sluggish acceeration

[justadodgeman]

I got an 03 1500 hemi and when i got the truck at about 85,000 miles and now has 110,000. i used to be able to do some badass brake stands but now i can barely the tires to spin and the acceleration just aint what it was when i first got it(if i smash the gas from a stop it takes off but doesn't really start hauling ass till like 3,500 rpms)? around 105,000 miles i cleaned the throttle body, MAP sensor(or whatever the hemi uses), changed tranny fluid and oil, spark plugs, and air filter hoping all this would get me back to doing burnouts haha but it didn't changed much. i also put did a muffler delete with a y-pipe and went back from there with 2 1/4" pipe after an incident where my exhaust got wrapped under my axle but would that take away that much torque? any suggestions of what it could be?

 

[DDean]

Could try not running it like it's a hot rod. Might be a good place to start.

I'm sure someone else will chime in with some actual technical advice.

 

[Ramunit]

Did you try resetting the pcm? Sounds like the adaptive learning has learned an easy pedal. Reset and drive it like you stole it.

 

[xb1230]

Lots of things can influence this type of performance.

TB Clean up is good place to start, but I'm not sure I would have cleaned the sensor array as these are very sensitive pieces and sometimes you do more harm then good by cleaning them.

Fuel rail pressure could be one thing to check, clogged injectors, O2 sensors, reset of the PCM/ECM...

If you have access to some OBDII gear grab the readouts from the sensors. Even though no check engine light is coming on, if the sensors are worned out and are not giving optimal readings that has a big impact on the Fuel/air mixture.

Sounds to me like you are running very close to limp mode, where the PCM sends default values to the engine so it can run to get you to the next service station...

If you don't have an OBDII adapter, a multimeter and our good friend Google can get you a long way in finding out if you have a bad sensor.

Hope this helps.

 

[RedRamHemi]

If this started after the exhaust work I would say thats the prob. I have seen many posts of people complaining of losing the low end torque from modifying the exhaust on a hemi.

 

[xb1230]

Less restriction could change the readouts for the PCM and have an adverse effect on performance for sure.

Does anyone know if just a PCM reset would fix that or if a tune flash would be required ?

 

[xtreme762]

2 1/4" pipe sounds pretty small for a 5.7. Unless you mean you used it before the cats.. If you used it after the cats., that's your problem. They come stock with 2 3/4" after the cats., and 2 3/4" after the muffler.

 

[Harley Harrold]

I would add to this list, the catalytic converters, which could be stopping up, impeding air flow thru the exhaust system.

 

[justadodgeman]

damn thanks for the replies guys. ill reset the pcm, its definitely not in limp mode(been there before when I had a bad MAP sensor), Ive been thinking really hard about a clogged converter but I don't have a for sure way to tell besides hitting it with a mallet and maybe using a temp reader to see the temp of each side of the cat. if i do decide that the problem is the cat then im gonna hollow it out and use a defouler until im not so damn broke. the 2 1/4 pipe is very small i know (I Wasn't there when it was put on) but the muffler is taken off so i would think it would add back the lost back pressure having smaller pipe after the y-pipe.

 

[MyOhFive]

Maybe you've nuked or really stressed your torque converter...

with stock cat still on (as long as its not clogged) you should have an alight amount of back pressure.

 

[Redtruck-VA]

Are you throwing any codes? The stock 03 cat is the best flowing cat I have found mostly because it is a single cat design for the 5.7 engine. 04+ all use dual cats. Do you have a larger Y pipe installed? From that to the cat should be 3". From the cat to the muffler is also 3". I have seen power lost when a Flowmaster muffler was installed, but haven't seen a hemi run just with a cat and don't know how it would run. Do you have any gauges to read fuel trims and AFR? Have you put bigger tires on it? How much of a change do you get with a reboot? Have you done the TMR mod?

 

[hemihustlin]

also put did a muffler delete with a y-pipe and went back from there with 2 1/4" pipe after an incident where my exhaust got wrapped under my axle but would that take away that much torque? any suggestions of what it could be?

Definatly this! Assuming everything else is in good working order, how the hell does anyone expect the hemi to breathe through a 2.25" straw?!?
You can delete all the mufflers and resonators you want but never downsize the pipe.

I cant believe only like one other person jumped on this...

 

[hemihustlin]

Also, unless the 03s are different, its 3" from the oem y pipe to the tip

 

[justadodgeman]

Definatly this! Assuming everything else is in good working order, how the hell does anyone expect the hemi to breathe through a 2.25" straw?!?
You can delete all the mufflers and resonators you want but never downsize the pipe.

I cant believe only like one other person jumped on this...

haha im thinking you are right but since it was only running back from the y-pipe right in front of the axle I didn't think it was too bad. the exhaust had to be redone and the ******* mechanic who was doing the body work after the incident for some reason went all the way from 3" to 2 1/4" pipe right after the ypipe

 

[xtreme762]

They must have changed the size of the pipes between 03', and 05'. Cause my 05' had 2 3/4" on it from cat back. Stock.

Here's my intermediate pipe. The pipe between the Y, and the muffler. The one folks normally put a cut-out in. Yes 2 3/4" exhaust pipe exists.

 

[Redtruck-VA]

Must have, 3" on my 03.

 

[xtreme762]

No tape?

 

[Redtruck-VA]

What you don't recognize 3"?? lol Trust me it's 3".. I have the original muffler laying out back I'll throw a tape on it tomorrow...

 

[xtreme762]

I'm just joshin ya, man. Chill!

What I really want to find out is why they changed the diameter of the pipe? Maybe to pick up low end, or fuel efficiency? Cause my 2012 has 3" also.

 

[Redtruck-VA]

IDK, mine is a base model and didn't come with resonators. Just a water heater looking muffler... actually sounded pretty good stock.. lol

Edit:
When I replaced the stock muffler with a flowmaster I lost a little power and mileage.