The Infiniti G35, powered by the legendary VQ35DE and later VQ35HR engines, remains a favorite among tuners and enthusiasts. Its balance of luxury, handling, and potential for power makes it an ideal platform for modifications. However, adding aftermarket parts without a comprehensive understanding of the engine management, fueling, and cooling systems can lead to a host of performance problems. From intermittent misfires to sudden overheating, these issues can turn a thrilling ride into a frustrating garage project. This guide examines the most common performance problems after mods and provides detailed solutions to keep your G35 running at its peak.

Engine Misfire After Modifications

Engine misfires are among the most frequent complaints after modifications. A misfire causes rough idle, hesitation during acceleration, and a noticeable loss of power. On the VQ platform, this is often directly tied to ignition and fueling changes.

Root Causes of Misfire

  • Incorrect spark plug gap: Many aftermarket forced induction or nitrous kits require a smaller spark plug gap (typically 0.028” to 0.032”) to prevent spark blowout under higher cylinder pressures. Stock gaps (0.044”) will cause misfires under load.
  • Faulty or weak ignition coils: The G35’s coil-on-plug design is reliable, but aftermarket injectors or increased boost can expose coil weaknesses. Older coils with cracked housings leak voltage to ground.
  • Inadequate fuel pressure: A larger fuel pump or injector may have been installed without proper voltage wiring. Low fuel pressure leans out the mixture and causes misfire.
  • Vacuum leaks: Aftermarket intake manifolds or blow‑off valve installations can introduce unmetered air, upsetting the air‑fuel ratio.

Diagnostic and Repair Solutions

  • Use a feeler gauge to verify spark plug gaps per the tuning setup. Gap them to 0.032” for naturally aspirated builds with high‑compression pistons.
  • Replace ignition coils in pairs. OEM Hitachi or Denso coils are recommended; avoid cheap no‑name coils.
  • Test fuel pressure at the rail with a gauge. For a stock engine, it should be around 51–54 psi at idle. Upgrade to a Walbro 255 lph pump if pressure drops under load.
  • Perform a smoke test on the intake system to locate leaks. Seal any leaks with high‑temperature silicone gaskets.

Increased Fuel Consumption and Rich/Lean Conditions

After adding a cold air intake, headers, or a cat‑back exhaust, many owners notice a sharp rise in fuel consumption. This is usually a sign that the engine management system is not properly calibrated for the increased airflow.

Why Fuel Consumption Rises

  • Untuned ECU: The stock ECU is calibrated for factory airflow. Without a tune, the engine may run rich to protect itself, dumping extra fuel.
  • Larger injectors without rescaling: Installing 440cc or 550cc injectors without a corresponding ECU flash forces the engine to run extremely rich or lean at idle.
  • MAF sensor contamination: Oil from aftermarket intakes can coat the hot‑wire MAF sensor, causing incorrect airflow readings and fueling errors.
  • Fuel pressure regulator mismatch: Adjustable FPRs set too high increase fuel trims and waste fuel.

Solutions to Optimize Fuel Economy

  • Invest in a professional dyno tune using UpRev or EcuTek software. A proper tune adjusts timing and fuel maps for the exact modifications.
  • Clean the MAF sensor with CRC MAF cleaner if intake oil contamination is suspected. Re‑oil air filters sparingly.
  • If using an aftermarket fuel pressure regulator, set base pressure to the factory spec (43.5 psi with vacuum line disconnected) and ensure the vacuum line is intact.
  • For high‑flow exhausts, consider a wideband O2 sensor and gauge to monitor air‑fuel ratios in real time.

Overheating Issues with Performance Modifications

When you add a turbocharger, supercharger, or simply increase compression with aftermarket pistons, the cooling system becomes a weak point. The G35’s stock radiator is adequate for daily driving, but sustained high‑RPM operation on track days or during aggressive driving can push coolant temperatures past safe limits.

Typical Overheating Triggers

  • Insufficient radiator capacity: The stock aluminum radiator is thin and prone to clogging after years of use. Higher heat loads from forced induction require a larger core.
  • Faulty thermostat: A thermostat that sticks closed prevents coolant circulation. Aftermarket 160°F or 170°F thermostats help but require tuning adjustments.
  • Low coolant level or air pockets: After a modification, technicians often fail to properly bleed the cooling system, leading to hot spots.
  • Failed water pump: The VQ35DE water pump impeller can degrade over time, reducing flow at high RPM.
  • Poor airflow from aftermarket intercooler placement: Large front‑mounted intercoolers block the radiator’s airflow, raising temperatures in traffic.

Cooling System Upgrades and Fixes

  • Replace the radiator with a high‑performance aluminum unit from Koyo, Mishimoto, or C&R Racing. Look for two‑row or three‑row cores.
  • Install a 160°F thermostat and ensure the cooling fans are set to engage earlier via ECU tuning or a manual switch.
  • Use a coolant flush kit to remove old deposits. Fill with a 50/50 mix of distilled water and high‑quality ethylene glycol coolant.
  • If running a front‑mount intercooler, upgrade to a pusher fan kit to improve airflow at idle. Also consider a hood vent or louver kit to vent hot air.
  • Replace the water pump with a new OEM unit every 60,000 miles or during major engine work.

Loss of Power and Hesitation

A sudden drop in acceleration after modifications is disheartening. Power loss can stem from a combination of tuning oversights, component restrictions, or sensor failures.

Common Contributors to Power Loss

  • Poor ECU tuning or base map: A generic tune from an online forum may not account for local fuel quality, altitude, or specific part variations.
  • Exhaust back pressure: If the exhaust system has a mandrel‑bent section with a crimp or a catalytic converter that has collapsed, exhaust flow is severely restricted.
  • Faulty camshaft position sensors: The VQ engine relies on accurate cam signals. A failing sensor will trigger a limp‑home mode that reduces power.
  • Dirty or failing throttle body: Carbon buildup on the throttle plate reduces airflow, especially after an intake upgrade that introduces more blow‑by oil.
  • Intake air temperature (IAT) sensor malfunction: An IAT sensor reading overly hot air can cause the ECU to pull timing and reduce power.

Restoring Lost Power

  • Book a custom dyno tune with a certified UpRev tuner. A remote tune via EcuTek can also work if you have a wideband and datalogging.
  • Inspect the exhaust system with a borescope or by removing the oxygen sensors to check for blockages. Replace cats with high‑flow units if needed.
  • Check camshaft position sensors with an oscilloscope or replace them if the engine has hesitation at mid‑range RPM. OEM sensors from Nissan are preferred.
  • Clean the throttle body with a dedicated throttle body cleaner and a soft brush. Perform an idle re‑learn procedure afterwards.
  • Ensure the IAT sensor is positioned in the intake stream, not near a heat source. Consider relocating it if you have a hot‑air intake.

Check Engine Light (CEL) After Modifications

Almost every modified G35 will trigger a check engine light at some point. The code itself points to a specific system, but the underlying cause is often related to the mod.

Typical Diagnostic Trouble Codes (DTCs)

  • P0300 – Random Misfire: Usually from spark plug gap or coil issues as described above.
  • P0171/P0174 – System Too Lean (Bank 1/2): Indicates a vacuum leak, faulty MAF, or fuel pressure problem.
  • P0420/P0430 – Catalyst Efficiency Below Threshold: Triggered by high‑flow or gutted catalytic converters. A tune can disable the rear O2 sensor readiness.
  • P0037/P0057 – Heated O2 Sensor Circuit Low: Often caused by wiring damage during exhaust installation.
  • P0101 – MAF Circuit Range/Performance: Result of oil contamination or an aftermarket intake that alters airflow characteristics.

Clearing the Light and Preventing Returns

  • Use a quality OBD‑II scanner (like the BlueDriver or Foxwell) to read codes before clearing them. Never clear codes without addressing the cause.
  • For catalyst codes, install a spark plug anti‑fouler spacer on the downstream O2 sensor to move it out of the exhaust stream. Some tuners also disable the sensor in the ROM.
  • After replacing parts, reset the ECU by disconnecting the battery for 30 minutes or using the scanner’s reset function.
  • If the light returns immediately, double‑check all electrical connections. Many aftermarket parts require resistor bypasses or additional grounds.

Drivetrain and Transmission Problems

While the engine gets most of the attention, modifications often expose weak points in the transmission and differential. The G35 came with either a 5‑speed automatic (RE5R05A) or a 6‑speed manual (CD009).

Manual Transmission: Grinding and Clutch Issues

  • Synchronizer wear: The CD009 is stout but can develop synchro grind on 2nd gear if driven hard with high‑RPM shifts. Aftermarket brass or carbon synchros can help.
  • Clutch slipping: A stock clutch cannot hold more than ~300 wheel horsepower. Upgrading to a stage 2 or 3 clutch from ACT, South Bend, or Competition Clutch is necessary.
  • Clutch pedal feel: Heavy aftermarket clutches can damage the stock clutch master cylinder. A CSC (concentric slave cylinder) failure is common; convert to an external slave or upgrade to a ClutchMaster kit.

Automatic Transmission: Slipping and Hard Shifts

  • Insufficient cooler: The RE5R05A runs hot under boost. An external transmission cooler (e.g., B&M or Hayden) dramatically reduces fluid breakdown.
  • Shift flare: If the transmission flares between gears, the valve body needs cleaning or an upgraded shift kit from IPT or Level10.
  • Torque converter lockup issues: High torque can cause the converter to unlock unexpectedly. A custom tune that adjusts lockup parameters can solve this.

Differential and Axle Concerns

  • Clunking from the diff: Worn differential bushings create play. Replace with polyurethane bushings from Z1 Motorsports or Whiteline.
  • Limited slip diff (VLSD) degradation: The viscous coupling loses effectiveness with age. Consider swapping to a clutch‑type LSD like the Nismo or Quaife unit.
  • Axle half‑shaft breakage: Under hard launches with sticky tires, axles can snap. Upgrade to Stage 1 or 2 axles from The Driveshaft Shop.

Proactive Maintenance and Tuning for Modified G35s

Many problems can be prevented by combining thoughtful part selection with a disciplined maintenance regimen. Here are best practices for a reliable modified G35.

Selecting the Right Tuning Solution

The VQ35DE and VQ35HR respond well to UpRev (OSiris or Ecutek) tuning. For naturally aspirated builds, an UpRev tune with a cold air intake and headers can yield 20–30 whp. For forced induction, a custom dyno tune with a standalone ECU (like AEM or Haltech) may be necessary for full control.

Routine Checks for Modified Cars

  • Every 3,000 miles: Check oil level and condition. VQ engines burn oil when driven hard; use a high‑zinc synthetic (e.g., Mobil 1 0W‑40).
  • Every 15,000 miles: Inspect spark plugs, replace if worn. For boosted G35s, replace every 10,000 miles.
  • Every 30,000 miles: Replace coolant, transmission fluid, and differential fluid. Use Nissan Matic‑S for the automatic.
  • Annually: Test compression and leak‑down to monitor engine health.

Essential Upgrades for Reliability

  • Oil cooler kit (Setrab or Mocal) to keep oil temps below 230°F on track.
  • Wideband oxygen sensor and gauge for real‑time AFR monitoring.
  • Reinforced motor mounts (e.g., Cusco or Z1) to prevent engine movement that stresses intercooler piping.
  • Catch can system to reduce oil vapor from the PCV system, preventing knock and carbon buildup on intake valves.

Conclusion

The Infiniti G35 is a rewarding platform to modify, but it demands attention to detail. Every upgrade—from a simple intake to a full turbo kit—shifts the delicate balance of airflow, fueling, and thermal dynamics. By understanding common pitfalls like misfires, fuel consumption spikes, overheating, and drivetrain weaknesses, you can keep your G35 running strong for thousands of miles. Invest in a professional tune, monitor vitals with gauges, and perform regular maintenance tailored to your setup. With these steps, your modified G35 will deliver the raw, reliable performance that makes this chassis truly special.