Cummins · Injector Cylinder 4High

Cummins SPN 654 FMI 5: Injector Cylinder 4 Open or Low Current

SPN 654 FMI 5 (FMI 5) — Injector Cylinder 4 - Current Below Normal or Open Circuit

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Quick Answer

SPN 654 FMI 5 means Cummins ECM detected below-normal or open-circuit current on cylinder 4 injector. Expect misfire, rough idle, and possible cylinder-disable derate until continuity and injector resistance meet OEM specifications.

Overview: Cummins SPN 654 FMI 5

Open-circuit injector faults spike after valve-cover work on Cummins engines, and ProfessionalDieselRepair.com always ohms the cylinder 4 branch from ECM to injector before approving injector replacement on SPN 654 FMI 5.

Repair Snapshot

Time

2 - 5 Hours

Difficulty

Advanced

Parts Cost

$300 - $950

Dealer Labor

$800+

Tools Required

  • Cummins INSITE
  • Diesel Laptops
  • Multimeter
  • Valve Cover Gasket Kit

What SPN 654 FMI 5 Means

Cummins SPN 654 FMI 5 indicates cylinder 4 injector current below normal or an open circuit on ISX/X15 common-rail systems. Broken harness wires, corroded connectors, or open solenoid windings stop injection on cylinder 4 and can trigger misfire derates or cylinder shutdown protection.

Symptoms Drivers Notice

  • Cylinder 4 misfire with SPN 654 FMI 5 in Cummins INSITE
  • Rough idle and vibration at low RPM
  • Balance rate shows cylinder 4 not contributing fuel
  • Fault may set immediately after valve-cover removal or injector service
  • Check engine lamp with possible white exhaust at idle

Most Likely Root Causes

Broken wire in valve-cover harness

Common

Flex fatigue opens the injector circuit while the solenoid itself remains good.

Open injector solenoid winding

Common

Thermal cycles crack coil wire and produce infinite resistance at the connector.

Corroded ECM or injector connector pin

Occasional

Pin fretting creates intermittent or permanent open circuit on cylinder 4 branch.

Common Misdiagnoses (Don't Waste Parts)

Replacing injector without continuity test from ECM

Why it happens: Open circuit sounds like dead injector by default.

Do this instead: Ohm from ECM pin to injector; if open mid-harness, repair wire — classic parts-cannon injector swap avoided.

Blaming high-pressure pump for single-cylinder fault

Why it happens: Misfire feels like global fuel starvation.

Do this instead: Rail pressure normal with one dead cylinder confirms localized open circuit, not pump failure.

Master Tech Commentary

Mechanic's Notes

ProfessionalDieselRepair.com finds open-circuit SPN 654 FMI 5 on Cummins X15 most often at the valve-cover pass-through, not inside the injector. A parts-cannon injector order without continuity testing wastes a $600 part when a harness splice fixes the open.

Step-by-Step Diagnostic Procedure

  1. Step 1: Run injector diagnostic test in INSITE for cylinder 4; open circuit flags instantly if harness continuity is lost.
  2. Step 2: Measure resistance at cylinder 4 injector connector — target 0.5-1.5 ohms on many X15 solenoids; OL reading confirms open coil or wire.
  3. Step 3: Wiggle-test valve-cover harness while monitoring resistance; intermittent OL indicates broken wire inside cover.
  4. Step 4: Inspect ECM injector harness pin for cylinder 4 at the ECM connector — look for pushed-back pins or green corrosion.
  5. Step 5: Repair open circuit or replace injector, then verify peak actuator current above 10A on cylinder 4 during cranking in INSITE.

Professional service / OEM-level scan tools are recommended before clearing this fault for good.

Live Data & Freeze-Frame Tips

In Cummins INSITE, view cylinder 4 injector actuation current during cranking. Healthy circuits show a sharp current pulse; flat zero with commanded injection confirms open circuit FMI 5.

Safety Warnings

  • Depressurize fuel system before opening high-pressure lines.
  • Label connectors before valve-cover removal to avoid pin mismatch.
  • Keep contaminants out of open fuel ports.

When to Limp In vs Tow

Tow if multiple cylinders fault, idle is too rough to maintain oil pressure, or engine protection limits speed below safe traffic operation.

Prevention Tips for Fleets & Owner-Operators

  • Support valve-cover harness during cover removal.
  • Replace cover gaskets at first sign of oil on connectors.
  • Torque injector connectors fully until click.

Related Fault Codes

SPN 652 FMI 6 — Injector Solenoid Driver Circuit - Cylinder #2

Cylinder 2 low current — similar harness failure pattern.

SPN 655 FMI 6 — Injector Cylinder 5

Cylinder 5 low current — may indicate widespread harness degradation.

Frequently Asked Questions

What is Cummins SPN 654 FMI 5?

It indicates cylinder 4 injector actuator current is below normal or the circuit is open, preventing proper injection.

How do I test for an open circuit?

Measure resistance at the injector connector; OL on a good meter means open wire or coil.

Can valve-cover removal cause this?

Yes. Pinched or stretched harness wires during cover R&R commonly open injector circuits.

Will INSITE identify the cylinder?

Yes. INSITE cylinder tests and balance rates pinpoint cylinder 4 contribution loss.

Is it safe to drive?

Limited driving may be possible but causes vibration, fuel dilution, and aftertreatment stress — repair soon.

Repair harness or replace injector?

If resistance is open only at the harness segment, repair wiring; if isolated to injector body, replace injector.

More Cummins codes on this system

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