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Discussion Starter #1
I've been trying to figure out what would be causing the PCM to have the stockish style soft shifts when I occasionally take off from a cold start.

After I notice the 1-2 or 2-3 shift being mushy, I'll kill then engine, and wait a few seconds and restart her. Then BAM I'm back to the Stage-3 transmission with the PCM line pressure boosted shifts.

The thing of note is that I replaced my TPS recently with an adjustable (The OEM one produced the same results as before; soft shifts). I set the adjustable @ .62 volts at idle. Everything seemed fine, except I still have soft mushy shifts; which suck!

ANy ideas on where to look?

Thx!
 

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Without knowing mileage I'm going with worn and variably hooking TC (if such a thing is possible), sludged up valve body, some or another solenoids getting weak (that's truly just TotallyOMA), broken servos springs?, or any other number of things causing varying line pressures. Is limp home mode affected by anything electric or fuel, like that TPS? The restart thing is interesting as a parameter being reset temporarily.



When's the last time you did a kooler kleen and fluid change? I bet a tranny guy has better things off the bat than I came up with, but add some more background and others may chime in.


I'd hate to think it's something as offbase as sticking brakes.
 

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Drop pan,new filter,and refill with Dex VI is where I would begin,and end... Problem persists, take to a specialist in the 4L60-E
 

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A bad TPS does cause erratic upshifts .. since your upshifts are correct then the TPS is good.

on a cold start the transmission may have a fluid pressure problem .. lower pressure softer upshifts or a delayed mush upshift..

as was mentioned do the pan drop filter clean and use the dexronVI.. not dexron III..
also If the pan does have a bit much debris I would also do the fluid exchange procedure ...

disconnect the tranny line at the radiator .. as one qt comes out dump one qt back in .. use a clear container premarked .. repeat till the fluid looks new .. have a hand pump with tubing on it so you can suck out excess tranny fluid .. set fluid below the max fluid line when engine is at temp and it has run a few miles .. too much fluid will cause soft shifts also if air is generated in the fluid..
 

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The old school mechanics I know would duct tape a pressure gauge and hose to the windshield and first connect it to the line pressure port. If this was OK the old transmissions had some other test ports to try to see if the shift solenoids were OK.



If you can get live data from the transmission's line pressure it would be worth logging it.


If I understand the 4l60e it can vary the line pressure for each shift. If the sensor goes bad, shifts will be bad.


One of the first things I learned about the 4l60e was change the programming or modify the transmission but doing both may damage the transmission.
 

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Discussion Starter #6
Without knowing mileage
Approximately 12,000 (MAX) On a Mike Harris unit.

I'm going with worn and variably hooking TC
Only a few thousand miles on a Circle-D 2000 RPM Stall unit, installed in March of last year with fresh fluids, as the pan was drawined and a new filter & gasket installed at that time. (Dextron III)

(if such a thing is possible), sludged up valve body, some or another solenoids getting weak (that's truly just TotallyOMA), broken servos springs?, or any other number of things causing varying line pressures.

Is limp home mode affected by anything electric or fuel, like that TPS? The restart thing is interesting as a parameter being reset temporarily.
Nothing else at all has been affected, it drives like normal.

When's the last time you did a kooler kleen and fluid change?
March when I replaced the 3,400 Vigilante with the 2,000 RPM Stall Circle-D Converter.

I bet a tranny guy has better things off the bat than I came up with, but add some more background and others may chime in.

I'd hate to think it's something as offbase as sticking brakes.
 

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Discussion Starter #7
Drop pan,new filter,and refill with Dex VI is where I would begin,and end... Problem persists, take to a specialist in the 4L60-E
This will be the next course of action after I get a few gallons of GM Dex 6, when my GM parts guy is back in the shop.
 

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Discussion Starter #8
A bad TPS does cause erratic upshifts .. since your upshifts are correct then the TPS is good.

on a cold start the transmission may have a fluid pressure problem .. lower pressure softer upshifts or a delayed mush upshift..

as was mentioned do the pan drop filter clean and use the dexronVI.. not dexron III..
also If the pan does have a bit much debris I would also do the fluid exchange procedure ...

disconnect the tranny line at the radiator .. as one qt comes out dump one qt back in .. use a clear container premarked .. repeat till the fluid looks new .. have a hand pump with tubing on it so you can suck out excess tranny fluid .. set fluid below the max fluid line when engine is at temp and it has run a few miles .. too much fluid will cause soft shifts also if air is generated in the fluid..
Yes, I'm familiar with the draining procedure Sherlock9C1 has outlined, and used it several times on my Tahoe as well as this car, and right before I installed an external oil cooler for the transmission.
 

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Discussion Starter #9
The old school mechanics I know would duct tape a pressure gauge and hose to the windshield and first connect it to the line pressure port. If this was OK the old transmissions had some other test ports to try to see if the shift solenoids were OK.
After contacting Sherlock9C1 offline about this he suggested I install the transmission pressure gauge; which I did (0-300 Stewart Warner)

I have Approximately 125PSI cruising, when I accelerate 150PSI. 1-2 or 2-3 shifts @ WOT can peak at ~ 200PSI.

When I let off the throttle completely and coast I see 55-65PSI.

If you can get live data from the transmission's line pressure it would be worth logging it.
I assume you mean what I just listed as opposed to the free OBD1 PGMs out there; as mine is still OBD2 at this time.


If I understand the 4l60e it can vary the line pressure for each shift. If the sensor goes bad, shifts will be bad.

One of the first things I learned about the 4l60e was change the programming or modify the transmission but doing both may damage the transmission.
When I contacted Mike Harris after buying it, I asked if I should be lowering those MAX (I assume thru Herter's Programming) pressures. He said no, not to worry about it at all.
 

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I expect that you want to compare psi of a hard and soft shift. If the cold soft, and hard hot are not repeatable I thought logging until it occurred would be easier.


Are you sure OBDII does not have line pressure as live data? A passenger could confirm that it is comparable to the gauge during a soft and hard shift.



Intermittent problems are the worst.
 

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your posting on those pressures are excellent on the detailed info..looks good .. but since intermittent that is the problem ...you sure no air bubbles in the fluid ? too much fluid can cause this soft shifting .
 

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junior -
Ok you wiped me out of ideas but others have pitched in areas to look. Just mentioning with whenever the NEXT fluid change be sure to do Dex VI. What I hear III's problem is it turns acid after some time, but I can't imagine any issues nearterm. Prepared for correction though. Hope you chase down the gremlin.
 

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Discussion Starter #14
[SNIP]

Are you sure OBDII does not have line pressure as live data? A passenger could confirm that it is comparable to the gauge during a soft and hard shift.
I don't know, as I've never used a logger except for a short time using my good old OB2 software AutoTap. I'll have to see if it can monitor line pressures.

Intermittent problems are the worst.
Yeah, they're never easy, especially on your own, but hopefully something will come out of this.
 

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Discussion Starter #15
What's the pressure you see when you put it in reverse while stopped and idling?
I will check today, as I hadn't thought of that one.

Gimme a few hours, as I have to finish installing the brass T in place of the plastic, Install a ball valve to shut off water to the heater core in place of the restrictor, and then finally pull my mechanical water temperature gauge from the RH cylinder head, and re-route it thru my new cluster bezel, to go along with the Z28 Cluster I installed yesterday, and finally reassemble the lower dash, and permanently mount the transmission pressure gauge.
 

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Discussion Starter #16
your posting on those pressures are excellent on the detailed info..looks good .. but since intermittent that is the problem ...you sure no air bubbles in the fluid ? too much fluid can cause this soft shifting .
I can't confirm on over fluid, as I have not checked since this started.
 

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Discussion Starter #17
junior -
Ok you wiped me out of ideas but others have pitched in areas to look. Just mentioning with whenever the NEXT fluid change be sure to do Dex VI. What I hear III's problem is it turns acid after some time, but I can't imagine any issues nearterm. Prepared for correction though. Hope you chase down the gremlin.
The Dex III installed has less than 10,000 (At the MOST) as the converter was replaced in the spring, and fluids were changed.

I got together with my GM parts guy yesterday, and picked up 4 gallons of GM Dextron 6, as well as a new deep filter and gasket.

I may not get to that 'till tomorrow as my dad has plans for the day, and I need an extra hand to hold the glass gallon jug for the fluid to pump to.

QUESTION: Which line is the pressure? The lower on the transmission? I ask because I flared and Installed AN fittings in place of the rubber hose (At/below the tensioner location) to an external cooler.
 

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If ti was me I'd be looking @ wiring/electrical/solenoid(s).
Generally, an intermittent issue won't be "fixed" by a fluid/filter change.

When rebuilt did it get new harness & solenoids?
Aftermarket stuff is such a roll of the dice now, and I'd wager that it's wiring/electrical/solenoid(s).
Verify good grounds as well, intermittent issues are frequently bad grounds.
 

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Trans fluid needs changed out anyway. Why people continue using Dex III type fluid escapes me. Actual Dex III hasn't been recommended,or even existed in years...
 

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Trans fluid needs changed out anyway. Why people continue using Dex III type fluid escapes me. Actual Dex III hasn't been recommended,or even existed in years...
dexron III banned by GM in 2006... 4l60 transmissions created huge GM warranty costs.
I converted to mobil synthetic dexron/mercon in 1999... aircraft engineer told me III turns to acid .

I cannot buy that fluid anymore so I now have to use dexron VI...
I still remember when I converted the tranny fluid in 1999 @21K miles that was the nastiest pan drop in my life .. the last time I did the tranny fluid pan drop , looks like I did it last week..
 
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