All,

My 66 Chevelle with LS3 and 4L75e is running well. First several shorter drives were no issue. This weekend I drove from Leander to Hutto (~33 miles, 40 minutes). It was probably 85° or 90°. When I was about 5 miles from the location, the tranny started slipping. 1st -> 2nd seemed fine, but when cruising between 40-60 MPH, it seemed to struggle finding a gear between 2nd &4th. Without moving the gas pedal, the RPM would jump up a couple hundred RPM and down a couple hundred. After sitting for several hours, the drive home was similar. Once it go warm (water temp was between 190-220°), it started to do the same thing. Even when the water temp is in that range, on shorter drives the trans does fine. I checked the fluid and it's full. Maybe even a smidge too full, but not WAY too full. I checked the TCM (Atomic), and all the settings seem right. The trans came attached to the engine (Blueprint engines crate) and I've never separated it.

Any thoughts?

 

So I decided to try troubleshooting it. Took the car out right after I posted and the transmission was still acting up. Even when cold. I looked at the TCM display to check my settings and everything looked good. Then I went to the diagnostics page. It was lit up like a Christmas tree with all kinds of errors. TPS CAL, TPS SPAN and a couple others. Instead of tracking them all down, I cleared the codes and Redid the TPS calibration. Took it for a quick spin and everything works as it should. Shifting great, etc. Not sure what it could have been.

Any idea what would have caused this?

 

Torque converter unlocking due to malfunction in brake light switch circuit ?

 

I've never heard of that. Can you expand on that?

 

I had some different issues this evening. I'm going to start a new thread though. Not sure if they are related or not.

 

Converter is designed to UNLOCK whenever PCM detects brake application, input data for brake application is from brake pedal mounted BRAKE LIGHT switch..

 

Interesting. I didn't know that. Although nowhere in the TCM harness is a brake light wire.

 

To close the loop, I figured it out. I called Holley to talk about the TCM. I asked where I should be getting the TPS ground reference. They were absolutely no help at all. Then I started thinking, what about the ground as a whole. I know you can have a "good" ground, but once things get warm and you are pushing enough juice through them, you can start having issues. And since my problem seems electrical, I figured I should look at the grounds.

I know I have good grounds in the car. Battery to frame, frame to engine, battery to body. However, I remembered I was grounding everything in the passenger compartment to one of the bolts on the dash. So I ran a ground from the frame into the passenger compartment and made a grounding post. EVERYTHING started working better. Voltmeter didn't vary as much when idling, tranny shifts better. Hell the engine idles better and has more power from the start (although that is probably more the TCM working better).

 

On LS swaps you can't have too many good grounds. Glad you made progress.