‘Spider’ Fuel Injector Misfire And Hydrolock (Troubleshooting Case Study)

This case study will help you to diagnose a 'Spider' fuel injector that is stuck open due to the PCM having fried and causing one of two things: A misfire condition or an engine hydrolock condition (a no-crank condition caused by gasoline filling up an entire engine cylinder).

This isn't something that happens everyday to a 'Spider' CPI or CSFI fuel injection system equipped vehicle, but it does happen enough that I thought it would be helpful to a lot of folks to write about it in this case study. Hopefully this case study will shed some light on what the symptoms are (when it does happen) and how to diagnose and repair this type of issue.

NOTE: Before I go any further, let me tell you that the info in this case study article complements the info found in the two articles below (that also deal with testing the 'Spider' fuel injection system):

1. How To Test The 'Spider' Fuel Injector Assembly (4.3L, 5.0L, 5.7L).
2. No-Start No-Fuel 'Spider' Fuel Injector Troubleshooting case study.

One last thing, the way I've organized this case study article, I'm gonna' jump into the story itself, which will detail the complaint, symptoms, diagnostic and repair solution. At the end of the case study story, I'm gonna' offer you specific safety precautions that should 'round out' what you just read.

Symptoms Of A Stuck Open 'Spider' Fuel Injector

When one of the 6 or 8 'Spider' fuel injectors stays stuck ON all of the time, you'll see the following symptoms:

1. A specific misfire diagnostic trouble code:
   • P0301: Misfire Cylinder #1
   • P0302: Misfire Cylinder #2
   • P0303: Misfire Cylinder #3
   • P0304: Misfire Cylinder #4
   • P0305: Misfire Cylinder #5
   • P0306: Misfire Cylinder #6
   • P0307: Misfire Cylinder #7
   • P0308: Misfire Cylinder #8
2. Smell of raw gasoline coming out of the tail-pipe.
3. The cylinder being affected gets filled with gasoline.
   • This condition is normally known as 'hydrolock'.
   • A hydrolocked engine will not crank over since the gasoline is preventing the piston from upward travel.

Right off the bat, I'll tell you that the most common cause of this happening is usually the PCM (Powertrain Control Module = Fuel Injection Computer) going bad.

What Vehicles Can I Apply This Info To?

Even though this is a case study of a 1997 CSFI 'Spider' equipped GM Suburban (with almost 200,000 miles), the core testing tips of this article will help you whether you have a 4.3L with CSFI or CPI 'Spider' or a V8 with CSFI 'Spider' (no matter what the year of the vehicle), if indeed this is the problem you're having with your vehicle.

For your info, these are the core differences between a CPI and CSFI system:

1. CPI 'Spider' fuel system:
   • CPI stands for: Central Port Injection.
   • The CPI system was used only on the 4.3L V6 engines from 1992 to 1995 only.
   • The 'Spider' assembly has only one fuel injector that feeds the 6 nylon fuel lines.
   • The CPI fuel injection system does not use a MAF sensor.
2. CSFI 'Spider' fuel system:
   • CSFI stands for: Central Sequential Fuel Injection.
   • This system 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 that feed 6 or 8 nylon fuel lines.
   • The CSFI system does use a MAF sensor.

The Complaint

Like a lot of folks, in this tough economy, my buddy Charles doesn't take his older vehicles to a repair shop anymore. He does most of the repairs that he possibly can himself (tune-ups, alternator replacement, starter replacement, etc.), in order to save money.

Every now and then a problem pops up, in one of his two vehicles, that gets him stumped. He doesn't give up easily though since he does a lot of research on the internet (not to mention that he has a whole library of repair manuals) and/or calls me to find answers and/or testing tips.

On this occasion, he called me on the phone and told me his 97 5.7L GMC Suburban was giving him a headache. His complaint was that the Suburban was running rough. The check engine light was on and the PCM was spitting out a P0306 diagnostic trouble code (DTC) and that he could smell raw gas coming out of the tail-pipe (when the engine was running).

He had already replaced:

1. Spark plugs.
2. Spark plug wires.
3. Distributor cap and rotor.
4. The entire 'Spider' fuel injector assembly.

...and the Suburban was still misfiring and giving a P0306 diagnostic trouble code.

Let's turn the page and find out how I diagnosed the issue to get his Suburban back on the road.