Instructions to change an 03 Hemi PCM to an 05

[Ricky Rodder]

In this link, the poster used his 03 4.7 harness and spliced in the 04 5.7 hemi coil plugs to make hemi work with 03 4.7 computer.

https://www.dodgetalk.com/forums/showthread.php?t=484049

 

[finally03gt]

Curious to know what the swap ended up costing?

 

[chrisp2493]

Curious to know what the swap ended up costing?

About $100 for a used pcm, then a couple new oxygen sensors, wire and an extra pcm connector from a junkyard. Around $200 total I think


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[finally03gt]

No CEL? We have emmissions, but its basically checking for codes, and being sure all the "readiness" checks are completed. I probably also hacve to flash the VIN to the new ECU also.

I saw one guy here did an '04 swap. What's the significance of '04 vs '05. Also, I'm 4x4, so I assume I'd need a 4x4 ECU? Does trim level have any impact?

 

[chrisp2493]

No CEL? We have emmissions, but its basically checking for codes, and being sure all the "readiness" checks are completed. I probably also hacve to flash the VIN to the new ECU also.

I saw one guy here did an '04 swap. What's the significance of '04 vs '05. Also, I'm 4x4, so I assume I'd need a 4x4 ECU? Does trim level have any impact?

You’re going to have a check engine light for EGR, and you’ll also have to add in your second new downstream sensor behind your single cat to keep that check engine light off. My truck doesn’t have cats so in my custom tune I have the egr and downstream sensors turned off. The 04 swap isn’t really worth doing because it’s only slightly better then the 03. I know a few 04 guys that just plugged in an 05 computer and they got full trans tuning abilities. There is a place called B&G Performance that does pcm flashing for vin numbers, turning on or off egr and any other codes, but they run about $400 for that service. The 4x4 doesn’t matter, as far as I know the only issue you’ll have with the swap is the 4x4 light won’t come on in the cluster, so you have to look at your shift handle to tell if it’s in 4wd. No codes related to that though.


So first off, what do you want do you need the swap for? The only reason it needs done is for tuning cams and power adders, and gaining trans tuning. But you’ll have to have a tuner for it to take advantage that. If you have a relatively stock truck, this won’t really make any difference


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[finally03gt]

On a road trip pulling the Travel Trailer and realized that the truck needs just a little help to cut the wind. So if I could pick up 20-30 ponies, although it's not much, it might make the difference.

Also, never really had any problem with the transmission shifting before. But I noticed that about 65 when overdrive kicks in it sits at about 2,000 rpms and it's pretty happy if there's no wind. But there's a fine line and if I'm back out just enough it makes another shift and drops it 200 RPMs and then I have to get in it get to get It out of overdrive again. So if I could get that second OD shift locked out for towing, it'd help.

Cam may be it the picture down the road. Bottom line, I really like the truck, but need it to pull at 2000 rpm, the way it currently does at 2500 rpm, and not catch that second OD shift where it sits at 1800 at 65. Just trying to figure out jf that's realistic, or if I need to begin researching my next truck.

 

[chrisp2493]

Sounds like that’s the convertor locking up. I don’t think the trans tune is really gonna fix that. I would suggest trying out the overdrive off or tow/haul mode button on the end of the column shifter. Some long tube headers may help get some extra low end power


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[finally03gt]

I thought that too. But, lets use a steady cruising of 63 mph with the trailer. Humming along at 1750, but a mosquito hits the windshield and now the motor is lugging. Hit the OD switch and about 3000 rpm comes on and we're pulling again. This feels like my 1:1 gear with TC unlocked. Give a bit and drops to 2500. 500 RPM is just about right for TC lock..... Hit OD switch and it settles in at about 2000 rpm, now we have OD, And presumably TC still locked, unless it unlocked to shift to OD. Then start downhill, speed picks up and one last shift to about 1800 @ 65 mph. 200 RPM doesn't seem like enough for a TC lock. Then I find this on wiki......

The 45RFE later became the 5-speed 545RFE

• Gear Ratios:
  • 1st 3.00:1
  • 2nd 1.67:1
  • 2nd Prime 1.50:1
  • 3rd 1.00:1
  • 4th 0.75:1
  • Reverse 3.00:1
• 545RFE only:
  • 5th 0.67:1

So about .12 for 5th (double over?) Seems about right for 200 RPM.

 

[Redtruck-VA]

Being a 03 fan, I thank you for hanging with the old girl. The 03-05 hemi stock to having a few bolt on's really like to cruise 2100-2400 rpm. This makes for a simple solution but unfortunately since you are 4x4 a bit expensive. At the same time I would install Detroit Trutrac differential. So what gear do you have now? If you have oversize tires then that makes make my comments even more valid. 2300@65mph cruising would be perfect for the old girl IMO...

 

[chrisp2493]

Yeah if you just want better towing, 4.10 or 4.56 gears swapped in would be the biggest gain. That will bump your rpms up to 2000 at 60 with 4.56 gears and 33” tire


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[finally03gt]

I'm running stock tire, I believe 33". I'm not certain but I believe my gears are 3.92. I considered the gear route, because obviously that puts you in a different Power Band. But the truck spends about 75% of its life on the highway at 70 unloaded, and the gas mileage already sucks. That kind of scares me away from the gears. I can pull the travel trailer with overdrive off, but then I'm running 2500 to 2600 RPM consistently on a 1300 Mile Road Trip, and honestly even at that, if the wind hits me or I've got to go to the grade or both it even struggles to keep 60 in 3rd. I agree with the 2100 to 2400 RPM happy spots. That's why I think if I could get 5th gear locked out and pull a few more ponies out of the bottom end I'd be much happier with the truck

 

[Redtruck-VA]

03 Ram 2500 hemi standard axle is 10.5 " with a 3:73 gear. The oem optional gear is 4:10 which is what I would use. There is a long debate on gears verses gas mileage. My belief is your gas mileage would actually improve with the 4:10 gear as you would not need to be into the throttle as much as you are now. Overall it would make your truck much more enjoyable to drive.

 

[finally03gt]

03 Ram 2500 hemi standard axle is 10.5 " with a 3:73 gear. The oem optional gear is 4:10 which is what I would use. There is a long debate on gears verses gas mileage. My belief is your gas mileage would actually improve with the 4:10 gear as you would not need to be into the throttle as much as you are now. Overall it would make your truck much more enjoyable to drive.

I don't disagree. I have a 2003 mustang gt with 3.73's that runs 2600 at 75 ish and gets 22 MPG.
I can't speak for unloaded, but I've been monitoring load, TB % and instant MPG with torque pro, and long term MPG with the on board monitor. I can say in the world scenario with the travel trailer, 62 at 2000 RPM with enough throttle to be right on the edge of a downshift, I get better gas mileage than kicking overdrive off at 2500 rpm and less throttle. I do understand the gear argument, but I'm not convinced that's the direction I want to go right now.

What I'm really looking to find out is if I did an ECU swap and possibly a cam could I get 20 to 30 horsepower in the bottom end and locked out that second overdrive fifth gear.

 

[chrisp2493]

A small cam like a comp 260 would help, that one is a torque based cam grind. With the right tuner it can still run on an 03 pcm and tune. The 05 pcm is a good swap but not exactly necessary in every situation. It’s not necessarily hard or all that expensive, but it isn’t going to give you much more power with a stock setup then you would get in an 03 pcm. It’s mainly used to gain trans tuning and tuning for big cams and boost. I can’t stress it enough, a gear swap will get you exactly want you want to accomplish. I also think longtubes will get you a nice little bump as well.


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[HemiLonestar]

A small cam like a comp 260 would help, that one is a torque based cam grind. With the right tuner it can still run on an 03 pcm and tune.

Comp 260 runs just fine on a Superchips 91 tune, there's an 04 RC on here running around with that exact combo. It was what I had planned before finding out about converting the PCM (still have a comp 260 sitting around if you're interested) and changed plans.

 

[finally03gt]

Well, thanks for all the info. A lot to chew on.

 

[finally03gt]

. The 4x4 doesn’t matter, as far as I know the only issue you’ll have with the swap is the 4x4 light won’t come on in the cluster, so you have to look at your shift handle to tell if it’s in 4wd. No codes ......


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My truck is a Laramie with the electronic 4wd rotary knob. If the dash doesn't indicate, will it be able to process the command?

 

[HemiLonestar]

My truck is a Laramie with the electronic 4wd rotary knob. If the dash doesn't indicate, will it be able to process the command?

Rotary knob sends a signal down to the solenoid on the transfer case, the dash light is there to let you know, not as a command function.

Sent from my HTC U11 using Tapatalk

 

[finally03gt]

I didn't elaborate.....

With the rotary the signal likely travels on a bus. That signal will then be interpreted one of the control modules. I don't know if it's bcm, tcm, or ECM, but either way one of the control modules will then receive and interpret the signal. My concern was if the wire pathways that signal the dash indicator were compromised by integrating the TCM with the ECM (which is part of what seems like is happening with this swap) then its possible the signaling wire ways were incumbered also.

 

[chrisp2493]

I’m pretty sure there is a sensor on the transfer case that sends out the position to the computer.


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