I have noticed lately my cruise RPM is up about 100. It will also go back down at times and there is a noticeable change in sound. When the rpm is up, it is more quiet. I guess I better take the time and figure out what is going on.

maybe your torque convertor is not locking up. while cruising, if you give it slightly more throttle, do the rpms jump up a bit? when the convertor is locked, the rpms should only go up as the vehicle speed increases. when the convertor is unlocked, then slippage occurs, which results in higher rpm, and revs will be out of proportion to vehicle speed.

On my edge insight you can see if the converter is locked or not. Do you still have yours?

Thats right my old Insight has transmission PIDS. The new Insight CTS does not have them yet. I will have look for it or I guess I could also hook up my EFILive. The sound is just like when you are idling and the vanes open and close.

I hooked up my old Insight and went for a drive. Flat road, cruise set at 72, it would lock and unlock every couple of miles. Now I need to figure out why.

I talked to PATC and they have 2 converters they could build for me. One is a billet single clutch for $ 759 and a triple clutch for $ 1169. I do not know anybody that has used there products so I am not sure how good they are. I am going to go see my tranny guy today and see what he thinks. I am also starting to have some random vibrations after it is warm and driving for a while.

I talked to PATC and they have 2 converters they could build for me. One is a billet single clutch for $ 759 and a triple clutch for $ 1169. I do not know anybody that has used there products so I am not sure how good they are. I am going to go see my tranny guy today and see what he thinks. I am also starting to have some random vibrations after it is warm and driving for a while.
Who is PATC? I would go with Suncoast over any other converter. I used precision for my 1st two and they won't last.

http://www.transmissioncenter.net This is PATC.

I talked to my tranny guy and he said might as well rebuild it instead of just put in a converter or whatever else it might need. It does have 170,000 miles on it. His quote for a rebuild was $ 2,500 without a Suncoast converter. He was going to call Suncoast and see how much. He is talking about putting in a heater so maybe we could do some trading.

http://www.transmissioncenter.net This is PATC.

I talked to my tranny guy and he said might as well rebuild it instead of just put in a converter or whatever else it might need. It does have 170,000 miles on it. His quote for a rebuild was $ 2,500 without a Suncoast converter. He was going to call Suncoast and see how much. He is talking about putting in a heater so maybe we could do some trading.

Once you drive it with a nice built converter you will see the difference right off idle.
Suncoast does full rebuilds as well but you will have to ship yours down and back, OK if you have a core or no job:D

I should go on welfare for month and have them build it. I would probably make more money.

I should go on welfare for month and have them build it. I would probably make more money.

Just call suncoast and see if they take EBT cards:D

i've bought a few rebuild kits and parts from PATC before, when i rebuilt a few 700r4's and a 4l80e.
never had an issue with them.

i havent installed a shift kit in my van transmission yet, and i think i've noticed 3rd gear slip a bit a couple times when under heavy throttle, and shifting into 3rd. i'm thinking of maybe yanking it out when i have some free time and build her strong...

I did notice today that if I turn the cruise off and go by pedal it seemed to stay locked.

I did notice today that if I turn the cruise off and go by pedal it seemed to stay locked.

Yes the TCM or ECM or both?? controls it on and off when you got the cruise on. I have 468k on my trans and it has been do this since it was darn near new. Also the air is getting cooler and this may cause a bump in your cruise RPM. I know mine definitely does. It was 8 Celsius in Baie-des-Sables QC. Friday morning and I was running 1908-1930 @ 57mph and I usually only turn 1820-1840. But when I got in to Maine it got a little warmer and went back down to its usual cruising rpm.

maybe the ecm is unlocking the convertor to warm up the engine??

The engine is warmed up and it would do it on 90* days. I went to town today which is a 60 mile round trip and it would definitely only do it with the cruise on. Is this something to do with maybe a brake switch, pedal sensor etc ? I still have no codes, trans and coolant temps seem accurate. It would really piss me off if I still had it after a trans rebuild because I missed something simple.

so when you hooked up your insight, what did it say when your convertor was unlocking? sounds to me like your ecm is commanding the convertor to unlock for some reason. does not sound like a trans problem to me.

My van will unlock the converter on any slight downhill grade to keep the truck from going over my set speed on the cruise control, it locks right back up again.

The Insight would show lock/unlock and it would match RPM change. It does not tell you why it is doing it. It will do it on flat ground, no wind at random.

I ruled out brake switch since the cruise and TCC use the same wire and the cruise always works.

The pedal has no dead spots so I am going to rule that out.

VSS should be good since the speedo always reads good no jumping around or reading way off.

I am going to check and clean all grounds.

What am I missing that the cruise program uses ?

You get the 100rpm bump when it unlocks right?? then when it locks up it is at normal cruising rpm?? That is what mine has done since it was new. As some one else posted the ecm commands it on and off to keep you at your desired cruise speed. Heck I have been driving in a strong head wind and the second I go in to a tunnel or if there is a break in the wind I will feel it unlock and then work its way back up to 100% locked. On the insight I watch the TCC % and I drive with the cruise on 90% of the time and it has always done this. (read last paragraph in post added after the fact)

Lets say I am driving on flat ground no head wind rolling 57mph turning 1820 rpm and 100% lock-up. Then I hit a slight downgrade I will feel it unlock and the rpms will go to like 1900-1930. Then when the road flattens out again the rpms will start dropping and the lock-up % will start climbing when I get to 1830-40 it will be at 100% lock-up and within a second or two I will be back at 1820 putt'in along. If this is what you are noticing then you are not alone.

Just thought of something I notice it will happen allot less for a good 6-8k after I change the fuel and air filters. I don't know why, you would think it makes no sense. How many miles on your air and fuel filters?? I could not tell you which filter maybe doing this as I replace both at the same time every 30k.

Mine has only been doing it for about month and I have 170,000 miles on it. RPM up 100-200 when unlocked. Then when it locks goes back to normal cruise RPM. It is very inconsistent when it starts to lock and unlock. On the same stretch of road it will lock/unlock differently every single time. Air and fuel filters are good. Clean MAF. I had 3 tanks of 25 MPG this Summer then drop to 21-22 MPG when this started. I want my 25 MPG back !

I did a Google search and found other people with GM drive by wire vehicles have the same issue. Some had it since new and some had it start later on. Nobody had a fix for it and GM obviously said it was normal. There is a glitch somewhere.

Mine has only been doing it for about month and I have 170,000 miles on it. RPM up 100-200 when unlocked. Then when it locks goes back to normal cruise RPM. It is very inconsistent when it starts to lock and unlock. On the same stretch of road it will lock/unlock differently every single time. Air and fuel filters are good. Clean MAF. I had 3 tanks of 25 MPG this Summer then drop to 21-22 MPG when this started. I want my 25 MPG back !

I did a Google search and found other people with GM drive by wire vehicles have the same issue. Some had it since new and some had it start later on. Nobody had a fix for it and GM obviously said it was normal. There is a glitch somewhere.

Wow that's a big hit in fuel mileage. I wonder what mine would be if the thing would stay locked up longer. As started earlier mine has done it since new so I thought it was normal. Maybe it is a sign of the TCC solenoid going bad, maybe a internal short in the solenoid it self making it randomly lock and unlock. I doubt it is a glitch in the ecm software as it would have been doing this since you last update at a dealer. Maybe unhooking the battery cables and letting the ecm/tcm reset may fix the problem if it is software related, but I doubt it as when I just recently had my water pump done we had the cables unhooked most of the day and it started doing it about 6-7k after that job(had the fuel and air filters replaced at the same time) but it may work for you.

I hope you figure it out as I am interested in this now that I know it is not normal, and if the repair is not to costly I will fix mine as if would bring my fuel mileage up, so it would be paying for itself in the long run.

Maybe Piper will pipe in as he is very knowledgeable about the mechanical aspect of vehicles and have some answers for ya.

If it was a bad solenoid or short somewhere it should do it with cruise off. With the cruise off everything is normal. I have never had my ECM/TCM flashed by GM. I do not think it is the cruise program since it has never been changed. I think it is a input from something that the cruise program uses to make adjustments. Maybe that one input has a to wide of range of failure to not set a code but cause a problem such as this ?

Brake switch would cause it to unlock, but it would also kick off the cruise...

When you say the trans temp is normal, where are you getting the reading? From the TCM or from a separate gauge?

The transmission temp sensor is one of 2 places depending on the lineage of your transmission. Some are an actual sensor threaded into the valve body, others are in the wiring harness that goes under the valve body. This harness sits in the fluid and gets cooked brittle after a while. If I remember right, the actual thermistor is still available from GM to solder into the harness if it is bad (and its easy to do). If it fails, TCC lockup goes weird, but again, shouldn't matter if you are on cruise or not.

I suspect more likely, you have a throttle value issue. At 55 mph on the same stretch of road, does the cruise return a different APP (throttle pos) value than you using your foot?

When I get back home I will go through my 4L80/85E notes and see if I find something. I have had a lot of odd things happen with them but can't recall a situation like this.

Trans temp comes from TCM and it has the internal wiring harness sensor. Temps are the same as before the issue.
I have not compared APP values yet since I have no dead spots in the pedal and the RPM change came after the lock/unlock so I ruled it out. I will compare them tomorrow to double make sure.

My van will unlock the converter on any slight downhill grade to keep the truck from going over my set speed on the cruise control, it locks right back up again.



Mine does the same thing. Always has since it was brand new with 3 miles on it

I have just been driving by foot and my mileage has gone back up to 23-24 MPG. APP value is zero when cruise is on since the pedal returns to the up position. I did notice today all of my dash gauges are reading a little low as compared to the Edge Insight CTS. Not sure what is going on there but I will check to see if it does it tomorrow. I still need to check and make sure all my grounds are clean and tight.

Bump...any update on this yet shop??

I have been thinking that maybe the BG trans fluid might have some play in this. I need to service it and I will go back to Dex 6 and see if anything changes.