How To Test The 'Spider' Fuel Injector Assembly (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.
   • 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).
   • 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: autotecnico-online.com).

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. Safety first -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:

• Rough idle
• Black smoke coming out of the tail pipe (when the engine is running).
• Really bad gas mileage.
• Check engine light is on with misfire codes (usually a P0300: Random Misfire) and air/fuel mixture too Rich codes (P0172, P0175).
• 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.

TEST 1: Fuel Pressure Leak Down Test

The very first test (and the most important) to do is a fuel pressure leak down test. Why?

The reason why is that the fuel system in all of the CPI and CSFI equipped Vortec engines are designed to maintain fuel pressure for a few minutes after engine shut off.

So, when the fuel pressure regulator (or a fuel injector) is leaking, the fuel pressure will drop down to 0 PSI as soon as you turn the engine off (and if this happens, then you know that you have a problem).

Therefore, very first thing you need to do is a fuel pressure leak down test with a fuel pressure gauge.

The photo above shows the Schrader valve location on the fuel rail where you'll connect your fuel pressure gauge to.

NOTE: If you don't have a fuel pressure tester, and need to buy one, see my recommendations in this section: Where To Buy A Fuel Pressure Gauge.

Alright, here are the steps:

1. 1

   Connect your fuel pressure gauge to the Schrader valve (see photo above).
   
   Before you do, place rags under and around the Schrader valve (as a safety precaution, since fuel will leak when you install the fuel pressure gauge).

2. 2

   Activate the fuel pump to pressurize the line.
   
   You can easily accomplish this by having a helper cycle the key ON and OFF a few times (without cranking the engine). Once the pressure rises on the gauge, the next step is to check for fuel leaks around the Schrader valve (it's critical that no leaks are present for the accuracy of this test).
   
   If no leaks, go on to the next step. If the gauge is leaking, you'll need to tighten it some more and recheck.

3. 3

   Now that you have verified that the fuel pressure gauge is not leaking, crank the engine.
   
   If the engine starts, have him (or her) turn it off.
   
   Observe the fuel pressure gauge's needle, as soon as you turn off the engine. You'll see one of two results:

   1. The fuel pressure gauge's needle will drop 5 PSI only and remain steady for at least one full minute.
   2. Or the fuel pressure gauge's needle will immediately drop to 0 PSI.
4. 4

   If the fuel pressure drops down to 0 PSI within seconds, then you've got a problem. In a system where the fuel pressure regulator or fuel lines are not leaking, the pressure should hold steady (not dropping to zero) for about 5 minutes.

Let's interpret the results of your fuel pressure leak down test:

CASE 1: The fuel pressure gauge's needle DID NOT drop down to 0 PSI immediately after the key was turned to the OFF position. This tells you that the fuel pressure regulator and the other components that are part of the fuel injector assembly are NOT bad.

This test is very accurate, so you don't need to remove the intake manifold plenum to visually confirm it's effectiveness and/or truthfulness! If your specific vehicle is having a rough idle problem, take a look at the following case study, since it might help your troubleshooting:

• How To Diagnose A Hard To Find Misfire Case Study (GM 4.3L, 5.0L, 5.7L)

CASE 2: The fuel pressure gauge's needle DID drop down to 0 PSI immediately after the key was turned to the OFF position. This tells you that there is something leaking inside the plenum. More than likely, it'll be the fuel pressure regulator, to make sure go to: TEST 2: Visual Inspection.

TEST 2: Visual Inspection

The following test is a test I have done every time I have gotten a failed leak down test, and it involves visually checking for fuel leaks after removing the intake manifold's plenum.

Now, you might think this test step is a little overkill but I can tell you that it has saved me a lot of time by making sure where the leak is coming from (after all, I can tell you from experience that the fuel pressure regulator is not the only thing that can leak fuel).

Alright, here are the steps:

1. 1

   After removing the upper intake manifold plenum, make sure that the ignition coil is disconnected from its electrical connector. It's important that the ignition system be disabled before continuing.

2. 2

   Now, reconnect the fuel lines to the ‘Spider’ fuel injector assembly (these had to be disconnected to remove the plenum).
   
   DO NOT RECONNECT the fuel injector's electrical connector.

3. 3

   Now have your helper pressurize the fuel system by opening and closing the ignition switch several times, but without cranking the engine, as you keep your eyes on the fuel pressure regulator and the nylon fuel lines.

4. 4

   Once the fuel lines and the fuel injector assembly have been pressurized with fuel, you'll be able to pinpoint the exact component that's leaking fuel.

Once you have identified the source of the fuel leak, the next step is to replace the part with a new one.

At the bottom of the page are my recommendations on where to buy the parts you need to replace so that you can save some money and avoid getting scalped at your local auto parts store.

Where To Buy A Fuel Pressure Gauge

You can buy a fuel pressure gauge just about anywhere. Your local auto parts store will sell you one, although at a much higher price than the one listed here on the left.

If you are in need of a fuel pressure gauge, to take advantage of the testing info in this article, the one I recommend is the: BETOOLL 0-140 PSI Fuel Pressure Tester (Amazon affiliate link). This fuel pressure gauge priced reasonably and will help you with the fuel pressure leak down test.

You don't have to spend an arm and a leg on a fuel pressure gauge:

6%

BETOOLL 0-140PSI Fuel Injector Injection Pump Pressure Tester Gauge Kit Car Tools (Master)

$32.99

50%

Innova 3640 Professional Fuel Injection Pressure Tester

$56.99

OTC 5630 Fuel Pressure Test Kit, Black

Where To Buy A CPI Spider Fuel Injector And Save

If your specific vehicle has the CPI fuel injector assembly (1992-1995 4.3L V6) and the fuel pressure regulator and/or one of the fuel injectors are leaking, you've no choice but to replace the entire thing. If you buy it from your local auto parts store, it's gonna cost around or over $300 (US) -this sucks big time!

Well, if you want/need to save some money, you can buy it here:

• AUS Injection CP-10721 Remanufactured Central Port Fuel Injector Assembly (Amazon affiliate link).
• You're also gonna' need the plenum gasket, which you can buy here: Fel-Pro MS95818 Plenum Gasket Set (Amazon affiliate link).
• If the internal supply and return lines are cracked and leaking fuel, you can buy them here: Dorman 55163 HELP! CMFI Fuel Return Line (Amazon affiliate link).

AUS Injection CP-10721 Remanufactured Central Port Fuel Injector Assembly

FEL-PRO MS 95818 Plenum Gasket Set

Dorman 55163 Central Point Fuel Injection Feed And Return Line Compatible with Select Chevrolet / GMC / Oldsmobile Models

Where To Buy The CSFI Spider Injector Components And Save

Below are the links to the fuel pressure regulator, individual fuel injectors and the upper intake (plenum) gaskets you'll need:

ACDelco GM Original Equipment 19210686 Fuel Injection Pressure Regulator Kit with Regulator and Clips

AUS Injection MP-50103 Remanufactured Fuel Injector - Chevrolet/GMC/Isuzu With 5.7L V8 Engine (Renewed)

27%

FEL-PRO MS 95816 Plenum Gasket Set

$24.55

If this info saved the day, buy me a beer!