torque converter’s lockup intermittent issue

[Kran]

i have a 99 tahoe with factory tow package. 4l60e with shift kit, corvette servo, and billet 4th apply piston. truck weighs 8000lb - a lot of audio equipment. trans parts mentioned were installed about five years ago, 30k-ish miles.

the last few drives i’ve noticed when merging onto the highway the converter seems to attempt to lock up but doesn’t. after about five minutes of cruising at speed it will successfully lock up, almost like the pcm attempts a second try. cruising around town it locks up every time, as normal. issue only occurs, sometimes, when merging onto highway or accelerating back up to highway speeds when traffic slows down. i never go above 3k rpm in any gear

any ideas? do not want to just throw parts at it. was going to schedule a trans service to drop the pan and change filter. fluid does not appear burnt.

 

[PlayingWithTBI]

any ideas? do not want to just throw parts at it. was going to schedule a trans service to drop the pan and change filter. fluid does not appear burnt.

Check your TPS, the PCM uses it to lock/unlock your TCC. You can just check it with a volt meter and see if it smoothly increases as you depress the pedal. It's better to put a scanner on it and watch where your TCC unlocks. When you're running/accelerating @ highway speeds, it will be sending more voltage to the PCM as apposed to when tooling around on surface streets.

 

[Sean Buick 76]

Look at the brake switch. There is a switch on the brake that shuts off the lockup when it’s not needed.

 

[NickTransmissions]

any ideas? ... was going to schedule a trans service to drop the pan and change filter. fluid does not appear burnt.

Have the trans shop diagnose it. They'll take it for a test drive with a bidirectional scan tool plugged in showing live engine and trans/ TCC data and will likely spot/ID the cause. You can do the same if you have such a scan tool. Otherwise it's just guesswork, esp if you dont have any codes stored (or dont know if you do or not).

 

[1998_K1500_Sub]

i have a 99 tahoe … truck weighs 8000lb - a lot of audio equipment.

Wow!

My 98 Suburban weighs 3020# in front, 3160# rear, 6180# total with me in the driver’s seat and a mannequin and a 12pk of Blatz in the back.

That’s a heavy ‘Hoe

 

[Kran]

Have the trans shop diagnose it. They'll take it for a test drive with a bidirectional scan tool plugged in showing live engine and trans/ TCC data and will likely spot/ID the cause. You can do the same if you have such a scan tool. Otherwise it's just guesswork, esp if you dont have any codes stored (or dont know if you do or not).

i have a buddy with a good scan tool so i should be able to check what you and the other members mentioned. otherwise ill take it to get diagnosed. thanks so much

 

[Kran]

Wow!

My 98 Suburban weighs 3020# in front, 3160# rear, 6180# total with me in the driver’s seat and a mannequin and a 12pk of Blatz in the back.

That’s a heavy ‘Hoe

yes i paid a visit to a CAT scale. nice surprise when that yellow sheet printed out

 

[df2x4]

Just a thought... Are you cranking the tunes when this happens? If so, any voltage drop?

I'd imagine with that much audio equipment your charging system is probably beefed up immensely, but I've seen vehicles do some really strange things with intermittent voltage sag.

 

[1998_K1500_Sub]

I'd imagine with that much audio equipment your charging system is probably beefed up immensely, but I've seen vehicles do some really strange things with intermittent voltage sag.

^^^ Yes.

Too, if the equipment's ground path is to the body (e.g., connected under a seat bolt or the like) then all its ground current has to return to the engine / battery through the single ground strap in the engine bay... a "weak link".

 

[Kran]

Just a thought... Are you cranking the tunes when this happens? If so, any voltage drop?

I'd imagine with that much audio equipment your charging system is probably beefed up immensely, but I've seen vehicles do some really strange things with intermittent voltage sag.

^^^ Yes.

Too, if the equipment's ground path is to the body (e.g., connected under a seat bolt or the like) then all its ground current has to return to the engine / battery through the single ground strap in the engine bay... a "weak link".

i dont often listen to music loud on the highway. more so podcasts on these 2+ hour trips. save the music for the car show.

for what its worth, the charging system is fairly stout. i charge around 15.4v and playing music sits 14.8v if i really crank it that last 10%. triple 370a alts. 290ah of lithium cells from a ford cmax hybrid (3 vehicles worth). ground distribution block under the hood connecting an added 2/0 fender ground, 2 grounds per alt, and i believe 5 frame grounds to the front of the frame near passenger tire. 5 separate frame grounds in the rear.

all other wiring, like to the factory power box by the master cylinder, whatever you call it, is untouched