HydroStream6

iTrader: (16)

I've had my 4L80 in my GTO now for 3 years and it's performed flawlessly. When I was coming home one night about a month ago, as I was about a 1/4 mile from home in 4th gear it started acting like the lockup was locking and unlocking at weird times. I was able to get it home but it was definitely weird. I looked at it the next day, and when I reversed out of the garage all was normal, but as soon as I put it into Drive it stalled the engine. I verified this a couple times. So I hooked up the logger to my computer and logged what the transmission was doing and it was acting very erratic. It was indicating gear changes while idling, losing TPS and RPM signal randomly, etc. I sent the manufacturer the log and they had me send in the unit. They checked it out and said it worked fine for about 5 minutes then it wouldn't do anything, so they gave me a new one. Thumbs up to them.

Anyways, it's a month later and I get the computer back. Put it in, flash my tune, and the damned car does the same thing

I'm thinking I may have an electrical gremlin, but does anyone have any ideas before I tear into this? I can't confirm that it's the converter lockup that's causing the stall, it could just be trying to go into a gear other than first for all I know, but that's what it seems like.

Ideas? I work 40 hours a week and go to school half time for ME, so I don't have a whole lot of time to be chasing this

Thanks as always!

Adam

***UPDATE*** See post 19 below.

mrvedit

About the only thing that can stall an automatic is the converter going into lockup; doing into something other than 1st gear won't do that.
Sure sounds like an electrical gremlin; I would start by running a 12-gauge ground wire from the trans to the chassis to be absolutely sure the trans is well grounded.

BTW - I had the lockup clutch in a converter partially bind up; the engine was then likely to stall in both reverse and in drive.

Hopefully someone else has more ideas.

HydroStream6

iTrader: (16)

A buddy of mine had a very similar problem in his Dodge pickup. It ended up being the lockup solenoid was bad. I'm gonna try to find the wire for the lockup and cut it and see what happens.

Gonoma

iTrader: (15)

I'm not 100% sure but I think the "other" speed sensor is responsible for converter lockup.

Also are you sure your file that you flashed isn't corrupt? Idk how long it has been since you last flashed the computer before it started acting up but if it was recent it could be a problem.

mrvedit

Good suggestion. I actually removed it to be absolutely sure there was no TCC apply fluid. (In case the lockup solenoid was stuck.)

slow67

iTrader: (2)

In a 4L80E, NO fluid gets the the lockup solenoid until 2nd gear. If your getting TCC lockup in any other gear than 2-3-4, its a pump or converter problem.

HydroStream6

iTrader: (16)

That's not cool.

FWIW, I unplugged the power to the trans computer and the car runs and moves around without locking up and stalling.

HydroStream6

iTrader: (16)

Gonna swap valve bodies tomorrow and see what that does. Sound like a decent idea? If that doesn't fix it, it's gotta be in the pump?

HydroStream6

iTrader: (16)

Swapped valve bodies today and it still does it. This time however I got to drive it for about a minute before it happened. Guess the tranny will come out next weekend. What specifically should I look into? I

mike13

iTrader: (27)

wouldn't that mean the computer is commanding it to lock up?

HydroStream6

iTrader: (16)

It also didn't shift out of first without the computer plugged in so I don't think there was any fluid at the TCC solenoid without the computer. I'm kinda lost on this one.

fat60

It is definately a computer issue, something is telling the computer lies, a faulty inhibtor/PRNDL switch will do it.

mrvedit

Without the computer plugged in the trans goes into "Limp mode" which is 2nd gear on a 4L80E. Only the computer can make the trans shift.

HydroStream6

iTrader: (16)

So if I was in second gear with the computer unplugged, it should have had fluid at the TCC solenoid, which should have allowed it to locked. Hmm so maybe it is more electrical.

I'm going to find the TCC wire in the harness and cut it tonight. Then see what happens
with the computer plugged in.

Thanks for the help guys, and keep it coming!

HydroStream6

iTrader: (16)

The car doesn't have a PRNDL switch. When I swapped the valve bodies I effectively changed all solenoids and that little pressure switch manifold thing. What's this inhibitor?

The only thing electrically connected to the car is the TPS, RPM signal, big grey connector on the side of the trans, and the speed sensors on the trans.

mike13

iTrader: (27)

"what the transmission was doing and it was acting very erratic. It was indicating gear changes while idling, losing TPS and RPM signal randomly, etc"

Check to see if this issue was fixed? It looks like it's a problem that affects all aspects of transmission function. I would look for grd and power issues.

KRAZY K 2000 TA

iTrader: (5)

that pressure switch manifold thing you refer too tells the computer what is going on in the transmission

HydroStream6

iTrader: (16)

Well that got switched too

HydroStream6

iTrader: (16)

UPDATE

So we cut the wire in the trans harness for the converter lockup. Car now goes through all of the gears and seems to be working perfect, with no lock up of course. I drove it around for about 10 minutes tonight with no issues.

Anyways, I'm not sure what that leaves as the culprit but I will investigate more tomorrow. A few questions.

Is the lock up solenoid just fired by 12v? If so I will wire in a switch so I can manually apply the lock up and then I can see if it releases when I flip the switch back.

Also, what is the difference in a 4L80e valve body with a PCS accumulator and without? I have one of each and was just curious.

All ears for any other opinions as well

slow67

iTrader: (2)

The PCS and vacuum modulated solenoids modify torque signal oil pressure. This acts on the boost valve, accumulators, etc.

The lockup solenoid controls a valve in the valvebody. No fluid gets to this valve until 2nd gear gets oil.

Your lockup wire grounds to activate lockup.