No Start - No Fuel 'Spider' Fuel Injector Troubleshooting Case Study

The most common type of failure in the CPI 'Spider' fuel injector system is usually fuel leaks (inside the intake manifold plenum).

But, every now and then, instead of leaking fuel, the 'Spider' fuel injector assembly won't spray any fuel into the engine cylinders.

When this happens, you'll see one of the following:

1. One or two (at the most) cylinders are affected.
   • This leads to a misfire condition and usually specific cylinder misfire trouble codes.
2. The entire 'Spider' assembly stops injecting fuel.
   • When this happens, the vehicle cranks but doesn't start.

In this article, we'll take a look at this phenomenon (no fuel being injected in one or several nylon fuel lines) and how to test it, via a real life case study of a reader of troubleshootmyvehicle. Com who was kind enough to share his diagnostic and repair experience with us (thanks Jim M.!).

What Vehicles Can I Apply This Info To?

Although this case study is about a 1995 4.3L GMC Jimmy, the info and tests in this article apply to all of the 'Spider' injector types on the road, whether it's a 6 or an 8 cylinder.

Now, in case you was wondering:

1. CPI 'Spider' Fuel System:
   • CPI stands for: Central Port Injection.
   • This system was used on the 4.3L engines from 1992 to 1995 only.
   • The 'Spider' assembly has only one fuel injector that feeds the 6 nylon fuel lines.
2. CSFI 'Spider' Fuel System:
   • CSFI stands for: Central Sequential Fuel Injection.
   • This system is used on all 4.3L, 5.0L, and 5.7L engines from 1996 to present.
   • This 'Spider' assembly has either 6 or 8 individual fuel injectors which feed 6 or 8 nylon fuel lines.

Again, even though this case study is about a 1997 4.3L GMC Jimmy with a CPI 'Spider' system, you can still apply the core test steps to the CSFI 'Spider' system.

The Complaint

Jim initially used the following article: How To Test The 'Spider' Fuel Injector Assembly (4.3L, 5.0L, 5.7L) to test his 'Spider' fuel system.

But, that article only covers testing the 'Spider' assembly for fuel leaks and Jim's Jimmy didn't have any, so he emailed me:

Last spring my fuel lines sprung a leak on a 1995 Jimmy. The Jimmy was running at the time. So I waited till October to replace them.

After replacing them the Jimmy wouldn't start. It turned over really good though. I replaced the fuel pump, fuel regulator, fuel filter, fuel lines and checked for power at the relay, which it is getting. The meter shows 11.6 Volts for 2 seconds.

I checked the spider connector with a Noid light, which shows power going there: it flashes as the Jimmy is turning over. I checked the fuel pressure at the valve and it shows 60 lbs. Of pressure. I'm assuming the oil pressure switch is still good since the oil pressure gauge goes to normal pressures while turning the Jimmy over.

Everything seems to be pointing to the spider; gummed up from sitting all summer? Is there anyway to check the spider or can it be rebuilt by me?

Now, in case you're in a hurry and need to know now what the solution was, Jim replaced the 'Spider' assembly (you can read his last post here: Repair And Solution). The one on his Jimmy wasn't spraying fuel into the cylinders even though it was getting an activation signal from the PCM (Powertrain Control Module = Fuel Injection Computer).

Now, since this is an issue that I've seen before and other readers have reported similar problems, in the next headings and pages, I'm gonna' dissect Jim's diagnostic and repair experience. So if you're facing a similar situation, you'll know what to look for and what to test.

From the above email, we can see the following:

1. Fuel pressure test showed that:
   • No internal leaks were present, since the pressure did not leak down.
   • Fuel pressure was normal at 60 PSI.
   • Since no leaks were present and pressure was normal, then the fuel pressure regulator is OK.
2. Noid light test showed that:
   • The PCM was indeed trying to activate the injector.
   • This indirectly confirms that the crank sensor is OK, since without a Crank Sensor Signal, the PCM will not activate the fuel injectors.
3. Ignition coil and ignition module were good:
   • We can assume the ignition module and ignition coil were good since Jim did not report any lack of spark.

Let's turn the page and see what advice I sent Jim and what he did to find out that the CPI 'Spider' assembly was bad and needed to be replaced.

The Test To Find The 'Spider' Problem

When I read Jim's e-mail, I knew the next step (for him) was to see if the 'Spider' injector assembly was injecting fuel.

This is what I e-mailed him back:

There is a way to see if the spider fuel injectors are clogged and not spraying and I have done it several times but this is not a test for everyone. This method is used at the shop were I work quite a bit, and it's done by taking several important safety precautions. This is the test:

1. Remove the plenum.
2. Reconnect the metal fuel lines to the spider assembly (if you disconnected them).
3. Disconnect the ignition coil's and ignition module's electrical connector -THIS IS CRITICAL- do not proceed without doing this.
4. Pull one fuel injector from its cavity in the intake manifold.
5. Have a helper crank the engine while you observe the fuel injector. If it's not clogged, it will spray fuel. You should have a rag somewhere between it and the engine so that the fuel sprayed will not spray all over the engine.
6. Repeat this test on the remaining injectors (nylon fuel lines).

Now, you need to make sure that nothing falls into the open ports in the intake manifold, 'cause the only way to fish anything that falls into to them is to remove the cylinder head.

This test works to check them, now having said that, it's a bit risky for the reasons mentioned above. So if you try it, take all necessary safety precautions. Your safety is your responsibility and I offer this test only as advice and as an opinion and therefore assume no liability.

If you do find they are clogged, the only viable option is to replace the whole assembly once again.

The steps to see if the 'Spider' is actually injecting fuel are pretty straightforward and in the reply to Jim (above), the steps are pretty much self-explanatory but I'm gonna' add some more thoughts on the subject.

Here are the main points of the steps listed above:

1. Remove the upper intake manifold plenum.
2. Disable the ignition system (ignition coil and ignition control module).
3. Reconnect the 'Spiders' injector's electrical connector.
4. Remove one and only one fuel injector nylon tube from its place on the intake manifold.
5. Have helper crank the engine to see if the nylon fuel line sprays fuel.
6. Once you've verified if the injector is spraying or not, RE-INSTALL the injector back into its cavity (in the intake manifold) and proceed to the next one.

It's a pretty simple test, although I can't claim that it's easy to do (since quite a few things have to be removed to do it) AND you have to keep in mind the following important safety precautions:

1. Prevent objects from falling into the lower intake manifold.
   • Since the upper plenum has to be removed (for this test), this opens up the possibility of something falling into the open lower intake manifold ports.
   • If something does fall into them, it'll usually end up inside the engine cylinder and usually the only way to retrieve it is by removing the cylinder heads.
2. Fuel is extremely flammable.
   • You need to have the nylon fuel line pointing to a rag (shop towel). The shop towel's job is to get hit by the fuel being sprayed and keep the fuel from soaking the intake or the valve covers.
   • You need to test them one at a time.
3. Disable the ignition system.
   • This will prevent spark from reaching the spark plugs and causing a back-fire thru' the intake manifold.

As you see/read above, this test does have some inherent risks which are fire and engine damage (if something falls into the open intake ports without your knowledge and you crank the engine). These can be overcome with a few precautions but the risks remain. So you might be asking yourself: Is this the only way to test for a clogged 'Spider' assembly?

The answer is: No, this is not the only way to do it. The above test works (I personally have done this test several times as have my fellow techs at work and well, Jim did it too without any dire consequences). But, this method might not be your 'cup of tea'. In this case, there is a different method and it involves using a fuel pressure gauge and the OTC 3398 Fuel Injection Pulse Tester:

Why didn't I recommend this other way in the first place? These are the main reasons:

1. You might not have the tools.
2. The tools are expensive.
3. You're an experienced 'wrench-er' and have removed the intake plenum before and are comfortable working around and in the engine.

Let's turn the page and find out about the second method.

Using A Fuel Injector Pulse Tester

Using a Fuel Injector Pulse Tester is the safest way to see if the entire assembly is bad on the CPI 'Spider' system (this is because this assembly only has one fuel injector solenoid inside).

Although on the CSFI 'Spider' type, you've got 6 or 8 separate fuel injectors, you're still able to test each one with the Fuel Injector Pulse Tester.

How does the Fuel Injector Pulse Tester work? The purpose of the tester is to pulse the fuel injector independent of the vehicle's PCM. In plain English, this is how it's done:

1. You connect a fuel pressure gauge to the fuel rail and activate the fuel pump.
2. You manually activate the tester to supply power and an activation pulse to the fuel injector.
   • Since the tester provides the power and activation signal, there's no need for you to crank the engine.
   • The Fuel Injector Pulse Tester has two big alligator clips you connect to your vehicle's battery. This is how the tester gets power and provides power to the fuel injector you're testing.
   • The tester has a fuel injector connector that you use to connect to the injector you want to test. In case the tester's connector doesn't fit the particular injectors on your vehicle, the tester comes with a dedicated jumper wire so that you can 'rig' up the connection.
3. When the fuel injector gets these two signals (from the tester), it has to inject fuel.
4. Injecting fuel will cause the fuel pressure value registered on the fuel pressure gauge to drop.
5. Seeing this drop or lack of a drop in fuel pressure let's you know if the 'Spider' assembly on the CPI is fried or not (this is because the CPI system uses only one fuel injector solenoid within the assembly to feed all of the cylinders -via the nylon fuel lines).
   • On the CSFI system, you'll need to test each fuel injector solenoid within the assembly.

Like anything in life, using a Fuel Injector Pulse Tester has advantages and disadvantages.

Let me start out with the advantages:

1. This method is safe. No worries about engine damage and the risk of fire is minimized a lot.
2. This is the most professional way of testing to see if the 'Spider' fuel injector assembly is injecting fuel or not.

Here are the disadvantages:

1. This method is not 100% effective.
   • On the CPI system, you can't test each individual cylinder's nylon fuel line.
2. The tester isn't cheap.
3. You need to use a fuel pressure gauge.
4. The Fuel Injector Pulse Tester's connector does not fit the 'Spider' connectors for the CPI and CSFI. You'll need to rig it up somehow.

Repair And Solution

In conclusion, this is what Jim did to finally get the problem solved:

Solved. I put the new spider in and it fired right up. I never thought that would be it since the old one is only 2-3 years old.

I checked the Ohms on the new one which was identical to the old one so I'm assuming it wasn't an electrical failure. Maybe it was mechanical. I plan to dissect the old one just to see if I can figure out why it failed. Thanks for all your help.

Hopefully this case study of Jim's diagnostic and repair experience helps you. If there's any advice you'd like to add or want to contribute your own diagnostic and repair experience, you can use the contact form below: