4L80E Not shifting into o/d????

655.7Vortec · January 15, 2002

Ok, Im new and need some help...

I recently bought a 2wd 1965 chevrolet pickup truck. It is restored and has the whole drivetrain out of a 1997 2500 chevy truck. (5.7l Vortec, 4L80E, rear end and 3/4 ton leaf springs). It has no cats and a K&N Cone filter. Other than that it is all stock (as far as I know) Now on to the problem.

After about 40minutes of driving, the Check engine light comes on. Shortly after that, the truck stops shifting into overdrive. Off throttle it kicks in, and as soon as you press the gas agian it goes back into 3rd. Anyone know what it could be? If you disconnect the battery for a few hours the computer resets itself, and the process repeats itself(40minutes of driving, the Check engine light comes on. Shortly after that, the truck stops shifting into overdrive.) Does anyone have anyy idea what it could be? Please let me know, Tim

:angry:

Also... It has a few other minor problems (might be major.. but it makes me feel better to call them minor)

See, Some people have told me "Oh, just take it down to the dealer and have them scan the computer, they can fix it"

Thats another problem with the engine swap. For some reason... when you hook the computer scanner up... It doesn't establish a connection. Just like its not hooked to anything. I also need to get that solved. So, I guess the problems are related then right?

Think it could all be computer related? Should I take the chance and replace the whole computer? Its something like $250-300 from the dealer. What do you all think? Please help me....

I assumed (when I bought it) the CE was b/c of no cats. The CE code didn't come on in any of the 2 test drives I had it, or the 50min drive home. Please help , Tim

Shaners · January 15, 2002

Welcome to the forum...

I don't think I'll be much help with your problem though. I do think it is probably computer related.

The only reason I know that the Tranny won't shift into overdrive is for warm-up reasons. (Which obviously isn't your problem). The computer won't let the tranny go into OD unless a certain temp is reached. This keeps the engine at higher rpm's allowing for a quicker warm-up. This is similar to the 4L60E that modifies/delays the 2-3 shift for the same reason.

It sounds like you have a really cool truck if you can get the "bugs" ironed out.

Since the port won't establish a connection, then you wouldn't be able to use a HyperTech programmer either...

Electrical/wiring problems are a nightmare (sorry to scare you), but when you do a swap like this there is bound to be a gremlin somewhere.

You might be better off going to a "hotrod" shop that has done similar swaps in cars, and they may be able to help better than the GM shop...

ps.

You might want to start by checking the harness between the computer and tranny. If you are using stock gages from your old truck then they would be mechanical. All new gauges are electronic, and that may be screwing things up...

I had a '88 S-10 that had to have the guage pod sent in for warranty repairs, and the dealer said I could drive the truck, but don't use OD because the electronics were disconnected, and that the tranny could overheat or malfunction. I wonder if your problem could be similar?!?!?

655.7Vortec · January 15, 2002

It has a dakota digital dash... so the gauges are all electrical. That shouldn't be causeing any problems.

What is proper operating tempiture? My truck runs right around 195-200 degrees once Its warmed up. Does this sound right? Thanks, Tim

Shaners · January 15, 2002

Your operating temp is good...

Will those dakota gauges interface with you computer?

Shaners · January 16, 2002

Tim,

I'm assuming you mean engine operating temp. If that is the tranny temp I think it is warm. The only time I have seen 190 degrees in my tranny (4L80E) is when towing 8000 plus pounds on a 92 degree summer day. Otherwise it runs about 130 in the summer and about 110-120 in the winter. The engine runs about 195 degrees year round...

655.7Vortec · January 16, 2002

yes that was the engine operating temp. I don't have a tranny temp gauge.... yet....

Hmmm... I wonder if they make a matching digital one??? lol

Please help. I am doing research, and have found out who built it, I am trying to contact him as I type this. -Tim

Shaners · January 16, 2002

I'd sure like to see a picture of your truck if you have one...

655.7Vortec · January 16, 2002

I'll have some up in the next few days. I haven't uploaded them to my photo album yet. I don't have any that are that good yet either. But I'll work on it, Tim

655.7Vortec · January 16, 2002

Here ya go... bad pictures sorry... I'll have better ones later

Hope you have a fast connection

PS: Are you the only person that posts on this board? lol

-Tim

655.7Vortec · January 16, 2002

Pictures of my truck

Shaners · January 16, 2002

That is a sweet conversion!!!

Also, I'm surprised nobody else has helped out with your problem... ???

655.7Vortec · January 19, 2002

Could it be some sort of limp home mode or something? Please help me.... the truck is almost worthless w/o overdrive.

-Tim

mike56BA · January 20, 2002

Tim, the first thing you need to do is establish a connection with the scanner to see what code it is setting. When you plug the scanner in, does the scanner power up or does it remain dead ? If it doesn't power up, you might not be getting power to the diagnostic connector due to a blown fuse or a wire that didn't get hooked up. If you do have power, is the info you enter into the scanner correct? I am only familar with the snap-on scanner, but does your give you the option of generic OBDII in the menu, you might want to try that. Due to all the various inputs that the transmission uses, reading codes and data is a must. There a numbers of things that could cause it to drop out of 4th, from a tps glitch, incorrect trans temp reading, speed sensors to shift solenoids, The 4l80e is notorius for leaking shift soleniods. You don't want to be throwing parts at it trying to fix it without the data the scanner can give you. HTH

Mike

Shaners · January 22, 2002

What does the tranny fuid look like and smell like?

CapnDean · January 23, 2002

Yeah...without OD your truck IS worthless. Since you & I agree on that lemme give you a couple of grand for that worthless truck hehehe.

You definitely have a new technology vs old truck problem.

Now since the engine & gear are out of a 97 chevy....we need to figure out what electronic devices were on the 97, that weren't on the 65, that don't come out with the engine & tranny set up.

I'll betcha it's going to be in the transmission temperature sensing apparatus somewhere. If you are shifting properly until your CE light comes on then clearly it's a temp thing.

Yes the tranny has a gizmoid that keep it outta OD til it's warm...also has a throttle position sensor (we used to call em transmission modulator..which is basically a cable that forces the tranny to downsift when you floor it). Have you made note of where your pedal is in relation to the OD? Perhaps in the swap over the TPS was screwed up... Of course if it works well when cold...that nixes that idea.

PLEASE: let us know if you find that gremlin....we all like to hear em.

CapnDean