Isuzu Injection Pump 4HE1: Discerning between fine and coarse tooth gears

One of our most popular selling items is the Isuzu Injection Pump 4he1 and one of the most common problems customers have in ordering this product is knowing which pump they have -- fine tooth or coarse tooth.  The Isuzu 4he1 Injection Pump is found primarily on Isuzu NPR and NQR and in the GMC W series -- the GMC W3500 truck, the GMC W4500 truck and the GMC W5500 truck.  All of those trucks use the same Isuzu engine, but they use different ECMs (engine computers) and RPM sensors depending on whether the engine has the fine tooth gear or the coarse tooth gear.  Busbee's Truck Parts offers the Injection Pump for the Isuzu 4he1 engine for all of these trucks.

Isuzu started out with the fine tooth gear (pictured above), but found that the gears were stripping so in mid-year 1999, Isuzu swapped to the coarse tooth (pictured below).  However, discovering which injection pump you have isn't as simple as checking your model year because the engine can be made as early as January 1998 and still be called a '99.  While anything made prior to '98 definitely has a fine tooth gear and anything after '99 definitely has a coarse tooth gear, those made during '98 or '99 can go either way.  There's a huge gap in the transition period.  For those made during '98 or '99, you really need to take a look and see what you've got.  Use our photos to guide you as you evaluate your 4he1 pump and we have a video below that is also very helpful.  Isuzu used these in year models 1999 - 2004.  In 2005, they went to the Isuzu 4hk1 diesel engine which seems to be very reliable from what we've seen so far.

If you swap the whole engine and replace it with the coarse gear engine, it requires swapping several things including the ECM engine computer and the RPM sensor.

Here's a photo of both pumps with the fine on your left, the coarse on your right:

We are currently working on a video that will show you how to time the injection pump properly upon installation.  Watch for these videos here on our blog, our Facebook or our You-Tube Channel to see that video and more instructional videos in the near future.  All these videos should ease the process of ordering your Isuzu used truck parts, Isuzu NPR parts, UD parts, UD transmissions and engines, whatever it is you need from us.  It's a complicated world and we just want to make it a little easier for you.

Let us know if this was helpful to you and what other videos you'd like to see.  What has been your experience with the 4he1 Injection Pump, have you had any difficulties or any helpful hints you'd like to share?  Leave a comment, we love hearing from you.

Busbee's Truck Parts has a wide selection of used Isuzu truck parts that incorporate the Isuzu 4he1 engine.  We offer body and mechanical parts for UD Nissan, UD diesel engines, used Isuzu trucks, Isuzu NPR and Isuzu NQR, as well as GMC W3500, W4500 and W55oo trucks and parts.  For all your commercial Isuzu truck parts needs, call on Busbee's Truck Parts.

Go to www.YouTube.com/BusbeeTruckParts to view more helpful videos about Mitsubishi Fuso, Isuzu NPR, NQR and GMC W-Series trucks.