So, nobody has EVER fixed their speedometer.

[gteater97]

My tach works fine....Im not sure about the psom. I've never had to do anything to one of those. I'd just really hate to spend a couple hundred dollars on a pcm for nothing

 

[stamp11127]

So by the tach working we know the pcm is seeing rpms and feeding that info to the cluster. Does the cruise work?
I'll look around the web and see if I can find the pinouts for the pcm. Then tie into the vss feed and see if it drops out when the speedo acts up.

 

[gteater97]

No the cruise doesn't work and the radio was cutting out today

 

[gteater97]

This might make sense to someone else but there was an extra ground added to the pcm for some reason

 

[SJBikesaws]

As for mine. A bad solder joint was one of the first things I looked for. And the PSOM is in the cluster. I have no cruise control either. If it isn't speed related it works. I am not sure what AC values I should see, but I am seeing voltage. I wish I had a known good PCM to test it.

 

[gteater97]

Me too... im also wondering if it could be the GEM? I've seen alot of complaints about water getting past the windshield and leaking down to the fuse panel and GEM.

 

[stamp11127]

Did the cruise work prior to the speedo problem?

 

[gteater97]

Im not sure. I haven't had the truck too long and it had this problem when i got it

 

[1stGeExpedition]

SJ...

I didn't read anything about whether you checked the condition of the wires that connect the two boards inside the cluster. Mine were tan in color and they were bare right where they bend at each connector. I had to disconnect that harness and separate both boards to fix my wires. I could imagine one breaking over time once they are bare and free from the rubber outer shell.

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[gteater97]

Would a broken wire on the speedo effect the tranny?

 

[1stGeExpedition]

Pretty sure it would it's all tied together

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[stamp11127]

I'll see if I can find the input from the cluster to the pcm so that you can check if it is recieving a signal. Any of the scan tools at your work have an oscilloscope feature? If so you will be looking for a digital signal. DVM probably isn't fast enough to capture it.

 

[gteater97]

I don't think we have a scan tool that's worth a crap...lol. I work on alot of Cats and Cummins that are mostly mechanical. Im starting to get frustrated with it really. I haven't had anything stump me this long in a long time

 

[1stGeExpedition]

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.

What about the Output Shaft Sensor?

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[stamp11127]

gteater97 don't toss the towel in just yet. You should work on school buses, that will prepare you for anything. I worked on DT608s, 7.3, a few C7s. Lets not talk about the C7 Acert boat anchor.....

PCM connector pin 58, circuit 679, GY/BK wire is VSS+
Multiple grounds are used, pins: 51, 71 both BK/W
Signal return: pin 91 GY/R

If you have a signal on pin 58 then the pcm is toast, assuming it feeds directly from the VSS or cluster. Is the VSS a single wire or 2? If two they are probably using the signal return.

If you need the diagram of the connector send me your email address. If they numbered the connector like they should have you should see the number or one close to it.

 

[gteater97]

It's a 2 wire vss. I swapped out the output shafts sensor also and it's getting a signal also. I still wondering about that GEM....my radio was acting up today. Plus the rear window wiper and interior lights aren't working.

 

[1stGeExpedition]

Any signs of moisture? Look for the notorious windshield leak. Are your tires the same size on all 4 wheels? Mismatched tires can cause this too.

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[gteater97]

[email protected], thanks for the help

 

[SJBikesaws]

Fixed!!!!

Just checking back in. Mine ended up being the GEM after all. It also goes to show that there are no dead on methods to pegging the GEM as the problem, I sort of took a chance before going the route of a new PCM. There were no signs of moisture contamination, it just stopped working. I bought a $50 junkyard GEM module and swapped it out. Speedo works again, shifts again, and I lost a few other ghosts too (the timer for the interior lights was always kind of funny, and it never would go into 4wd low before).

Unfortunately I gained a ghost too. Now my wipers just decide to turn on every now and then, no biggy though, I will take that over what I had, and I am not beyond stuffing an extra toggle switch on the dash. I guess I figured out what was wrong with the wipers in the Expo that was sitting in the junk yard.

Thanks all for the help

 

[IMINYOURCHAIR]

well, in that case, you're likely to need a good gem replacement to fix the wiper issue. but good to see it's been fixed. congrats