A New Holland sprayer guest case study
At Pico Technology, we pride ourselves on providing technicians with the diagnostic tools and insights they need to tackle some of the more complicated vehicle issues. One of our automotive scope users had the opportunity to work alongside a field technician on a New Holland SP310 sprayer with just 80 hours on the clock. The customer complaint here was a frustratingly slow and hard-to-start machine. We hope you enjoy reading about it below!
The initial troubleshooting by the field technician had rightly focused on the fuel system, a common culprit for starting woes. In an attempt to resolve the issue, the high-pressure pump (which integrates the lift pump) and the main fuel filter housing (containing a critical check valve to prevent fuel drain-back) had both been replaced. Despite these efforts, the problem persisted, indicating that the root cause lay elsewhere.
When I joined the technician, our first step was to comprehensively assess the fuel supply. We meticulously scoped the metering valve PWM signal, monitored the rail pressure sensor outputand performed a crankshaft (CKP) and camshaft (CMP) correlation check. To ensure thoroughness, we conducted a “3 start/stop test.” This initial round of diagnostics confirmed that the fuel system was, in fact, operating precisely as it should. The various signals and pressure readings were within specifications, ruling out any fundamental fuel delivery issues. This was an important step, as it allowed us to confidently shift our focus.
With the fuel system acquitted, our attention turned to the engine’s mechanical health. We swapped our fuel pressure leads for an amp clamp to perform a relative compression test. This non-intrusive method allows us to quickly assess the consistency of compression across all cylinders by analyzing the current draw of the starter motor. Any significant dips or irregularities in the waveform can indicate a cylinder with lower compression, pointing towards potential valve train issues, piston ring wear, or other mechanical problems.
To further validate our findings and establish a baseline, we decided to check a known good machine – another New Holland SP310, albeit a 2019 model. We performed both the CMP/CKP correlation and a relative compression test on this reference vehicle. This comparative analysis is often invaluable, as it provides a clear picture of what a healthy system’s waveforms should look like, making it easier to identify deviations in the problematic machine.
Once all the data was collected – the fuel system parameters, the relative compression test from the problematic sprayer and the comparative data from the known good machine – we sat down to meticulously go over the results. This is where the true power of the PicoScope comes into play. The ability to overlay waveforms and zoom in on specific events allows for an unparalleled level of detail and comparison.
Our comprehensive analysis revealed several key findings. As anticipated, the fuel system was indeed “spot on,” confirming our initial assessment. Similarly, the CMP/CKP correlation was also within acceptable limits, ruling out timing issues. Unlikely with a gear-driven engine, but considering how easy it is with Pico, it’s worth ticking off the list. It also allows us to see the amplitudes from the sensors, which, if incorrect, can cause extended crank times. However, the starter current waveform on the problem machine immediately stood out as “odd.”
When compared to the known good machine’s relative compression waveform, the difference was stark. The problem sprayer exhibited a consistently higher current draw during cranking, over 750A compared to the known good at 400A, suggesting an abnormally high load on the engine. This was our “aha!” moment; we knew we were on the path to uncovering the true source of the problem.
The higher-than-normal load during startup pointed away from the engine itself and towards an auxiliary system that might be placing undue strain on the cranking process. After a collaborative discussion with the field technician and the service manager, our suspicions zeroed in on the unloader valve for the main hydraulic pump.
The function of this valve is critical during startup. It is designed to be commanded “on” (unloading) during the engine cranking phase, effectively destroking the hydraulic pump and reducing the load on the starter motor and engine. Once the ignition is released to the “run” position, the coil for this valve de-energizes, allowing the pump to transition into a full load state to power the sprayer’s hydraulic functions. If this unloader valve were to malfunction and remain in a loaded state during cranking, it would undoubtedly add a dramatic load on the engine and therefore the starter motor, leading to the slow and hard starting condition we were observing.
To confirm our hypothesis, the technician first performed a continuity and resistance check on the valve coil, looking for any shorts or open circuits. These tests came back good, indicating the coil itself wasn’t the issue. The critical next step was to bypass the machine’s control system and supply an independent 12-volt feed directly to the unloader valve coil. The results were immediate and conclusive: with the valve properly commanded to unload, the engine cranked and started in less than 4 seconds. This was a significant improvement from the previous cranking times, which were upward of 10 seconds. Unfortunately, I did not capture this using the scope.
Since the valve coil and its internal wiring were sound and there were no other shared ground issues on the machine, our attention turned to the control side of the circuit. The hydraulic control system on this New Holland sprayer is a Parker iQAN system. Given our findings, it was determined that the most probable cause was a broken wire somewhere in the harness running from the iQAN control node to the unloader valve coil. This broken wire would prevent the iQAN system from properly commanding the valve to unload during startup, leading to the excessive load on the engine during cranking.
This case served as a powerful reminder of the diagnostic journey. It began with addressing the most likely suspects, then systematically eliminating them being driven by the data. The ability to capture and analyze waveforms, compare them to known good examples and logically deduce the source of the problem is at the heart of modern vehicle diagnostics. In this instance, it allowed us to swiftly move beyond component replacement to precisely identify a seemingly elusive wiring issue that was causing significant operational headaches for the customer.