I have a 92 Astro Van with the 4.3 liter CPI engine that is only firing on three cylinders. This malfunction occurred upon starting the vehicle, after it had set a while from a short trip. The three cylinders that are not firing are all on the passenger side of the motor. I replaced the spark plugs on this side, after measuring the resistance across these plugs, and finding it to be 250K ohms or less. I also check the compress on these three cylinders, and they were within the specified range. Replacing the spark plugs did not fix the no fire problem.

If I disconnect the spark plugs from the distributor for the three driver side cylinders, that do fire normally, and hold the accelerator to the floor while attempting to start the engine. The passenger side cylinders fire, with the motor running very rough, as long as one holds the throttle near the wide open position. I’ve check the fuel pressure at the connection just outside the intake manifold, with it reading 65 PSI. When the ignition switch is turned to the off position, the reading drops to zero within a couple of seconds. Has anyone seen this kind of motor failure problem before? If so, do you know what caused it? Any suggests for what to test next would be appreciated.

I suspect it’s the fuel injector spider, but can’t explain why the malfunction of that device effects only the three cylinders on the passenger side, and not the other three cylinders.

 

Sounds like the classic FPR failure... Pop off the MTV (~3" round piece under the VORTEC cover on top of the engine) and have a look down inside. If you see pools of fuel, then you have a leak. Next, pull off the upper plenum and find the source of the leak. You can do this by pressurizing the system with the plenum off. Track it down and replace what is necessary. One thing that may have to be replaced just because of the work being done is the internal fuel lines, commonly referred to as the nut kit. These lines are typically installed only once and cannot be reinstalled without a high probability of leaks.

Hope this helps! Good luck!

 

Thanks much Kyle for your helpful suggestions and info on the nut kit. I’ll post the results of looking for a fuel leak, via the MTV hole, and keep you posted on how it all turns out.

 

I removed the Manifold Tuning Valve (MTV), as suggested by Kyle, to get a peek inside the intake manifold. With the aid of a mirror and a flashlight, I could see that fuel was leaking from somewhere inside the manifold. Removing the manifold revealed that the fuel pressure regulator had sprung a major leak, see pictures below. The regulator, which is located on the side of the fuel injector spider, was replaced with a new one without removing the spider from the manifold. I checked for leaks, by turning the ignition to the run position, which pressurizes the fuel rail at 66 PSI. With the ignition in the off position, the pressure held steady at 58 PSI, which meant there were no leaks at either the regulator, or the fuel injector valve. The manifold was reinstalled. The engine is now running normally again.



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WOW! With a leak like that you definitely want to do an oil change! Glad you were able to get it all fixed back up!!

 

Yes, I had lots of fuel in the oil. The oil pressure gage had a very low reading at idle, much lower than normal. I replaced the oil before driving the vehicle very far. Replacing the oil brought the pressure back up to normal at idle. This motor only has 238,000 miles on it.

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I know this was posted a while back, but I'd really like to see those pictures. How do I work with those images so I can see them?

 

Should be a few other threads with pictures that are still here. Unless the poster above still has a copy, the pictures are gone.