Got a 1994 Firebird with an LT1. For some reason it does not want to take off in first gear. I can manually shift it to second and it will take off from there, but it feels like it’s skipping bad in first. Upon further investigation, it seems like it’s not slipping. It’s in third gear. Once moving, by taking off in second then putting it in drive, it up shifts perfect but won’t downshift and won’t go back down to first when stopped.

the transmission was rebuilt one year ago.

Could this be something simple? Like a vacuum hose, plug, or electronics?

 

It seems that you are uncertain with how the Transmission is operating...
or NOT operating properly.

So, I would recommend first trying to look at the PCM data for the 4L60E Transmission.
1994 however uses the GM specific OBD1 Data System...
and may be more difficult for you to find a Shop/ Business that can read the Data for you.

 

I have driven it more now and have a better description. While in drive, I takes off in 4th gear. If I manually put it in second, it takes off in second and can manually shift up to 4th, but will stay in 4th even when I stop and want to take off in 4th.

per a YouTube video… the guy described my exact symptoms and said it was the solenoids.


What are your thoughts on shift solenoids

 

Do you know how many miles are on the Valve-Body?

I would be concerned that the AFL Valve-Train may be worn...
Low AFL pressure can cause: "what I think you are trying to say is happening".

Do you know if the AFL Valve has ever been replaced?
Has the Valve-Body ever been Vacuum-Tested?

 

I don’t know if any of that has been done. The transmission was rebuilt 2 months ago. The previous owner has it done. The shop won’t honor me the warranty. Besides, that shop is over an hour away.

there is a local transmission guy that is reputable near me.

here is where I’m stuck. I can take it to a reputable shop known for specializing in GM cars, particularly this era, or the local reputable transmission guy. I’m worried that trans guy will just say it’s a bad rebuild or just swap out solenoids and not fix the problem. I also worried the regular mechanic will just say it’s a bad ECM or transmission without really digging.

 

With regards to this thread…..

https://ls1tech.com/forums/automatic...e-problem.html

I’m 100% experiencing symptoms 11 and 12. It’s intermittent. Goes back and forth from what 11 describes and 12. Maybe this helps.

 

Took the car to a local reputable GM mechanic. Scanned it and got code for a bad B solenoid.
he changed both A and B and all is perfect.

the issue is that this transmission has been rebuild two months ago. I called the transmission shop that did the rebuild and he said that they replace all solenoids and he did not know what caused the bad solenoid. He said it could be a bad ignition switch. That was replaced 2 months ago as well.

hopefully this will not be a reoccurring issue.

Any underlying issues that cause premature solenoid failure? Line pressure issue maybe?

 

That is good news!


Parts like Shift Solenoids can unfortunately stop working at anytime.
This is a big part of why people were reluctant to have electronically operated Engines and Transmissions, when they started being available as options for automobiles.

I have had parts like Shift Solenoids and other electric/ electronic parts be bad in the box just after purchase...
as well as dying a few days later without warning.

Most of the Name Brand parts will have a 12 Month Warranty.

 

Great info. Thanks!

 

This is why some of the pro's were advocating vacuum modulation for these trannies back in the day. You don't hear that being advocated much anymore.

Dana tried to convince me to go vacuum when we did my first converter and shift kit, but I decided against it - for reasons I don't really remember. But comparing my old school TH400, it feels like there is a more variable and graduated shift timing per throttle input as opposed to the calculated electronic shift timing - if that even makes sense.

 

Years ago Vacuum Modulation for Transmissions like the 4L60E, was a solution for SLOW Line-Pressure/ EPC Solenoid control/ response when abrupt pressure changes were needed.
At this time, the PCM/ Processor was unable to process the monitored input-data quickly enough... (such as the TPS and RPM data)...
and unable to control the EPC Solenoid quickly enough to properly control the Line-Pressure when abrupt pressure changes were needed.

What it ultimately came down to, was that the technology of that era could not do its job quickly enough...
While GM Executives demanded that the Hydra-Matic Engineers produce a result, that current technology could not provide.
This was a bad time for the guys on the 4L60E Team... Many excellent Engineers became fed-up with GM (and quit) over the Early 4L60E.

When Computer processing Technology finally advanced; the PCM was able to process the monitored input data, and control the EPC Solenoid quickly enough to properly control Line-Pressure.
The Vacuum Modulator solution was now no longer needed.
I remember talking to Dana about this... we even discussed it again as recently as 12 to 18 Months ago.
He likes to reminisce a lot.

 

What PCMs are we talking about here? TBI? LT1? I assume when the LS stuff came out this wasn't an issue anymore?

 

PCMs from 1991 through the early 2000s for the 4L60E and 4L80E.

 

What control es the line pressure in my 1994 LT1 unit? Could that be defective and could the line pressure cause premature solenoid failure. Initially, the first symptom was hard shifting like a shift kit.

 

The 1994 Model-Year PCMs are definitely some of the slower-processing PCMs.

As long as the Line-Pressure is rising quickly enough when the Throttle is pegged...
and there is minimal to no Clutch slipping...
Then all is good.

There should be no need to be concerned of Solenoid failure.

Any time the Line-Pressure is elevated, shift firmness should increase.
You should get a Line-pressure Gauge with a long hose...
tape the Gauge to the Wind-Shield and Drive the vehicle while monitoring the Line-Pressure.

 

Is it possible some of this could be calibration related? LT1 and even TBI PCM hacks have come a long way since the early 2000s

 

Absolutely.

 

Plus as vorteciroc knows much better than I, the 94's had a funk factor as the transition to electronic control from the old 700R4 platform was in its infancy and the torque of the LT1 played havoc with an as yet underdeveloped transmission. Ask me how I know? I've owned two of them.