Many old-school tuners and hot rodders know their way around a carburetor and distributor. They also know today’s technology enables better performance and gas mileage than we ever imagined. I'll admit, your old-school author was a bit intimidated to learn the powertrain control module (PCM) needs to be changed in order to tune a ’15-up Gen III Hemi. After watching the PCM installation video on the DiabloSport website, I learned how easy it is for anyone to change to a modified PCM on their 2015 and later LX body. As we found, it will take an average or inexperienced person only 20 to 30 minutes to install a DiabloSport-modified PCM. This will allow you to extract maximum performance without setting off check-engine codes or evoking “limp-home mode” in your late-model hot rod.
In the previous installment, we used my brother Andy’s cool stripe-delete '15 Scat Pack 392 Shaker Challenger to test a set of TTi long-tube headers. Before the header installation we ordered the aforementioned DiabloSport-modified PCM and opted for the Trinity tuner/programmer. Again, it’s important to remember that before tuning or bolt-ons are done to a ’05-up Chrysler product, you should use the appropriate software. For over 10 years, experienced tuners have been relying on DiabloSport software for serious Dodge tuning.
Before installing the TTi headers, the DiabloSport-modified PCM was in place for baseline dyno tuning. Tune Time Performance of Lakewood, New Jersey, graciously provided the use of its Mustang dyno. Typically, the Mustang dyno will show power numbers of 10 to 12 percent less than other dynamometers, and our baseline was 371 rear-wheel horsepower. Next, we plugged in our new DiabloSport Trinity tuner/programmer. We opted for a 93-octane tune instead of a 91-octane tune as there’s plenty of 93-octane fuel available here in the Northeast. After installing the Trinity electronic tune, the Challenger spun the rollers showing power increasing to 384 for a gain of 13 hp at the wheels!
With an established stock tune baseline, we were back at Tune Time to dyno test the TTi long-tubes. Expert tuner Matt Hauffe (owner/proprietor of TTP) is a DiabloSport CMR (Chip Master Revolution) dealer. Matt is part of DiabloSport’s large network of CMR dealers, which allows them to write a custom tune and dyno test at their location, or send tunes via email. After Matt downloaded the custom headers tune into our DiabloSport Trinity device, we were ready to take a hit on the dyno. As a reminder, the TTi headers we installed are stepped and have nearly equal-length tubes to produce more power than other long-tube headers. The Diablo tune and TTi headers showed us gains of 26 hp and 28 lb-ft. With that, we’re shooting to get this stock-tire Scat Pack into the 11s with only headers and tune. Stay tuned!
Tuning a late-model means no more dirty hands. On the right is the DiabloSport Trinity performance programmer (PN T1000, $599.99) for tuning performance and economy into most OBD-II equipped vehicles. To tune a 2015 or later model, the stock PCM needs to be replaced with a Diablosport modified PCM (LX 2015, $599.99; Trinity and PCM, $999.99 pair). Tuning without a modified PCM in place can result in a no-start situation.
No worries, there’s nothing to be afraid of. It’s so easy to swap-out the stock PCM for a DiabloSport modified PCM on a new LX-body. A few basic tools are needed and in 20 to 30 minutes you can be tuning with your power programmer. All you need is a 3/8-inch drive ratchet, a 10 and 13mm socket, a panel puller, and a small towel.
A 10mm socket loosened the nut for the negative battery terminal. We placed a towel under the terminal to prevent an accidental connection during PCM installation.
The panel tool removes the pushpins holding the plastic cowl cover. Hiding under the cowl cover you'll find the stock PCM.
There’s only one bolt holding the PCM in place. To remove, use a 13mm socket to loosen the bolt and disconnect the hood light switch. Now the PCM is ready to remove.
Pull the PCM out enough to access the upper and lower connectors. Pull back the red locking clasp on each connector starting with the top connector. Once both connectors are disconnected the PCM comes right out.
The PCM connectors are color coordinated. The tan one is top and the gray one is for the bottom connector.
The PCM connectors are color coordinated. The tan one is top and the gray one is for the bottom connector.
Installing the Diablo-modified PCM is easily done in reverse order. We reconnected the battery and it fired right up. All the accessories functioned the same without any changes whatsoever, that included all the pre-set radio stations, U-connect apps, and engine coolant temp sensor. Again, no worries and now we’re ready to tune!
We packed our Trinity tuner and drove the 392 Hemi Challenger to Tune Time Performance (TTP). There we’ll learn the bone-stock, stock-tune, and after-headers power numbers. Our bone-stock number was 371 hp at the wheels. (You’ll remember our press car tested at 432 rearwheel horsepower to the wheels on a Dynojet.) That sounds low compared to other Scat Packs because TTP’s Mustang dyno will show 10 to 12 percent less power.
Plugging the Diablo programmer into the OBD-II port begins the tuning process. We just followed the instructions and chose to program in a 93-octane tune. The Trinity will add horsepower, torque, throttle response, and improved fuel economy. We were impressed to find an additional 13 rearwheel horsepower (up to 384) and better driveability for our ride home.
In our previous installment (Happenin’ Hemi Headers) we bolted-on this set of TTi stepped (1 7/8 into 2 inch) stainless headers (PN TTISRT81782-CO, $990.00). TTi stainless 3-inch mid-pipes with race cats (PN MCHB30WRC, $774.55 set) made the transition into the factory 2 3/4-inch X-pipe active exhaust. Bolt-ons like headers, heads, cam swaps, and power adders always require custom tuning.
Once we installed the headers, we needed to drive back to TTP for our custom tune. TTP is part of the worldwide network of DiabloSport CMR (Chip Master Revolution) custom tuning dealers. Super-tuner Matt Haffe wrote a “special tune” on his laptop, changing many of the tuning parameters like spark timing and fuel tables to enhance header performance. That special/custom tune was then downloaded into the Trinity.
With Matt’s custom tune loaded into the Trinity tuner, we plugged it into the OBD-II port. We were loaded for bear and ready to rip the rollers! The TTi headers and Diablo custom tune showed us an added (over the stock baseline) 26 hp and 28 lb-ft to the wheels. Those gains were felt at the go-pedal during any type of pedal depression for much improved driveability.
