T402742 vs T402743: What's the Real Difference Inside a Perkins 4000 Injector?

They look identical, share the same cylinder-head bore and the same solenoid plug, yet T402742 and T402743 are not interchangeable. Here is what actually changes inside, which engines each one belongs to, and how to read the nameplate so you never fit the wrong one.

If you source aftermarket fuel injectors for Perkins 4000-series engines — 4006, 4008, 4012 or 4016 — you have almost certainly seen these two part numbers next to each other. Both are Mechanical Unit Injectors (MUI), meaning each cylinder gets its own pump-nozzle assembly with no common rail. The external envelope is shared, which is why traders often list both as "universal fitment" — and why engines end up smoking or misfiring after a replacement.

1. Quick Identification

Figure 1 — T402742 (left, flow group 858-34) and T402743 (right, flow group 858-35) share the same external envelope but are calibrated differently.

2. Internal Difference: Calibration, Not Housing

The body, the cylinder-head seal, the high-pressure fuel port, the return port and the electrical connector are all the same. What changes is the fueling calibration inside, in three places:

2.1 Nozzle flow group — 858/34 vs 858/35

The suffix after 858/ is Perkins' internal flow-rating code. It governs the nozzle hole size and count, needle lift, and plunger-barrel clearance — in other words, the amount of fuel delivered per stroke. 34 and 35 are adjacent flow grades; the difference is a few percent of rated fuel, but it is enough to shift power output, smoke level and emissions calibration.

2.2 Top Woodward solenoid

T402742 uses solenoid KCCOT120A0020; T402743 uses KCCOT140A0033. The two valves have different coil resistance and flow characteristics, which matches the injector timing and fuel-map curve to the engine's calibration. Swapping the injector without matching the solenoid means the ECU can no longer command the right fuel quantity at the right timing.

2.3 Internal shims and pressure spring

The nozzle-opening pressure shim and the governing spring are selected per flow grade. They are not user-adjustable on the field.

3. Fitment Difference: Which Engine Prefix?

You cannot identify the correct injector by engine model alone (e.g. "4008"). You must read the seven-digit engine prefix stamped on the dataplate.

T402742 — official Perkins application list

• Engine prefixes: DGA, DGB, DGD, DGE, DGK, DGN
• 4006-23TAG2(A), 4006-23TAG3(A), 4006TAG1
• 4008-30TAG1, 4008-30TAG3, 4008TAG2(A)
• 4012-46TAG1(A) / TAG2(A) / TAG3(A)
• 4012-46TWG2(A), 4012-46TWG3(A)
• 4016TAG1(A), 4016TAG2(A)

T402743 — confirmed applications

• Engine prefixes: DGDF (e.g. DGDF6116 / serial U15285V)
• 4006-23TAG3A at 1500 rpm genset (typical FG Wilson / Dorman 50 Hz set)
• Matching 4008 / 4012 / 4016 builds in the same calibration family

Trade catalogs routinely label T402743 as "fits 4006 / 4008 / 4012 / 4016", but that is a marketing simplification. The authoritative answer is the engine serial number and the Perkins Build List — two engines of the same model may carry different injectors depending on build date and emissions calibration.

4. How to Order the Right One

1. Read the 7-character engine prefix from the dataplate (e.g. DGA, DGD, DGDF).
2. Read the engine serial number below the prefix.
3. Match either the injector part number directly (T402742 vs T402743) or the cross number (858/34 vs 858/35).
4. When in doubt, quote both the prefix and the serial number to your supplier — do not quote just the engine model.

5. Stocking Note for Resellers

T402742 is the higher-volume SKU in official Perkins fitment, covering most DGA-DGN prefixes. T402743 sees strong demand in 50 Hz / 1500 rpm FG Wilson and Dorman gensets (DGDF prefix). They are adjacent flow grades, not substitutes — list them as separate SKUs, not as a single "universal" line item.