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Unread 11-09-2006, 12:21 PM   #1
wccf91
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Acceleration

I have a 06 5.7 QDll Limited , I have been noticing a delay in the Acceleration , I mean sometimes I will mash the pedal and you can allmost count 1001 1002 befor it kicks in . Anyone heard of this ?

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Unread 11-09-2006, 02:15 PM   #2
soldierguy
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You're learning the joys of an electronic throttle. Doesn't sound like anything is wrong from what you describe.

Electronically controlled throttles tend to have a small but noticable lag in response. This lag is most noticable if you have been off the gas pedal, then hit it. The hemi activates MDS when you are off the throttle and RPMs are above about 1200, so it takes a second for the computer to open the throttle and deactivate MDS. It's also very noticable when sitting stationary then hitting the gas to move out.

I've found it is far less noticable (and much smoother too) if I gently roll into the throttle, then once the throttle is open I can do whatever I want with the gas pedal and it responds immediately.
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Unread 11-09-2006, 03:03 PM   #3
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I don't have a Hemi, but the 4.7L has electronic throttle as well. According to Allpar's article on the 4.7L when it was first introduced, it was electronic throttle from the start.

There's certainly zero delay with both of my 4.7L vehicles -- no problem lighting up a tire from a standstill, and zero noticeable delays. Ditto with my previous 2001 4.7L Durango.

The computer can switch MDS modes in 40ms -- 1/25th of a second -- so where's the additional lag of a full second or two coming from? It's hard for me to imagine that normal operation is to take a full second or two to start opening the throttle.
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Unread 11-09-2006, 03:50 PM   #4
drewman141
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The ESP system is also a contributor to the delayed acceleration from a stop. It will not let you spin the tires. Try turning off the ESP and see how it changes. But like soldierguy said - the throttle is a drive-by-wire system where there is no throttle cable attached to the pedal. The computer measures how hard you are pressing on the pedal and then activates a solenoid to open up the throttle on the engine accordingly. There is definately a large delay if you are idling and then mash the pedal and sounds like you are experiencing normal operation of the Hemi WK.
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It's a 94 5.2L Limited - trxus 33's on 15x7 steelies, 4.56s w/ front OX and rear trutrac, NP242 swap, novak shift kit, Kevin's ultimate 4.5" lift + ACOS, ARB front bumper w/warn M8000, rear tomkin machine bumper w/ tire carrier, kevin's hardore railz, kevin's ultimate tc skid, kevin's trackbar conversion, rusty's gas skid, flexalite efan, Kolak's performance ignition and brake upgrades. ViAir OBA, custom storage/sub box and I'm sure there's a bunch of other things I'm missing. Everything is a little over 3 years old with less than 10K miles. Looking to get around $4k.



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Unread 11-09-2006, 04:21 PM   #5
Intrepidjeep
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He seems to indicate that there's a one or two second delay before the acceleration begins.

Drive-by-wire is not the cause of such a long delay unless it is a very poor implementation in the Hemi, otherwise I would see a similar delay in the 4.7L vehicles I've owned. In my experience, drive-by-wire provides instantaneous throttle response.

There are some quirks evident with drive-by-wire. For example, if you let off the gas pedal very suddenly, the computer will hold the throttle open slightly so that it can close more gradually. Closing the throttle abruptly from a high-speed condition would otherwise cause a spike in emissions.

ESP is designed to detect instability and intervene at that time. It should not be contributing to a delay just to accelerate, assuming that no instability, such as wheelslip, has been detected. Unless, of course, it's not a well designed system and is far too aggressive.

At any rate, I would test-drive another Hemi to see if it seems to act the same.

Actually, I realize now that WCC doesn't say if it's a delay from a standstill -- that was my assumption. But perhaps he was referring to mashing the accelerator while cruising? It could be just the delay in a downshift? There's a varying amount of pedal input required to induce a downshift, so you may have to be more aggressive, or downshift manually.
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Unread 11-09-2006, 06:45 PM   #6
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I ran under the assumption that when he said 1-2 seconds, he actually meant far less. It may seem an eternity when there's a delay, but I guarantee that if everything is working right, it's not 1-2 seconds. If there is actually a full 1-2 second delay, then something is absolutely wrong.

Mine responds very differently under different circumstances:

- Dead stop. If I hit the gas pedal, there's a small but noticable delay, then it takes off fast and hard. If I roll into the gas pedal gently, there's no noticable delay.

- Cruising: If MDS is active, there's a small but sometimes noticable delay IF I hit the gas pedal, then it moves out fast. Again, if I roll into it gently, there's no noticable delay. If MDS isn't active, there's no noticable delay regardless of if I hit the pedal or roll into it gently.

- Coasting: If I hit the gas pedal, there's a noticable delay followed by moving out fast. Roll into it, and there's no noticable delay.

I've had to adjust my driving style...I roll into the gas pedal gently much more in my WK than in any other vehicle I've owned.

I chalk up the delay to a combination of factors: whether or not MDS is active, the small delay between my right foot moving and the throttle actually opening, the ESP/traction control (if it thinks there will be wheelspin, it'll tighten up the diffs & transfer case variable lockup before the throttle is opened)...add all these up and there can be a noticable delay. Not 1-2 seconds, but there can be a small delay.

Again...if I've been off the throttle, I've just learned to roll into the gas pedal gently...makes a WORLD of difference in how the vehicle responds and feels.
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Unread 11-10-2006, 10:12 AM   #7
drewman141
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Soldier - that is exactly what I have experienced in mine. I also assumed his delay was exagerated but it does seem like a long time especially when you are trying to do some emergency manuever. Like you said, if you mash the pedal to the floor from stop it does not instantly WOT it kind of ramps up into it and then your head is stuck to the headrest. If you turn off the ESP there is a slight decrease in the delay from a stop but you might also get a wheel chirp out of it.
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MUST GO! 1994 Limited ZJ 5.2L V8 - Light Driftwood Satin Glow
It's a 94 5.2L Limited - trxus 33's on 15x7 steelies, 4.56s w/ front OX and rear trutrac, NP242 swap, novak shift kit, Kevin's ultimate 4.5" lift + ACOS, ARB front bumper w/warn M8000, rear tomkin machine bumper w/ tire carrier, kevin's hardore railz, kevin's ultimate tc skid, kevin's trackbar conversion, rusty's gas skid, flexalite efan, Kolak's performance ignition and brake upgrades. ViAir OBA, custom storage/sub box and I'm sure there's a bunch of other things I'm missing. Everything is a little over 3 years old with less than 10K miles. Looking to get around $4k.



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Unread 11-10-2006, 10:21 AM   #8
wccf91
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It may be a bit exagerated in the delay but driving in Los Angeles traffic stop and go , when you try to jump out into another lane it seems like a LONG time.
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Unread 11-10-2006, 11:53 AM   #9
drewman141
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Quote:
Originally Posted by wccf91
It may be a bit exagerated in the delay but driving in Los Angeles traffic stop and go , when you try to jump out into another lane it seems like a LONG time.
That is exactly what we were talking about. We have the same here in NYC. If you want to kick it up faster use the autostick to downshift for those certain maneuvers
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[SIZE="1"]2008 WK Overland HEMI - Modern Blue Pearlcoat
Fully loaded with slush mats of course.

MUST GO! 1994 Limited ZJ 5.2L V8 - Light Driftwood Satin Glow
It's a 94 5.2L Limited - trxus 33's on 15x7 steelies, 4.56s w/ front OX and rear trutrac, NP242 swap, novak shift kit, Kevin's ultimate 4.5" lift + ACOS, ARB front bumper w/warn M8000, rear tomkin machine bumper w/ tire carrier, kevin's hardore railz, kevin's ultimate tc skid, kevin's trackbar conversion, rusty's gas skid, flexalite efan, Kolak's performance ignition and brake upgrades. ViAir OBA, custom storage/sub box and I'm sure there's a bunch of other things I'm missing. Everything is a little over 3 years old with less than 10K miles. Looking to get around $4k.



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Unread 11-10-2006, 03:26 PM   #10
soldierguy
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Quote:
Originally Posted by drewman141
If you turn off the ESP there is a slight decrease in the delay from a stop but you might also get a wheel chirp out of it.
Now just for the heck of it, next time I drive it I'm going to play with the ESP button and the tow-haul button just to see if I notice a difference in that delay.

The tow-haul mode might help reduce it as well...I know that tow-haul mode prevents MDS from operating, so it might reduce the delay.

And naturally I'm going to have to spend some time nailing the gas pedal, but it'll be purely in the interest of research...no fun involved.
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Unread 11-10-2006, 05:17 PM   #11
drewman141
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Hey soldierguy - you put better tires on your heep right? Mine are still the stock SRA garbage and I beat on them pretty hard over the past 27K so I can get a good deal of chirping, lateral movement and of course hydroplaning out of them - they are pretty much road slicks rapidly approaching baldness. I don't know if you'll get yours to sing but good luck trying!!
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[SIZE="1"]2008 WK Overland HEMI - Modern Blue Pearlcoat
Fully loaded with slush mats of course.

MUST GO! 1994 Limited ZJ 5.2L V8 - Light Driftwood Satin Glow
It's a 94 5.2L Limited - trxus 33's on 15x7 steelies, 4.56s w/ front OX and rear trutrac, NP242 swap, novak shift kit, Kevin's ultimate 4.5" lift + ACOS, ARB front bumper w/warn M8000, rear tomkin machine bumper w/ tire carrier, kevin's hardore railz, kevin's ultimate tc skid, kevin's trackbar conversion, rusty's gas skid, flexalite efan, Kolak's performance ignition and brake upgrades. ViAir OBA, custom storage/sub box and I'm sure there's a bunch of other things I'm missing. Everything is a little over 3 years old with less than 10K miles. Looking to get around $4k.



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Unread 11-10-2006, 05:25 PM   #12
soldierguy
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Yeah, I put different tires on mine. After dealing with the stock tires last winter and their TOTAL lack of traction on anything but dry pavement (I actually had to abandon my Jeep once last winter due to just a couple inches of snow on the ground), I did a lot of research and bought a set of Goodyear Fortera SilentArmor tires. There's a little less dry grip (not that the Jeep is a sports car anyway), but wet grip is drastically improved. We'll see how they do in the snow...they are rated well in that area, but I'll see for myself soon enough. There's already been a little snow that fell last week, and the weather is cold enough to have snow if a storm moves through. Snow doesn't pile up in Seoul...we just get a few inches now and then and it's usually gone within a few days, but it's enough to make me want good tires.

Perhaps if the esp button and tow/haul button let me have some fun, I might end up shaving a few hundred miles off the life of the tires!
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