4L80e 1987 C 10 ls swap not shifting

[WFO]

RPM gauge

Tachometer or Tach

 

[Markmx6]

What is the "stand alone harness" connected to?

Unplug the large connector on the driver's side of the transmission, get in, fire it up and put it in Drive. If it feels different then you're in second gear when plugged in which means limp mode. If it feels different (i.e like its in a deeper gear), you're in first gear and have an comm issue between the vss and pcm.

Will it do the same thing if you do not have power to the transmission? I thought the 4l80 was second gear with the solenoids all off, and no power would cause that too.

I had a 4l80 that I installed in an 85 and when you first put it in drive it would go into first, shift into second when driving and then not change again until you took it out and put it back in drive. That turned out to be the VSS signal.

To the OP, what are you using for a PCM? I'm assuming the 2002 0411 PCM, but I figured I would ask to be sure.

A cheap scanner that can give live data would also be helpful. It can tell you what gear the PCM thinks it is in.

Like Nick said, if you don't have a good VSS signal the PCM won't even try and shift the transmission because it thinks you aren't moving.

 

[NickTransmissions]

Will it do the same thing if you do not have power to the transmission? I thought the 4l80 was second gear with the solenoids all off, and no power would cause that too.

I had a 4l80 that I installed in an 85 and when you first put it in drive it would go into first, shift into second when driving and then not change again until you took it out and put it back in drive. That turned out to be the VSS signal.

To the OP, what are you using for a PCM? I'm assuming the 2002 0411 PCM, but I figured I would ask to be sure.

A cheap scanner that can give live data would also be helpful. It can tell you what gear the PCM thinks it is in.

Like Nick said, if you don't have a good VSS signal the PCM won't even try and shift the transmission because it thinks you aren't moving.

If no power is getting to the trans, he will start out and remain in 2nd gear...If it's a speed sensor problem, he will start out and remain in first gear...So the purpose of the test is to see via process of elimination what gear he is actually in when everything is plugged into the trans...Since there's no change in terms how it feels between plugged and un-plugged, I'm thinking he's in limp mode, which is second gear (and reverse).

If it felt different to him, i.e. it was more responsive and felt like it was in first gear when plugged in but felt like it was in a taller gear when unplugged, then I'd figure he had a speed sensor problem.

 

[Markmx6]

If no power is getting to the trans, he will start out and remain in 2nd gear...If it's a speed sensor problem, he will start out and remain in first gear...So the purpose of the test is to see via process of elimination what gear he is actually in when everything is plugged into the trans...Since there's no change in terms how it feels between plugged and un-plugged, I'm thinking he's in limp mode, which is second gear (and reverse).

If it felt different to him, i.e. it was more responsive and felt like it was in first gear when plugged in but felt like it was in a taller gear when unplugged, then I'd figure he had a speed sensor problem.

That makes perfect sense.

 

[Bextreme04]

I bet you have the connector plugged in upside down. It's a common problem on swaps, especially with standalone harnesses. Make sure that the person that built the harness put the pins in the right spots and also that you are plugging it into the transmission in the correct orientation. Make sure you have 12v between Pin E and Pin D with ignition power on.

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[TotalyHucked]

Yep^ First thing is to make sure the plug isn't backwards. If you're not sure, just unplug and turn 180* and see if you can plug it back in and see what it does. If it won't plug back in, don't force it. I had this issue on my LS swap, plug was backwards on the 4L65 to start with.

Another question, exactly who's harness are you using? Did you spec the harness specifically for a 6.0 and 4L80?

 

[bkhrla]

Yep^ First thing is to make sure the plug isn't backwards. If you're not sure, just unplug and turn 180* and see if you can plug it back in and see what it does. If it won't plug back in, don't force it. I had this issue on my LS swap, plug was backwards on the 4L65 to start with.

Another question, exactly who's harness are you using? Did you spec the harness specifically for a 6.0 and 4L80?

I purchased from a guy Andy LSX specialties. He sent me the specs he used for the tune based on my trans and engine. I’m going to double check to make sure I’m getting power. Hoping maybe Nick can come check it out since he’s in Vegas also

 

[Camar068]

If no power is getting to the trans, he will start out and remain in 2nd gear...If it's a speed sensor problem, he will start out and remain in first gear...So the purpose of the test is to see via process of elimination what gear he is actually in when everything is plugged into the trans...Since there's no change in terms how it feels between plugged and un-plugged, I'm thinking he's in limp mode, which is second gear (and reverse).

If it felt different to him, i.e. it was more responsive and felt like it was in first gear when plugged in but felt like it was in a taller gear when unplugged, then I'd figure he had a speed sensor problem.

good to know