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.
    1. This leads to a Misfire condition and usually specific cylinder Misfire trouble codes.
  2. The entire ‘Spider’ assembly stops injecting fuel.
    1. 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:
    1. CPI stands for: Central Port Injection.
    2. This system was used on the 4.3L engines from 1992 to 1995 only.
    3. The ‘Spider’ assembly has only one fuel injector that feeds the 6 nylon fuel lines.
  2. CSFI ‘Spider’ Fuel System:
    1. CSFI stands for: Central Sequential Fuel Injection.
    2. This system used on all 4.3L, 5.0L, and 5.7L engines from 1996 to present.
    3. 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 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 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 that 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:
    1. No internal leaks were present, since the pressure did not leak down.
    2. Fuel pressure was normal at 60 PSI.
    3. Since no leaks were present and pressure was normal, then the fuel pressure regulator is OK.
  2. Noid light test showed that:
    1. The PCM was indeed trying to activate the injector.
    2. 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:
    1. 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...