It would be nice if every new cell phone and electronic device was equipped with the same charge cord. The same can be said for electronic fuel injectors. Just about the time we get comfortable with a certain injector, a new version debuts and we have to learn a new set of parameters.

This isn’t a bad deal for the repair industry – you just swap the dead injector with its intended replacement and the repair is complete. However, for performance engine builders, EFI swappers, and inveterate engine tinkerers, this ever-expanding range of fuel injectors offers both opportunity and confusion. After researching these different injectors for our own edification, we realized we could save our friends a bunch of time if we just passed along what we’ve discovered. Or, you could just listen to your brother-in-law – he knows everything, right?

This story will take an overview approach to GM fuel injectors. We will focus on all the important injector fitment specs such as overall length, O-ring sizes, and electrical connectors. We’ve even delved into adapters that will allow you to install a late model injector, for example, in an earlier truck engine, as well as info on the confusing array of electrical connectors. The connector part of this story would not be too bad if the industry could stick to one name – but with multiple names for each connector – it can get perplexing. It’s like having a friend who’s name is Bob on odd days and Fred on even days.

This injector family portrait includes four of the five popular GM fuel injectors. From left to right: original Bosch Jetronic EV1, the tall LS1 style followed by the early LS truck injector, and on the far right the late LS3 EV6 style. The one missing version is the late truck injector that is the same height as the early truck LS piece but using the EV6 electrical connector.

What you will notice is a lack of flow rate information – since this would add a cumbersome volume of material to this story. If there is sufficient demand, we can easily create a Part II and add that material along with descriptions of the differences between high and low impedance injectors and why that’s important and how to calculate flow rate with different fuel pressures.

We’ve also created a chart listing all the physical injector dimensions. Combined with the accompanying images, the chart is probably the easiest way to differentiate and make sense of all the different GM injectors.

All cathedral port LS engines use the same injector spacing which allows using aftermarket fuel rails like this Holley. We placed this Holley LS1 / LS2 fuel rail to a cathedral port TrailBlazer SS intake manifold using Z-shaped aluminum mount adapters. Aeromotive does not recommend mixing and matching fuel rails due to the possibility of a high-pressure fuel leak.

Physical Size and Connectors

We’ll start with the physical size of the injectors because through the years they have changed drastically. We’ll begin with the earliest Bosch style multi-point injectors that first appeared in the GM TPI engines around 1985. These injectors are physically the largest and tallest of all the GM injectors. These units are becoming less popular now mainly because they don’t deliver the high flow rates now demanded by today’s more powerful engines.

These Bosch injectors used a connector that is referred to by no less than three different aliases. The earliest reference is the Jetronic –the Bosch name for its early fuel injection system. This connector evolved into the Minitimer that now morphed to EV1. Right away, this becomes mystifying with three different ways to describe this electrical connector. This injector was used all the way up into the mid-2000 model-year in certain vehicles.

Next in line in terms of height is the first-generation LS1 injector. This unit is much slimmer and slightly shorter than the early Bosch injectors, taking up much less real estate. These early injectors were used in the passenger car LS1 applications and while appearing more modern, retain the EV1 or Minitimer/Jetronic connector. Unfortunately, GM didn’t carry this injector over to the trucks, choosing instead to go with an entirely different injector.

The early Gen III truck engines such as the 4.8L, 5.3L, and 6.0L LS engines spec’d a much shorter injector body that retains the upper and lower O-ring dimensions of the LS1/EV1 but is substantially shorter than the LS1 injector. Making this early truck injector unique is its Multec 2 connector. Since most aftermarket EFI systems target the more modern EV6 injectors, using the early truck injectors will often require an electrical adapter.

Getting Modern

Somewhere around the 2007 model year, the truck injectors changed again. Their height and O-ring dimensions remained the same, but the electronic connector changed to match the current LS3-style injectors using a USCAR(U.S. Council on Automotive Research) / EV6 connector. This truck injector is 0.370-inch taller than its LS3 cousin, but uses the same electrical connector.

Perhaps a bit earlier, around 2005, GM switched the passenger car injector style to the Gen IV, short LS3 style that uses the EV6 or USCAR connector. This is the shortest injector of all the factory squirters, but its size should not be confused with a lack of flow potential as these injectors can crank out the fuel.

Swapping these newer, shorter injectors, in taller intake manifold applications opens up the opportunity for aluminum extension fittings that can increase the injector length to adapt these injectors to earlier applications. For example, ICT Billet offers three different length adapters for specific applications. We’ve listed their specs in a separate chart.

Another subtle change that occurred with the Gen IV LS3 style injector is the lower O-ring diameter which increased from 0.540-inch to 0.565-inch. These larger O-rings are sometimes distinguished by color. The AC Delco versions are blue for the 0.540-inch O-rings on the top while the larger 0.565-inch bottom O-rings are red. It’s important to keep track of these things because using a set of LS3 style injectors in an earlier engine will require changing the lower O-rings to the smaller version to allow the injector to seat properly in the manifold.

The newest LS3 fuel injector uses a larger diameter lower O-ring compared to all the previous injectors. The difference is 0.025 to 0.030-inch (see chart). If you are adding an earlier injector to a later intake like an LS2 or LS3, you will need the larger diameter 0.570-inch O-rings. These O-rings are readily available. We found them for later model LS3 engines through RockAuto. The AC Delco ones are color coded with blue on the top and red on the bottom.

It should also be noted that Aeromotive warned us that they don’t recommend adapting fuel rails to different engines because of the potential for a high pressure fuel leak between the fuel injector and the rail. This warning would likely also extend to use of adapters. So the point here is to tread carefully and make sure any fuel rail or injector change you make is accomplished properly.

This is quite a bit of material to digest in one sitting but studying the information will help cut a trail across most – if not all of your fuel injector interchange questions.