Hello all, i need to get some clarification on what can make a tranny blow up after a chip was burned for the IP.


after $1444 of rebuild cost, i found the reverse piston in 2 parts, and the rest of the tranny in sad shape. the person that burned the chip said it was from line pressure, but not b/c of his chip. according to the chip burner (i will disclose the diesel shop later) it is PURE coincidence that i had a tranny shift patter different from stock with the first mile out of his driveway. according to the chip burner, there is no possible chance that his chip could have caused the line pressure to break the reverse piston. this may be true? not sure so i hope to find out.

the chip burner said the problem was not his chip, it was a EPC Solenoid that just happened to stick in my tranny while i was in his parking lot after the chip was burned.

i tested in with 3 different ohm meters, and even compaired it to a stock part off the GM shelf new in the box. the ohms matched 100%, mine VS new in box. the chip burner said that this is normal, and that it will ohm as good, and even as a new one, but it must have stuck (coincidence of course) and thats what caused the line pressure to go sky high leaving behind alot of damage.

i let the chip burner know of the difference in shift (real soon and VERRRRY hard) from first to second, and he said this was normal and thats how he likes to set them up, and that i had nothing to worry about.

if anyone knows of a rational solution to this, or might know of the cause, please let me know.

i can post more in detail later if needed.

Not sure about your problem but the 1st to 2nd shift should not be hard like that, in a heavy truck it will only break things. Quick and firm is what you need

4L80E's are plauged with trans pressure spike issues. Not uncommon.

I would have to put a vote for bad coincedence

when it shifted from first to second, it was too soon, and VERY hard. our secretary drove it up town and before she got a mile away she called me asking if she was going to break anything by driving it. our shipper took it up town to get emblems and came back and said "holy crap, that drive train is going to fall out" with it shifting like that. all this time the diesel shop knows how it is shifting, and says it is fine.

from all the research i have done, that is caused by the shift points in the newly burnt chip, and keep in mind in this entire problem, i had a defective stepper motor in the brand new pump (that was the wrong one to begin with)from this place. could the computer have had confused signals and tried to bump up line pressure by using the EPC?

the good thing is after i took out this chip, it never shifted like that again. i had to go to another diesel shop and get the correct IP, and then use the old 80HP chip that i already had. it drives like a dream now with the correct pump and correct chip.

Here is my take on this. Tuners are too gung ho to play with trans pressures when most of them have no idea what they are doing. They feel that if they do not drop voltage to the force motor ( Electronic Pressure Control solenoid ) which increases pressure you will burn up your trans because of all the power they just gave you. Trans pressures are best regulated at the pump and on a 4L80 need a blow off valve ( Transgo ) to keep spike pressures in check. Tuners need to stay the hell out of the trans unless trans has been modified and then talk to the shop before bumping pressure.
I have seen a lot of posts by 4L80 owners with very high mileage trying to modify their trans. I think they are nuts for doing this.

i feel the same! i did not ask for any change in my tranny, and yet it was done. he did not ask me if i had a stock trans or a modified valve body to handle a spike in pressure. i just had the spiked pressure, leaving me with hard shift's, VERY hard shift's

Thanks for the update. I had been wondering about the outcome of this.

SnowDrift

only good out come so far is he refunded me for the defective/incorrect pump. i am still out the tranny work, but before i push the issue with him, i want to cover all bases that the problem was in the in the chip & or incorrect/wrong IP.

i have done more and more research to help back my claim against this shop that burnt the chip, and all fingers point to the chip making the trans shift different/wrong.

can anyone give me a reasonable reason that this could not be the case?