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6.4L Power Stroke Engine and Drivetrain Discussion of the 6.4L Power Stroke diesel engine and drivetrain in the 2008-Up Super Duty trucks. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 6.4L Power Stroke engine.

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Old 08-01-2007, 12:24 PM   #1 (permalink)
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hesitation on rapid acceleration

I don't really know if this is a problem but I wonder if I am alone. When I get on the throttle hard I notice what I think is a hesitation or stumble. It kind of feels like one turbo is spooling then a brief lag until the 2nd turbo spools. At that point it hauls the mail. This condition is very noticeable too.
At part throttle the power is smooth and this condition does not occur.
I have about 3000 miles on it so far so and I have noticed this since new. (I mention this because I am running 37" tires.)
Mike
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Old 08-01-2007, 01:15 PM   #2 (permalink)
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Re: hesitation on rapid acceleration

Don't worry I have a bit of turbo lag also. A car was stopping in front of me to pull into a driveway and I went around them but saw traffic coming pretty quick on me so I stabbed it and .....ummm waiting, waiting, boost gauge swings to 20psi then it's rocket time. It was a little scary because I'm used to a gasser and acceleration is instant. You almost have to give yourself an extra second if you plan on a aggresive lane change or stop light launch.
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Old 08-01-2007, 03:22 PM   #3 (permalink)
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Re: hesitation on rapid acceleration

Mine does the same thing. It even seems like lifting off to 1/2 throttle gets it to spool up faster... It's taking some getting used to.. I can't jump on it and expect to get out of someones way or be able to pass when it's close.

My old 02 7.3 did this until I chipped it.. Then all the lag was gone and it launched VERY hard... It also made A LOT of smoke until the engine spun up over 2500 rpms..

The big delay when I tromp on it is about the only time I wish I still had my old truck.

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Old 08-01-2007, 03:27 PM   #4 (permalink)
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Re: hesitation on rapid acceleration

I encountered the same thing so it's basically learning how to drive the new truck. I find that as long as you have even a little rpm going over idle it will respond immediately. I tried it once by stopping at a light and spooling up the turbo slightly. When the light changed I stepped it down a bit and the truck shot through the intersection like a bullet. Couldn't believe the power. [img]/ubbthreads/images/graemlins/grin.gif[/img]
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Old 08-01-2007, 04:05 PM   #5 (permalink)
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Re: hesitation on rapid acceleration

[ QUOTE ]
I encountered the same thing so it's basically learning how to drive the new truck. I find that as long as you have even a little rpm going over idle it will respond immediately.

[/ QUOTE ]

mountie,

I'm wondering if mine is being a dog... Even if I am above idle, there is still a huge delay.. It seems if I'm going 10-15 mph and floor it, the wait is even longer since the trans has to decide what gear it wants to down shift into before the rpm's come up and then the boost. I've even nailed it going 65 on the highway and nothing much happens until it downshifts and then no real thrust until the boost comes up (another second or two).

I need to quit typing about this. I'm starting to really want my old 02 back. [img]/ubbthreads/images/graemlins/vulnerable.gif[/img]

I haven't tried brake torqueing it to see how much it helps. As bad as it is until the boost comes up, I didn't figure it would do the tranny any good torqueing it hard enough to get the boost up for a decent launch.

j
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Old 08-01-2007, 04:57 PM   #6 (permalink)
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Re: hesitation on rapid acceleration

You can have it checked out but I think what you're experiencing is normal. Matting the throttle seems to create a lot of lag. My 03' did it and my 08' does as well. I've found the quickest acceleration is achieved by depressing the throttle smoothly.
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Old 08-01-2007, 05:43 PM   #7 (permalink)
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Re: hesitation on rapid acceleration

nascarj,
I've complained about the same thing on the forum before. My big problem is at 65 mph and needing to pass someone. Part throttle acceleration is very poor - truck stumbles and curses before even starting to move. I didn't experience this on my other trucks before or after they were chipped.
I am having hard time believing it is turbo lag because sometimes the truck runs fine. I stopped for lunch --turned the truck off-- got back in 20 mintues later and it ran fine.
I wonder albeit without much knowledge if it is associated with the regen cycle not turning completely off????? I know it wasn't supposed to be in regen for 200 miles!
Rjeffj
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Old 08-01-2007, 05:59 PM   #8 (permalink)
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Re: hesitation on rapid acceleration

Along with the posible turbo lag, fly by wire throttle systems do not like to be "matted". Also it is very posible that both the engine and transmission have torque management settings programed into the ECM and TCM.
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Old 08-01-2007, 06:53 PM   #9 (permalink)
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Re: hesitation on rapid acceleration

[ QUOTE ]
You can have it checked out but I think what you're experiencing is normal.

[/ QUOTE ]

I agree with you... That's the unfortunate thing.

I suspect it has a lot to do with controlling emissions... With the amount of black smoke my old truck put out when launched hard, this new 6.4 would be regen'ing every 2 or 3 stop lights if it had the same throttle response. [img]/ubbthreads/images/graemlins/shocked.gif[/img] [img]/ubbthreads/images/graemlins/smile.gif[/img].

j
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Old 08-01-2007, 06:57 PM   #10 (permalink)
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Re: hesitation on rapid acceleration

[ QUOTE ]
nascarj,
I wonder ... if it is associated with the regen cycle not turning completely off????? I know it wasn't supposed to be in regen for 200 miles!
Rjeffj

[/ QUOTE ]

It will definitely be low on power during a regen. Mine won't make over 20 psi of boost and feels like it is only making 100 lb/ft of torque. My old 80 HP Suzuki Sidekick felt like it accelerated better than my truck during a regen.

j
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Old 08-02-2007, 12:16 AM   #11 (permalink)
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Re: hesitation on rapid acceleration

[ QUOTE ]
You can have it checked out but I think what you're experiencing is normal. Matting the throttle seems to create a lot of lag. My 03' did it and my 08' does as well. I've found the quickest acceleration is achieved by depressing the throttle smoothly.

[/ QUOTE ]


This is what I've found also.

I've never actually floored mine. I haven't had to. I passed a guy on the highway last Friday. I was doing about 65 then stepped it down to over 80 and the truck just took off. No stumble or lag whatsoever. If anyone is experiencing stumble when passing it should be looked at if it is a repeating problem.
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Old 08-02-2007, 03:05 AM   #12 (permalink)
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Re: hesitation on rapid acceleration

I'm pretty sure what you guys are experiencing is kind of a turbo lag, but its not totally all turbo lag thats causing this. I read awhile ago that when you put your foot to your floor off the line with no boost, the computer in your truck will increase the amount of fuel it injects as the boost comes in. So off the line when theres no boost your computer wont allow the injectors to put in as much fuel as they can, but less until you get some boost, and then it will add more fuel so you get more boost, then it will add more fuel, so on and so forth until you have enough boost so that your computer will allow the injectors to put in there max fuel flow rating. So its half turbo lag, half computer not allowing 100% of fuel flow at low boost levels.
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Old 08-02-2007, 09:06 AM   #13 (permalink)
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Re: hesitation on rapid acceleration

[ QUOTE ]
So its half turbo lag, half computer not allowing 100% of fuel flow at low boost levels.

[/ QUOTE ]
Computers, sheesh! who needs 'em? Lol [img]/ubbthreads/images/graemlins/biggrin.gif[/img]


Like I stated in my original post at part throttle the motor sings without any lag or hesitation but damn that can lag can get you into trouble in a sticky situation...
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Old 08-02-2007, 09:32 AM   #14 (permalink)
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Re: hesitation on rapid acceleration

I guess the turbo lag it why I was able to out run my neighbor, in his 6.4 with my 7.3 which has a chip. I thought he would blow my doors off. The look on his face was priceless.
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Old 08-02-2007, 09:33 AM   #15 (permalink)
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Re: hesitation on rapid acceleration

I agree with you there. It does take some time to get used to it's characteristics. Coming from a gasser makes the situation worse. Instinct tells you to hammer it. On a quick left hand turn that can get you into trouble. At least it doesn't experience the 6.0L's dead peddle. Now that was scary.
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