shifting problems after LS swap

[williscr3]

did a ls swap last summer and cant figure out what the deal is with this. when i slow to a stop my speedometer is so slow to respond. ill come to a complete stop and its reading 20mph and slowly decends but takes 10 to 20 seconds and i can feel the transmission is still in a higher gear then finally downshifts and almost wants to stall because of it. im using ls droid for flashing and tunerpro RT for tuning. i changed vss pulses per mile to accommodate my setup. am i missing something? im using regular 4l60e that was in the truck. 4l60e is selected option for tune. should i have changed the VSS to a newer one? brake switch is connected to 0411 for overdrive disengage. what about primary pulses per mile output 4k and secondary 128k should these be changed?

 

[Dropped88]

4k is for speedo the 128k is for abs and maybe something else I can't remember.

But check your vss wiring very well it sounds like its picking up some interference

Also something else ive seen with almost the same symptoms except its always been fords is a diode is bad in the alternator which causes voltage spikes in pulses and it screws with the vss. I could see on the scan tool where the vehicle thought I was moving until I would unplug alternator

So my opinion off what you described is check vss wiring if it checks good then unplug alternator run around the block and see IF speedo drops then

 

[williscr3]

good idea on the wiring. the vss wiring is a bit of a mess under there. im heading outside now. ill sort out the wiring and check the alternator. thanks.

 

[williscr3]

So did some digging around and sorting. The vss wires are not shielded at all. Assuming it should be within shield loom? When I did my swap I bought a stand alone harness and adapted it to my existing wiring that was staying I never paid any mind to the vss wires. So this is probably my problem? Now... how do I go about correcting this? Create a new section of wire and just run straight to computer maybe?

 

[stutaeng]

So did some digging around and sorting. The vss wires are not shielded at all. Assuming it should be within shield loom? When I did my swap I bought a stand alone harness and adapted it to my existing wiring that was staying I never paid any mind to the vss wires. So this is probably my problem? Now... how do I go about correcting this? Create a new section of wire and just run straight to computer maybe?

Shielded? Like magnetically shielded? I think it's worth a shot to get a VSS wire set to the ECU.

When I did my 4L80e swap I repinned that gray tranny connector and just used the extra 2 wires within the existing harness for the new input VSS. The existing wires were not twisted (as the aftermarket set comes,) but it worked just fine. I don't think there's any kind of magnetic shielding on any of the wires in the harness.

Can you hook up a scanner to see the speedometer from the ECU directly? You kept your torque converter from your original transmission, right? Anything else you changed or modified? Maybe lift the rear axle and see if it does the same on the air?

 

[williscr3]

Yeah sometimes they wrap foil around the length of wire and ground one side to prevent any interference from stray voltage. In this case I think its supposed to have it. It's definitely something with the VSS once I'm at a complete stop the speed from Ecu is still slowly descending and is at 20mph every time. It takes another 10 seconds to get to 0.

 

[stutaeng]

Yeah sometimes they wrap foil around the length of wire and ground one side to prevent any interference from stray voltage. In this case I think its supposed to have it. It's definitely something with the VSS once I'm at a complete stop the speed from Ecu is still slowly descending and is at 20mph every time. It takes another 10 seconds to get to 0.

I undid all of my harness on that truck, and there was a small portion that did have the foil tape, but based on the location I thought it was for radiant heat protection from the exhaust?...didn't undo the transmission harness, but you can see the man trunk wire bundle is just plain wires. Probably different for a stand alone harness.

Yeah, not sure what could be causing that. Could it be that the tranny is actually not downshifting? Try a new VSS sensor and new wire; pretty sure all VSS are the same. Hopefully it will work for you. Did it just start doing that? Or it was like that after the swap?

 

[williscr3]

hey thanks man for the pic reference. still working at it. re-sorted all wiring to transmission so its all by its self. pulled the vss out and tried to install a new one for a 99 silverado, doesnt fit lol. so need to get correct one for 96 truck. made sure all wires were by themselves. read online people were eliminating the PWM for ls swap with 4l60e so i tried that. set it so basically the TCC would just lock and unlock. 99% on min and 100% on max. no more slipping, still as i slow and come to a stop the downshifting is delayed. also updated my tire size, and gear ratio, so speedo and computer read correctly. yet it it still reads 20mph after completely stopping and then slowly drops to 0mph. once i actually stop i can feel the trans down shift to 2nd then 1st. Im going to get a new VSS but also got some new software thats gm specific so i can see what gear the ecm is actually calling for. i even tried putting it in neutral as i approached a stop sign. it keeps the rpms at 1500rpm then still feels like it wants to stall. im not sure if its because of tune and cam upgrade or if its an actual problem with trans. im honestly wanting to drop the auto for a manual trans anyway. cant find one and lack of funding after LS swap, straight axle, 1 ton rear axle, and full exhaust round 2.