Part 10: Pump it Up
Last month we left off with the cab six feet in the air while we installed a bigger modified ProMax 64 VVT turbocharger from High Tech Turbo, some better-flowing exhaust manifolds and up-pipes from Profab Performance, and a high-flow charge air piping kit from HSP Diesel. The last time the truck was on the chassis dyno it made 496 hp, but data logs had showed that fuel rail pressure was dropping considerably from the commanded 29,000 psi to just 21,000 psi actual pressure. This told us the truck had more power in it; we just needed the extra fuel pressure to find it. We knew the stock turbo was capped at around 520 hp, so if we were going to be pulling the turbocharger to gain access to the stock CP4.2 injection pump, it was a no-brainer to install a bigger turbo.
Exergy 10mm CP4.2
To increase performance much further than 500 hp, the LML needs more fuel than the factory CP4.2 can provide. The CP4.2 is capable of more pressure than the previous CP3 design used in the ’01-10 Duramax, but it means less displacement. The earlier CP3 used three plungers, each pumping once per revolution. In the CP4.2 you’ll find two plungers, each pumping twice per revolution. Inside, it uses a camshaft with two opposing lobes. The factory plunger bore and overall stroke will limit this pump to around 500 horsepower.
While more power was the focus with upgrading the stock injection pump, there’s also something else to point out. The OEM CP4.2 on ’11-16 Duramax engines has been commonly known to fail due to poor lubricity or contamination in the fuel supply, compared to the earlier CP3. A good lift pump like the FASS Titanium we installed on this truck can aid the CP4’s performance and longevity because the extra fuel supply helps lubricate the failure-prone internal camshaft, followers and bearings, guarding against premature wear and catastrophic failure.
When the followers riding on the camshaft cease rolling along the lobe, friction between the two can create a flat spot, generating metallic debris within the pump case and causing damage to the camshaft itself. It won’t take very much run time before catastrophic internal pump failure sends all that debris downstream to the Fuel Control Actuator (FCA), where a simple 80-micron screen can then fail, letting the debris through the high-pressure fuel rails and into the fuel injectors. This means that $600 failed injector pump just wiped out your entire high-pressure fuel system, which is likely to cost you thousands of dollars in repairs.
Looking to overcome the lack of volume to support 500+ horsepower and the flimsy design of the FCA screen, engineers at Exergy Performance set out to design a better, performance-oriented CP4.2 for the LML and 6.7L Power Stroke. With a target of 800 hp in the single CP4.2 injection pump, Exergy designed a new camshaft to increase pump displacement by roughly 50 percent, creating a new lobe profile to optimize performance and longevity. Changes also had to be made to allow the plungers to refill more quickly on the intake stroke to make the pump more efficient at peak rpm.
To prevent loss of the entire fuel system should any part of the pump fail, Exergy also looked into modifying the FCA as a failsafe within the system. The most important difference is the FCA screen. The factory single-layer, 80-micron screen can tear and collapse, allowing debris to flow downstream. The Exergy FCA—which is sold as a stand-alone piece for those not ready to replace their pump but who want the peace of mind—uses a two-layer, 25-micron screen. This screen not only filters better; it won’t delaminate or tear and will load up more quickly in the event of a pump failure, meaning the high-pressure system will be starved of fuel and the engine will shut down before the contaminants can reach the expensive injectors and fuel rails. So even if the pump were to fail, you’ve got a much better chance that it is all you’d need to replace to get you back up on the road. With that said, Exergy strongly suggests owners add a safe fuel additive with a good lubricant to every tank of fuel and keep up on filter changes to keep lubricity in the pump and water and contaminants out.
There are kits out there that allow you to convert your LML’s CP4.2 system over to the earlier CP3 design, but that would be moving backward technologically. For this application, sticking with the CP4.2 seemed most logical as it wouldn’t require custom tuning, it could run on a bone-stock application, and it can still meet emissions compliance tests.
GDP EZ Lynk Tuning
To take full advantage of that better-flowing CP4.2 and the modified variable-vane turbocharger we installed, we opted to switch over to some custom tunes from GDP Tuning via their EZ Lynk tuning platform. With full control of both the engine and transmission control modules, Jeremy Pierce at GDP could make a few minor changes to the fueling, timing and turbo vane tables to make sure the truck and new combination of parts all worked at their full capacity. Tweaks within the TCM would also help with overall drivability by allowing the truck to hold gears longer, downshift sooner and lock the torque converter earlier, helping to keep the engine inside its peak powerband when we need it.
The EZ Lynk hardware GDP uses is easy to understand and uses Wi-Fi and Bluetooth technology to send information from your preferred smart device using a downloadable Auto Agent app to the supplied box you plug into the truck’s OBD-II port. You can then download new tunes, monitor engine vitals, read and clear diagnostic codes, and even data-log engine parameters or chat with GDP customer service reps to fine-tune your package even further. While using your smartphone as an in-cab monitor is convenient, we opted to install the newly released GDP monitor, which offers some additional features like a built-in dash cam and full GPS navigation. This also allows us to keep the monitor mounted in the truck all the time and always have our gauges available for monitoring needs.
So now you’re asking, after going through the trouble of lifting the cab to swap these parts out, where did we land performance-wise? We can assure you that even on our first round of tuning from GDP it was worth it. Initial driving feedback was impressive. The new turbocharger works well on the street. It’s still very responsive and comes up on boost quickly, something we’d been worried about when going to a bigger compressor and turbine wheel. The new 10-blade turbine wheel helped cut down on some drive pressure and makes for an incredibly cool-sounding, throaty exhaust note with plenty of whistle. The new Exergy pump seems to offer plenty of fuel as we’re not holding the 29K rail pressure on bigger tunes that we used to, and the truck is making more power.
To back up our seat-of-the-pants analysis, we strapped the truck back on the dyno for back-to-back comparisons. Our previous daily driver tune had made 440 hp and 815 lb-ft, whereas our new Level 3 tune from GDP made a very impressive 509 hp and 976 lb-ft. That’s more than our previous best in the hottest tune of 496 and 932. You can imagine our excitement as we clicked over to Tune 5 in our Shift-on-the-Fly tuning package and put down 592 hp and 1,211 lb-ft to the tires!
There’s no stopping Project LML now—at least until our basically stock, 127,000-mile Allison begs for mercy. We’d expect some clutch slippage and torque converter shake to stop us dead in our tracks if we can’t fight the urge to rip around town with 600 hp under our right foot.
With a target of 800 hp in the single CP4.2 injection pump, Exergy designed a new camshaft to increase pump displacement by roughly 50 percent.