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.

If you saw last month’s Project LML installment, you’re already up to speed on what’s going on here. Since we’d planned to install a new turbocharger, exhaust manifolds, up-pipes, downpipe, injection pump, and high-flow piping kit, removing the cab seemed the easiest route.
The factory injection pump is buried down in the valley of the block and will require a bunch of fuel lines to be removed to gain access to its mounting bolts.
Removing the EGR system, turbocharger, wiring harnesses, and fuel lines to get to this pump can be done with the cab on the truck, but cab off made life so much simpler.
With the factory pump sitting on the bench next to the new Exergy 10mm unit, you can see there are no external differences. The new Exergy pump has internal modifications, however, that increase fuel flow to support 800 hp, along with changes to increase durability and longevity.

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.

The biggest design flaw inside the factory CP4.2 is the screen on the Fuel Control Actuator (FCA), which meters fuel flow and signals the ECM. The OEM screen is single-layered and in extreme cases it can tear and send debris through the high-pressure fuel rails and injectors. Exergy engineered a new double-layer, 25-micron screen that will not delaminate or collapse.
Here’s an example of an FCA (removed from a failed pump) that sent significant debris through the pump downstream to the fuel rails, injector lines and injectors. The new Exergy Inlet Metering Valve is standard equipment in all Exergy pumps, but it can be purchased separately to install in your stock pump at any time. This simple change could save you thousands in repairs if your factory CP4.2 were to ever fail.
The CP4.2 injection pump can make more rail pressure (29,000 psi) for the LML platform, but it has been more failure-prone than its predecessor. A common failure is when the follower that rides on the cam lobe stops spinning due to lack of lubricity or contaminated fuel.
To better understand how the injection pump works to create those crazy rail pressure numbers, you can see here how the two followers ride along the cam lobe that rotates on the shaft gear driven by the engine. Tight tolerances and the extreme demand put on these pumps require excellent fuel filtration and constant positive pressure to the pump.

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.

Exergy Engineering is one of the top shops in the country when it comes to high-pressure fuel system parts. Their facility is packed with state-of-the-art equipment and every single pump they produce, whether it’s a stock replacement or a modified unit, goes through rigorous testing on this test stand before being packaged and shipped.
While the modified 10mm, 12mm and even 14mm CP3s are more popular sellers, the 10mm CP4.2 like the one we’re installing has received excellent feedback from owners. Since it’s still a CP4.2, tuning wouldn’t be required for the truck to run properly, but to take advantage of the stroker 10mm’s capability, custom tuning can help overall performance. Exergy has had numerous customers report making over 800 rwhp with this pump.
Since the pump is gear-driven by the engine and the timing of injection events from the pump to the fuel rails is vital for the system to run correctly, the pump must be timed with the engine. The access port on the front cover shows the two gears. The punch marks on the teeth need to be lined up or you may experience poor running or even no-start conditions.
To make sure the new turbocharger and 10mm CP4.2 work to their full potential, some new custom tuning was in order. Based on previous experience, going to an EZ Lynk tuning package from GDP Tuning was a no-brainer. GDP’s EZ Lynk software allows total control of the ECM and TCM to fine-tune the combination. Changes to the vane position, timing, fuel quantities and shift strategies would make this combination of parts highly drivable while ensuring maximum performance can be achieved.


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.

The EZ Lynk system will use an Auto Agent app that can be downloaded onto any smart device like your phone or tablet. This allows you to connect to the Wi-Fi capable box to download your new tunes into the vehicle’s ECM and TCM. While a smartphone can do it, we opted to install the newly released monitor from GDP Tuning as well. The system is easy to use and will walk you through tuning the engine and transmission. The Shift-on-the-Fly tune package gives us five tunes, in varying horsepower levels, that we can select while driving with a simple twist of the knob installed next to the OBD-II port.
Once connected to the EZ Lynk box, you can connect to the vehicle using the Auto Agent app and select from the various tunes supplied by GDP. They offer single tunes that can be downloaded by themselves, or a Shift-on-the-Fly option for full adjustability from the driver’s seat. The Auto Agent app can also be used to scan and clear diagnostic codes, as well as data-log engine parameters to help GDP better adjust your tuning specifically to your truck.
The GDP touchscreen monitor offers good resolution and mounts just about wherever you’d like with a suction cup mount. The gauge package is easy to read and offers dozens of parameters to keep your eye on while driving. EGT, coolant temp, trans temp, rail pressure and boost are the most common.
With just the base files loaded into the truck, we made a few runs on the chassis dyno. The new 10mm CP4, ProMax 64 turbocharger, HSP Max Flow piping, and Profab Performance manifolds and up-pipes showed an almost 100-hp gain over the stock setup. Our previous best was 495 to the wheels. The basic daily driver tune is now making more than that, with the Max Effort tune putting down 592 hp. With some tweaks and minor adjustments to the software, GDP is confident this setup could easily produce 610-620 hp.


Exergy Performance

GDP Tuning

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