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I'm having problems with my 4L80E again. What happened is, my alternator died before the race, and I made few runs on batteries only, with voltage dropping down to 10.5V. During those runs transmission was acting crazy, not changing gears, or changing erratically. Now I replaced the generator, but still even during normal driving transmission behaves weird:
1) during mild acceleration, after changing to second gear, RPMs rise a bit instead of dropping
2) when it needs to change to 3rd, it hesitates for some time (maybe a second or 1.5), and only then changes to 3rd.
Could I damage the tranny racing on low voltage?
What can I do to diagnose what had happened? I could make some HP Tuners logs, but what should I log?
I've studied logs, compared input and output shafts speed, and it looks like transmission slips in 2nd gear badly... What's even more more surprising to me is that now there is ~1 second pause between when HP Tuners logs gearchange and actual engangement of 3rd gear... I can't imagine what happens during that second or so...
I've attached couple of pics to illustrate both input shaft slipping even at lightest throttle, and delay shifting from 2nd to 3rd gear...
Why this delay happens?
Also I've noticed that during the runs on batteries voltage was around 10.8V as opposed to usual 12.4V. Could such small voltage drop make tranny immediately smoke clutches holding 2nd gear???
P.S. In the graphs at the top section white line is in put, blue is output, and yellow is gear
have you disconnected the battery at all.. I found that running the car that low on voltage, seems to goof up the cpu and the car flat out drives like ****. I found this out when i lost my alt and drove it home on low voltage... I would pull the battery off and clear out the cpu, then let it re-learn
Im having a similar issue with my 4l80 after driving home with the alt dead. I just drove with light throttle down the road watching the guages go dead from low voltage. I pulled into the driveway as the car died and charged the battery enough to turn it around and back it into the shop. Now when I put the trans in 1st gear it dosent seem to pull as good with light throttle as it did before the alt issue. I havent road tested it as I havent had time to change the alt but just driveway testing it there seems to be some slipage at light throttle in 1st. I hope I didnt ruin the trans as it only has about 1000 miles on it since I built it. This exact same thing happened once before with the stock high mileage 4l60 with no issues so how could it have hurt a 4l80 and not a 60?
So I've drained the oil, and only about 5 liters came out... I've no idea how I could loose that much fluid, no leaks...
Questions is, should I try to add fluid and run it? Or low fluid is result of slippage, not the cause?
I've removed the pan, there was no particles in the pan but oil is black, and some thick black stuff is on the bottom of the pan and doesn't even want to drain easily...
Is it rebuild time?
At this point Id clean out the pan and try it out with a new filter and fluid. You might get lucky. On a side note mine is ok after changing the alt and clearing the computers memory. Best of luck.
06-01-2015, 11:40 AM
Think I damaged my 4L80E again... 
