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#2376 |
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Location: Visalia California
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Re: Crusty Rusty Leaky Squeaky 67 Step
You could probably scope the single vss wire going to the sn74z to see if the signal is getting there. Just a thought Vic.
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#2377 | |
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Location: Manitoba, Canada
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Re: Crusty Rusty Leaky Squeaky 67 Step
Quote:
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
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**RED SEAL CERTIFIED JOURNEYMAN SINCE 1993** My 1966 GMC Value Van Project 1951 GMC 9430 1-Ton I'm just going to put an OUT-OF-ORDER sign on my forehead... and call it a day. |
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#2378 | ||
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Re: Crusty Rusty Leaky Squeaky 67 Step
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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.
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2379 |
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Re: Crusty Rusty Leaky Squeaky 67 Step
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...
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2380 |
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Location: Visalia California
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Re: Crusty Rusty Leaky Squeaky 67 Step
Check engine light should be on with a vss code if it's not seeing vss
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#2381 | |
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Re: Crusty Rusty Leaky Squeaky 67 Step
Quote:
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2382 |
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Re: Crusty Rusty Leaky Squeaky 67 Step
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.
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#2383 |
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Re: Crusty Rusty Leaky Squeaky 67 Step
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.
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2384 |
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Re: Crusty Rusty Leaky Squeaky 67 Step
Sounds like a plan, Jason, I'll double check them.
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2385 |
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Re: Crusty Rusty Leaky Squeaky 67 Step
Do you have good ground straps from block to frame and cab to frame etc.
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#2386 |
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Re: Crusty Rusty Leaky Squeaky 67 Step
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.
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2387 |
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Location: Manitoba, Canada
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Re: Crusty Rusty Leaky Squeaky 67 Step
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
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**RED SEAL CERTIFIED JOURNEYMAN SINCE 1993** My 1966 GMC Value Van Project 1951 GMC 9430 1-Ton I'm just going to put an OUT-OF-ORDER sign on my forehead... and call it a day. Last edited by Aberdare; 03-09-2018 at 09:23 PM. Reason: Added a question |
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#2388 | |
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Re: Crusty Rusty Leaky Squeaky 67 Step
Quote:
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...
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2389 | |
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Re: Crusty Rusty Leaky Squeaky 67 Step
Quote:
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
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**RED SEAL CERTIFIED JOURNEYMAN SINCE 1993** My 1966 GMC Value Van Project 1951 GMC 9430 1-Ton I'm just going to put an OUT-OF-ORDER sign on my forehead... and call it a day. Last edited by Aberdare; 03-10-2018 at 02:19 PM. |
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#2390 | |
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Re: Crusty Rusty Leaky Squeaky 67 Step
Quote:
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.
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2391 |
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Location: Visalia California
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Re: Crusty Rusty Leaky Squeaky 67 Step
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.
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#2392 |
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Re: Crusty Rusty Leaky Squeaky 67 Step
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.
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#2393 | ||
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Re: Crusty Rusty Leaky Squeaky 67 Step
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2394 |
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Re: Crusty Rusty Leaky Squeaky 67 Step
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.
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**RED SEAL CERTIFIED JOURNEYMAN SINCE 1993** My 1966 GMC Value Van Project 1951 GMC 9430 1-Ton I'm just going to put an OUT-OF-ORDER sign on my forehead... and call it a day. Last edited by Aberdare; 03-10-2018 at 10:22 PM. |
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#2395 | |
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Re: Crusty Rusty Leaky Squeaky 67 Step
Quote:
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. ![]()
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2396 |
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Location: Raleigh
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Re: Crusty Rusty Leaky Squeaky 67 Step
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...
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#2397 |
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Location: Manitoba, Canada
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Re: Crusty Rusty Leaky Squeaky 67 Step
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
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**RED SEAL CERTIFIED JOURNEYMAN SINCE 1993** My 1966 GMC Value Van Project 1951 GMC 9430 1-Ton I'm just going to put an OUT-OF-ORDER sign on my forehead... and call it a day. |
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#2398 | ||
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Re: Crusty Rusty Leaky Squeaky 67 Step
Quote:
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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.
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Victor 57 Chevy Wagon - California Dreamin'"Mecum'd" 9/2022 Dallas, TX Crusty Rusty Leaky Squeaky 67 Consigned 4/2019 Dresden, Germany Maybelline - my '57 Ford 2dr Sedan "Mecum'd" 3/2016 Location unknown Silver Streaker "Mecum'd" 4/2013 Somewhere in Texas |
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#2399 |
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Join Date: Aug 2012
Location: Topeka Kansas
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Re: Crusty Rusty Leaky Squeaky 67 Step
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.
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#2400 |
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Join Date: Dec 2009
Location: killeen tx 76542
Posts: 193
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Re: Crusty Rusty Leaky Squeaky 67 Step
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
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A C Ward Retired US Army 66 El Camino 67 SWB underwent major Surgery- http://67-72chevytrucks.com/vboard/s...d.php?t=776475 Last edited by a.c.ward; 03-11-2018 at 09:46 PM. |
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