This time of year gives some time to go a bit deeper into some of the oddities of our vans, and this is another step into trying to determine why the 4 speed Chevies get hot, primarily transmissions, on long climbs. Lots of things make incremental improvements, like big coolers, two core radiator, add on electric fans, etc, but none of them really seem to address the root causes, I think.
I have been digging everywhere I could to find out what is different between the later model 6 speed and the four speed models like we have. Nothing stood out beyond the transmission change. We have found with our van that it tended not to get hot climbing mountains in high gear, but would get very hot climbing in lower gears in other places. Since the major part of the heat in a transmission comes from the torque converter when it is unlocked, I started looking for specs, or a way to test, when the torque converter was locked.
I did find a "tuner" which also did the trans settings as well as engine settings, tire size, drivetrain settings, etc. and finally decided just to get it it see what was up. The tuner piggybacks on the factory program, so you can change just what you want and leave the rest as is, so easier than a start from scratch programmer.
The first thing I did was read our existing program.
Here is the data table for the "normal" mode, which is basically the one you get most of the time, unless cruise or tow/haul are on.
This is the same thing when in tow haul mode
They basically show what the shiftpoints are in mph based on TPS reading and the gear in use and similar for the converter locking and unlocking.
What these table show, it appears is that the 4 speed transmission rarely has the converter locked under the conditions we see when climbing in other than 4th gear. For instance, we were able to climb to 12K feet in Rocky Mountain Nat Park in 3rd or 2nd gear within the 35mph speed limit, but there is no time that the converter would be locked. No wonder we got hot, even with the addon cooling stuff.
Compare those table above to what they have programmed to cool the transmission if it get too hot.
The converter is basically locked all the time, except in low gear.
To me, this made it pretty clear it was time to try to figure out what kind of changes could be made to the tables to keep the converter locked more of the time to prevent excessive heating.
I did go to a local high performance transmission shop to ask if the trans could handle locking more of the time, and they said no problem.
Next post will start to look at what I think can be done successfully to reduce heat, while keeping decent driveability.
The tuner manufacturer keeps a library of user tunes on their website, and lots of folks have posted their results, including stock tune programs.
There was nothing for 6 speed vans, but I did find one for a 6 speed 2015 Silverado pickup, which should be similar to the vans, as the older 4 speed pickups matched our van program.
Here are same tables for the 6 speed for normal and tow haul.
Without going into detail, it gets pretty clear that the 6 speeds have the converters locked a lot of the time, and at much lower speeds and gears, than the 4 speeds. This is another piece of evidence that the 4 speeds should probably have the converters locked under the high heat generating conditions.
Again without a lot of details, here is what I have currently put together for normal and tow/haul for our van, and loaded it into the PCM.
All I really did was chose what I thought I would want for shift points, up and down and put them in, and then made the torque converter apply 2mph higher than shift up, and the torque converter release 2mph higher than the shift down settings. There are some areas in the low throttle area where this doesn't apply because of some practicality issues.
The above stuff is where I currently am at. The normal program was driven today and seemed to work very well for driveability. Of course it is not as radical as the tow/haul because it won't be used for the big climbs. The tow haul really won't get a good test until we get to mountains, but I hope to get it out soon to see how if does for driveability on the flatter roads around here.
All comments, questions, and suggestions are encouraged, as this it really uncharted ground for me at this point
It will be very interesting to see how this works out. For me it's really important as I'm in the Rockies regularly and like the idea of pulling over and changing the tune when its needed.
The hotrod shops can sell you a gizmo that you can use to dial in the exact parameters of all the engine functions -- from the turbo wastegate psi to the fuel-oxygen mixture ratio... to shifting points. The wonders of electronically controlled engines.
The hotrod shops can sell you a gizmo that you can use to dial in the exact parameters of all the engine functions -- from the turbo wastegate psi to the fuel-oxygen mixture ratio... to shifting points. The wonders of electronically controlled engines.
Yeah, there are a lot of different methods around, although I think they are changing a bit over time. Most that I found now days seem to have a premade program, or programs that you can switch, and piggy back onto the factory program like this one does. Others are pure hot rod programs that don't piggyback and are true standalones. I have had several of them in the past that I put on my old Dodge Challenger when I turboes and fuel injected it. The standalones often allow tuning on the fly, which is really cool, but can be very hazardous to parts if you mess up.
This tuner appears to totally rewrite the entire program each time you make a change, so there could be no on the fly with this one.
You can still get some "trimmers" for some things like timing and mixture, but most of them I have seen just uses some electronics to send a bogus signal from a sensor to a factory PCM to get a different output.
One good thing is that a lot of the "tuner" shops around now have this kind of tuner, so if you knew what changes were necessary, all you would do would be to tell them or give them a printout of what you wanted. My guess is that it would cost maybe $200 or so. Probably take an hour or two tops. That's less than hiring a radiator change, and way less than adding a bunch of coolers and fans, so might be the least expensive change that could be done easily. I don't have a shop license for the tuner, and it costs $100 for each extra vehicle I license, so that would be the only cost I would have in doing another vehicle.
When I was trying to figure out where to put the shiftpoints and lockups, I discovered I needed a good chart for what the rpm is at the various speeds and in different gears. I put together this spreadsheet to make it easier to visualize what was going on. This is a screenshot jpg, but if anyone wants the spreadsheet I will add it. For your tire size, as ours are oversize, just go to Tire Rack and get the revs/mile for your tires from the specs tab for them, and divide it by our 657 revs/mile. Then multiply that answer times the rpm numbers in the table. I think it will be about 3-4% different.
Will this program allow the changing of tire size and axle ratio?
Also, what is the name of the tuner?
Yes, you can set rear axle ratio and the tire size is incorporated in a transmission output revolution per mile calculation that you can set.
HP Tuners.
If you go to their home page, there is a demo download you can get on the left side half way down page. It is the real program you get when you buy, but without ability to write or read a PCM. It does have about a dozen sample tunes you can look at to see how it all works and what is settable.
I found an error in the rpm vs mph vs gear chart in the first gear area, so disregard that in the previous version. Here is the latest
The spreadsheet file has also been updated, with the added internal calculations and entry fields for gear ratios for the trans up to 6 speeds, rear axle, and tire revs per mile. I don't see a way to attach a spreadsheet file, but I will try to find one. If not and you want to be able to do the calcs, message me and I will email it to you.
Maybe putting it in a zip file will get through, they list that option.
I decided to run the same table for the 6 speed used in the newer vans.
In the speed ranges we run when we get hotter than we like, there really aren't large differences in overall ratio or engine rpm, it appears. More evidence pointing toward the lockup being a heat contributor.
Was wondering about normal city driving, looks like you will locked up a lot of the time. Any concerns about stress on the tranny, or just driving comfort?
Was wondering about normal city driving, looks like you will locked up a lot of the time. Any concerns about stress on the tranny, or just driving comfort?
The certainly was an initial concern for me. I am less concerned about it now, as when you look at the 6 speed trans lockup table, they have that locked up nearly all the time except for in the super low first gear. I have driven ours a couple of times now with it locking much of the time, and found that as long as I had the timing of the lock and unlock staged correctly it drove nicely. The only noticeable thing was slightly less power when locked compared to unlocked. I did also talk to a transmission shop about if the trans would be able to handle being locked more of the time, and they said no problem, so that was encouraging. I may also call TCI and see what they say about it, as they build lots of 4L80e units for high performance applications.
Another point is that you have normal, tow/haul, and cruise that you can program separately, so if there are concerns about everyday driving you don't have to change that area at all. Just do the tow/haul reprogram for big climbs. I am trying to do all three to possibly improve mileage a bit, and get a bit better driveability by changing the shiftpoints a bit, especially in cruise.
Only time will tell for sure if it is a good or bad idea overall, but I am pretty optimistic at this point. I am looking forward to doing the climb into Rocky Mountain National Park again to compare to what we have seen in the past.
Sounds good, you did mention that you talked to a tranny shop about this.
Can't wait to hear how it affects your temps.
PS regarding temps, I have not noticed you talking about adding a tranny temp sensor, but I think you use an OBD 2 based reader. I don't get tranny temp at least not with my stock setup, how are you getting it?
Sounds good, you did mention that you talked to a tranny shop about this.
Can't wait to hear how it affects your temps.
PS regarding temps, I have not noticed you talking about adding a tranny temp sensor, but I think you use an OBD 2 based reader. I don't get tranny temp at least not with my stock setup, how are you getting it?
Thanks.
We have a Scangauge mounted, that you can get the codes for from Scangauge, so it will display transmission temps from the factory, in transmission, sensor. I recently also added a plain old pan temp standalone gauge to see how they compare. All the temps we are used to seeing from back in the day were pan temps, so the big question was if the built in sensor was reading higher than the pan temp, or not. This will answer if the higher temps we are seeing in the van are really higher than they would be with the old school gauge. So far it looks like the pan does run cooler all the time, from 20* to 5* cooler, but the only testing I have done is in very cool weather, and no big climbs. The built in sensor temp does increase much, much, faster than the pan temp does when accelerating or climbing. The longer we are at steady state driving, the closer they get together.
We got a stretch of nice weather for this time of year, so I have been able to get some testing in that I didn't think I would get to. I am now on Rev 12 of the tuner programming and think it is pretty close, or at least as close as I can get without some big climbs and long cruise control runs in hills. It looks like, to do what we want, changes to the shift speed tables, shift time, and converter lockup are the only ones needing changes. There are multiple modes to setup, though, Normal, Performance (tow/haul), and cruise were changed, and the Hot mode was left stock.
Here are the shift speed tables for Normal mode. You set part throttle and full throttle independently, and also have a full throttle threshold setting available. I moved some shift points around a bit, mostly to get rid of the irritatingly easy downshift on rolling hills, but also to short shift a bit for economy.
Same for Performance which is for long, steep climbing, and locks are done to get the right rpm to match the converter lockup for cooler temps.
The very brief table for Cruise mode. There doesn't appear to be any WOT settings other than 100% on the part throttle table. I am trying to get an answer on the HPtuner forum about what if references for sure in Cruise.
Here are the torque converter lock and unlock tables for all the modes. The settings are primarily chosen to keep the converter locked up nearly as much as possible.
As long as I didn't muck up the actual filling in of all the entries with what I wanted, most of it has tested out well in quite a few test runs around here.
I spent a lot of time chasing what I thought might be a serious glitch, but turned out to be OK. Especially on the 3-4 shift, we were getting what appeared to be shift "flair", which is usually a bad thing because it is caused by slipping at clutch engagements. I changed a bunch of shift times, pressures, torque reductions, etc with no affect at all, so I finally took the time to setup and learn how to use the data logger that comes with the tuner. It actually works quite well once you learn the quirks, and you can step through a test drive in something like 1/5 second increments if you want. Once I got the first good, complete, log, it was obvious what was going on. What I was seeing, hearing, and feeling as flair was just the converter unlocking just before the upshift, which is exactly what it is supposed to do. In those fractions of a second, you get a bit of rpm increase from the converter slip, until it shifts and drops a full gear and locks up. That is a big rpm drop from the shift and lock after a small rpm increase, so it gets more noticeable. It is also more noticeable at lower rpm shifts as the converter slips a bit more then. I did put the OEM program back in to see if the issue was there also, and it was, but only a couple of places because the converter was rarely locked in third gear.
Weather is turning tomorrow, so likely done for the year, but it does look like we are getting what was intended. About all that is left is to test the climbing temps to see if it all helped, and maybe tweak the rolling hill shifts a bit. Time will tell if it was good or bad for the trans and if it will also give an increase in fuel economy, which is a possibility.
Teach your old Chevy new tricks?
Linear Mode
