7427 bnkm as standalone trans controller?

**jalatl** · 03-01-2018

I haven't been able to get my OE ecu to work with my system and it seems to be a wiring issue with my OE harness somewhere. Can't for the life of me fine the short, etc so I bought a standalone ecm system for my vortec 5.7. It controls both ignition and fuel management but no option for trans control for my 4L80e. My trans shifts fine using the 7427 ecm but timing control and/or fuel delivery is off so I'm trying to see what I can do to get it to control my transmission as a stand alone option. From my understanding the trans requires VSS, CTS, TPS, and Tach signals to control the shifts. I have the splitter cables necessary to give both ecu's what they need (if this is correct and that's all the trans needs).

So I have three questions:
1. Are these signals really all the OE 7427 BNKM needs to control the trans? If not, what would I need to do to make it work (or is it even possible with this ecu)?
2. What, if anything, do I need to turn off in the OE ECU so the trans will shift without the OE ECU freaking out?
3. Does anyone know of any reasons (if this really is doable) that this would be a bad idea? IE, losing other things such as gauges, interior functions, etc (not sure what all goes thru the ecm wiring)

My truck is a 1995 GMC K2500 with a 5.7 Vortec from a 1997 GMC Yukon with TBI intake. 4L80e transmission w/ 4.10 gears. NOT push button 4wd, it has the manual engage 4wd shifter.

Also, out of curiosity, is the transmission control software in the OE 1995 ECU or on the memcal? While troubleshooting my system before getting the standalone engine controller I swapped out the OE ECU for a refurb ECU to see if the original one was the issue but I lost all shifting. I was thinking that the trans control was on the burned chip... Sorry, may be a stupid question but I'm new to chip burning.

Any help y'all could give me is greatly appreciated!! Thanks in advance!

**DavidBraley** · 03-01-2018

I am not smart enough to know for sure, but I'm positive someone on this forum who does know will chime in. I did stumble across this site that might be of some help:

http://mattw.dyndns.org/4L80E/

Good luck and take care,

David

**jalatl** · 03-01-2018

Thanks David! That link does seem to indicate that it's possible... Off to a good start!

**jalatl** · 03-01-2018

Anyone know if I need to maintain my MAP sensor? I saw a post somewhere that stated it may be required as well.

**jalatl** · 03-01-2018

Hmmm. I just saw a post that said it's better not to use the 5v/ground wires and only use the tps signal wire for trans controller when splitting and let the engine controller deal with the 5v/grd wires.... but they were using an aftermarket trans controller, not an OE ecu as the trans control. Wonder if the same holds true for what i'm doing.

**delcowizzid** · 03-02-2018

You can't run the 5v and ground from both units will have to pick one and will have to remove the est bypass system from the ecu used for trans control so it only sees rpm and can't adjust ignition timing .then mask all the error codes that arnt trans related sharing sensor feeds etc can be a pain in the arse sometimes

**jalatl** · 03-02-2018

Cool, thanks for the reply! do you know of any simpler and affordable way to control it without all the headache? Or maybe I'll go thru it and if I get it working I can compile a list of things to change and post it up...

**buddrow** · 03-02-2018

Ok, let's discuss your situation. You are using the 7427 pcm to run the engine side correct? And you suspect a wiring issue which is preventing you from using the 7427 to run the 4L80, correct? What mask are you running on the 7427? What bin?

Bud

**jalatl** · 03-02-2018

No, I'm using a FiTech Go EFI system for fuel and ignition. Long story lol. Basically its my daily driver and I've been fighting wiring gremlins for over a year now. The symptoms have been all over the map. I've replaced EVERYTHING (other than entire harness), some things more than once. I don't typically throw parts at problems (I'm pretty decent with diagnosing running problems) and every time I traced down a problem and repaired/replaced parts it would run GREAT!... for a day or two, at best a couple of weeks, and then I'd have similar issues pop up again. I had finally come to the conclusion a few months ago that I needed a tune and bought what I needed from Moates to burn my chips and it seemed to be helping a lot after 5-6 tunes. Not perfect, but much better. I figured a few more tunes and it would be running well enough to get a good baseline. I went on vaca for a week with my gf and when I got back and started the truck up it was idling at 2500 rpms. Can't drive it like that! So... I started diagnosing. Tried to pull DTCs. Nothing. Tried to datalog and no communication with ecm. Pulled the ecm, checked all pins, checked all connectors, wiggled some wires.... and it connected!... for about 45 seconds. checked connections, wiggled again etc, got a very brief connection again and then lost it. Crawled around under the dash and hood for a couple of days checking and rechecking everything with zero results. That's when I threw my hands up and looked into standalone options. I wanted to get the megasquirt but this truck has been totally out of commission for the last 2.5 weeks and it's been hell getting materials to the job site in my gf's jetta (I work in construction) so I was looking for the simplest plug and play system I could afford that would get me back on the road ASAP. I couldn't afford a separate aftermarket trans controller so I was hoping to find a way to get the 7427 to shift the gears for me. I had seen that a few ppl were doing it with OE ECMs but I couldn't find enough info on how they did it to feel confident in doing it myself without some input from folks more experienced than myself in tuning... so here I am! haha.
Long story short: I'm trying to use the 7427 to control my 4L80 while using the FiTech EFI system to control fuel and ignition. The 7427 has always shifted the trans well so I'm hoping to get it to work in conjunction with my setup in the shortest amount of time possible. I'm realaly hoping to have it on the road again by the end of the weekend. I have to pick up a decent amount of lumber on Monday.

**jalatl** · 03-02-2018

Truck specs:
1995 GMC K2500
Vortec 5.7 from a 97 Yukon with TBI intake, currently finishing up installation of FiTech Go EFI system for engine management.
4L80e with 4.10 gears
All new sensors, all new sensor pigtail connectors
OE 7427 ecm to control trans (hopefully). I had swapped ecms at one point to see if that was my issue a few months ago but never could get it to control the transmission so I swapped it back to the original. The engine ran the same with either ecm installed.
All bolt on's are new (alt, starter, etc)
All new vacuum lines and several extra ground points, all clean and tight
New fuel pump running 14+ psi, will be changing to 60 psi pump for FiTech system with all new fuel lines and filter.

**lionelhutz** · 03-02-2018

The concern I would have is that if the 7747 harness and operation is that messed up that it not keep operating the transmission correctly.

The only variables typically used for transmission control on the ODBI stuff are %TPS, speed and rpm so I would think that is all you need to make it work. You can open your XDF and BIN and look through the transmission stuff and confirm this.

I'm not sure I fully understand your TPS comment, but you would first have to confirm the voltage and output signal on the FiTech TPS to see if you could parallel to it.

**CDeeZ** · 03-03-2018

I'll be following this as I have friends from who from time to time try to figure out how they might control an 80e swap in something without buying one of the aftermarket controllers.

That link David posted is one I have been reviewing for a while now. Another option is to control it with a 411 PCM as a standalone which is described here:
https://sites.google.com/site/sloppy...ans-controller

**buddrow** · 03-03-2018

If you're going to go thru the effort of using a 411 for the trans, sell the Fitech and just use the 411 for everything, fuel, spark, trans. I will ultimately be more reliable and less frustrating. Are you a member of the Fitech Owners fb group?

Bud