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So I just finished my t56 to 4l80e swap, the car is a 93 z28 with a 5.3 turbo 411 ecm tuned by EFI live, COS5, bar 2 map SD tune and original ls1 4l60e 01 harness modified to work with the 4l80e changed over the brown wire and wired in the extra vss, I did the segment swap with Efi Live, The issue is that after the segment swap the car will only idle for a couple seconds and seems runs really rich, then it dies, I switch the tune back to the t56 tune it idles just fine, but obviously it won't shift, car still in the jack stands, today I followed all the wiring to the transmission plug and made sure all the wiring is right @ the ecm side and it is, but after I disconnected the 4l80e big round plug I flashed the 4l80e segment swap tune again and the car idles just fine, so Im thinking could I have a bad solenoid inside the transmission causing this? Or what else could this issue be? I'm lost and I've tried everything that I thought could be an issue, even my friend figured out a Cax file to change the input on the tune to say that I'm not running a parking neutral safety switch just to see if it would change anything but still no luck, sorry for the long post and thanks oft your help in advance.
Last edited by Jose93z28; Apr 21, 2015 at 12:33 AM.
If the car idles with the trans plug disconnected, but dies with it connected, I would suspect a wiring problem that is activating the lockup clutch solenoid.
Perhaps someone with 4L80E segment swap experience will have a more precise suggestion.
Thanks Mrvedit, so I looked at every single wire that goes from the pcm to the 4l80e plug and checked continuity, every wire looks correct with the exeption of 4l80e pin M wich in the case of the F body it goes to pin 53 of the blue pcm connector and is a low reference wire, on a truck it's suppose to go to pin 41 and it's also a low reference wire. Now pin 19 on the 4l80e plug wich on the pcm it goes to blue connector pin #19, wich is ignition voltage, only difference on a truck tune it's wired to pin #75 and it's called off/run/crank voltage, but I'm assuming it's the same.What Mrvedit says about the tcc engaging almost sounds like that's whats going on but how can I make sure? Do I disconnect the brown wire that goes to pin s?thanks for your help in advance.
So I just went ahead and disconnected the round plug wires to the 4l80e plug one by one until I found wire R is the problem, @ least once I disconnected that wire the car stays running, it says it is circuit #1225 ecm blue plug #17 and it is Transmission fluid signal B, now I dont know where to go from here but Im thinking my next step is to pull the pan and follow that wire and see if it could be a bad sensor or solenoid maybe??? Or possibly grounded out
So I pulled the pan and this pieces were on the bottom of the pan, funny thing is they werent damaged so I reinstalled them and filled the transmission back up and started the car but it still dies right away, I dont know what to check next, is there any body here that has any suggestions?
I wonder if your line pressure is so high it blew the boost valve out? Even possible?
Very high line pressure puts a heavier than normal load on the engine which might be killing it.
I know nuthin' about 4L80E, but I would suggest hooking up a pressure gauge to it. You can buy one on Amazon for $34 - search "ATD-5550".
I only the know the 4L60E well, but there are many electrical similarities. The PCM controls the line pressure in both transmissions through a PCS (Pressure Control Solenoid). On the 4L60E removing the electrical plug maxes the line pressure and I suspect the same is true on the 4L80E. I think you would have very low line pressure if the boost valve fell out.
Sorry I don't know the normal line pressure in a 4L80E, but at idle in Park I doubt it is more than 100psi.
Currently the "decision tree" of what is wrong with your trans is too big. Getting the values from the pressure gauge will significantly reduce it to few possibilities.
Hopefully SnIpEZ or another 4L80E expert can chime in here.
No, it's almost guaranteed that was the result of a misinstallation. Pressure varies depending on the boost valve spring used. Can't tell if that one you put in was the stocker or a TG part. Looked like a stocker though, which is a no-no.
I only the know the 4L60E well, but there are many electrical similarities. The PCM controls the line pressure in both transmissions through a PCS (Pressure Control Solenoid). On the 4L60E removing the electrical plug maxes the line pressure and I suspect the same is true on the 4L80E. I think you would have very low line pressure if the boost valve fell out.
Sorry I don't know the normal line pressure in a 4L80E, but at idle in Park I doubt it is more than 100psi.
Currently the "decision tree" of what is wrong with your trans is too big. Getting the values from the pressure gauge will significantly reduce it to few possibilities.
Hopefully SnIpEZ or another 4L80E expert can chime in here.
Ok I'm gonna ask one of my buddy's see if he has a gauge or can get one if not I'm gonna have to order one and report back after I get the line pressure.
No, it's almost guaranteed that was the result of a misinstallation. Pressure varies depending on the boost valve spring used. Can't tell if that one you put in was the stocker or a TG part. Looked like a stocker though, which is a no-no.
The part is the one that came with the TG kit it's green and the small spring purple, and the weirdest thing is that even after I reinstalled it and It didn't fell out the car still dies and acts as if the tcc was being engaged the whole time, funny thing is that when I unplug the 4l80e plug it stays running and it doesn't die, but when the plug it's connected it stalls right away so that has lead me to believe it could be an electrical issue, but I may be wrong.
No fix yet 😕, I actually just borrowed a pressure gauge and checked pressure today, with the 4l80e plug disconnected its right avobe 120psi thats @ idle
But the moment plug the 4l80e plug back up it goes down to 75 psi also @ idle, and I have to give it gas to keep it running, but it smells really rich, the moment I stop giving it gas it dies, also I unpluged pin#R from the plug and hooked the 4l80e ug back up and it runs doesn't die but the pressure stays right @ 75psi
Also forgot to metion I drove the car with the plug unpluged and It drives If I shift it manually just it feels like it starts on second gear, and today that I was checking pressure with the plug connected just pin R unplugged pressure @75 psi idles fine but died when I moved the gear to first
Last edited by Jose93z28; May 3, 2015 at 10:07 PM.
I don't know what the "plug disconnected" pressure should be on a 4L80E, but on a 4L60E, it is more in the 200 range. The 75psi with the plug connected sounds about right.
Lower line pressure puts slightly less load on the engine as the pump is not working as hard.
Since connecting the plug stalls the engine, it sure looks like the TCC is getting partly activated. I know you checked the wiring. It makes no sense that disconnecting the Blue #17 (Pressure switch Signal B) would keep the engine running. This simply tells PCM which position the shifter is in.
I assume when you say it won't idle that the shifter is in Park.
SnIpEz or other 4L80E expert will have to confirm, but the "plug disconnected" pressure of 125 sounds very low. If true, perhaps there is a valve body problem.
Thanks for the reply mrvedit, The car is in park when its idling and dies correct, and I did check the wirin but I will double check to confirm I know it dont make sense and thanks for letting me know what that cable pin R does cause I didnt know, if I have a valve body issue I could have done something wrong when installing the transgo hd2 kit, possibly but I followed directions carefully, but again you never know
So after messing around with the car some more I tested all solenoids and they checked out fine, I decided to pull out my valve body and found the problem, I don't know how it happended but I think It could have been an issue with the transgo kit, again I double checked all the steps in the instructions so I don't know what caused this, but it looks like the transmission did build a stupid ammount of pressure, spitting the pump boost valve and and also splitting the case, heres some pics of the carnage, if someone knows what could have happend please share, also the separator that its sandwiched between the valve body and transmission didn't suffer any damage just the gasket on that end.
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No idle after 4l80e swap. 
