This is the Alliant Power D20494, a new pencil fuel injector, not a rebuild. It is Alliant Power’s own version of the Stanadyne 20494 and replaces John Deere AR50781. It is the pencil injector for the John Deere 3020, 4020 and 4520 tractors and the 400 Series engines in them, and it is also used on the 4000 tractor and the 6600 and 7700 combines.

These tractors were built with more than one injector. Early ones used a different, larger style of nozzle, and the 4520 used more than one pencil injector by engine serial number. A pencil injector that is worn or stuck shows up as a miss, white or black smoke, a fuel knock, hard starting or fuel wash on one cylinder. Pencil injectors for these engines look almost the same from one number to the next, but the nozzle and the opening pressure differ, so match the number stamped on the body of your old injector before you order. One injector per cylinder.

Specifications

Fits / Applications

• John Deere 3020 tractor with pencil injectors
• John Deere 4020 tractor with pencil injectors
• John Deere 4520 tractor, by engine serial number
• John Deere 4000 tractor, 6600 and 7700 combines
• Engines that use Stanadyne 20494 or John Deere AR50781. Match the number on your old injector.
• One injector per cylinder

Pencil injectors seal on the tip and at the carbon stop seal, so clean the bore, fit new seals and tighten the clamp evenly to the John Deere figure. Do not bend the body or clamp it in a vise. Fit new leak-off boots or grommets if the old ones are hard.

Part Numbers & Cross Reference

Stanadyne (genuine version) 20494  ·  John Deere AR50781  ·  Stanadyne (older number) 18767

Cross-reference numbers can change with engine serial, build year and emissions tier, so treat this list as a starting point. Send us your engine serial number and we will confirm the exact match against your build before anything ships. That check is free and takes a few minutes.

Frequently Asked Questions

Will the D20494 fit my John Deere 4020?

It fits 4020 tractors built with pencil injectors of the 20494 type. Early 4020s used a different style of injector, so send us the tractor serial number or the number on your old injector.

What numbers does the D20494 replace?

It is Alliant Power’s own new version of Stanadyne 20494, not a Stanadyne part. It replaces John Deere AR50781 and the older Stanadyne number 18767.

Does it fit every John Deere 4520?

No. The 4520 used more than one pencil injector depending on engine serial number. Call 530-668-0818 with the serial number and we will match it.

Is it new, and do I send a core back?

It is a new injector, not a rebuild, so there is no core to return.

Related Parts

• John Deere 300 Series 3.152, 3.164 & 4.219 Pencil Fuel Injector | Stanadyne 27333 New (AR89564)
• Stanadyne 02731 New DB2 Injection Pump | John Deere 4202D (AR69819)
• Stanadyne 02802 New DB2 Injection Pump | John Deere 4219D & 4219T (AR15747)
• Stanadyne DB2, DB4 & DB 310 Diesel Injection Pump Rebuild Service

Why Buy From Valley Fuel Injection

We are a diesel fuel-injection and turbocharger shop in Woodland, CA, rebuilding pumps, injectors and turbos on our own benches since 1993, not a drop-ship storefront. When you call, you talk to the people who test these units. We verify fitment against your engine serial, VIN or build date before anything ships, so the right part arrives the first time.

Not sure the injectors are the problem? We test and diagnose in-house before you buy. See our common rail injector testing and rebuild service.