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Proud new 6.5 owner

W

WPA

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Howdy ya'll,

Quick question for you 6.5 enthusiasts. Just bought a 94 6.5 TD half ton and the transmission likes to drop into second and then not shift out. I will be driving along and give it some fuel, causing a down shift, and it will drop into second and there it stays until I pull over and let it sit for a few minutes. After the rest period, it shifts fine. What gives?

Pretty sure it has the 4L60e. Can I easily replace with a 4L80e and is this advised?

Thanks for all your help and info.
 
Welcome to TTS.

I can't help with your shift problem but I'm pretty sure all 6.5's have the 4L80e trans. The 94's on.
 
Welcome!

It is a 4L80E.

Have you checked for codes? If its safe next time pop it in nuetral, turn truck off and back on. If that fixes it I would "think" its and ECM issue. Again do it only when safe.
 
Sounds like its going in to protection mode (often called limp mode).

When the PCM sees certain fault codes, it defaults to second gear to limit what you can do with the truck and prevent further damage.

Use a paper clip to short pins A and H in the diagnostic connector and see what is stored in the PCM. Yours is obdi, so you will have to count the flash's on the check engine light. Hense the term "flash out code".

There are lots of fault codes that can drop the PCM into protection mode.

Even the infamous pmd can cause it to drop into protection mode if it is starting to fail. I had one do this very thing. The only odd thing about your description is that most fault codes that kick it into protection mode are " hard codes". Meaning: they don't go away on their own, you have to clear them. Just sitting by the side of the road shouldn't make them go away.

Of course, that damned pmd has been known to do some funny things when it's on the way out and no consistency as to what its going to do from one vehicle to the next (or even one pmd to the next).

I lost a couple and then spent the extra bucks on a bill heath unit. Knock on wood, I'm at 6 years and counting without a pmd problem...

Here's a trick that usually works to narrow it to the pmd: try you cruise control. If it doesn't work, your pmd just became suspect. Cruise is one of the first things that the pcm drops with a pmd fault, sometimes not coding. Only problem with your is you have a 94, the multifunction stalk is a common point of failure for cruise so it could also be that if you have no cruise.

Early 6.x engines could have had the 700r4 behind them, but by 94 they were all 4L80e if an auto. Never had the 4L60e (which is a good thing).

Good luck.
 
A ECM 'reset' via key off-on is all it takes to get it out of 'protection mode'. (Also called limp home mode.) The OBD1 ECM's like to stay alive after key off for up to 30 seconds so it may take this long to get it to reset and exit the protection mode. Transmission fault codes are NOT emission related and generally do not turn on the Service ENGINE Soon light.

In addition to above: something is putting it into this protection mode. Transmission or TCC clutch slipping could be the cause. That would leave a code. The 4L80E's are known to wear out the TCC solenoid cylinder in the valve body if the trans oil isn't changed every 25K. This causes the TCC to slip. The main connector on the side of the trans likes to leak and oil up the connections - short term fix is cleaning - long term is replace the connector to an updated one. The speed sensor wires like to have the insulation fall off and short them - specifically the one 2 wire connector at the front driver side of the trans. Follow the wire back to where it joins the main harness and inspect all the wire length for this.

Changing the trans oil is a waste of money until you know for sure what is causing the 'protection mode' as you may have to rebuild a slipping trans.
 
Thanks guys. I just learned more here in two days than Google has been able to show me in three months. That being said, sounds like I have a laundry list of things to check. That's good though, helps me get familiar with my truck. After I check out a few options I will get back on and tell you how it went. Thanks again.
 
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