Crusty Rusty Leaky Squeaky 67 Step

[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.

[Aberdare]

Originally Posted by Vic1947

Thanks, Dale, I know what you mean. The younger guys take to it like a duck to water, but at my age, an HEI is high tech, baby!

Hey Vic:
Thought I'd chime in here after reading all the previous posts about your speedo function fault. Just a few quick questions to help you along the troubleshooting path.

1) Does your truck's new electronics include a Central Electronics Module (CEM)? -- or the equivalent as part of your electronics conversion installation.

2) Does your truck have an AFTER 1994 OBDII DATA LINK CONNECTOR? This will allow you to use a Diagnostics Scan Tool to troubleshoot the Data Stream information.

I have a background in Industrial Electronics and Automotive Electrical Systems... so with a little bit of information, I can point you in the right direction.

Cheers, Abe

[Vic1947]

Originally Posted by 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.

We're thinking along the same lines, Jason. I got my $25 oscilloscope calibrated and assembled this morning... finally. Woke up with a stomach bug, so I've been moving slowly and carefully. Plan to hook the scope up in a little while after I read the instructions. Probably wouldn't take a lot to blow up a "value priced" electronic box.

Originally Posted by Aberdare

Hey Vic:
Thought I'd chime in here after reading all the previous posts about your speedo function fault. Just a few quick questions to help you along the troubleshooting path.

1) Does your truck's new electronics include a Central Electronics Module (CEM)? -- or the equivalent as part of your electronics conversion installation.

2) Does your truck have an AFTER 1994 OBDII DATA LINK CONNECTOR? This will allow you to use a Diagnostics Scan Tool to troubleshoot the Data Stream information.

I have a background in Industrial Electronics and Automotive Electrical Systems... so with a little bit of information, I can point you in the right direction.

Cheers, Abe

Thanks, Abe, I can use the help for sure. I'm running Classic Instruments gauges with a SN74Z interface box which may be what you're calling a CEM. The SN box will accept either a single wire digital square wave (the SPEEDOUT from the TCU) or a two wire sine wave input. From what I've been able to get out of the GM Powertrain folks, the VSS TISS sender on the tailshaft of the trans sends a speed variable AC signal to the ECU which then conditions it and sends it to the TCU. The VSS TOSS high and low signal are also available at a weatherpack connector on the ECU harness which might be a potential source for the SN74Z if there's no signal coming out of the TCU.

The ECU does have an OBDII port, but the scanner I ordered hasn't arrived yet. The GM tech said that if the tailshaft sensor was good, I should hook into the OBDII port to check the VSS signal there. I'm not scanner educated, so I'm going on faith that there's a menu there that will allow me to gather that information.

[Vic1947]

Hooked the scope to the orange SPEEDOUT wire and saw no signal at all. Also tested the VSS TOSS hi/lo wires out of the ECU harness with no luck either. I have a feeling that when the scanner arrives on Saturday, I'll have no signal at the OBDII port either. The Supermatic software on the laptop registered everything but speed, so somewhere along the line, the signal coming out of the tail shaft sensor is either not present or, if it makes it into the ECU, it's not making it out. Unfortunately, the documentation is very minimal. The trans came with a .pdf file that has a partial schematic and part numbers for the plugs but the engine I-sheet only has some pin out information and not enough to know exactly how the VSS signal is routed. I have one more place to check at the bulkhead connector. Stay tuned...

[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.

[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]

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.

[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.

[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.

[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.

[Vic1947]

Originally Posted by 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.

Thanks for the info, Jason. Not sure if the ECM and TCM are paired but the line items were separate on the receipt from the dealer. As for the codes, I wouldn't trust that my el-cheapo scanner is telling the whole story. As I recall, the coil resistance of the VSS in the tailshaft was virtually zero. I was able to read the AC voltage across the pins with the output shaft turning, though. The pin sockets in the TCU plug are so small I'd need to use needles to get a reading but I might be able to manage that if I'm careful. I previously measured the continuity of the wiring from the VSS plug to right where the wires enter the TCU plug and it was good.

Originally Posted by cornerstone

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.

Thanks for the kind words, although, I fear re-reading the thread will confirm there's been an awful lot of "two steps forward, one step back" going on.

[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.

[Ramjet51]

Great thread and I’m being tutored by an incredible forum. Great talents. I found your thread, started reading and just really liked the bumper treatment, even was late for a doc appointment because I got so engrossed in the reading. So closed the iPad down and couldn’t find the tread again for hours and hours....why??....I was mainly searching for a SWB thread and never thought it would be a “Step”....got back on the read and now I’m up to date, what a great thread.....don’t know if it’s been said, but ground loops in signals can occur if you ground both ends of a shielded cable. I’ve always practiced this, maybe Chris will chime in...

[Aberdare]

Vic:
Even though it has been past the specified warranty period... If your local dealer wants to continue to covet the business of people like yourself, regardless of the warranty period... they may give you some serious consideration for a replacement WITH a software upgrade. Of course if you ask nicely (with your wallet poised to head out the door)... word will get around quickly whether that word is pos(+) or neg(-) will be up to them of course.

Here in Winnipeg the dealers are all the same... if your vehicle is more than 10 years old, they just don't want your business... and some of the dealers are worse than others... but it never hurts to ask of course - the worst they're going to say is NO then watch you AND your wallet walk out the door.

Abe

[Vic1947]

Originally Posted by Ramjet51

Great thread....don’t know if it’s been said, but ground loops in signals can occur if you ground both ends of a shielded cable. I’ve always practiced this, maybe Chris will chime in...

I know I have some twisted pairs, but no shielded cable in the GMPP harness from what I can see. Thanks for the read!

Originally Posted by Aberdare

... and some of the dealers are worse than others... but it never hurts to ask of course - the worst they're going to say is NO then watch you AND your wallet walk out the door.

We'll see how it goes, Abe. I'm guessing at some point I could be looking at new parts or service fees for repairing mine.

I got kinda worked up a couple of times today, only to suffer a letdown. Pin 17 on the TCM connector plug is labeled SPEEDO OUT and the schematic showed an orange/white wire coming out of it. Realized there's no wire in that cavity, just a dummy pin. Then I took a closer look at the schematic and despite the label, it shows the pin as unconnected. It also occurred to me that the cruise control wiring harness has a pigtail that splices it into the electronic pedal. The CC also requires an input from the orange SPEEDOUT wire. I'd disconnected the speed wire to the CC early on after talking to the first tech at GM, but never removed the pigtail going to the pedal, so I did that as well, but to no avail... still nothing.

So, my latest line of thought is that the VSS signal coming from the tailshaft may actually need to go to the ECM instead of the TCM. The following text is from the I-sheet that came with the package.

Vehicle Requirements
Vehicle Speed Input - optional
The ECM is programmed and looking for 40 pulses per revolution
typical for automatic transmissions. The LS Control System harness
is designed to plug into the output speed sensor of 4L60 & 4L80
Transmissions, which have a 40 pulse output. NOTE: If you are using
the CP Supermatic Connect and Cruise Transmission Control
System, the vehicle speed input must be plugged in.

These things (I think) I know:

1) The speed out cavity in the TCM plug is blank and I see no other speed signal coming out of the TCM according to the schematic. So apparently the TCM isn't tasked with sending out a speed signal to the speedo.

2) The orange SPEEDOUT wire is connected to a brown wire via the bulkhead connector which comes out of the ECM on pin 39 of the blue (C1) ECM plug.

3) The gray (C3) ECM plug uses pins 66 & 67 for the VSS TOSS high and low.

4) I see no path whereby the TCM takes the signal coming from the transmission tailshaft (VSS TISS) connector and passes it thru the TCM and out to the ECM. Admittedly, I don't have a full set of schematics for the ECM, only the pinouts, but I haven't stumbled across the way the signal might move between the two controllers.

5) Somehow the ECM has to get a VSS signal if it's going to send the square wave out thru the bulkhead connector to the unterminated orange wire that feeds the speedo. Which brings me back to the above quote from the I-sheet.

Tomorrow it looks like I'll be back on the phone. Maybe I'll get a tech who will give me so useful pointers. Will post up what I find.

[Xeen]

I know this is frustrating for you but on the bright side you are gaining knowledge about GM electronics, enough that you will be able to help other people that are running into issues and asking for help with diagnostics, so something good will come out of all this trouble in the end.

[a.c.ward]

vic, we did a connect and cruise on a customers car and experienced similar speedo problems, we used Dakota Digital gauges, so I cant help with the gauges, but check out the following information I found on line:
Circuit # Position Wire Gage Color Description
818 D 22 Brown Vehicle Speed - Out

description in manual of what the brown wire does:
Vehicle Speed (BROWN) – This is a non scaled output for use with
auto-scaling speedometers and will not function unless a vehicle
speed sensor (VSS) is connected to the ECM through the VSS wire
in the harness.

this in on the 12 pin connector engine side of the harness. I connected this brown wire to the DD box and speedo worked, maybe worth a try for you.

maybe check out also

circuit #121 position 25 wire gauge 22 wire color white engine speed bulk head pos c on the blue C1 engine connector, also shows speed out.

if you have any further questions or need to talk this thru, you should still have my number, we talked thru the Vintage Air hardlines once before, if you need my number PM me.

AC