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3k rpm @60+ on highway

RodDog416

94Burban K25 7.4L EFi
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I'm driving a 94 burb k25. It's running 3k rpm @60+mph on highway. It was lower last year for sure. Any ideas on what can be the issues/fix??
 

Will L.

Well-Known Member
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Torque converter not locking up most likely.
Idk how to check that without a scanner on there. Keep checking back, this is an active forum with people way better on transmission than me.
 

ak diesel driver

6.5 driver
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sounds like more than the torque converter to me. Torque converter not locking would only be about 400 rpm, he's talking 1000 rpm. Assuming it has 4:10 gears he should be around 2k
 

WarWagon

Well it hits on 7 of 8...
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Pull codes. Sounds like OD has blown a sprag in the transmission and you get only 3 gears and no TCC lockup. Your trans temps will be extreme with an unlocked TC risking more damage and fire.
 

RodDog416

94Burban K25 7.4L EFi
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Pull codes. Sounds like OD has blown a sprag in the transmission and you get only 3 gears and no TCC lockup. Your trans temps will be extreme with an unlocked TC risking more damage and fire.
So I figured out how to read the codes w/out obd1 scanner with a paper clip hack. It gives me (3×12) and (3×45). 45 being the o2 sensor..?
 

WarWagon

Well it hits on 7 of 8...
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Manually shift the gears and count the shifts. You should have 4 and be careful not to count a TCC lockup in 3rd. A misadjusted shift pointer can have you selecting 3rd (direct) by mistake.

In some cases TCC lockup can be locked out if the engine is misfiring or not running well.

We working on a gas rig?
 

RodDog416

94Burban K25 7.4L EFi
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Manually shift the gears and count the shifts. You should have 4 and be careful not to count a TCC lockup in 3rd. A misadjusted shift pointer can have you selecting 3rd (direct) by mistake.

In some cases TCC lockup can be locked out if the engine is misfiring or not running well.

We working on a gas rig?
Yea it's gas automatic
 

RodDog416

94Burban K25 7.4L EFi
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I initiated truck into 4x4 went off road all bit. I put it in neutral to disengage the 4x4 and I drove off around another lap and it's empty lot and then I stopped and re-engaged the 4x4 and when I went up a hill and it stopped it I don't know what happened I couldn't go anywhere and just stopped so I was trying to get it back out into regular drive and I could not. everything kept grinding and all the gears and I had to go to park and then always to drive and then back to park and then it was able to get me back into regular drive now when I kept putting in the park it kept making a sound like it was spinning but nothing was engaging not loud just like light sound....so yea definitely something with the transmission.
 

WarWagon

Well it hits on 7 of 8...
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so yea definitely something with the transmission.
Bluntly an assumption. Shifting the 4X4 transfer case and then grinding noises sounds like a transfer case problem. Transfer case not in gear or shift fork worn out in it. Hint: when shit's grinding and going "Bang Bang Bang!" on the parking pawl: SHUT ENGINE OFF IN NEUTRAL! Wait for spinning stuff to stop spinning then and only then can you shift to park. This way you don't grind up gears or snap the parking pawl clean off. It is a bit of an art to shift from 4X4 low to 2WD or 4X4 high. Screw it up and your only choice is to shut the engine off in neutral as neutral has enough internal drag to spin the output shaft of the transmission up. You may have to roll very very slowly some to shift the transfer case.
 
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