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4l60e wont stay in overdrive after it's hot

 
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rickm_b rickm_b
New User | Posts: 8 | Joined: 02/14
Posted: 02/11/14
05:32 PM

Hi,
1995 S10 pickup 4wd. 4l60e Tranny rebuilt about 30,000 miles ago. Transmission works great in all gears, no slipping, flaring, etc. However, from day one after rebuild it will drop out of overdrive into 3rd as soon as tranny gets hot. Lockup on converter is working correctly(it unlocks with a touch of the brake) When driving uphill it stays in overdrive, or will shift out of 3rd into overdrive. When going downhill, it downshifts into 3rd. Exact opposite of what it should do. On flat ground it drops into 3rd, unless giving it more gas pedal, then it will stay in OD. Stays in OD only when resistance on truck is present, or let off gas, then it will upshift to OD. On cold days, will take much longer to drop out of OD. Have replaced brake switch, TPS, MAP, and installed a corvette servo (and adjusted travel to 1/8"). Cruise control works properly.  Problem persists.   Any ideas?
Thanks so much,
Rick  

wayne712222 wayne712222
Guru | Posts: 1428 | Joined: 03/13
Posted: 02/11/14
06:12 PM

software controls overdrive as i recall..

there may also be an overdrive pressure switch..

i know there is a temp sensor in the transmission..

do you have a scan tool that will plug into the connector..

the 94 models are OBD1.5 and use a 12 pin OBD1 connector..

the 95 models are OBD1.5 and use a 16 pin OBD2 connector to diagnose ..

this is a list of OBD1 live data that some of them will be viewable with a proper scan tool..

note near the bottom of the list..the transmission data..

and something you might need to change.. make sure that you have a 192F thermostat.. and that your cooling system on the scan tool displays 185 to 215F..  if you have a 180 thermostat in an attempt to force the truck to run below design temps.. it can cause your truck to run above 215F at 235F or around there.. the PCM will kick the transmission out of overdrive..

i also worry that you may be feeling the torque converter clutch unlocking..

can you prove this is not the issue by pulling the gear shift out of overdrive and into drive.

don't forget.. that at some engine loads. the PCM will kick it out of overdrive and also release the Torque converter clutch...

Scandata  

wayne712222 wayne712222
Guru | Posts: 1428 | Joined: 03/13
Posted: 02/11/14
06:22 PM

here is a list of OBD2 sensors..

Obd2scandatachart Zps65411833

Obd2scandatachart2 Zps6e93e7de

there is another set of data stream numbers for the transmission control section..

print these images and the images above.

see if you can find a scan tool that will take a snap shot of data when it shifts out of overdrive.. and post those numbers..

i have the older and the newer Harbor freight scantools.. i don't know if they will work on a 95 chevy truck.. i know they will plug in..

i also have an OTC monitor extended with a bunch of cables. so i really have not thought about trying it the last time there was a 95 in the shop..  

rickm_b rickm_b
New User | Posts: 8 | Joined: 02/14
Posted: 02/11/14
06:28 PM

Hi, Thanks for responding. Yes I have a scanner, and yep its the obd1.5 16 pin. No codes set, but my scanner doesn't show much on the Trans data. It does show TCC lockup, and unlock though, and thats working properly. I usually just shift it into 3rd once the overdrive drops out. Unless I'm really speeding,(above 76mph) then it will stay in OD. I assume cause its sending more pressure to the OD circuit?
195 degree thermostat installed, and its running at that according to the scantool.
I will drive it tommorow with the scan tool and update anything else going on.
Rick  

rickm_b rickm_b
New User | Posts: 8 | Joined: 02/14
Posted: 02/11/14
06:29 PM

Hi, Thanks for responding. Yes I have a scanner, and yep its the obd1.5 16 pin. No codes set, but my scanner doesn't show much on the Trans data. It does show TCC lockup, and unlock though, and thats working properly. I usually just shift it into 3rd once the overdrive drops out. Unless I'm really speeding,(above 76mph) then it will stay in OD. I assume cause its sending more pressure to the OD circuit?
195 degree thermostat installed, and its running at that according to the scantool.
I will drive it tommorow with the scan tool and update anything else going on.
Rick  

rickm_b rickm_b
New User | Posts: 8 | Joined: 02/14
Posted: 02/11/14
06:29 PM

Hi, Thanks for responding. Yes I have a scanner, and yep its the obd1.5 16 pin. No codes set, but my scanner doesn't show much on the Trans data. It does show TCC lockup, and unlock though, and thats working properly. I usually just shift it into 3rd once the overdrive drops out. Unless I'm really speeding,(above 76mph) then it will stay in OD. I assume cause its sending more pressure to the OD circuit?
195 degree thermostat installed, and its running at that according to the scantool.
I will drive it tommorow with the scan tool and update anything else going on.
Rick  

Redhawke Redhawke
User | Posts: 193 | Joined: 10/11
Posted: 02/11/14
06:54 PM

Ok, just my two cents but here goes.

It sounds like, from your initial description, that the trans is cancelling OD....not lock up.  Lots of things can cause this, like the VSS dropping out, loss of pressure, 3/4 clutches burned or 2/4 band.

I would look at the parameters Wayne provided, a sensor could fail and not cause a code.  The VSS is notorious for doing so, as is the TPS. I personally feel that you have a "control problem", which is usually valve body related.  

Could also be a leaky 3/4 accumulator, which is in the valve body area.  You see, after a trans is rebuild, sometimes the "soap" or wash material stays in the channels, and this can sometimes erode the rubber material (accumulators are really sensitive).

The more I think about it, and read your description, the more I'm inclined to think that is the case.  Had quite a few come back on me for that scenario.  

The reason it seems to stay in OD when you're giving it gas, is that the pressure is increased (slightly), so this also makes me think you have a slight leak.  Now, I mentioned the accumulator, but that is just a guess, and rather easy to check, as compared to other internal leaks, which would require a transmission removal.

That snapshot Wayne asked you to do would be EXTREMELY helpful.  

rickm_b rickm_b
New User | Posts: 8 | Joined: 02/14
Posted: 02/13/14
08:39 AM

Hi guys,
Couldn't log in yesterday, must of been a problem with forum. Here's everything my scanner came up with in a capture. Was doing 66mph on flat ground, pushed capture as soon as it dropped out of OD.   Thanks so much for your help!

1) Prom Id: 9985
2) Desired idle Pos: 160 steps
3) Idle air mtr pos 160 steps
4) Coolant temp: 177.3* F
5) Battery voltage: 13.7v
6) Throttle Sensor: 1.13v
7) Map sensor: 1.54v
8) Oxygen sensor: 96mVolts
9) Trans selection: Drive 4
10) Barometric Pressure: 3.48v
11) Vehicle speed: 66mph
12) Engine Rpm: 3050 rpm
13) EGR Duty cycle: 65.1%
14) Engine run time 624 seconds
15) Desired idle: 650 rpm
16) Throttle angle: 16%
17) Knock sensor: 4
18) Integrator: 125
19) O2 crosscounts 202
20) Blk learn cell: 6
21) Block learn: 120
22) Injector pulse: 2.3 mS
23) CCP duty cycle: 99.0%
24) Knock retard: 0%
25) O2 sensor: Ready
26) A/C: Disabled
27) Park/Neutral: Not detected
28) Idle Kicker: Not active
29) A/C: not requested
30) Brake depressed: No
31) Fuel cut off: disabled
32) CCP purge: On
33) Learn control: enabled
34) Battery voltage low: No
35) Async mode: On
36) Rich Lean Flag: Lean
37) Loop status: Closed
38) TCC Solenoid: On
39) TCC Status: Locked
40) Idle Air Coil A: motor On
41) Idle Air Coil B: motor On
42) Battery Voltage high: NO
43) A/C Forced off: No  

Redhawke Redhawke
User | Posts: 193 | Joined: 10/11
Posted: 02/13/14
10:52 AM

Ok, I don't see anything out of whack from that list....maybe Wayne will.  Too bad it doesn't show if the shift solenoids are off or on (commanded that is), but on a 95 it probably won't.

Here's something to chew on (and this does happen), the 1-2 solenoid HAS to turn on for 4th gear to happen.  I have seen them fail when hot without setting a code.  They are relatively cheap and very easy to change.  Although the 1-2 is the culprit, changing them both would be a good idea.

Even though the tranny was rebuilt, a lot of times, people reuse the solenoids over.  It has it's benefits, but does come with a potential problem like you have.  There is really no way to test it, without buying expensive solenoid testers (which don't always work right).

Please note, this is the cheapest way to try to fix it and it's also assuming you don't have a pressure leak inside the unit.  If you do, then a teardown is the only way you'll find it.

The only thing that is "bothering" me, is that you state it does come back on if you increase the throttle.  If that is really happening, then I can't recall a "sticky" solenoid, or one that fails when hot causing that.  

wayne712222 wayne712222
Guru | Posts: 1428 | Joined: 03/13
Posted: 02/13/14
01:26 PM

is it really cold there...

i would like to see #4 above 190F since you had it running about 10 minutes when you pushed the button..

#14 = 624 seconds is just over 10 minutes..

can you post your scan tool brand and model so i can look up a manual for it to see if you can get it into transmission mode..  

rickm_b rickm_b
New User | Posts: 8 | Joined: 02/14
Posted: 02/13/14
04:11 PM

Redhawk- I was going to change the 1-2 but not only does it hold with gas on, but also as soon as you let off (when its in 3rd) it goes back in to OD. Maybe the EPC solenoid weak or faulty? If I change any of them, I will change all of them.

Wayne- was about 50 yesterday. The 624 seconds was after I stopped at Walmart for 10 minutes. I had put 1562 seconds on it before that stop. After watching the engine temps on scantool, I went ahead and got a 195 thermostat and installed it (was already a 195 in there, but wasn't positive, so just got another one).
My scantool is a Autoxray EZ-Scan 3000. It's not supported anymore BTW.
Is it possible my ECT sensor is partially failing? Does it send info to the PCM for shifting?

Just remembered: One weird thing is... about a year ago, my brake switch broke up inside the switch. I had no brake lights, and my cruise control quit working... but it seemed to be  shifting properly when the switch was cross-arcing or whatever was going on in the switch. Switch is installed properly, and a light depress on it shows depressed on the scan tool and at brake lights.
Hell, I even changed a burned out  high mount 3rd brake light bulb last night, thinking one of the elements might be going to ground causing the computer to think brake is on.
Also have tried Shudder Guard, and some Lucas Tranny additive (hoping it might increase viscosity)... to no avail

Thanks for all your help,
Rick  

wayne712222 wayne712222
Guru | Posts: 1428 | Joined: 03/13
Posted: 02/14/14
01:26 AM

an AZ or wells SU102 is a ECT sensor and pigtail.. for under 20 bucks..

yes.. a bad ECT sensor or even the pigtail connector throwing glitches will cause issues..

do you have a digital volt meter..

you could also run a voltage drop test...

only takes a few minutes...


Voltagedroptesting


the 4 part test is the important one but post results by number...


1._____

2._____

3._____

4._____

you will also want to test from the positive battery to the alternator output stud...


and from the positive battery to the underhood fuse box..

why..

because i have found both of these with loose connections..

i ran into a 98 C2500 that had 8.5 volts on test 4.. between the engine and the body.. man that was a different truck after i cleaned all the grounds ..


on a side note.. about 15 years ago.. there were a bunch of gm's and range rovers that had an issue with the ECT sensors.. they leaked coolant.. not in any way that was visible. because the pigtail connects in a proper water tight seal..  the leak was around the terminals.. since it could not escape. it pushed right up the wire strands and dripped into the computer. this caused all kinds of issues.. i noticed a range rover all covered with dust at a friends transmission shop.. i ask whats wrong.  they said.. it won't go over 35 MPH. i said.. change the coolant temp sensor and connector.. and use steam distilled water to wash out the computer .. then let it dry for a day before you attempt to power it up..  they were amazed.  that range had sat there for 6 months unfixable.  

wayne712222 wayne712222
Guru | Posts: 1428 | Joined: 03/13
Posted: 02/14/14
01:32 AM

you might also slowly sweep the  TPS by pressing the gas pedal down and up with the key on, engine off and looking at the live data .. make sure there are NOT glitches..

a TPS glitch. will drive you crazy.. as will a loose ground.. to the TPS..

find the computer ground connection to the engine .. you might want to take that connection all apart and clean it..  i don't know if its connected to the thermostat bolt.. a stud behind it.. somewhere on the side of the block above the oil filter ..  on the back of one of the cylinder heads..   or ALL OF THE ABOVE.. please have a look and clean them..  a stainless steel wire tooth brush is under 5 bucks at most hardware or paint stores.. and works great for cleaning the ring terminals..  

Redhawke Redhawke
User | Posts: 193 | Joined: 10/11
Posted: 02/14/14
11:19 AM

Wayne, wasn't there also a problem with the fusible links on that model?  I have a bulletin buried in my basement somewhere that said something along that line (I think).

Here's the thought behind it.....while under a load it stretches the link one way, and off load another.  If that is happening, that would cause the trans to lose power, which would default to 3rd gear.

All the AAMCO shops have a breakout box, which we used to see if it was electrical or not.  We were able to watch the signals to the trans and/or override them to see what was the culprit.  Made diagnosing a hell of a lot easier.

Maybe he could just raise the rear wheels up and move some wires around (wiggle testing), to see if that might be the problem.  This is of course, after doing that voltage test.  Trust Wayne on that test, it does work well and has helped me many times before in the past.  

wayne712222 wayne712222
Guru | Posts: 1428 | Joined: 03/13
Posted: 02/14/14
01:56 PM

Icon Quoterickm_b:
Hi guys,
Couldn't log in yesterday, must of been a problem with forum. Here's everything my scanner came up with in a capture. Was doing 66mph on flat ground, pushed capture as soon as it dropped out of OD.   Thanks so much for your help!

1) Prom Id: 9985
2) Desired idle Pos: 160 steps
3) Idle air mtr pos 160 steps
4) Coolant temp: 177.3* F
5) Battery voltage: 13.7v
6) Throttle Sensor: 1.13v
7) Map sensor: 1.54v
8) Oxygen sensor: 96mVolts
9) Trans selection: Drive 4
10) Barometric Pressure: 3.48v
11) Vehicle speed: 66mph
12) Engine Rpm: 3050 rpm
13) EGR Duty cycle: 65.1%
14) Engine run time 624 seconds
15) Desired idle: 650 rpm
16) Throttle angle: 16%
17) Knock sensor: 4
18) Integrator: 125
19) O2 crosscounts 202
20) Blk learn cell: 6
21) Block learn: 120
22) Injector pulse: 2.3 mS
23) CCP duty cycle: 99.0%
24) Knock retard: 0%
25) O2 sensor: Ready
26) A/C: Disabled
27) Park/Neutral: Not detected
28) Idle Kicker: Not active
29) A/C: not requested
30) Brake depressed: No
31) Fuel cut off: disabled
32) CCP purge: On
33) Learn control: enabled
34) Battery voltage low: No
35) Async mode: On
36) Rich Lean Flag: Lean
37) Loop status: Closed
38) TCC Solenoid: On
39) TCC Status: Locked
40) Idle Air Coil A: motor On
41) Idle Air Coil B: motor On
42) Battery Voltage high: NO
43) A/C Forced off: No


i just figured it out.. you have a VIN Z TBI motor...



   6 Cylinders W 4.3L CPI (found in 39% of 1995 Chevrolet S10 P/U 4WD)
   6 Cylinders Z 4.3L TBI (found in 61% of 1995 Chevrolet S10 P/U 4WD)


look at the #17  KNOCK sensor counts.. 4... it really should be ZERO.. at that speed..

get up and look at the ignition system..


examine the sides of the coil..  i bet you are going to find white patterns of dust around the sides of the coil center..

Untitled25 Zps16ca2dfc

Untitled24 Zpsddcbb213


now that you found your coil is leaking high voltage..  and you won't believe how different it will run with a new coil...


pull the distributor cap and rotor..


look for cracks ...


Untitled27 Zpsf08c7b4c


pick up a reman distributor that looks like this on top...


Untitled35 Zps221e4fa9


to save you a BUNCH of time swapping distributors..


with the cap off.. after you figure out which wire is #1.. turn the crank.. u you can use a 15/16" socket on the alternator pulley nut..  until the crank timing marks line up with the timing mark listed on the emissions label on the core support.

the arms on the reluctor on the shaft should line up perfectly with the pick up coil..  if you turn the motor  in normal direction of rotation to the right on the alternator and crank.. you can stop when the reluctor lines up at the pickup coil.. look at the timing marks.. if the line on the damper lines up with the timing pointer.. thats where the base timing is..  

you can remove the distributor.. insert the new one with the rotor pointing in the proper direction.  and even if you have to turn the engine 2 turns at the crank with the distributor in.. you can preset or reset the damper marks to the spot you noted before.. turn the housing and to align the pickup coil to the reluctor and then lock the distributor down..

if the aligned distributor does not match the base timing. .you might want to think about turning the crank slightly to bring it to factory timing marks.. and then align the distributor pickup coil and reluctor..

i preset the engine by looking at the reluctor and pickup coil .. i can then remove the distributor work on it.. reinsert it.. reset it by aligning the pickup coil to the reluctor .. lock it down and reach thru the window and turn the key and it will start on the first try.. and usually be within a degree or two of perfect base timing...

there is a tan and black wire to disconnect to set the timing on these with a timing light... its outlined on the emission label.. probably inside the truck.. passenger side.. above the carpet..

misfiring will cause it to kick out of overdrive.

why do the cracks make a difference.. because of the time delay of the ignition system for the electronic spark timing to operate..

the cracks create a random timing pulse that interrupts the count down timer to the next ignition trigger event.. causing random misfires and those will kick the transmission out of 4th gear..

let us know what you find.. take some pictures also.. post them on photobucket..

please run the voltage drop tests also..

a bunch of years ago.. an 94 camaro Z28 came in the shop i worked at.. it had a misfire.. the bosses were working on it. i said. the coil is bad.. change that first..  nah.. they went for the distributor cap and rotor behind the water pump and crank.. they started it.. still had a misfire.. so they changes the spark plugs and wires..  a day later. those are hard to do on that car.. it still misfired.. i always kept a new gm coil on my tool box.. as i change a LOT of them.. smooth.. perfect idle.  i ask said.. why did you hire me if you don't want to listen to my experience..  

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