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Rpms stick!

1552 Views 21 Replies 6 Participants Last post by  jburger76
2nd gear from stop. Throttle pinned rpms wouldn't come down was kinda stuck at shift point (6 speed man) any ideas??? Hasn't done it again tho. Also lost some mpg after I played with the smarty took it from 5 to 3 and back to 5 but lost about 100 miles per tank of fuel.

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Where were the rpms at when they stuck?
FCA would be the first place I'd look.
I have had failed hanging injectors do it.
In first gear the brakes could just barely hold it back. The tires would spin a hair until it came down. IN that case parked truck and ordered injectors. All good when done.
How long did it hang? And did it feel like full throttle or just accelerating on it's own?
It was weird it was definitely outta power range needed to shift but it came right down after I got it into 3rd. What is FCA?

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Did it look like this? When the rpms stop increasing the first time, the clutch is in.
Double post
I asked Les about it thinking it might be tuning and he said some trucks just do that and it's nothing to worry about.
Sounds like rail hang.

How bad was it and how long did it last?
Rail hang as mentioned is normal on these trucks. It happens when your hard on the throttle then let off quickly. The rail pressure is up and it needs to be expended before it can drop back down. Not more than a second or so.

Some have been able to minimize it with EFI live playing with FCA duty cycle and pressures..

If yours was not after a hard acceleration then you might have something to worry about.
It was after hard acceleration. Full throttle burning rubber

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Go reproduce it. Get in your truck get in second gear and mash the throttle until 2800 rpm. Let as quick as you can. It will probably continue to haul butt for a second. That's what's called rail hang. Is that what it did?

If you push the clutch in at the same time the rpm will rise even though you took your foot off the pedal.
Then it will settle out right about the time you get to the next gear.

Go try it.
Tried it and it kinda did it. I just don't wanna tear it up.

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I'm gonna have to guess your fine. Your descriptions aren't giving much to go on.
This is what Les said about that video I posted. I'd say he usually knows what he's talking about when it comes to trucks :thumbsup:
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This is what Les said about that video I posted. I'd say he usually knows what he's talking about when it comes to trucks :thumbsup:
Sometimes I know...others I just told im wrong by others.

Some trucks will not drop RPM immediately but will take a sec or so. Seems that its not exclusive to auto/man trucks....sometimes it can be OS related, but not usually.
Thanks for the education guys!!

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My truck stays up top for a sec before it idles back down. They say the common rail motor does that? Kinda scary tho
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