View Full Version : DB2 Conversion now speedo reads half speed?
Hi all,
I have recently deep-sixed by hated Ds4. I am super happy thus far and now trying to work out a few bugs. The engine seems to be running well. I ahd to create my own throttle cable bracket that comes off the thermostat (single) and the AC backet. Mine was one with a single t'stat and the A/C compressor on the D/S. THis ended up being a bit more than I expected due to the throttle cable issues.
I chose to use the TCI-TCU/Fast for several reasons. THe truck has the 4L80E and is 4WD.
I found that it was in my best interest to fabricate my own accelerator pedal assy using the original (with the APP) so I could continue feeding the APP signal to the old PCM. When I did not, and left the CKP sensor signal feeding the PCM, it would cut off the wires originally for the fuel shut off on the DS4, which I use through a solenoid to power the DB2.
I hooked the TCI TCU up (speed sensor) to a covered pig-tail on the top of the trans toward the t-case. THis seems to work well as I get accurate signal to the TCU readout. However, and this is where my question is: Is there some reason I am unaware of that would make my speedometer read half the accurate speed? THis just started when doing this modifcation, and I can't seem to figure out why. THe ONLY disconnection to the drivetrain was the big round plug on the D/S of the trans. THe pigtail I connected to for the TCU speed input was unused and covered on the top of the trans. ANy guidance, suggestions or ridicule is appreciated.
Neo
(oh and my 4wd seems to work!)
More Power
08-12-2013, 11:27
I'm a little confused....
The 4L80-E makes use of three speed sensors that are used by the TCM.
The two on the forward half of the transmission are used to measure input and output rotational speed to help determine whether the transmission is slipping internally.
The tailshaft sensor is for vehicle speed.
Jim
Jim,
Thanks for the reply. I probably did not describe this well. Since I have converted over to the DB2, I diconnected the PCM (big-round connector) from the 4L80-E (drivers side) and plugged in the TCI TCU. The TCI TCU harness has a small connector (two pin IIRC) grey colored labeled "Speed sensor." Everything I read says to plug it in at the back nearest the driveshaft. I initially plugged it in (and removed the PCM plug) that is right near the big round plug on the D/S side of the trans. It was just a little behind the big round plug. I did not get a speed signal from that connection on the TCI TCU, I then unplugged the TCI TCU harness "speed sensor" from this port, and plugged the original PCM harness back in to the small port. While doing this, I found an Identical port on the transfer case. I found that on the harness (factory) that comes over the top of the rear part of the trans, there was a plug, with a coupling taped to the harness. THe "speed sensor" plug on the TCI harness also fit that coupling, so I plugged it in.
I now recieved the correct speed signal on the TCI TCU readout. However, my speedo now indicates half speed.
I am not 100% this is becuase of the changes to the trans controll off the TCI TCU or because there was something that came back from the DS4. I am hoping that the mismatch of the speedo on the dash and the wheel speed sensors used for the ABS is the reason I am not getting an ABS error. I hope that by fixing this, my ABS will work again.
Any ideas? THanks!
Neo
The speed sensor on the Tcase is what the speedo is calibrated to. This is what the ECM should be sensing.
I would think that the TCI unit should be plugged into the tailshaft of the 4L80E so that it can shift at the proper output shaft speed (directly related to engine speed through gear ratio) and not be affected by the 4lo ratio of the Tcase.
More Power
08-13-2013, 09:52
The internal speed sensors used to determine internal slip are shown in the following 4L80-E image. The sensors pointed to in this photo are NOT what you want to use for vehicle speed.
http://www.thedieselpageforums.com/photopost/data/500/4L80-sensor01.jpg
The vehicle speed sensor is the one located on the transmission tailshaft housing (if 2WD) or on the transfer case tailshaft housing (if 4WD) AND is not shown in this image.. Scroll farther down this page to see an image of the Vehicle Speed Sensor.
I can't imagine a TCM kit not using all three sensor inputs. Jim
Thanks gent's for the suggestions/ideas. So I finally felt well enough to do a little testing. Here is what I found.
1. the plug that goes into the sensor (from the OEM harness) on the right of the picture Jim posted feeds the dash speedo signal - or that is as it seems. BUT, that sensor provides a signal that is half speed. When/if I plug the TCI harness plug into the sensor at the right of the picture, I get the half speed indicator. If I take that OEM harness plug that came out of the right side sensor, (that goes to the dash I believe) and plug it into a port on the harness on the top of the trans, near the back of the trans, the speedo reads correct. I can plug the TCI TCU harness in there and get the same, the correct speed.
What seems like the utopian scenario is to plug the TCI speed input into the sensor on the right of the picture, since as I understand that indicates tailshaft speed, which may allow the TCI to shift properly in 4wd. And plug the one that was landed there into the port on the harness (pigtail) on the top of the trans.
I just need to know how to get the proper speed reading from the sensor at half the speed.
I hope this is not confusing, cause it really is to me. I don't understand why the OEM plug/sensor at the far right used to provide the correct speed. This is really wierding me out.
Any guidance is greatly appreciated.
Neo
Okay, my apologies for beating this one into submission, but this is driving me nuts and quite possibly the last major hurdle before I can confidently use the suburban again. Especially if my wife will be needing to drive it.
Is it reasonable that the rear most (to the RIGHT in Jim's picture) sensor goes bad and shows half speed? The reason is this:
1.THe shaft speed there should be the same exact shaft speed as that of the tailshaft except in 4WD Low range, correct?
2. Originally, the speedo was correct and was plugged into this sensor
3. THe Sensor seems a little flaky, like if I slow down coming to a stop, the truck is still rolling (driveshaft should still be spinning) the speed will drop to zero. It seems to jump from 0 to 7 or so after I start moving.
I have tried to "calibrate" for the half speed on the TCU, but it does not apear to be either a linear calibration or response - can't tell really which one is the issue.
I am about ready to try replacing the sensor to see if I get a more reasonable signal. WOuld there be any reason this signal would be half speed, like the relucto had half the points on it?
THanks for the info. I am about nuts over this.
Neo
More Power
08-15-2013, 09:14
The two sensors pointed to in the above photo have nothing to do with reading vehicle speed.
If you're attempting to use one of them to provide input for vehicle speed, you're doing it wrong.
Jim
Now I am really lost Jim. I thought those were speed sensors that read the shaft speed? I understand these are really designed for evaluating the slip inside the transmission. However, I can only assume the original TCU derived speed signal from the one on the right because when I unplugged it, the speedo does not work at all. When I plug it in now, I get half speed.
Would this speed sensor not provide output shaft speed?
I also read someplace that this is the best one to use for trans speed since the signal is not effected by low-range on the t-case.
Am I completely off-base on this?
Yes, I am getting frustrated with this. It just does not seem to make sense. Everything I have read, says the input I shoul dbe using is the rear one on the trans, but I get half speed there. I have tried to adjust for that, but the response does not apear to be linear, thus by speed is low at low speed, and high to very high at higher speeds.
So, here is the fundamental question:
Since the t-case does not multiply speed, and only reduces, and that is only when in 4Lo, is the front speed sensor NOT reading the input to the t-case? Is there some speed multiplying that goes on before, or could the reluctor ring on the trans output (far right sensor) be a 2000 ppm reluctor and not the 4000 ppm reluctor like the one on the transfer case exit?
THank you for any help/information on this.
Neo
DmaxMaverick
08-16-2013, 09:10
The "rear sensor on the trans", may not be what you think it is. To most, "rear" should mean the one that's most to the rear. Problem is, that one isn't actually on the tranny. The sensor you should be using for the speedo is NOT on the transmission, as Jim said. The tailshaft housing is an adapter, or part of the transfer case, to allow various application uses, and that is where the VSS is located, regardless of where the tailshaft housing is actually located. The sensors on the tranny are intended for transmission control, not vehicle speed, and probably the reason you can't make it make sense. Don't use that one. Use the one designed to do what you want it to do. Make it work as it should, or expect results that aren't what they should be.
You should be using the sensor on the tailshaft housing, and correct it as necessary for gear ratio and/or tire size through the VSSB.
More Power
08-16-2013, 10:14
Sorry I didn't make it more clear. I hope the following helps, but please ask if you need more info.
I'm holding the vehicle speed sensor in my hand in the following photo. This photo is of the tailshaft of a 4WD's transfer case used behind an Allison. Those transfer cases used behind a 4L80-E will be similar. If you're running a 2WD transmission without a transfer case, it'll still have a tailshaft housing that looks very much like this, except it may be cleaner.... :)
http://www.thedieselpageforums.com/photopost/data/500/SpeedSensor.jpg
The two sensors shown in an earlier photo (and earlier posted message) are used by the vehicle's transmission control module to monitor internal slippage. If the transmission control module senses more than x% amount of slippage, it'll put the transmission into "limp" mode, which helps to prevent further damage and may allow you to limp toward help. In addition, a transmission related trouble code will be set and a service engine soon or service transmission warning lamp may (should) illuminate.
If some aftermarket TCM isn't monitoring the two slip sensors, it is one I wouldn't want to use. Jim
Jim, i am not trying to be beligerant in any way. Aparently, the old tci tcu did use both sensors in the image, but now only specifies (and has wiring) for the rear one. They explicitly direct in the instruction, to use the rear sensor. That said, my speedo signal was originally coming from the rear sensor. Now that sensor drives the speedo and the tcu (whichever i plug into it) at half speed, but strangely. They (TCI) say to use the rear (right in ur picture) sensor so it (the tcu) can compensate for when the truck is in 4-lo
I am getting super frustrated, but i can always tap the current (tcase) Sensor and it wlll work.
Thanks!
Neo
DmaxMaverick
08-17-2013, 18:07
Why would the TCU have to compensate for anything regarding 4-low? How does 4-low affect transmission operation? At all? In any way?
The "rear" sensor, as far as the tranny goes, is the rear sensor on the transmission, NOT the sensor on the tailshaft housing, regardless where the tailshaft housing may be. The tailshaft sensor is NOT a transmission control sensor, and should not be used as such. If you are using either/any of the transmission sensors for speedo, it's not a surprise it doesn't work correctly. Connect the TCU to the tranny sensors, and forget about that thing on the tailshaft. Worry about that when you need your speedometer to work.
More Power
08-17-2013, 23:35
Jim, i am not trying to be beligerant in any way. Aparently, the old tci tcu did use both sensors in the image, but now only specifies (and has wiring) for the rear one. They explicitly direct in the instruction, to use the rear sensor. That said, my speedo signal was originally coming from the rear sensor. Now that sensor drives the speedo and the tcu (whichever i plug into it) at half speed, but strangely. They (TCI) say to use the rear (right in ur picture) sensor so it (the tcu) can compensate for when the truck is in 4-lo
I am getting super frustrated, but i can always tap the current (tcase) Sensor and it wlll work.
Thanks!
Neo
Neo, I'm not taking what you're posting negatively. It's good that you're asking questions.
If someone from TCI will, perhaps you could ask them to read this thread.
I suppose it's possible some control module programmer might use the rear slip sensor to calculate output shaft speed for use as a vehicle speed sensor, though I can't imagine why. Why not simply use the VSS, unless people are putting these transmissions in non-electronic vehicles that require a cable speedometer or something other... Still, if I were doing it, I'd look for another way to monitor transmission output shaft speed than by disabling the slip sensors. Let us know what TCI says.
Jim
Thanks so much for the conversation. I sincerely appreciate the information.
I really like the idea of asking the TCI folks to read this thread. Hopefully, it will help others as they try to do the same things. I have calls to them on this issue.
The weird thing is when I pulled off the read TRANS sensor (TOSS) or transmission output shaft sensor, as I was instructed to do in the instructions, and plug in the supplied (TCI) connected on the harness, I lost the speedo on the dash and the TCI handheld only read half speed, and a little erratic at that.
Now that that has happened, I tried plugging everything back together as original it does the same speed, 1/2 speed (and a little erratic at slow speed - it goes to zero when the truck is not sitting still.)on the dash.
TCI says this is the place to get speed so the shift points are consistent whether in 2WD or 4 Lo/Hi. THe problem with using the t-case sensor (which does give an accurate speed) is the TCI TCU uses vehicle speed for shift points, so in low, you never get to the speeds necessary to shift. If you can use a sensor ahead of the t-case and set your shift points there, low/hi range won't effect the shift patterns.
I have spoken with the folks at TCI about setting up the TCU for 4wd applications. You would think this would be reasonably easy since they have the ability to set it up for "performance" mode using a grounded trigger. There seems to reason they could not alter the program so that instead of performance mode, it goes into "lowRange" mode.
Thanks again, I will keep you all posted on my progress. Again, I can't express my appreciation to you all for the dialogue on this and other technical issues. It is so great to have a place we can share ideas and information. As I have said in the past, without this site, I would have never built the hummineer, and it is still an awesome truck.
Neo
Neo.
DmaxMaverick
08-18-2013, 06:44
That doesn't make much sense, at all. There shouldn't be a "low" mode, or a "high" mode. The tranny should shift the same, regardless of the TC range selected, and the speedo should read the same, according to ground speed. I think it's a communication error, between TCI and the user (you). If the TCU is reading the tranny input and output sensors, it should control the tranny the same, regardless of TC range selection. Like you said, if you are using the tailshaft sensor for tranny control, it will not shift correctly, no matter what, when in low range. TCI should have this thought through, and probably do. All TC's do NOT have the same reduction gear ratio, even if the TC models are the same, which may present another issue, even if TCI corrected it with programming "modes". Add to that, how would the TCU know which range is selected, and how would the speedo know what range is selected?
Also consider, not all applications will even have a speedometer, or the sensor in the tailshaft housing (or transfer case). They make no mention of that anywhere in their instructions, other than the "option" of adding a speedometer feature, with optional products (for mechanical speedo), or optional wiring (for electronic speedo).
We're right back where you started. If you have a "bad" sensor, it needs to be replaced, but that may not be the case. It seems to me there is only one way to wire the sensors to the TCU, and that's what Jim and I have been saying: The two sensors on the tranny need to be sending to the TCU, and the 3rd sensor, on the tailshaft housing (or transfer case, if 4wd) should only be expected to operate the speedo, independent of any tranny harness modification.
I was able to locate and download TCI's instruction manual for the TCU (http://www.tciauto.com/tc/tcir-ez-tcutm.html) (click the "instructions" tab). You're right, it is a bit vague. However, I did find a few things that should be helpful.
They only suggest using the tranny rear sensor for output speed, and they do not make any distinction for 2 or 4 WD. This suggests the sensor needed MUST be common to both, which is the rear TRANNY sensor, NOT the VSS (the actual rearmost sensor). Their language isn't clear, but according to their instructions, it's the only way it will work. All other instructions NOT related to output speed is related to an optional speedometer driver, be it electronic or cable-driven. Therefore, you should not be wiring into the "rearmost" sensor at all, for the TCI-TCU (although, their language suggests it). The 2 "forward" sensors are all that is needed, to provide input speed (engine speed), output speed (BEFORE the transfer case), and vehicle speed for the speedometer should remain the same as it was before you made any changes. They make accommodations for vehicles that do not, or never had, an electronic interface for speedometer sensing. I think this is where the confusion is, in your case. They show the two very separate devices and instructions in the same manual, and don't really make a definite separation of them. They say to "use the 'rearmost' sensor connector, but show a picture, and point to, the output speed sensor. The sensor they are suggesting and showing is NOT the VSS, located on your transfer case, and they make no reference to it.
You should also use the "forward most" sensor for "Tach In" (this is what they were originally designed to do, using the GM PCM/TCM). Both sensors on the tranny will operate at the same frequency, so should be compatible for the TCU sensing needs. If you are using another source for "Tach In", that may be part of the problem, as they may not be operating at the same frequency. In any case, they should send 4 pulses per revolution, according to the requirements in the instruction manual. This is another very vague area of the instructions. They specify the needed pulses to be "once per cylinder firing", but don't make any mention of accommodation for different engines, that may have more or fewer cylinders. I don't think the specific frequency is critical, as long as all sensors are operating the same. Any accommodations needed are done by programming the handheld.
Wire your system according to what we've suggested here (that is now consistent to what is suggested in their instructions). Once that is done, your speedo should work correctly, and the tranny should shift normally. If the tranny doesn't work right, troubleshoot that as a "new" problem, but don't try to rewire what is irrelevant to the problem (such as the VSS). Any problems will likely be related to specific programming choices in the handheld, which should be easily corrected. Again, the VSS (the 3rd of the 3 sensors) should be left wired as it was originally, and should not be part of the new TCU wiring.
Thanks so much for the very clear perspective. I really appreciate it. Unfortuantely, I am not there yet. I played with it some yesterday.
You are correct on the instructions you posted in your thread. THat is exactly what i ahve been working from. I agree wholeheartedly about the fact the "OUtput Shaft Speed" (top of page three) specifies to use the "TOSS" or trans output speed sensor as the proper place to connect. THis is the one that I originally tried to use, but the speed on the TCI shows half speed and then the unit will not shift correctly, regardless of how I tune it.
As a side note, tuning it is actually quite simple. Essentailly, you choose rear axle ratio, tire size, max shift rpm and a few other minor things and it is done.
As for the forward sensor, there is nothing in the TCI literature that references that forward (near bellhousing) sensor. Please correct me if I am worng. At this point, I am willing to try anything to fix this as I am now on month three since it has been sitting dead.
The only person to bring into the equation the rear sensor on the t-case has been me. I did this as a last resort. SInce the TOSS was not doing the trick, and there was another identical connector attached to the the harness on the top of the trans, I plugged in the TOSS lead from the TCI into it and it read an accurate speed and began shifting correctly.
Once I removed the original factory harness connection to the TOSS, i lost the speedo! That is the part that has frustrated the heck out of me, so I plugged that original OEM harness connection back into the TOSS (Where it was originally!) and I just get the half speed.
THis is why I am probably sounding like a babbling idiot.
I have explicitly followed the TCI instructions and it simply does not work.
As for the tach signal, I can get that from (according to the TCI manual) the W lead on the tach. I bought the dakota digital signal conditioner to help with that since hte frequncy of the signal was off. However, I found I can also get that from the CKP sensor as well and it works perfectly.
I am going to call the folks at TCI again today.
In adition, I tried to "correct" for the half speed on the TCI when connected to the TOSS and could nto make that work either. I used several diferent tactics, including setting r/p ratio and tire size to compensate as well as using the "correct speed" fucntion on the handheld. Neither worked correctly. Both would have correct speed only at one speed. at slow (<6 mph) speeds it drops all the way off to zero, where at 35mph it says I am doing 70 mph.
As a last resort, yesterday I tried taking the rear t-case signal and splitting it, providing an input to the TCI and to the Speedo, then niether worked! I can only assume that it did this becuase the voltage on the t-case tailshaft sensor (2 wire) is too small to drive both?
I did also change out the sensors on the trans, both the forward (TISS) and the rear (TOSS) and that did nto fix the issue.
I'm about at a loss as to what to do next.
Thanks again for the dialogue all, I think I would have burnt it in my front yard if it was not for this forum.:(
THought I would follow-up and let folks know what I ahve found as I dug deeper than I had ever through I would have to on this. I remain confused about one thing, that i will mention at the end.
So, my burb is a 96 K2500 6.5 4L80E that I am (still) converting to use the DB2. The speedo input originally used the reluctor ring and sensor on the output drum in the 4L80E (this is the part I am still confused about.) I know this is the case, becuase when I disconnected the TOSS from the orignal harness, I lost the speedo signal on the dash, gone, evaporated. Now, that said, there could be some weirdness going on, where it was used in conjunction with somethign else, like the t-case sensor.
THe TOSS has a 20 tooth reluctor ring on it, and in addition, it is pushed far back on the drum and barely visible through the sensor hole. The images are on my photobucket share (http://s1048.photobucket.com/user/rosbrughjb/media/Suburban%20Conversion/SensorHoleLookingBack.jpg.html) but I can't link them cause i am at work.
THis 20 tooth reluctor gives a 1/2 accurate speed, which I am going to try and get the TCI folks to comensate for in the TCU code. IT expects a 40 tooth/revolution reluctor, hence the half speed.
I'll post back one last time to let you all know how TCI helps out with the reluctor issue. In my opinion, it is importnat to get the speed info from the tail fo the trans so that 4Lo will shift correctly, tailshaft/t-case won't do it, unless an "alternate" shift pattern can be programmed in and triggered.
THe only thing that leaves me puzzled to today is the fact that the original OEM harness was plugged into the TOSS, the speedo read accuratley, then in installing the TCI, I unplgged it, lost the speedo and used the TOSS for the TCI, getting half speed. THen removed it, plugged back in the OEM harness tot he TOSS and NOW GET HALF SPEED! THat boggles my mind. I just don't understand how or why that would happen.
I have changed sensors three times now. I have (in the photobucket) a comparison of the signals form teh tailshaft and the TOSS. THe TOSS is lower amplitude and longer period (higher freq) by factor of two, hence the 1/2 speed. Really wierd. Thanks again to all.
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