TCC locking up at 74MPH at W.O.T

[Kitch]

Does anyone know what parameter would be letting the TCC lock at 74MPH while at W.O.T?
I've just been doing some W.O.T test runs in my van and noticed that the TCC is locking on once I reach 74MPH and stays locked until I lift off.

It's a 1993 4L60E running an $OD bin, 8625 PCM in a modified G20 van.

[Fast355]

Does anyone know what parameter would be letting the TCC lock at 74MPH while at W.O.T?
I've just been doing some W.O.T test runs in my van and noticed that the TCC is locking on once I reach 74MPH and stays locked until I lift off.

It's a 1993 4L60E running an $OD bin, 8625 PCM in a modified G20 van.

There are WOT or Kickdown mode TCC lockup settings in the ECM. From my experience it helps to lock the TCC slightly above peak torque and drag the engine back down to peak torque again. Keeps your engine in its powerband longer and creates more HP to the wheels.

[Hog]

Compared to stock, keeping the TCC from locking at WOT was worth a full tenth in the 1/4 mile on a stock longblock L31 with 4.10 gears with a 28" tire trapping at about 4900rpm, 4000lb truck.. The 2-3 upshift would happen, then moments later the TCC would lock. I used to hold the brake light on as that would prevent the TCC from applying.

peace
Hog

[Kitch]

I still haven't found what causing it but it is quite annoying, one because it can't be good for the clutch and two when your overtaking another vehicle at W.O.T. the last thing you want is the engine to drop RPM as the TCC engages.

[Hog]

It is the ECM that's locking the TCC at WOT at 74mph in third gear, all 4l60es do this. The 4l80es usually lock in 2nd gear at WOT.

peace
Hog

[Fast355]

It is the ECM that's locking the TCC at WOT at 74mph in third gear, all 4l60es do this. The 4l80es usually lock in 2nd gear at WOT.

peace
Hog

Maybe its the difference between 4L60E an 80E but mine accelerates quicker and puts more power to the wheels locked.

[Kitch]

How good is the clutch in a stock 4L60E converter, I thought they were only supposed to operate under light load conditions?

[Hog]

Maybe its the difference between 4L60E an 80E but mine accelerates quicker and puts more power to the wheels locked.

It could be because of the trans difference, but I think its probably moreso your cam. It was worth a tenth to avoid TCC lockup in the 1/4 mile, but I had the stock cam. It just didn't have enough power to recover from the 2-3 shift then immediately lock the TCC.

All else equal, a locked TCC will put down more power to the ground, whether or not that extra rear wheel power increase from increased trans efficiency aids in acceleration depends on the individual setup. The 3.8 turbo guys liked to lock their TCC's as it loaded the turbo more.

peace
Hog

[Fast355]

It could be because of the trans difference, but I think its probably moreso your cam. It was worth a tenth to avoid TCC lockup in the 1/4 mile, but I had the stock cam. It just didn't have enough power to recover from the 2-3 shift then immediately lock the TCC.

All else equal, a locked TCC will put down more power to the ground, whether or not that extra rear wheel power increase from increased trans efficiency aids in acceleration depends on the individual setup. The 3.8 turbo guys liked to lock their TCC's as it loaded the turbo more.

peace
Hog

The 395' Marine cam LOVED having the torque converter locked around 60 mph in 2nd gear. You could feel the acceleration increase the moment it locked up. Then again the 4L85E has closer gear spacing and does not have as much RPM drop between gears. Shifting with a locked converter is a bit rough but my acceleration was great and still is for that matter. Even better with the 4.56s and SPO 357 HP 350 cam.

[Kitch]

I may have solved my problem with the TCC locking up at 74MPH @ W.O.T, while tweaking some of the other TCC settings for my van today I found "Kickdown pattern TCC engage/release" and in "Engage MPH vs gear" 3rd gear factory was set to 75MPH.
I changed it up to 125.5 and for the first time I got to 78MPH @ W.O.T without the TCC engaging. Typically I had two cars in the lanes in front of me so I had to lift off before I could I get a higher MPH reading!

[Kitch]

I can definitely confirm that solved the problem, I've had the van up to 84MPH without the TCC engaging at W.O.T.

[Fast355]

I may have solved my problem with the TCC locking up at 74MPH @ W.O.T, while tweaking some of the other TCC settings for my van today I found "Kickdown pattern TCC engage/release" and in "Engage MPH vs gear" 3rd gear factory was set to 75MPH.
I changed it up to 125.5 and for the first time I got to 78MPH @ W.O.T without the TCC engaging. Typically I had two cars in the lanes in front of me so I had to lift off before I could I get a higher MPH reading!

Awesome! Mentioned the WOT/Kickdown mode table back on post#2 on Feb 22. Glad you finally got it figured out.

With the low-end torque monster that is a TBI 350, I really do not see how unlocking the converter and losing HP to the wheels will help your acceleration. With 3.42 gears and stock height tires that are between 28 and 29" tall, you are locking the converter around 3,200 rpm, which drops the rpm down to 3,000 rpm. That is basically pulling you through your torque peak twice. The 299 ECM from a 1992 G20 I ran my 350 TBI/700r4 on in my 1983 G20 for nearly 2 years had a TCC Unlock prevent setting that kept the TCC from unlocking above 65 mph regardless of throttle position. With a gm crate 1 ton 190 HP 350 TBI, edelbrock performer rpm intake, 454 tbi unit, tri-y headers and a dual 2.5 to single 3" exhaust with a single in/dual out muffler I never felt the TCC locking up at 65 mph to hurt the acceleration. With the stock cams and heads these are not high rpm screamers.

[Kitch]

I don't know how I missed it before!

Part of the problem I've been trying to get rid of ever since I upgraded the motor to Vortec heads is counts knock under W.O.T. (Wideband AFR's 12.5-1) and now knock counts when I lift off. I could get about 200 KC's in a W.O.T. test run from 30-70 MPH and another 900 KC's if I reached 74 MPH and the TCC locked.
I would get noticeable a knock count increase when the TCC would lock and drag the RPM back down under load.

Interesting, just looked at the last log I had with the TCC not locking and it I still got about 800 KC's in 3rd gear at 3400RPM @ W.O.T. with 27.8º timing.

[ony]

lean?

[Kitch]

I just had a look at the AFR's while it was in 3rd gear and they varied between 12.5-12.8, I could try and richen it up a little and see what happens.

[Fast355]

I don't know how I missed it before!

Part of the problem I've been trying to get rid of ever since I upgraded the motor to Vortec heads is counts knock under W.O.T. (Wideband AFR's 12.5-1) and now knock counts when I lift off. I could get about 200 KC's in a W.O.T. test run from 30-70 MPH and another 900 KC's if I reached 74 MPH and the TCC locked.
I would get noticeable a knock count increase when the TCC would lock and drag the RPM back down under load.

Interesting, just looked at the last log I had with the TCC not locking and it I still got about 800 KC's in 3rd gear at 3400RPM @ W.O.T. with 27.8º timing.


False knock? I would try a new OEM knock sensor torqued to the OEM value.

[tamperedchevy]

what octane fuel do you run? i run 93 on the stock cam and 195* thermostat and all the engine mods(headers, afpr and whatnot) with top rpm/map spark at 29 and no knock. is something rattling around down there causing false knock?


oops, didnt see fast355's post on page two. he already asked about the false knock

[Kitch]

I fitted a new AC-Delco Knock sensor and torqued it into place when I put the new Vortec engine into the van.
It could be false knock but if it is I don't know how to eliminate it.
It could be noise from my narrow body ComCams roller rockers or it could be the aggressive lobes on the cam as there is a bit of lifter noise that I can't adjust out at idle.
I use 98 octane fuel in it.
I had the brand new Vortec crate engine pulled apart and zero decked and I've now got 9.6-1 compression ratio, it could be that my cam is too small CS 252XFI HR-13 has 202º intake and 212º exhaust at .050 and I've got too much cylinder pressure.
The combo makes more power than the stock TBI motor did and it idles with 18" of vacuum @ 600RPM in gear but I can't get it to break traction if I stand on it.