reseat all connections to it plus the 3 large connectors on the firewall driver side. Check for corrosion on the pins also. This is no different from the heavy trucks, parts are just smaller and considerably lighter - electronics are similar.

 

[01yellerCobra]

What controls the needle? Is it a stepper motor?

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[1stGeExpedition]

Hope you guys figure it out. It's something that I'm sure most of us will encounter at sometime or another.

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[gteater97]

So it was at the shop all day and they say PCM.....is going to check those plugs tomorrow. Anyone know if a new PCM has to be flashed

 

[bedrck46]

yes the NEW PCM needs to programed

 

[stamp11127]

Yep and tied to the instrument cluster. Not sure on these speedo heads but the old style used magnetic field strength to move the needle. If your handy with a soldering iron I would go over all the solder joints on the cluster. It is known for cold solder joint on the odometer might get lucky on this one.
What data are they using to fail the pcm?

 

[1stGeExpedition]

So if someone gets a PCM from like a junkyard they need to either get the matching instrument cluster with it or have the new PCM flashed? Just curious.

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[stamp11127]

Yep, google ford pats

 

[gteater97]

Lol....everything else is fine so has to be the pcm. It's just weird be sometimes it works and sometimes it doesn't

 

[SJBikesaws]

Disconected the positive cable and grounded it out over night and put the PCM in reset mode. re hooked it up and drove it for 20 minutes, Nope.

I busted all of the main harness's on the firewall loose, no corrosion, stuck em back on, Nope.

Next I am busting the PCM harness loose.

 

[superexpy]

So if someone gets a PCM from like a junkyard they need to either get the matching instrument cluster with it or have the new PCM flashed? Just curious.

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No. I used a PCM from a junk yard with matching #'s and had no problems. My tuner in my truck self-destructed and took my PCM out with it so I went to the junk yard and found a new one and it worked perfectly. I have also swopped out gauges on other expys and never had a problem

 

[superexpy]

I also have PATS. When my PCM went that was the first thing i trouble shot....

 

[stamp11127]

To prove the pcm has failed you would check the signal coming in from the speed sensor and the signal to the cluster. Unfortunately you need 2 breakout boxes and the specs in order to do that.
One other test that would validate the harness would be to swap a known good pcm and cluster with your current set.
I would take a close look at the clusters solder connections.

Food for thought. In your original post you stated you had a signal from the vss to the cluster. Why send a signal from the cluster to the pcm and then back to the cluster? Why not have the signal go from the vss to the pcm and then to the cluster?

 

[SJBikesaws]

To prove the pcm has failed you would check the signal coming in from the speed sensor and the signal to the cluster. Unfortunately you need 2 breakout boxes and the specs in order to do that.
One other test that would validate the harness would be to swap a known good pcm and cluster with your current set.
I would take a close look at the clusters solder connections.

Food for thought. In your original post you stated you had a signal from the vss to the cluster. Why send a signal from the cluster to the pcm and then back to the cluster? Why not have the signal go from the vss to the pcm and then to the cluster?

I really don't understand it. I have signal coming into the clusters (I say clusters because I have 2 of them). I can watch AC voltage value change as I accelerate from the grey and black wire into the speedo head, or straight off the sensor with it jacked up and running in gear, or anywhere else in its path. The ground values show good on the ground side (Pink and Orange). Both clusters have the same problem, nothing for speed, nothing for odometer. I also noticed that the mileage computer is reading nothing. Also, I read nothing for speed on my ODB2 scanner when moving in live data mode. I went through harness and wire paths again, and again. I have busted every connector loose I could find, no corrosion, everything looked good. I haven't been stumped this bad in years. I am going to bite the bullet and buy a PCM I guess.

 

[1stGeExpedition]

SJ...

Have you opened the cluster (either one) to check for bad solder joints or frayed wires etc? These clusters are famous for internal problems. It wouldn't surprise me at all if you got two of them with exactly the same problem.

I just did the odometer solder repair on mine a couple weeks ago and the wires that connect both boards inside the cluster were bare in some spots. I would imagine that if there's something wrong inside the cluster it would cause your symptoms.

When you turn your key to the on position what lights illimunate on the cluster?

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[stamp11127]

The Ford Service Manual doesn't give a wire by wire schematic for the pcm/instrument cluster assembly. But it does indicate a connection between the pcm and cluster - through the fuel pump module. Probably not the problem.

There is reference to the microprocessor on the cluster for controlling the gauges among other things on the cluster.
If the cruise control works and the pcm really is tied into the cluster as an output device, that would indicate at least the pcm is reading the vss and able to maintain speed.

Two bad clusters - maybe but doubt it. A bad ground for the signal would be common to both clusters though. Run a new ground from the cluster to chassis ground and for giggles to the pcm ground. I'll do some digging and see if I come up with anything new. This will turn out to be one of those problems that once you determine the cause you'll say WTF.

Update: If Ford used the same logic from the Rangers to the Expy's then the signal runs from the vss to the cluster then to the pcm as noted below:
"The programmable speedometer/odometer module (PSOM) receives input from the rear brake anti-lock sensor. After processing the signal, the PSOM relays it to the power train control module and the speed control module. Information from the PSOM is used to help determine shift scheduling, torque converter clutch operation and electronic pressure control (EPC)."

Seeing that you have a signal at the cluster it would seem the PSOM is the microprocessor on the cluster.

Does the tach work?