Recently ive noticed a strange shift issue. While driving in either OD or 3rd, at about 45-60 mph, usually just off idle, the trans feels as if someone is engaging and disengaging the e-brake erratically for about 3 seconds. Doesn't happen while accelerating or deccelerating. I have replaced the TPS recently (aftermarket) and seafoamed thru the booster hose as well. Problem didnot exist before these issues. Is there anything electricaly involved i should check first before assuming its a poss. mechanical issue? Im aware of typical 4l60e issues with 1-2 hard shifts and such, but anyone have this happen before? Thanks in advance , folks

 

Sounds like you are experiencing torque converter shutter.

I would inspect the TPS sensor output and see if that may be causing the issue. The information from the TPS sensor is used to determine lockup and a host of other things in the trans. If the signal is choppy at that throttle position, it can cause the transmission to do very weird things.

 

Thank you for the info, this is what i suspect will be the issue. Only seemed to start since replacing the TPS. Why did i replace the TPS? Good question: no good reason. I have a good Haynes reference book concerning codes that goes into depth about testing of sensors, ohm readouts, etc. Not specific to Blazers, but a good start. Thanks again!

 

Found a great qoute from my Haynes Computer Codes diag book: "when the vss indicates speed above a certain range and the cts is warm, the TPS determines throttle position (acceleration or deceleration) and the transmission sensor relays the particular gear the transmission is operating in to the ecm for analysis. IF ALL PARAMTERE ARE WITHIN A CERTAIN RANGE, THE ECM SIGNALS THE CLUTCH TO LOCK UP." This being said, if "the converter is not locking up, the driver might not notice any differences unless he/she checks fuel consumption and the INCREASE IN TACHOMETER READINGS. Without the TCC operating, the engine will turn an additonal 300 TO 500 RPM AT CRUSING SPEED (usually just off idle position at the throttle)"

Since the MAP, IAT, and TPS share either sensor grounds or 5v reference voltages and the ECM uses info from the MAP for TCC enabling, ANY hiccup in these sensors can cause the TCC to engage and disengage. Mine seems to do this only when at crusing speeds (45mph and about 60 mph), so i attribute my issues to my newer TPS, since it is most vulnerable to issues just off idle if there is any play in the sensor housing, poor construction, etc. Hope this points folks into some direction. It is amazing how much is affected by electrical issue as apposed to mechanical. But its much easier to ohm out a sensor than to start pulling everything apart!