Tranny torque converter unlocks

[Christophe Salvaing]

Hi

I own a 97 K1500 Suburban. 5.7L 4L60E. 121,000 miles

I recently had the 5.7 engine replaced.

After change the engine, I notice that from 60mph to 90 at stabilised speed (no accelarting no braking), and only when in overdrive the torque converter is unlocking and generates a shock in the whole tranny.
It's very fast : 1/10 sec.
It also shakes the truck a bit when it does it.

I recently change the tranny too and ... the problem remains ...
I'm afraid to damage the new one.

The brake pedal switch works fine this is not the issue comes from.
It's like the PCM send furtively an "unlock" signal to the tranny.

No CES on dash. All is electrical is news (plugs, O² sensor etc etc)

I wonder to reprogram the PCM ?

I want to know your thoughts on the possible fix's
Please let me know what you guys think.

Thanks,

Chris

 

[someotherguy]

Hi Chris,

Are you 100% sure it's the TCC unlocking? With the miles you have, if you re-used your original distributor - it may be worn. I experienced a similar symptom on a '96 many years ago and the distributor was worn, causing an occasional stumble while trying to maintain a steady highway speed.

If you have access to a scanner that can read the cam retard angle, see what it looks like. It may just need to be set, assuming your distributor was out for the engine replacement. While holding RPM's to at least 1,000 for a good reading, adjust the distributor until the cam retard angle is within +/- 2° from zero. This setting can be way off and not trigger a check engine light, though it absolutely will impact how the engine runs.

Richard

 

[98_k1500]

I second this.^^^^^ My 98 had the same almost hiccup like symptom after putting a motor in it. Its a manual so TCC was out of the question. One of the pins was bent on the cam sensor in the distributor and had the computer reading -45° cam retard. No CEL. After changing the cam sensor and setting the cam retard, she still runs perfectly to this day.

 

[Christophe Salvaing]

Thank you very much for these advices.
I will change :
- Distributor : http://www.rockauto.com/catalog/moreinfo.php?pk=4048398&cc=1303063
- Camshaft Position Sensor : http://www.rockauto.com/catalog/moreinfo.php?pk=87488&cc=1303063

What else ?

Bst rgds

 

[Christophe Salvaing]

Cutoff append 2 or 3 times for 10 miles only when tranny is on overdrive.
Never on 1st-2nd or 3rd speed.

It's looking like as the engine cuts for 1/10 second.
It's very fast and suddenly.

 

[98_k1500]

Thats exactly what mine felt like. Like the engine just cut power for a split second, then was fine again. Mine was more noticable just as you top a small hill. Do you know how to set the cam retard on one of these engines?

 

[someotherguy]

Check it before replacing. To do either you need the scan tool discussed earlier, so you might as well check before spending money or effort on replacement. Reading the actual cam retard figures from the scanner is your best bet...but you can also physically check it to a degree by removing the cap, and try to shove the rotor from side to side. If it doesn't budge, turn it a little bit and you'll see it pop up some, try moving it side to side again. If you get much movement the distributor is worn.

Another suspect when dealing with a "skip" under those conditions would be the rest of your ignition system. If the cap, rotor, or wires are marginal - they can cause this. If you replace the cap buy the best quality you can find (Delphi should be a good bet) as many Vortec caps have gone down in quality and can cause you trouble. Re-use your existing cap screws as they're more likely to fit your distributor without issues; the distributor body is plastic and almost always cracked where the screws go in...so be careful.

Richard

 

[Christophe Salvaing]

Thanks guy.

Cap & distributor are brand new (AC Delco)
My mechanic will set the cam retard first and check the cam & rotor.

BUT if that was that issue , the phenomenon would occur in all cases and not just on overdrive ? No ?

 

[98_k1500]

Mine only did it while cruising in 5th gear. That cam retard sets the injector timing. It can do some strange things. If you shifted mine to 4th the issue went away. It can cause some strange load vs rpm issues.

 

[df2x4]

Glad I found this thread again, thanks for the info here guys. I have a very similar problem with my truck that I also assumed to be some sort of TCC problem, but I recently had my transmission completely rebuilt and this didn't solve it. I will be looking into ignition issues now, great to know where to start!