4L60E slipping out of overdrive

bbullsj · #1 03-01-2016, 05:19 PM

I have a 97 k1500 cheyenne with a 5.7 vortec and a 4L60E transmission. I initially had an issue with the central port injection system so I replaced with an upgraded Delphi unit. I then developed an issue with the transmission. It will shift into overdrive and then with low load it will stutter. It feels like the transmission is slipping and then slams back into gear. I have watched for misfire data on a tech2 and there is none. I read that dexron3 is terrible fluid and can gel up. I ran some Gunk trans medic fluid through it for a couple hundred miles and then did a drain and fill with a new filter and Mobil1 ATF synthetic fluid. I was told it could also be the TCC lock up solenoid so I replaced that with a GM solenoid. After about 15 miles it started to do that same thing again. it only happens on low load in overdrive and is worse once the fluid has warmed up. Am i going to damage the transmission if I continue to drive it like that? What are my next steps to check or parts that I may need to replace?

maxwedge · #2 03-01-2016, 05:33 PM

This didn't happen til the work was done? Can we assume any more load in lock up causes it to down shift and shudder stops?

bbullsj · #3 03-01-2016, 06:31 PM

Correct, everything was fine before the injection system was replaced. Yes if I push the pedal down more the transmission will downshift and accelerate properly and the shift back into overdrive.

j cAT · #4 03-01-2016, 07:41 PM

Quote:

Originally Posted by bbullsj

Correct, everything was fine before the injection system was replaced. Yes if I push the pedal down more the transmission will downshift and accelerate properly and the shift back into overdrive.

this does sound like the dexron III acid fluid eat out the a b shift valve bodies. those valves if worn will cause a drop in system pressure . low pressure will kill the transmission . possible much more is in need of replacing. shift solenoids are just electrical these do fail over time . The valve bodies with dexron III do take a beating . This is usually how these gradually die. very common Dexron III damage. pressure testing by a tranny shop should know if its just those valves need replacing.

maxwedge · #5 03-01-2016, 08:15 PM

I would drive this moderately til a code is set, which will happen, this will give you an accurate diagnostic path.

bbullsj · #6 03-03-2016, 07:23 PM

At this point am I going to damage anything that I wouldn't have to replace anyways? I've done some more reading and I've found it could be the brake switch messing up, The steel ball for the TCC solenoid hammering on the aluminum valve body and causing a drop in line pressure due to losing pressure around the deformed aluminum and TPS sensor (since it only happens around the same throttle position). ANy way to clean the TPS or check it's values? I do have access to a Tech2.

Schurkey · #7 03-04-2016, 11:07 AM

The title of this thread involves "Slipping out of overdrive".

Have you determined that this is a gear-ratio problem (actually losing overdrive, dropping to a lower gear) or is this a TCC problem (stays in overdrive, but the converter clutch disengages).

First step in diagnosis is describing the problem properly.

bbullsj · #8 03-04-2016, 02:17 PM

It is not downshifting. It feels like you cut spark for half a second. It is a distinctive stutter/hesitation.

Schurkey · #9 03-04-2016, 02:34 PM

Quote:

Originally Posted by bbullsj

It is not downshifting. It feels like you cut spark for half a second. It is a distinctive stutter/hesitation.

It's possible for that to be a symptom of transmission problems. I would not rule out that it may just be plain ol' misfire. I'd hope that the computer would spit out accurate misfire data...but I'd want to see the O2, MAP, TPS, and RPM data just before, when, and just after it's stuttering/hesitating.

I'm not familiar with the '97 transmission. Can you install a pressure gauge on the case? Are there temperature and pressure sensors in the trans that can report to the computer--and thus to the scan tool?

What info does the scan tool show for transmission operation? I assume there's more available than just TCC and shift-solenoid operation.

j cAT · #10 03-04-2016, 02:51 PM

Quote:

Originally Posted by bbullsj

It is not downshifting. It feels like you cut spark for half a second. It is a distinctive stutter/hesitation.

with what you say here as was mentioned this can be the tranny or engine miss fires. using a scan tool see if the engine is good. also check for proper fuel pressure 60-65 PSI key on eng OFF......... all that good then good chance tranny has worn valve bodies / possible electrical connector at tranny or even the ignition switch.

bbullsj · #11 03-04-2016, 03:35 PM

I will check on Monday about transmission data available. I'm pretty sure it can be pressure tested, not sure I have the tools to do it though. I'll check fuel pressure as well. New fuel pump and injection system was installed immediately prior to this issue. The spider poppet valve system failed and was filling the crankcase.

I have replaced the ignition due to a code.... P2780 I think? It's been a couple years. CEL would come on and I wouldn't not have overdrive at all. Has been fine since that was replaced.

bbullsj · #12 03-11-2016, 04:21 PM

Ok, so I was sick this past week and just had a chance to put a tech2 on it. It is definitely a misfire. As soon as it happens I can watch random misfires happen. It's usually at least 2 cylinders at once, sometimes more. I have a bunch of snapshots I can post but it won't let me do it from my phone. The CEL is not on but I have 3 history codes. P0300, P0141, and P0157.

j cAT · #13 03-11-2016, 04:37 PM

Quote:

Originally Posted by bbullsj

Ok, so I was sick this past week and just had a chance to put a tech2 on it. It is definitely a misfire. As soon as it happens I can watch random misfires happen. It's usually at least 2 cylinders at once, sometimes more. I have a bunch of snapshots I can post but it won't let me do it from my phone. The CEL is not on but I have 3 history codes. P0300, P0141, and P0157.

all those codes I would guess is 2 bad cat converters.

miss fires from restricted exhaust. both downstream O2 sensors reporting low voltage output to the PCM.

check for restricted exhaust . fix all exhaust leaks check fuel pressures and do the fuel pressure test. check the fuel trims should be close to zero +/- 10 ..
If the O2 sensors are old replace . if the converters are bad find out why they are damaged. injector leaking or other fuel ratio issues.

bbullsj · #14 03-11-2016, 05:29 PM

About 2 months before the fuel issue I did have to cut open a converter and pull out a piece of metal that was rattling around :/ Plugged cats could be a good possibility. They are at least 10 years old at a minimum. 02 sensors were all replaced in 08.

j cAT · #15 03-11-2016, 06:38 PM

Quote:

Originally Posted by bbullsj

About 2 months before the fuel issue I did have to cut open a converter and pull out a piece of metal that was rattling around :/ Plugged cats could be a good possibility. They are at least 10 years old at a minimum. 02 sensors were all replaced in 08.

excessive back pressure will cause 300 code. the other codes would indicate the converters are dead. or the O2 sensors are. with fuel delivery failures not properly controlling the fuel mixtures this will damage the converters. remove the upstream O2 sensors leave the holes open see if the engine has much more power if so then the converters may have melted down also converter internals may be in the muffler restricting flow.

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