This sounds very interesting as I've changed my VSS and still have a similar problem. Where do I find this circuit board on a '98 RHD?

 

All RHD and LHD Disco's will have the same layout, just opposite sides.
So if it is behind the passenger kick panel on a LHD truck it will be behind the passenger kick panel on the RHD truck too.
The circuit board they speak of is behind the instrument cluster.

 

I'm loosing my mind. I'm so wiped out from two weeks of non-stop work, 12 to 14 hour days and then personal obligations when home that I'm starting to hallucinate. I only realized my mistake when I looked up the VSS in microcat and while reading Buzz's comment about the Crank Sensor......if you can believe it the error still had not registered.....WOW, that's tired.

So I will politely bow out of the conversation for now and get some needed rest. I have four days off.......it will take all four.

 

ihscouts - thanks for jumping in to help out - even if you are overworked. Keep your eyes on this post, we have been making some progress, but may still hit the wall

 

Further diagnosis of the ECM/ECU

I have likely further isolated the problem to the speed sensor processing in the ECM. I disconnected the speed sensor wire directly at the ECM, and the problem is solved. Speedo on dash works and other outputs work when disconnected downstream. No hesitation or -25% short term fuel trim on Bank 2 and truck runs perfectly on the highway. Unfortunately, with the speed sensor disconnected, it does not always hold idle when decelerating to a stop and occasionally the RPMs drop to zero. So, I need to fix the root cause of the problem - probably inside the ECU

Based on Spike's recommendation I pulled the ECM out of the engine bay, and it was a mess - see the pictures. There was extensive corrosion on the outside, and extensive corrosion and water marks on the housing on the inside. There was loose rust and corrosion flying around inside amongst the circuit boards. There was also one mystery circular, corroded metal disc floating around. The circuit boards looked ok, but you can't tell what components are messed up.

I have ordered a new (used) ECM model number ERR6355 from Rover Cannibal in Oklahoma and will install to see how if she runs. Looks like I will need to have the sync done with Testbook or Autologic to connect to the alarm/Immobilizer on this GEMS engine.

After cleaning this up, resealing and reinstalling,the problem persists...it was worth a try.

Here are the pictures:

Outside corrosion




Back of one of the two circuit boards




Note the rust bits flying around




Strange metal disc flying around - right side




Heavy corrosion on lower right side - note that this is the lowest corner when the ECM is angled down in the engine bay and it looks like it may have been holding water




Back of the second circuit board - note the pile of corrosion and rust bits sitting at the bottom

 

The rust/metal sliding around could short out the circuits and make it run rough.
Spray the whole thing with electrical cleaner, let it dry and put it back minus the rust, see how it runs.
If all is well then seal it, if not dont bother sealing it.
Once you get the "new" one open it up.

 

Still watching.....and resting although my form of rest is what most people would call a full day.

This morning I was helping my son change his spark plugs. Normally a simple one hour chore....except it's a Dodge. I started working on his truck at 8PM yesterday, I hadn't stepped one foot into the house yet, had just arrived home after a 13 hour work day and noticed his truck in the pole barn. When I walked in to see what was up I saw every large tool I have on any available horizontal surface, pieces of plugs all over the floor, his hands solid black and the look of absolute desperation. It was comical. He wasn't laughing. First things first, calm the kid. We're a team.

7 heat shields removed and two plugs that left their threaded body in the heads later (we got the nut with complete insulator, snapped clean from the body) we finally had all eight out and replaced by 2:30AM. Another 2 1/2 hours I would have been up for 24. My rest consisted of waking at 7AM to get my son up for his work (sleeps like a rock) and heading out to remove a good fender (to replace my deer dinged one) from a friends donor before the wrecker came. They backed up to my truck before realizing the white one goes, the silver one stays. I got a good laugh, my version of life lately is a bit epic twisted........

Pain is a terrible thing to waste, reminds me I'm alive.

 

Exactly.

 

I am looking forward to those days with my son.....great story!

 

Y-e-a-h...its not as fun as it sounds.
You work a 12hr day in the freezing rain, you went to work in the dark, you came home in the dark.
You are tired, hungry, your body aches and your son has your garage floor covered in your tools, parts of his car, there is 5qts of used oil on the garage floor and he is ready to burn the whole thing to the ground.
You just want to shower, eat leftovers and go to bed, but he has to get to school in the morning and he needs his car back on the road, even though you told him you'd help him Saturday, he didnt listen and now you get to fix his mess.
Yeah, good times.