Electric Speedometer Diagnosis

[ZooMad75]

Hey all. Been focusing on figuring out why my speedometer does not work in my 91K5. Here's a quick rundown of where I'm at.

Swapped in 5.3, original TBI PCM has been deleted.
Rest is stock 91, VSS in the 241, DRAC module and electric speedo cluster.

Going through diagnosis from the service manual I've got AC voltage that increases when the rear wheels are turning with it up on jackstands in gear. I have battery voltage on the blue/black wire which is the output to the speedo. I've checked that at the DRAC and the cluster connector. If I switch over to ac voltage on my meter on the blue/black wire it does not change.

Part of the diag was to check the ground at the DRAC. I was surprised that I did not have a good ground. I ran a new ground and confirmed that it's good. I retested and it's still working the same way. Which is to say it's still not working.

I've got three DRAC modules in my supply. Can't find the third, but of the two in my hands one was modified via the TBIChips website instructions for my axle and tire diameter specs. The other one is unmodified. Either one I put in the system still does not work.

One other thing, I've got a second electric speedo cluster and it's behaving the same way. Which in my mind proves I'm not getting the output out of the DRAC I'm supposed to.

So I guess I need to find out what I should be seeing on the blue/black wire to the speedo. Should I be monitoring it as a AC or DC voltage value? I'm having a hard time beliving I have 2 bad DRAC modules and 2 bad clusters, but I'm not sure what the problem is. Any ideas?

 

[Bent77]

Hey all. Been focusing on figuring out why my speedometer does not work in my 91K5. Here's a quick rundown of where I'm at.

Swapped in 5.3, original TBI PCM has been deleted.
Rest is stock 91, VSS in the 241, DRAC module and electric speedo cluster.

Going through diagnosis from the service manual I've got AC voltage that increases when the rear wheels are turning with it up on jackstands in gear. I have battery voltage on the blue/black wire which is the output to the speedo. I've checked that at the DRAC and the cluster connector. If I switch over to ac voltage on my meter on the blue/black wire it does not change.

Part of the diag was to check the ground at the DRAC. I was surprised that I did not have a good ground. I ran a new ground and confirmed that it's good. I retested and it's still working the same way. Which is to say it's still not working.

I've got three DRAC modules in my supply. Can't find the third, but of the two in my hands one was modified via the TBIChips website instructions for my axle and tire diameter specs. The other one is unmodified. Either one I put in the system still does not work.

One other thing, I've got a second electric speedo cluster and it's behaving the same way. Which in my mind proves I'm not getting the output out of the DRAC I'm supposed to.

So I guess I need to find out what I should be seeing on the blue/black wire to the speedo. Should I be monitoring it as a AC or DC voltage value? I'm having a hard time beliving I have 2 bad DRAC modules and 2 bad clusters, but I'm not sure what the problem is. Any ideas?

Maybe contact someone who works at a dealer...

 

[nocoasthardcore]

Is that VSS clockable like the ones in Jeeps?

 

[6872xtc]

I think that @bent72 is a smart-ass even in his sleep.....

And I don't have any help with this except, come over and we can test crap with my '90!!!!

Mine lost the speedo once, but it blew the fuse for the ABS and A/C clutch, which killed the speedo. You already confirmed power...
Mine was a chafed spot on the A/C clutch wire.

 

[ZooMad75]

Maybe contact someone who works at a dealer...

Very funny. Actually if it wasn't for the service and electrical manuals at work I wouldn't have got as far as I did.

After starting this thread I went back outside and rechecked my work. Starting first by grabbing my spare cluster and trying it again. It didn't work before but I wanted to check again. I plugged it in and turned the key on and I noticed the needle twitched and went to the bottom of the scale. So I started it up and pulled it into gear to let it roll. Sure enough the speedo was working. I swapped back to the other cluster and retried it and no dice again. I went ahead and swapped the speedo head from the spare cluster to the main one. It worked. I put the original speedo back in the spare and tried it one last time and sure enough it started working too. One more time swapping stuff back again and I buttoned it all up. I tried it one last time before getting the rear axle off of the jack stands and it was still working.

I was pretty happy so I went to grab a limeade from Sonic and go for a cruise to check and see how accurate it was against the GPS on my phone. I'm surprised to say that the changes made to the DRAC were spot on. The readings matched all the way up to 80 mph on my run. The odometer was accurate to the mile markers on the side of the road too.



Found a really good long dirt road to run again once we swap out the shocks. I got a really good shot of Pikes Peak from out there too.

 

[Bent77]

So I just needed to mock you?

My work is done here...






Oh, good yob mang

 

[6872xtc]

So are you thinking that it was just dirty connections?
All of that plug/ unplug action took care of it?

 

[Bent77]

So are you thinking that it was just dirty connections?
All of that plug/ unplug action took care of it?

Kinda made me wonder. Or maybe broken wire at the molex connection

 

[ZooMad75]

So I just needed to mock you?

My work is done here...






Oh, good yob mang

Mocking is one hell of a motivator. Had I seen your post before I went back outside it might have helped!

What actually fixed it was probably the bad ground at the DRAC module. Since both clusters and speedos ended up working it's the only thing I actually did to repair anything today.

 

[Bent77]

At least it works now

 

[ZooMad75]

At least it works now

Totally. It's a bonus that it's actually accurate!