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5-O Cummins

Engine shudder at high speed after WOT

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While on the interstate I was passing a vehicle and had some engine shudder which doesnt seem to be good. I was traveling about 70mph and gunned it, by the time I passed the vehicle I was going approx 85mph, as I let off the accelerator the engine began to shudder (almost like a hopping). I eased into slowing down and the shudder went away. I have experienced this before but now that it has happened again I need to figure out what the deal is. Any ideas what the problem could be?

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I think you know what the engine sounds like when it is getting fuel and isn't, how it knocks when you give it fuel and it is prius quiet when you let off, did it sound like it was getting fuel while it was doing this shuttering? Like getting fuel then not, then fuel then not.. You say it was hopping and that makes me wonder about some things but I want to know this part first. Basically when you let off, the governor pulls the throttle to shut, as in 0 fuel. This means the injectors/pump are basically out of the engine, like you turned the key off. The turbo would be spooling back down after a WOT run as well. I am just wondering if the governor is screwing up and not going all the way back, though I might be thinking wrong about this.

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I'm trying to think of a better way to explain. Pretty much when I floor it the truck goes and seems like it's still getting fuel. Right when I begin to let off the engine hop begins. That's when I have to slowly let up to keep the hop under control. The other night I tested the speed limit of the truck. I was traveling on the interstate and did a smooth throttle acceleration and the truck pegged out at 85mph, with my tires I'm guessing it was approx 90mph. The truck wouldn't go anymore. I backed off and it was fine. Only seems to happen after a heavy acceleration.

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Is it like the throttle is sticking and jolting back as you let off. I think there was a recall on that. Hmm that wouldn't cause it to hop exactly. It sounds like it is getting a little then a lot of fuel rapidly but letting off slowly controls it. I can't think of how it would do something like that. Actually if you have to let off slowly then the governor is not going back to 0 fuel. I still can't figure out how the governor would make it hop. I know there are things in it that adjust the rates of change, that might be an isochronous thing. Maybe someone else will have some ideas. I would like to see a video of this or something. I will keep thinking about ideas though.There is one thing that could be possible such as oil being sucked through the turbo under high boost conditions and a little gets into the intake and causes the engine to run without diesel, but rather running on the oil it is sucking in. Far fetched but so is your issue. I did read something about a guy with a VP44 truck where he let off after WOT and the sudden rush of full fuel to 0 fuel would actually suck the fuel system dry somehow, or something like that, but this was WOT to 0 instantly, and it killed his engine when it did it, you say it hops continuously for a while. If you have a 5spd and it was doing this, the direct connection (being a manual) would be restarting the engine constantly. But that is far fetched as well. Hmmmm

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Ok thanks, I'll try to get a video asap. I'm planning on doing some valve springs, gov springs, del valves, fuel plate etc... here soon, if I can't get it figured out was going to see if that changed anything.

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I got a few other ideas but since you seem apt to do a video that would help a bunch. It's always hard to describe a weird problem like that with just words lol.

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I got a few other ideas but since you seem apt to do a video that would help a bunch. It's always hard to describe a weird problem like that with just words lol.

Ha exactly, very hard to explain and the same to diagnose.

--- Update to the previous post...

Ok here's the video. Had to edit it down a bit to keep the time down. I was having trouble getting the issue to happen at first then got the sweet spot. HTH

http-~~-//www.youtube.com/watch?v=zGHZeetrMqE

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Alright that's completely different from what you were saying :lol: I thought it did it when you let off. As for that, that looks more like something not in the engine, something like a slight death wobble. The engine sounds fine and looks like it is all running fine so I think it is a steering/suspension component issue. Maybe even something with the U-joints. I am not the greatest steering/suspension guy so someone else can give you a little more input. I am thinking something gets unbalanced and sometimes it stays in balance, but once it gets knocked out of round (bump in the road) then it knocks it all out of whack and does the vibrating. Still thinking about this though, the movie helped a ton.

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Ok thanks. Yeah I wasn't thinking a suspension issue because it only happened upon acceleration at those specific speeds no bumps etc... Almost like the engine was tapped out and doesn't want to go anymore. I'm clueless to the problem so who knows. Any suggestions would be great. :banghead:

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Start by checking your ball joints, then the tierod ends. Has there been any work done to the front end recently? Are the tires wearing straight and smooth?

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Unknown if any work has been done recently. Not since I've owned and thats only been a few months. I'll start looking into the front end parts.

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Yeah I agree need to check out the entier front axle... Wheel bearing, tire balancing, ball joints, etc... Since its a 4WD check all your driven axles and front driveshaft. For the front driveshaft you'll have to remove it to check the double joint back by the transfer case...

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I had a very simular think happen a few weeks ago. I was not driving that fast though. The carrer bearing was bad. Would not do it all the time but would squeak.

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