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I have a 4L80e with a low line pressure problem. My gauge showed 75psi at idle in park and all forward gears. 125 psi in reverse at idle. Driving in all forward gears it creeps up to 80-85. WOT it gets to around 100. I pulled the epc and tested it. Showed 4.5 ohms which is around out what I've read is normal. Put 12v to it and could clearly hear it working. Trans has a HD2 shift kit in it. The pressure relief valve (plate) was left out when the kit was installed. Jake recommends omitting the relief valve when installing the HD2. The pump was in good shape when it was assembled. Fluid was clean except for some minor dust from new clutches. Boost valve is also inatalled properly per trans go instructions. Any more ideas on what could be causing this? It flares/slips bad on the 1-2 at WOT but shifts fine at light throttle even despite the lack of line pressure. My old epc noid is pn 24209276. This is an older one that has been superceded by a new part number I believe. I am needing to know the current correct pn for the epc noid.
Jake/anyone, can you confirm that leaving out the pressure relief valve is OK to do? If so, does another modification need to be done in place of it or can you omit the relief valve without having to do anything else?? Thanks
Jake/anyone, can you confirm that leaving out the pressure relief valve is OK to do? If so, does another modification need to be done in place of it or can you omit the relief valve without having to do anything else?? Thanks
Yes you can leave out the pressure relief, make sure the hole didn't get drilled.
As mentioned the frictions for second surely are probably fried at this point but I would try and solve the pressure rise issue before pulling the unit, 80 or round about is ok for idle but 100 at wow is very low, I do not think you have a pressure leak as such because the idle line pressure seems normal, I would replace the EPC PRESSURE CONTROL SOLENOID AND REINSTALL PAN start with harness unplugged and trans ful of fluid and do line pressure test even at idle in this condition you should see at least 180 but with the other transgo stuff I would expect to see around 220 certainly something between
If you do see those pressures in drive idling harness unplugged I would then turn off vehicle and plug harness in clear codes and start at idle again you should see around 80 psi in drive setting still at idle. Now check again by going WOT what pressure does at WOT you should see at least 90 percent of the pressure you saw with harness unplugged if you see little or no pressure rise like this as before then you have a vehicle tuning or wiring issue, If The rise is now in a normal range you have solved the pressure issue and can now put some new frictions in and go,
But as I said I would try and fine reason for low line at wot first and the PCS (EPC) is prime suspect, Making a click and being electrically sound is still no indication of functionality ,
For those finding this post.. I wanted to add that I was having issues with a 4L80E with low line pressure as well. Replaced the EPC, actually updated to the later style. No change. Vehicle would run and drive at low throttle input but would slip/flare really badly if you gave it any significant throttle pedal. We pulled the trans and installed an after-market machined pump with new gears-essentially a fully remanufactured drop-in pump. Yes, I'm sure I'm using the correct pump with the correct case. It's a 3rd design case with a late 04-07 pump. The problem continued once we put it back in. We then suspected potentially a valve body issue. Changed the valve body with a Sonnax remanufactured valve body. The problem continued. At that point I was suspecting something wrong with the case. Pulled that trans out, bought a used case from a local supplier and moved all of my internals over to that other case.. BINGO! Problem solved! Something wrong with the original case for sure.
When I was relating this story to another builder, he told me that he had experienced the exact same thing and swapping cases fixed his issues as well. I post this in case anyone else runs into this situation where you can't figure out what is causing the problem.
I will say this as well... Jasper transmissions is milling one of the dividing walls out of their cases... Why they are doing that I don't know.. But this was a Jasper case with the red Jasper tag affixed to it and the case has a milled wall allowing two cavities that are separated from the factory to be joined. I've attached a pic here for those that may know why Jasper is milling this cavity. The funny thing is the ATSG book DOES NOT SHOW that divider wall there. They picture the case having NO DIVIDER wall there at all in their pics. ATSG considers this cavity #14 to be "TORQUE SIGNAL".. I'm not sure if that is why this case is no good.. or something else entirely. Just something I noticed with this case. In the pic below you can see an actual image of an 80E case, and the milled divider wall on my case is painted red.
I know this is a zombie thread.. But at least it's recorded here for those that find this post when searching.
I do not have the sheet in front of me now, but I do have a service bulletin on this. Can't recall if it is from ATSG or Transgo or ATRA or GM etc
A single .093 hole through that wall will suffice just fine for anyone reading.
This is on the short list of acceptable times for a thread bump because it was bumped with good info and good results. Thanks Kawa
Only the earliest cases (first two years or less) should be without the divider.
We (GM) had internal Engineering documents and Service Information documents for GM Techs regarding this...
However, we never released this information in other forms.
Simply put; the cases without the divider, used a different separator plate and gasket design.
Here is an image of the 1st edition 4L80E GM Manual, showing what I am referring to:
In the Image above, look at the upper left corner of the separator plate for the Yellow holes #14A and 14B.
This is the shape hole (plate and gaskets) that matches a case with no divider.
The later cases with the divider use a plate and gaskets that look like this:
Again, look in the upper left corner, at holes #14A and 14B.
This is the design that matches a case with the divider.
When mixing and matching parts... you can drill a bleed hole, just as Maroon Monster said.
I am certain we never gave this information to ATSG...
ATRA or the Gasket companies would be the only people that we gave this information to.
08-23-2016, 11:13 PM
4L80e low line pressure, flare/slip 
