Crusty Rusty Leaky Squeaky 67 Step

[Jason7121]

No matter if speedo works or not you should be able to read vehicle speed with a scanner the two wire vss on back of tailshaft should be prewired with your harness I would think.

[Vic1947]

Originally Posted by Jason7121

No matter if speedo works or not you should be able to read vehicle speed with a scanner the two wire vss on back of tailshaft should be prewired with your harness I would think.

Yep, it's there. I'm waiting on an OBDII scanner doohickey I ordered last week, so I'm not able to check anything at this time. I am a bit confused, though, as to why the laptop transmission calibration software app didn't display the speed but everything else worked. It looks like the app is meant to allow you to modify rear gear ratio and tire size for an OEM speedo and maybe even tweak the shift points but not much else. That said though, you'd think it keys off the same VSS info that would be accessed via the OBDII port.

[knomadd]

Vic, You may need to test that speed signal sending unit (whatever it's called) to see if it's even operational. I know it's new, but you know as well as I do, even some new parts are dead right out of the box. It sounds to me like you either have a dead sensor/sending unit, or a signal wire that's not hooked up correctly.

I'd think the trans software would show you the speed too, otherwise what good is it to be able to log data and see what it's doing before just blindly changing settings?

[Vic1947]

Originally Posted by knomadd

Vic, You may need to test that speed signal sending unit (whatever it's called) to see if it's even operational. I know it's new, but you know as well as I do, even some new parts are dead right out of the box. It sounds to me like you either have a dead sensor/sending unit, or a signal wire that's not hooked up correctly.

I'd think the trans software would show you the speed too, otherwise what good is it to be able to log data and see what it's doing before just blindly changing settings?

I was thinking along the same lines, Duane. I called the GM Powertrain hotline this afternoon and discussed it with a tech. He said I should see a 1-3VAC signal right out of the sensor with the tires rotating. I need to get something rigged up where I can safely measure the sensor voltage with the truck in gear. Those pins on the sender are tiny!

The tech said if the sender was good, I need to hook a scanner to the OBDII port to see if the signal is making it to the ECU. It goes from the sender to the ECU and from there to the TCU. So if it makes it to the ECU and is readable at the diagnostic port, then I need to find out if it's getting in (and out of) the TCU. For that, I'll have to use the oscilloscope I have on order and don't have yet.

The tech was reluctantly helpful today. He said they were not really supposed to help consumers with diagnostics due to liability issues. But he gave me enough info to get me going.

[Low Elco]

Please tell me more of this Kamikaze charcoal vent of which you speak.

[Vic1947]

Originally Posted by Low Elco

Please tell me more of this Kamikaze charcoal vent of which you speak.

I was looking for a charcoal canister to connect to the vent on the gas tank when I ran across several listings on eBay for Kawasaki Ninja scoots. The size and shape looked easy to adapt to my needs, so I bought one that was a take off from a relatively new bike. I'm guessing bike builders remove them during the customization process. Mine came with an electric shutoff solenoid, so if you wanted, you could wire it to completely close the vent when the truck isn't running. Plumbing it into the intake would be the most effective, but I was mainly looking to neutralize any vapors coming from the vent. I'll try it like this and if I notice any fuel smell in the shop after filling up, I may hook up the shutoff solenoid.

[Low Elco]

Hrmnmn. I may have to investigate this. Thanks!

[AKC]

Vic, my hearty congratulations on the first fire-up of CRLS! Been a long time coming, you should be proud. And the missus' is to be commended for what must've been an exorbitant amount of patience!

Can't wait to see it all finished up.

But now I just feel like such a slacker...

[Vic1947]

Originally Posted by AKC

Vic, my hearty congratulations on the first fire-up of CRLS! Been a long time coming, you should be proud. And the missus' is to be commended for what must've been an exorbitant amount of patience!

Can't wait to see it all finished up.

But now I just feel like such a slacker...

Thanks, I appreciate it, and you're right that I owe a lot to Kathy. I was lucky in that way as she has always supported the drag racing and endless parade of projects over the years. Can't tell you how many times I've stored parts in the breakfast nook or rebuilt four speeds on the living room floor in the various places we've lived and she's never griped even once. Not all guys are that fortunate.

Brief update: I checked the VSS sender on the tailshaft today and it seems to be working. The tech at GM Powertrain said it should read 1-3 VAC, but it actually read between 1 and 13VAC. It might have gone even higher if I'd upped the speed some more, but at that point, I knew it was putting out a measurable signal. So I'll have to move on to the harness and modules. The scope finally arrived, but it was in pieces. Took me a while to assemble it, only to find that it needed to be setup first so I had to take it back apart since there was no provision in the case to access the calibration capacitors. Plus, I only had 6VDC power supplies and it needs 9V, so I have to make a parts run in the morning. Hopefully it won't take long to isolate the problem now that I have a double throwdown test gizmo.

[Jason7121]

You could probably scope the single vss wire going to the sn74z to see if the signal is getting there. Just a thought Vic.

[Jason7121]

Check engine light should be on with a vss code if it's not seeing vss

[Vic1947]

Originally Posted by Jason7121

Check engine light should be on with a vss code if it's not seeing vss

Well, that's another weird issue I was saving for the scan tool. The MIL on the dash and the one in the relay box both glow brightly with the key on but the engine not running. After startup, the light in the relay box goes out (as best I can tell) but the light on the dash flickers faintly. VIDEO I was going to research it some more after I got the speedometer sorted out... but since you brought it up.

[Vic1947]

Here's the waveforms I pulled off the brown Vehicle Speed - Out wire at the bulkhead connector. The square wave is with the key on but the engine not running. The noisy one is with the engine running. When I place the trans in drive, the noisy waveform doesn't really change. I expected to see the frequency increase as the drive wheels sped up, but all I'm seeing is noise. At least it's something. As I mentioned earlier, the SPEEDOUT wire isn't registering anything... not even noise.

[Jason7121]

Sounds like a ground is either poor or not hooked up. Ecm sends ground to engine light to turn it on. Also speedo would be erratic or not work. Have seen this on a few Ls motors.

[Vic1947]

Originally Posted by Jason7121

Sounds like a ground is either poor or not hooked up. Ecm sends ground to engine light to turn it on. Also speedo would be erratic or not work. Have seen this on a few Ls motors.

Sounds like a plan, Jason, I'll double check them.

[Jason7121]

Do you have good ground straps from block to frame and cab to frame etc.

[Vic1947]

Originally Posted by Jason7121

Do you have good ground straps from block to frame and cab to frame etc.

Yes, I have several, but it can't hurt to add some more. I have a roll of woven tinned copper that my buddy Jay gave me. I've added eyelets on the ends and used them as purpose built grounds in a few places. Made extras, so I'll go around and install them tomorrow. The one from the chassis to the engine is an extra heavy duty woven copper piece I bought.

[Aberdare]

Vic:
This is could be more than a simple ground issue. With Key On Engine Off (KOEO), the VSS should be a flat line on your oscilloscope. With Key On Engine Running (KOER), the VSS should still be flat line until put into gear and speeding up should begin to show a frequency change.

Checking the grounds is certainly not going to hurt... The Flashing Check Engine Lamp while the engine is running is a good indicator of a bad/missing ground somewhere. Are you using a NEW TCM? GM TCM's require programing/software download to function correctly, as they are BLANK (no software) out of the box. You may want to consult a local professional who deals in this sort of thing who can do a software load for your TCM.

Just pointing you in a new direction... hope it helps.
Abe

[Vic1947]

Originally Posted by Aberdare

Vic:
This is could be more than a simple ground issue. With Key On Engine Off (KOEO), the VSS should be a flat line on your oscilloscope. With Key On Engine Running (KOER), the VSS should still be flat line until put into gear and speeding up should begin to show a frequency change.

Checking the grounds is certainly not going to hurt... The Flashing Check Engine Lamp while the engine is running is a good indicator of a bad/missing ground somewhere. Are you using a NEW TCM? GM TCM's require programing/software download to function correctly, as they are BLANK (no software) out of the box. You may want to consult a local professional who deals in this sort of thing who can do a software load for your TCM.

Just pointing you in a new direction... hope it helps.
Abe

Thanks, Abe. As you said, it never hurts to insure you have good grounds, so I added several more today to connect the trans case to the chassis/cab and to tie the instrument panel ground post to another spot on the cab. While I had the instrument panel out I went back and re-tightened all the posts on the gauges and checked resistance values. I also verified continuity from the VSS TISS sender plug to the TCU plug and from the TCU plug to the SPEEDOUT wire that should be carrying the variable frequency square wave to the speedometer. I don't have a schematic for the ECU and its harness, so I can't see how it connects to the TCU. Which means I can't verify those wires. Long story short on the grounds, nothing I did made a difference.

The GM TCU (TCM) I'm using came pre-programmed to run the 4L65E transmission. When I connect the laptop cable to the port provided on the TCU harness, it downloads the trans calibration and I can see the maps and it will allow me to input the rear gear ratio and tire size to adjust for them. With the engine running I can see vital statistics like rpm, line pressure, voltage, coolant temp, trans temp, gear selection and whatnot. What I don't see is any movement on the virtual speedometer with the truck in gear and the tires rotating, even though everything else works. All of this makes me suspicious of the TCU. If it's getting the signal from the sender on the tailshaft, but not putting out a signal on the SPEEDOUT wire and the harness wiring is all good, it would seem the issue may be with the module.

I have a friend coming by tomorrow with an expensive, high end GM scanner. He's very knowledgeable in its use, so I hope we can come up with additional info from the OBD2 port. I've also heard that perhaps a dealership can "bench test" the computers to verify their operation. Whatever we learn tomorrow I'll document, then chat with the GM Powertrain helpdesk on Monday to see what they may suggest as well. I agree that the noise I observed with the scope is out of line with what I'd expect. If the noise is coming from some other source, shielding might help as you say. I'm a bit swamped at this point, so before I head down that path, I'm going to gather some more data with the scanner. Stay tuned...

[Aberdare]

Originally Posted by Vic1947

The GM TCU (TCM) I'm using came pre-programmed to run the 4L65E transmission...

I have a friend coming by tomorrow with an expensive, high end GM scanner. He's very knowledgeable in its use, so I hope we can come up with additional info from the OBD2 port... Stay tuned...

Vic:
I've seen this problem on a customer's 2014 Tahoe. His Vehicle's speedo and gauge cluster went blank... once the gauge cluster was repaired (Shorted Gauge Cluster Printed Circuit) by a contactor, the only portion not functioning was the Speedo. After thorough diagnostics, the TCU was found to be defective - which I found via the old school method of back tracing all the wiring with an OHM meter to verify no shorts or opens in the wiring between the TCU and the CEM. Also checked all the Transmission Sensor wiring using the same method. With everything verified, the only logical conclusion left is a bad TCU... which proved correct. Since the NEW TCU came BLANK out of the box, it had to have a software reload... after that was completed, everything worked exactly the way it was supposed to.

You may also want to verify the Speedo Gauge itself is in proper working order, by injecting a proper square wave signal using a Signal Generator - on the input side of the CEM (your SN74Z interface box)... and also that the VSS is producing the correct signal.

Yea, it may sound overly technical... but old school diagnostics will be your best skill to use, via the process of elimination.

Hope this points you in the right direction.
Abe

[Vic1947]

Originally Posted by Aberdare

I've seen this problem... after thorough diagnostics, the TCU was found to be defective - which I found via the old school method of back tracing all the wiring with an OHM meter to verify no shorts or opens in the wiring between the TCU and the CEM.

You may also want to verify the Speedo Gauge itself is in proper working order, by injecting a proper square wave signal.

It's comforting, in a perverse sort of way, that you found a bad trans controller as I'm slowly arriving at the same conclusion. As far as I can tell, the harness and the signal generator check out, which pretty much only leaves the box.

I did as you suggested and connected the SN16 signal generator to the SN74Z and used a drill to spin it up. Speedo worked perfectly.

My buddy wasn't able to retrieve his scanner from a friend who has it, so we rescheduled for tomorrow. Meanwhile mine arrived in the mail, so I connected it to the OBDII port and fired up the engine. It showed no stored codes and the live data read rpm, but no speed with the tires rotating. I don't know what other menus to check at this point. Need to familiarize myself with it more. As with most cheap stuff, documentation is sparse.

I hooked the Connect & Cruise laptop software back up to the TCM/TCU and it verified what I was already pretty sure of. The trans isn't shifting out of first gear. I can see line pressure, throttle position, gear selection, actual gear, rpm and etc. but it never shifts into second. Tried manually shifting it as well as leaving it in drive but no luck. I'm not sure what other data I may be able to acquire with the GM scanner tomorrow, but I hope it tells me something I can use.

The cooling fan issue isn't sorted all the way either. I ran the engine until the thermostat opened at 195 and the fans never came on. With the new, lower resistance probe and the calibration pot screwed all the way out, they should have fired off well below 180. With the thermostat open, the three core aluminum radiator was working so well the temperature dropped to 192 and stayed there even without the fans running. The module passes all the tests for low and high speed, so I need to call Derale back and see what they think.

I gotta tell you, I'm totally bummed at this point.

[cornerstone]

Originally Posted by Vic1947

I gotta tell you, I'm totally bummed at this point.

Man, I think we are all bummed for you. Another hurdle before you get to savor that beautiful work of art. I’m also anxious about getting my truck running again. I’m sure I will have to re read your thread a few more times. Thanks for your detailed posts and willingness to share everything.

[Jason7121]

When the tcm doesn't see speed signal often it will default to third and reverse only. The ecm and tcm share data for speed signal via data communication high speed gm lan. I wonder if ecm and tcm are programmed as a pair? Weird there are no codes associated with vss. You could measure resistance across vss and see what it reads then plug connector back in and measure resistance at other end at tcm and resistance should be about the same if it is then you know vss wiring and sensor resistance is good all the way to tcm. Hope that may help you Vic.

[Aberdare]

Vic:
You've been busy troubleshooting... After reading all of the above posts, I too am drawing the conclusion that your TCU could be at fault - meaning not that the TCU is defective, but the software/programing is incorrect and may need to be updated.

The fact that you found no Diagnostic Trouble Codes (DTC's) stored is also telling me you may have a defective TCU or at the minimum a software/programing issue associated with bad hardware. I would suggest rechecking the wiring and pin-outs to the CEM are all correct and the correct voltages are present where they should be, with grounds where they all should be. Your Local GM Dealer should be able to provide you with a schematic for a few dollars and a box of donuts if they're the neighborly type.

Was your TCU New or used? Any warranty? Please advise.

[Vic1947]

Originally Posted by Aberdare

...I would suggest rechecking the wiring and pin-outs to the CEM are all correct and the correct voltages are present where they should be, with grounds where they all should be. Your Local GM Dealer should be able to provide you with a schematic for a few dollars and a box of donuts if they're the neighborly type.

Was your TCU New or used? Any warranty? Please advise.

A schematic would be a big help, no doubt. Part of the problem is that the GMPP Connect & Cruise package is supposed to be customized to eliminate all unnecessary inputs/outputs that might otherwise be required in an OEM vehicle. As such, a "factory" schematic may not translate well. To further complicate matters, you can purchase their crate motors with or without transmissions, controllers or harnesses. However, a Connect & Cruise package is supposed to have everything you need... engine, trans, ECM, TCM and a harness with all extraneous plugs removed. Mine came in two crates. One box had the engine and electronics, the other had the transmission and converter.

Now, you'd assume that meant it all came as a matched set from GM, but I don't think that's always the case. I suspect the dealer may have pieced mine together from inventory. My invoice had part numbers that didn't satisfy the requirements for the $500 rebate GM offered at the time. Took forever for them to sort it out with the folks handling the rebate. I also noticed that the converter was labeled as "remanufactured" and the transmission (which looked new) was shipped in a used, well worn container.

However, the engine, modules and harness were all spanking new. I doubt though, that there's a warranty any longer. The purchase date was April, 2016 and the warranty was good for 12 months. Anyone that's plugged away in a one man shop knows you can't do a frame off rebuild, shoehorn in a new, high tech power train, wire, plumb, paint and upholster (along with a zillion other things) and get it done in 12 months. So even though the engine wasn't fired until a week or so ago, it's unlikely they would warrant anything. If they did, I'd be pleasantly surprised.