DodgeTalk Forum banner

Status
Not open for further replies.
1 - 20 of 23 Posts

·
All Around Great Guy
Joined
·
12,675 Posts
Discussion Starter #1
Ok, here is the deal. If I turn on the tow/haul mode on my 04 hemi, it will only hold 2nd gear until about78mph. If i leave it off, it screams all the way to about 86mph. Why is this? The only reason I ask is because I was looking for ways to get et's lower at the track. I reset my pcm just before racing and left it in OD, not tow/haul. It shifted at 78mph and felt like it dogged the rest of the way. Could I have gained on my et winding in second, or pulling in third? :huh:
 

·
Registered
Joined
·
976 Posts
My truck shifts the same speed, about 79 in OD or with the T/H on when I do a 1/4 mile run. However, if I'm in OD, on the freeway and punch doing about 70, it'll carry second till about 87. With the T/H on and on the freeway doing the same speed, it'll only carry 2nd until 79 like at the track. The trans has two second gears, one for the upshifts and one for downshifts. The upshift gear is used going zero to whatever, it's ratio is 1.67. The downshift gear is used for passing and it's ratio is 1.50, so it'll carry to a higher mph before shifting. The only thing I can think of is that the T/H locks out the passing second gear and keeps using the upshift second gear only. Only a theory, I have really no idea.
Jim
 

·
Banned
Joined
·
7,195 Posts
hemi1569 said:
Ok, here is the deal. If I turn on the tow/haul mode on my 04 hemi, it will only hold 2nd gear until about78mph. If i leave it off, it screams all the way to about 86mph. Why is this? The only reason I ask is because I was looking for ways to get et's lower at the track. I reset my pcm just before racing and left it in OD, not tow/haul. It shifted at 78mph and felt like it dogged the rest of the way. Could I have gained on my et winding in second, or pulling in third? :huh:
The only reason it shifted at 78mph with OD on is because the computer was still in the "learning" mode so you didn't see the full benefit. The other time the truck went all the way to 86mph with OD on because computer was well adjusted.

try this.. leave the gear selection in 2nd gear.(NOT "D") Leave the OD on.(T/H off) from 0-xx.xx see how fast you can go right when you hit the rev-limiter. It should be close to or dead at 86mph...

I personally think if you can get the computer to shift out of 2nd gear at 86mph and then get it into 3rd gear you'll get a faster ET. But if it shifts out of 2nd gear at 78mph and goes to 3rd than you'll lose ET time.

btw, what octane gas are you using?
 

·
All Around Great Guy
Joined
·
12,675 Posts
Discussion Starter #4
When I ran my 15.6, it shifted into third at 78, maybe it did it because I had just pulled the no. 23 fuse to reset computer. I run 87 octane, and I was thinking i probably could have got another tenth if it did not shift.
 

·
Banned
Joined
·
7,195 Posts
hemi1569 said:
When I ran my 15.6, it shifted into third at 78, maybe it did it because I had just pulled the no. 23 fuse to reset computer. I run 87 octane, and I was thinking i probably could have got another tenth if it did not shift.
try 89 octane and keep the gear selector in 2nd. Run your 1/4
 

·
RPM
Joined
·
168 Posts
Don't forget that the 545RFE transmission has TWO second gear ratios! If you are accelerating from stop you get a 1.67:1 ratio while a drop to second gear via a kick-down while rolling gets you a 1.5:1 ratio.

That could account for the speed difference. 1.67:1 would shift at a slower speed (MPH, not RPM) than the 1.5:1.
 

·
Registered
Joined
·
1,170 Posts
Try not resetting your computer before racing. By doing that you are setting it back to the factory default which is set at "less than optimal performance".

Also, it you don't have detination knock with 87 you probably won't see any difference running 89 except for the higher cost. Some don't understand.
 

·
Banned
Joined
·
7,195 Posts
DonRam said:
Try not resetting your computer before racing. By doing that you are setting it back to the factory default which is set at "less than optimal performance".

Also, it you don't have detination knock with 87 you probably won't see any difference running 89 except for the higher cost. Some don't understand.
What we do understand is the Hemi has dual knock sensors. By using 87 octane gasoline we won't get pinging/detonation BUT the computer will adjust to this and retard the timing, HENCE LESS POWER.

Hemi1569 for now start using 89 octane gasoline and reset the battery one more time after fill up. After that don't restart. Have the computer relearn everything and take it to the track.
 

·
C HEMI GO
Joined
·
1,739 Posts
In Tow/Haul mode, could the truck be using 2nd prime instead of 2nd? That could make a 10mph difference.
 

·
Registered
Joined
·
1,566 Posts
I've always used 87 octane in my truck.

I made my 15.2 run on 87 octane.

I finally switched over to 89 octane on this last tank of gas.
 

·
Banned
Joined
·
7,195 Posts
Mad Titan said:
I've always used 87 octane in my truck.

I made my 15.2 run on 87 octane.

I finally switched over to 89 octane on this last tank of gas.
you'll definitely feel the difference. just make sure you reset the battery after the 89 refill.

some people may say they didn't feel a gain with 89 after switching from 87. This is because they were using the 87 and the computer ALREADY retarded the timing BUT in actuality it is advancing slowly back. Reseting the computer just makes it a whole lot easier to adjust. Basically starting on a clean slate.
 

·
Registered
Joined
·
1,170 Posts
KaPPaBaLL said:
What we do understand is the Hemi has dual knock sensors. By using 87 octane gasoline we won't get pinging/detonation BUT the computer will adjust to this and retard the timing, HENCE LESS POWER.

Hemi1569 for now start using 89 octane gasoline and reset the battery one more time after fill up. After that don't restart. Have the computer relearn everything and take it to the track.

No, that's not how the system works. It doesn't prevent knock, it stops it and the system does not work fast enough to prevent you from hearing the knock. Depending upon how severe it is you can hear it knock for quite a while before it retards the timing, and when the timing is retarded you will feel an obvious power loss. The powerloss can be short term (until next engine start) or longer term depending upon how persistant the knock is.

I've almost always run 87, but have run quite a few consecutive tanks of 89. There was no knock with either, and no difference in MPG or performance. Just trying to help you understand why some might choose to run 87. :D
 

·
All Around Great Guy
Joined
·
12,675 Posts
Discussion Starter #15
I am running 89 from now on. Not to get off topic but does anybody know how to check codes without a programmer on a 04 ram? I tried the key trick, on off on off on, and got nothing, other people(I believe an 05 ram) said that it shows up in the odometer, what gives? My cel is on and I think it may be my 180 t stat causing it. Help please
 

·
Banned
Joined
·
7,195 Posts
DonRam said:
No, that's not how the system works. It doesn't prevent knock, it stops it and the system does not work fast enough to prevent you from hearing the knock. Depending upon how severe it is you can hear it knock for quite a while before it retards the timing, and when the timing is retarded you will feel an obvious power loss. The powerloss can be short term (until next engine start) or longer term depending upon how persistant the knock is.

I've almost always run 87, but have run quite a few consecutive tanks of 89. There was no knock with either, and no difference in MPG or performance. Just trying to help you understand why some might choose to run 87. :D
i see.. question. did you after the fill up with 89octane did you reset the computer? For me I was in the same ballpark as you thinking 89 isn't worth it and i truely believed it unless the engine was pinging right? But after learning more and more i said **** it, i'll try 89 one more time and reset the batt. Guess what, ever since then more power. It's not in my head i promise :D but to each his own. :)

p.s. try the reset battery thing after filling with 89octane. Never know.
 

·
voo doo 1 I am buggin out
Joined
·
6,355 Posts
Black05Hemi said:
I don't understand why anyone would run 87 in a Hemi?
Cheaper on the wallet and she doesnt ping or run rough a bit.
 

·
Registered
Joined
·
209 Posts
I thought it was just me, but after reading some of these posts I firmly believe that it did make a significant difference when I switched to 89 octane. Without resetting the computer or doing anything other than running a tank of 93, I noticed that it immediately started to have quicker acceleration when I gave it throttle. It accelerated smoother, and felt as if the kick down to a lower gear transitioned faster and carried it through each gear with more ease than it had on 87. I also felt quiet a bit of difference in the passing department, as I felt the truck would pick up to higher speeds for passing other cars MUCH faster than with regular octane fuel??

I have been wanting to calculate how much more it would cost per month using 89 instead of 87, but I have pretty much been to lazy and balk at the Go$$amned $2.18 a gallon for 89 vs. the $2.08 for regular. I usually just pick up the regular and try to not think about it twice while Im filling up. LOL!!!
 

·
harleyrider
Joined
·
185 Posts
When you say you are resetting the battery. Are you just unhooking the positive battery cable a few minutes? In other words, when you fill up with 89 octane you can go home and unhook it and it should be a difference when you drive it right?
 

·
All Around Great Guy
Joined
·
12,675 Posts
Discussion Starter #20
Remove fuse 23 from fusebox, turn key to start position until you hear a chime then reinstall fuse
 
1 - 20 of 23 Posts
Status
Not open for further replies.
Top