Killshot Series: Common Issues & Solutions

The handheld shows 0 RPM, and the engine will not start.

• No 12V on IGN SW wire during crank
• Wrong tach input configuration
• Faulty distributor or crank trigger (not connected)
• Broken tach input wire

1. Confirm IGN SW wire has 12V ON + CRANK
2. Verify the correct Tach Source selected
3. Test distributor or crank trigger module
4. Inspect tach wiring for damage

Handheld shows lean, AFR won't change.

• The O2 sensor is mounted incorrectly, causing damage to the sensor
• O2 sensor wiring is damaged
• Exhaust leak upstream of O2
• Failed sensor due to excess fuel, causing false lean

1. Confirm the O2 sensor is ≈10” from the collector
2. Verify good ground and clean power, not dropping below 11.3V
3. Check for exhaust leaks
4. Swap/test sensor
5. Correct fuel tuning

No fuel pump sound when keyed ON.

• Relay not used (pump wired directly — ECU cannot power pump)
• Incorrect relay wiring
• No 12V to relay coil
• Pump ground fault
• Firmware issue requiring reflash

1. Verify if the relay is used and wired correctly
2. Confirm ECU Fuel Pump Trigger output
3. Check relay wiring and 12V coil supply and fuse
4. Verify pump ground

RPM shows, but no spark.

• Incorrect coil wiring
• Coil type is incorrect for the system
• The coil is grounding out
• Damaged coil
• Damaged coil driver (internal of ECU)

1. Verify coil wiring matches the Killshot diagram
2. Confirm the coil driver type is correct
3. Verify the voltage to the coil
4. Test with a known-good and correct coil

The engine will not idle, or it surges badly

• TPS not calibrated
• IAC wiring damage
• Excess fuel due to improper setup
• The mechanical stop screw is misadjusted

1. Calibrate TPS
2. Verify IAC wiring
3. Check for rich condition, adjust accordingly
4. Reset the throttle stop screw
5. Check for vacuum leaks

The timing light does not match the handheld timing

• Distributor not locked at 15° BTDC
• Wrong ignition timing setup
• Slipped harmonic balancer
• Tach source mismatch

1. Lock distributor at 15° BTDC
2. Verify timing in handheld matches the light
3. Check the balancer slip
4. Confirm the correct tach source

Engine temp rises and fans won't trigger

• No relay used (direct wiring)
• Fan control pins miswired
• Wrong temp settings
• Damaged ecu

1. Verify relay used (required — fans cannot run directly)
2. Confirm fan pins wired per the Killshot guide
3. Check fan settings
4. Verify the fan wire is making a ground signal when flagged

No data is displayed, connect timeout, or flashing issues

• CAN H/L pins are swapped
• Handheld power/ground loose
• Handheld firmware mismatch
• ECU not powered properly
• Damaged CAN chip (internal HH/ECU)

1. Verify CAN pinout — H/L correct
2. Test handheld power/ground
3. Confirm firmware versions
4. Recycle ECU power

The engine stumbles off idle

• Poor O2 sensor location is corrupting lean data
• TPS not calibrated
• Mechanical vacuum leak
• Wrong injector settings
• Improper tuning

1. Verify O2 sensor < 24” from collector
2. Calibrate TPS
3. Check for vac leak
4. Check injector size/settings
5. Refer to the fuel tuning guide for adjustments

The engine cranks for a long time and/or is hard to start

• Incorrect cranking fuel value or pressure
• Low battery voltage
• Poor engine ground
• TPS/IAC calibration off

1. Verify IGN SW 12V ON+CRANK
2. Test battery voltage
3. Increase “Fuel prime %”
4. Re-cal TPS/IAC

No screen, no power to the handheld

• CAN pins swapped
• No ECU power
• Faulty handheld cable
• Broken CAN connector
• No ignition switched 12V signal to the system

1. Verify ECU has clean power
2. Confirm the CAN pinout is correct
3. Test handheld on known-good system
4. Replace the known-bad cable or connector
5. Find an alternate source for switched 12V, even if just for testing

Radio whine, static, and EFI interference with other electronics

• Poor coil grounding
• No shielding on VR wires
• Coils powered from a shared circuit
• ECU ground path is incorrect

1. This is rarely an issue with Aces hardware
2. Shield VR wires
3. Verify the power source is from the Battery
4. Confirm ECU ground to battery (-)

The engine stalls when letting off the throttle

• Improper IAC settings
• TPS not calibrated
• Poor idle timing
• Over-aggressive fuel cut

1. Calibrate TPS
2. Tune the IAC steps correctly
3. Set idle timing 15–18°
4. Adjust the decel fuel cut strategy

Lean AFR, weak performance, stalling

• Incorrect regulator setup
• Supply line too small
• Low-voltage pump wiring
• Bad pump
• Filter restriction

1. Verify fuel pressure at the rail
2. Confirm proper return line size
3. Test pump voltage under load
4. Replace the pump and filter if needed

MAP stuck at 100 kPa

• MAP sensor unplugged
• Broken MAP wire
• Sensor failed
• Boost block-off plug is installed in the throttle body
• Wrong MAP sensor calibration

1. Verify the MAP sensor is plugged in
2. Check wiring
3. Test sensor
4. Confirm MAP sensor config
5. Remove the block-off plug from the bottom of the throttle body

Injectors not firing- no fuel pulse

• No RPM signal to ECU
• Injector power missing
• Driver damaged
• Harness fault

1. Confirm RPM input to ECU
2. Test injector 12V feed
3. Inspect harness
4. ECU bench test if needed

Handheld show fails to read

• Wrong sensor type
• Bad ground or 12V feed
• Open WBO2 circuit
• Sensor failed

1. Confirm the correct LSU 4.9 sensor is used
2. Verify clean power and ground
3. Inspect WBO2 circuit
4. Replace the sensor if faulty

Blown fuse on key ON

• Coil wiring damaged
• Short in the injector harness
• Faulty component
• Ground loop fault

1. Verify correct coil wiring
2. Check the injector wiring for shorts
3. Inspect for a harness pinched or cut
4. Correct grounding paths

Battery voltage drops overnight

• ECU staying powered
• Fan relays back-feeding
• The CAN device is not shutting down
• Miswired IGN SW

1. Confirm IGN SW drops to 0V key OFF
2. Test for back-feed on relays
3. Verify the CAN device shuts down
4. Correct IGN SW wiring

RPM jumps or fluctuates badly

• The Tach input is wired wrong
• Incorrect tach source type
• Extreme EMI interference
• VR pickup is poorly adjusted

1. Confirm the correct tach source selected
2. Check tach wiring
3. Inspect VR pickup
4. Inspect for EMI from coils or alt

Handheld shows full rich or error

• O2 sensor heater failure
• Poor ground to the O2 controller
• Opening in the sensor wiring
• Bad sensor

1. Verify the O2 sensor heater function
2. Confirm ground path
3. Inspect O2 wiring
4. Replace the sensor if faulty

TPS % jumps, unstable idle

• TPS not calibrated
• Poor sensor ground
• Wiring damaged
• Faulty TPS sensor

1. Recalibrate TPS
2. Verify sensor ground
3. Check TPS wiring
4. Replace TPS if needed

Handheld disconnects during crank

• Low battery voltage
• Poor IGN SW wiring
• ECU ground path is weak
• CAN cable loose

1. Verify battery voltage stays above 9.5V cranking
2. Confirm IGN SW wiring
3. Test the ECU ground
4. Reseat the CAN cable

ECU remains in closed-loop, won't transition

• Target AFR tables are incorrect
• CL enable temp is too low
• Sensor data error
• ECU configuration

1. Verify AFR tables
2. Set the correct enable temps
3. Check sensor inputs
4. Reflash or reset config

No datalogging function

• No USB driver installed
• USB port conflict
• ECU in damaged
• USB cable bad

1. Install the correct USB drivers
2. Test with a known-good USB port
3. Power cycle ECU
4. Replace the cable if needed

ECU timing won't advance or change

• Distributor not locked ECU fighting itself
• Static timing mode on
• Wrong ignition config
• ECU has incorrect firmware loaded

1. Lock distributor at 15° BTDC
2. Verify timing settings
3. Check ignition config
4. Verify ECU firmware (killshot classic has no timing control)

ECU won't update, stuck on boot

• Power cycle during flash
• Battery voltage low
• CAN error
• Corrupt flash file

1. Reflash with the correct file
2. Ensure the battery charger is on
3. Verify the CAN cable
4. Follow the recovery flash steps

Hot start, long crank

• Heat soak on the ECU, hitting the thermal limiter
• Low voltage to coils
• Fuel boiling
• Incorrect parked air value for start-up

1. Verify underhood temps and ECU placement
2. Test coil voltage
3. Adjust fuel enrichment
4. Parked air vs ECT

Handheld shows the wrong voltage

• Poor ECU ground
• Voltage offset error
• Harness resistance
• Battery wires are too long due to relocation.

1. Confirm the ECU ground is directly connected to the battery
2. Calibrate voltage offset
3. Inspect harness
4. Use a minimum of 10-gauge wire if the battery is mounted in a truck to prevent voltage drop.

Dash tach inop

• Tach Out not connected
• Wrong tach type selected
• Bad dash input
• ECU firmware issue

1. Confirm Tach Out wired
2. Match tach type (voltage or pulse)
3. Test dash input
4. Reflash firmware and verify.