Volume & Flow Test

Volume & Flow (Bottle Test)

Prove pump volume with a real measurement, not a guess. If the pump cannot deliver clean, steady fuel volume, the rest of the fuel system is just noise.

Goal: Prove pump volume with a real measurement, not a guess. If the pump cannot deliver clean, steady fuel volume, the rest of the fuel system is just noise.
Use this test when you suspect starvation under load, weird pump tone, lean spikes, or a “prime but no fuel” situation.
Open Fuel Troubleshooting Hub -> Open QC Fuel ->

Safety first: Fuel System Safety Guide

Safety: Fuel vapors and sparks do not negotiate. Work ventilated, no smoking, no grinders, no hot bulbs. Keep a real extinguisher within reach and catch fuel in a stable container.

What This Test Solves

  • Lean spikes under throttle
  • Sudden fuel cut under load
  • Pump primes but the engine still starves
  • Suspected clogged inlet sock or main filter
  • Weird pump noise or tone change
  • Long crank / no fire

This is also your baseline before you start messing with regulators, return lines, or injector sizing. If it fails, fix flow first.

Quick-Start Bottle Test

  1. Kill ignition power. You want pump only. Do not crank the engine during the test.
  2. Disconnect the feed line at the engine.
    EFI Rail feed or filter outlet.
    Carb Carb inlet.
  3. Aim the line into a clear, marked container. A 1-quart bottle or marked jug works best.
  4. Run the pump for exactly 5 seconds. Time it. Do not guess.
  5. Read both amount and quality.
    • Bubbles = restriction, pickup issue, cracked hose in tank, or low fuel uncovering the pickup.
    • Surging output = cavitation, clogged inlet, weak pump, or vent/return problem.
    • Slow trickle = starving pump, clogged filter, blocked vent, collapsing hose, voltage drop.
Hard rule: If it fails the bottle test, stop chasing sensors, tune, or ECU logic. Fix the flow first.

Deep-Dive Bottle Test

Tools You Need

  • Clear 1-quart bottle or marked container
  • Fused jumper lead
  • Basic hand tools for fittings
  • Safety glasses and gloves
  • Rags and catch pan
  • Class B/C extinguisher within arm’s reach

Step 1 – Pick the Test Point

You want to measure pump output close to the engine, before injectors or carb circuits become the restriction.

  • EFI Return-Style Filter outlet or main rail feed
  • TBI Throttle-body feed line
  • Carb Electric Carb inlet or pre-regulator line
  • Carb Mechanical Between pump outlet and carb

Step 2 – Run the Pump Continuously

Do not rely on short ECU prime timers. You want steady pump run for the capture window.

  • Use a factory pump test pin if available.
  • Jump a standard relay: pin 30 to pin 87.
  • As a last resort, power the pump directly with a fused lead and a known-good ground.

Relay logic and bypass: QC 2 – 4-Pin Relay Test (then use QTS: Relay Bypass if you need deeper proof).

Step 3 – Capture the Flow

  1. Aim the feed line into the container (stable, cannot tip).
  2. Run the pump for exactly 5 seconds.
  3. Shut it off and record the volume.

Step 4 – Read the Results

EFI Electric Pumps (typical aftermarket range)

  • Expected: roughly 0.5 to 1.0 liter in 5 seconds at good voltage (varies by pump, filter, and line size).

Fail patterns:

  • Low volume = restriction, weak pump, clogged sock/filter, voltage drop, bad ground.
  • Foamy stream = pickup sucking air, split hose in tank, loose clamp, low fuel level.
  • Surging = cavitation, blocked inlet, return restriction, or vent problem.

Carb Mechanical Pumps

  • Expected: steady pulsing stream, roughly 6 to 10 oz in 5 seconds (varies by pump and cam speed).
  • Weak pulses = tired pump, worn eccentric, inlet restriction.
  • Bubbles = suction leak, boiling fuel, pickup issues.

Carb Electric Pumps (street style)

  • Expected: strong uninterrupted stream, often 0.2 to 0.4 liter in 5 seconds for common street pumps.
  • Tone changes = cavitation, blocked inlet, or vent/return problems.
  • Output drops after a few seconds = starving pump, restriction, heat soak.

Return-Side Check (EFI/TBI)

Once you know feed volume, verify the regulator and return are not choking the system.

  1. Reconnect the feed line.
  2. Move your capture point to the return line headed back to the tank.
  3. Run the pump for 5 seconds and capture return flow.

Rule of thumb: return volume should be within about 10 to 15 percent of feed volume at the same voltage. If return is way lower, suspect return restriction or regulator issues.

Return/regulator tests: QC 7 – Return-Style System Check and Fuel Pressure Regulator Function.

Voltage Reality Check

Real life is not always 13.8V. Cranking voltage can drop into the 10.5 to 11.5V range.

  • Repeat the bottle test during a cranking-voltage condition (or controlled lower voltage).
  • If volume falls hard with small voltage drop, you have wiring/ground/relay losses.

Use: QC 3 – Voltage Drop Under Load and Fuel Pump Voltage Sensitivity.

Common Failure Modes This Exposes

  • Clogged sock or pre-filter starving the pump
  • Main filter plugged from rust/varnish
  • Dying pump that still makes noise but cannot move volume
  • Voltage starvation through bad grounds, thin wire, or a weak relay
  • Collapsing rubber line on the suction side
  • Blocked tank vent causing vacuum lock
  • Split pickup hose inside the tank (half fuel, half air)
  • Return-side restriction making the pump fight itself

Vent test: QTS: Fuel Tank Vent / Vacuum Lock Test

Where This Fits in QC Fuel

Bottle test is volume proof. Pair it with pressure and electrical proof when you need closure:

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