How To Test A Leaking ‘Spider’ Fuel Injector Assembly (GM 4.3L, 5.0L, 5.7L)

Testing a leaking ‘Spider’ fuel injector assembly or a leaking fuel pressure regulator (GM 4.3L, 5.0L, or 5.7L ) can seem impossible, since both of these bad boys are located inside the intake manifold's plenum but they can be tested and it's far easier than you think. In this article I'll show you how.

At the end of the article, I've made some recommendations on where you can buy a CPI ‘Spider’ fuel injector assembly and CSFI individual components that will save you a lot of money!

One last thing, this article will help you to find a leak in the ‘Spider’ assembly, I've written two other articles that cover two other possible problems with the ‘Spider’ assembly:

  1. No Start - No Fuel ‘Spider’ Fuel Injector Troubleshooting Case Study.
    1. This case study will help you diagnose a No Start No Fuel Condition with the ‘Spider’ injector.
  2. ‘Spider’ Fuel Injector Misfire and Hydrolock (Troubleshooting Case Study).
    1. This case study will help you diagnose a fuel injector (within the ‘Spider’) that's stuck open and causing a Hydrolock condition.

You can find this tutorial in Spanish here: Cómo Probar los Inyectores y Regulador de Combustible (GM 4.3L, 5.0L, 5.7L) (at:

Important Tips And Suggestions

TIP 1: You'll need a fuel pressure gauge to troubleshoot the fuel injector assembly on your GM 4.3L, 5.0L or 5.7L pick up (van, mini-van, SUV).

TIP 2: You'll be working around fuel (gasoline), which is extremely flammable. Your safety is your responsibility... so be careful, use common sense and think and act safety all of the time.

TIP 3: This article will only show you how to test the fuel injector assembly (of which the fuel injectors and fuel pressure regulator are a part of)... there is no ‘Remove and Replace’ instructions. I recommend buying a repair manual for these instructions.

TIP 4: To test the Spider fuel injector assembly, you do not need to remove the intake manifold's plenum. The photo I'm using, in this article, shows the Plenum off just to make it easier to explain the test.

‘Spider’ Fuel Injection Basics

There are two types of the ‘Spider’ fuel injector assemblies used on the GM 4.3L, 5.0L, 5.7L engines and this article will help you with both types.

In case you're wondering... one type belongs to the Central Port Injection (CPI) system and the other to the Central Sequential Fuel Injection (CSFI) system.

How can you tell them apart? Well, in a nutshell, the CPI system does not use a Mass Air Flow (MAF) sensor and the intake manifold plenum is aluminum metal and was used from 1992-1995 on the 4.3L V6 engines only. The CSFI does use a MAF sensor and the plenum is plastic and was used from 1996 on up on the 4.3L, 5.0L and 5.7L engines.

Also, when anything fails in the CPI type system... you have to replace the entire fuel injector assembly. In the CSFI system, all parts can be replaced individually.

The cool thing is that you don't have to crack anything open to find out if anything is leaking inside, you can do a simple fuel pressure leak down test and based on the results of this test... you'll know if something is wrong with the ‘Spider’ fuel injector assembly (of either type).

Symptoms Of A BAD ‘Spider’ Fuel Injector Assembly

The most common type of failure (related to the ‘Spider’ fuel injector) is usually not the assembly itself going BAD, but the fuel pressure regulator going BAD.

The fuel pressure regulator is infamous for leaking fuel from its vacuum inlet nipple. When this happens, the engine can suffer backfire explosions (in the plenum due to the leaking fuel) that catch the nylon plastic fuel injector lines on fire. The end result is more fuel leaking into the intake manifold and causing some of the following symptoms:

  1. Rough idle
  2. Black smoke coming out of the tail pipe (when the engine is running).
  3. Really BAD gas mileage.
  4. Check engine light is on with misfire codes (usually a P0300: Random Misfire) and Air/Fuel Mixture too Rich Codes (P0172, P0175).
  5. Hard start, extended cranking time and possible No Start Condition.

OK, the very first test you'll need to do, to get to the bottom of the issue, is to do a fuel pressure leak down test.... let's turn the page and find out more...