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Need to get my speedo/odometer back in my old Burb.

D

Dick Wells

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Location
Morrisville, VT 05661
Put this in general discussion (first thread) and have been advised to put it in the 6.5 Forum, so, here goes a try at pasting it over here.

Got interested in TTS, when I ran onto a discussion on speedometer problems with a 94 6.5 from sometime in 2009, and decided to see if the site is still active.
Been a member of The Diesel Page since 99 and have had a lot of fun and learned a lot over there. But, I just installed a Quick 4 trans. controller in my Suburban, which has a mechanical pump in it, since about 2004. Although we took it cross-country, back then, twice, there was always a shifting issue that would pop up at random times. Required shutting down and re-starting to get it shifting again. Thus, the Quick 4, since we intend to keep the Burb in the family for summer use, by anyone, including those who aren't adept at adapting to this odd-ball vehicle.
Got the shifting all sorted, and it's going just fine,---- except ---- can't get the speedo/odometer to work! Got an AC signal to the VSSB (vehicle speed sensor buffer), but I'm at a loss as to what to do from there. Chevy dealer can only check the VSSB if it's installed. Well, it's in there, but I'd like to know how to check the signal beyond it (VSSB) to see if I have action at the gauge cluster.
There is a wire from the VSSB to the radio, that controls the volume as speed increases, which I clipped, because I don't care if it functions, and I wanted to eliminate that as a source of shorting, resistance, etc.. VSSB has a good ground.
BTW, there's a good signal at the VSS (vehicle speed sensor), required to run the Quick 4, which compares engine speed with vehicle speed and checks for slip. Being a 4X4, the VSS is at the transfer case.
The Quick 4 people told me to just "piggy-back" the two wires to the VSSB onto their wires, but couldn't explain the exact way to do it. So, having tried six, or seven, different combos, I feel that I just might have fried something in the VSSB, or in the inst. cluster.
Looking for advise, experience, ideas. Would especially appreciate a schematic of what happens at that buffer, and, or, the cluster.
Sorry for the long-winded discourse, but I'd like to nail this down, if possible.
Thanks, DW
 
Ahah! Can't say I'm too surprised to see a DP'er over here.
Having a bit of trouble learning to navigate the "new" site, but it'll come along. Just took about an hour of going through a lot of the DYI, projects and other experience that's been recorded here. Lots of info! Glad I finally found the site.
 
Welcome once again.

When @THEFERMANATOR sees this, he should be able to help you out. He's a very good transmission man. There are others on here that have that setup I think and will probably chime in once they see this thread to.
 
Welcome. Cool sounding Burb, I like pictures when you get some free time. Love the late 6.5 suburban's but won't own a ds4 again. And here dmv wont allow db2 conversion engines with yearly smogs required. Until they started that nonsense I owned a couple db conversion rigs.

Sorry, no help with the quick shift. Have you talked to Leroy?- Guessing that is who you bought it through?

If needed you could always go to a van or hummer tcm, use the 2 wire crank sensor from hmmwv in place of ess signal if you still have the reluctor wheel on your timing gear from when it was a ds4, or swap your oil pump drive for ess, but not sure what mid harness would be needed. The better control would be nice from the quick shift though.
 
For the vss connections, you want to keep it all stock, then splice the wires from the optishift into the wires at the vssb. This is how n8in8or did his, and his works correctly. When you clipped the wire to the radio, did you make sure it's not grounding out? Does this vehicle still have abs? If so, does it throw codes? The vssb sends out a 4k ppm signal to the speedo, radio, and ecm, and a 128k ppm signal to the abs. As to testing the cluster, you need a pulse generator to do so. You have to have something that can replicate the required square wave 4k ppm signal that the vssb makes in order to operate the speedo. I imagine most dealerships have gotten rid of there pulse generators, so even a dealer probably will beof little help if any.
 
Thanks for responding, guys. Please bear in mind that I'm all gears, chains, rods, steel, aluminum, brass, etc., as far as my brain goes. So, square waves and such are a lost cause for this 78 year old fart's brain.
Here are a couple of details on my Suburban, in hopes it might shed some light. * I put Phazer Gears in it, back in about 02, and don't remember ever having removed a reluctor wheel from it , though.
* I get my engine speed signal for the Quick 4 from the oil pump drive in the rear of the "V", and it's talking to the VSS just fine; having had "slip" codes on the controller display before I found the right frequency at said oil pump sensor.
*The ABS failed many years ago, but the brakes work just fine. So far, state inspection goes through fine, too, since the garage hasn't noticed that the bulb doesn't glow when the switch is turned on.
*The radio wire is totally isolated after clipping.
Correct me if I'm wrong, but I can't see how I could access a signal based on engine speed to drive the speedo, pre-transmission.

So, based on my ignorance, I'm guessing: If I open up the cluster and check continuity, or voltage from the VSSB to the connector (s) behind it, I should get some sort of reading on a vohm at that location; IF--- I'm running down the road, and, the AC signal from the VSS actually goes through the VSSB, to the speedo/odo connector? If I get nothing, I'm assuming that I've either opened up a component in the buffer, or fried a conductor or component beyond the buffer.

Just remembered another bit of info. I do get AC voltage to the buffer, when running down the road, but, I don't understand why it indicates so high. Starts out at low speed at about 5-10 V-AC and builds to ~40 V at an estimated 40 mph in 3rd gear! Is that to be expected? That's with the two wires to the Quick 4 disconnected and going only to the VSSB. Haven't actually done a road test like that with the four wires "piggy-backed".
 
2 wire magnetic pickup sensors put out a small a/c voltage charge when they trigger, as speed increases, so will the voltage. If you have an old style volt meter(analog, not digital), you could see the trigger signal from the vssb to the cluster.
 
Quote: 2 wire magnetic pickup sensors put out a small a/c voltage charge when they trigger, as speed increases, so will the voltage. If you have an old style volt meter(analog, not digital), you could see the trigger signal from the vssb to the cluster.
I'll hook the GM wires tomorrow, again, and see what I get while rolling. There's only two ways to piggy-back them, so I'll try them both. If I do get no signal of any kind, I'll assume that I have cooked something inside the VSSB. That 40 volts still has me baffled. I expected waaay lower than that. The only volt meter that I trust at all is an analog one.

BTW: I just had a really strange occurrence. I tried "clicking" on your post, and using it as a quote, like I would on The Diesel Page, and when I did that, I instantly got a short post from a DP member that I had looked at an hour ago! How the heck? Unbelievable. I clicked off that site completely before I came over here. ?????
 
Thanks, Nessmuk. Gotta confess I haven't been out there and chased any leads for a couple of days. Been fighting a lite case of pneumonia for about 3 weeks, now, and I'm so on-and-off, energy and enthusiasm-wise that I just plain stay contented to use the Burb for running around without a speedo and just enjoy the new shifting.

Did you ever try to access the signal from the original VSS? Did you use a 94, or later 4L80E? If so, the signal should have been the same as my 95, except, if your's is 2WD, then your signal would come from the rear of the trans, itself, rather than the transfer case. Curious to know why the Quick 4 people didn't furnish you a means to piggy-back your wires from the VSS. They (Quick4) tell me that I shouldn't have had a problem. But, I still think I fried something while trying every possible way to hook up their speedometer drive wire (tan) from the vehicle connector at the trans controller.

East Amazonian polar region? Really? Or, are you kidding us?

Thanks again for responding.
 
Fermanator: I've just made a run with my input from the VSS (now solid black and solid purple, instead of purple with white and light-green with white stripe), hooked directly (piggy-backed) to the VSSBuffer input. I've probed the output to the cluster (green), trying both a/c and d/c. I get a steady d/c voltage of right around one V at any speed. Set on a/c, I get an oscillating voltage at any speed that, strangely, will peak at just before a complete stop. Peaks at just over 3 volts. I get no reading at all, set on a/c, if I reverse my leads (pos. lead to ground), which tells me that the signal is d/c, if I'm correct in my thinking. Does any of this tell you anything as to the condition of my VSSB? Do you think that I could determine anything as regards what I may, or may not, have done to the speedo cluster, by removing it and looking for fried conductors, etc. on the printed circuit, etc.?
 
Are you sure you have power and ground to the vssb? Since you converted this truck to a db2, you may have cut the power or ground to it. From what you've done, it sounds like you're getting some ac feedback from the vss, but nothi,g from the vssb. I'm not sure how the optishift's speedo output works, but you may be able to use it to trigger the speedo. The cluster isn't very picky so long as it receives a square wave dc signal to it.
 
Thank you, sir.
I've been trying for an hour to copy and paste the section from the manal/disc, but it won't let me do that. Tried to move it to Word and can't get anywhere. So, I'll just type in what looks pertinent and hope I don't use up too much space for you.
Speedometer Output
We have provide an adj. speed signal on th tan wire on pin 12 of the vehicle connector that can be use to drive and elect. speedometer. Normally provided as a 5 volt square wave, but can be configured to provide a 12 V sq. wave. "(refer to "jumper settings" document for mor info.

There are 2 speedo. output modes that can be selected via the tuning software or the built-in tuning interface. It can also be disabled if not used. In the replicated speed sensor output the speedo output provides an amplified squared version of
the original speed sensor signal. Rplicated mode is useful for applications that require a signal with the exact pulse rate of the ss being used. There is also an adjustable corredted mode, very useful for coredting speeo errors or e providing unusual speeo output signal frequencies

Adjustable mode is essentially the elect. equiv. of a ratio correcor gear for a mech. speedo. Factor is the frequency ratio of the speedo. output frequency to the ss frequency. This number can be easily adjusted to synch the vehicle speedo. to a GPS or other instrument.

In some cases, such as driing the input of an engine control ECU, the 0-5 V (or 0-12 V) sq. wave signal will not be able to properly drive the device that it is connected to. This is because some devices are only designed to accept an input signal from a variable reluctance (mag coil) sensor. ( Is this what my VSS is?). To drive this type of input, use the included capacitor to "offset" the d/c value of the speedo. signal to 0 V. As a result, the driven device will se -2.5V to +2.5V, signal instead of 0V to 5V. to make this signal work, install the provide 10 uF, 25V, non-polar cap inline between the speedo output of the Quick 4 and the device that it is driving. To install the cap, cut the speedo output wire and dsolder a cap lead to each of the two cut wires. **

This just might be where I went wrong from the first! Their last paragraph confused me from the get-go. I just couldn't get my mind around the "two cut wires", thinking more about the two leads from the VSS , and NOT the one lead from the VSSB to the speedo. Is this where I may have messed up, yu think? BTW, I have the cap and can access it any time, just need to know what the actual location should be, I guess.
And, for some reason, my compuker won't let me go back and correct my typos. Every time I place my cursor in a spot, and back up to re-type, I lose my original typing; won't let me replace letters.

Sorry about being so long-winded and stupid. Appreciate all your effort.

DW
 
The last hoorah, this afternoon, with no luck. Here's what I have tried.

Have tried the US Shift speedo drive wire (tan) on each of the two wires from the speed sensor, pre vehicle speed sensor buffer, with and without the capacitor in-line. No speedometer movement. The wires were dead-ended down at the SS, because the Q-4 now uses those wires for sensing to the trans control.

Tried tying into the output wire (dk. greeen) from the VSSB to the speedo with, and without the capacitor between the Q4 tan wire and the green wire (VSSB to inst. cluster) otally disconnected from that lead. In both cases (capacitor, or straight thru), I get a signal to the speedo, because it goes up to 95 mph at no more than 9 mph! Jumps/oscillates quite a bit when the driveshaft is barely turning.

Since the green lead from the VSSB goes to a splice (S211) right near the PCM and branches off and goes to two locations at the PCM, I found a bundle where I could cut the lead to the speedo and isolate it without any influence from the PCM. Got GIANT needle movement at low speed without the capacitor in-line, and NO movement with the capacitor in-line. Now, this is going by memory from a few hours ago and admitting that I was running out of patience, so, I could be wrong about this last scenario.

What I get out of this in my faulty logic: Since I do get movement out of the speedo under certain conditions, I have to assume that I haven't fried anything in the inst. cluster. I'm also guessing that I'm missing something from the VSSB, since I get no movement whatsoever from the speedo is hooked up pre-VSSB. Fried component in the VSSB?

Hoping: That with a working VSSB, that I can somehow find the right combo of input (the right frequency/pulse) that will run my speedo.

Confused, because I fail to understand how I'm supposed to input a signal to the VSSB like US Shift describes, when I've used the leads(green/W and purple/W) to their controller, using one single lead (tan) for the signal to the VSSB.

I do have a huge manual from GM, titled C/K Truck Driveability, Emissions, and Electrical Diagnosis Manual. Sitting here, looking at that very VSSB wiring diagram and noting that the wires t the connector are the same number (8), and the same colors, but they aren't located at the same connector locations. This page is marked (Diesel Engines), and the previous page has a VSSB diagram for gas engines. Guessing that there are a couple of differences for the Suburban diesel.

Now, that was long-winded!
DW
 
No, the capacitor checks out. It's the one that came with the Q4, and is non-polar (see my previous post). It has a definite affect on the "signal", but I don't think that it's the intended affect.

At this point, I feel that the VSSB is probably "fried", and it's time for someone with a lot more smarts than the "Old Fart", here, to show me how to prove that, and then show me what to do to obtain the right signal to the speedo from that tan wire. I need info from a source that will tell me, explicitly, which wire goes where. Yep, I'm that ignorant.
 
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