cpi fuel injection systems help?

Question

gmc jimmy 4.3 vortec engine need help diagnosing fuel system known as spider or crab no fuel spray at injection nozzles

Answer 1

So is it already diagnosed? When part of the spider goes bad and you loose fuel pressure you have to replace the whole thing. It's not easy or cheap.
Good luck.

Answer 2

I own a shop, and a 4.3 that is just like yours. The fuel pressure regulator is attached to the spider, and you have to replace the whole thing @ about $400 or more. You must first test the rail pressure to make sure you have the proper PSI of 58-64 lbs. with the key on, motor not running. With the motor running it should decrease about 3-10 psi. An ohms test of the injectors should be 1.37-1.77 ohms. You should be able to hear them click with the engine running. The common problem with them is the pressure regulator will leak, and the fuel will run down into the lower half of the plenum. This whole system is under the top plenum, and is not servicable, therefore must be replaced as a unit. A noid light must be used to determine if the computer is sending fire to the injectors when you try to start the engine. You must also determine if the injectors are firing, and this is what I meant by they should click when you are cranking the engine. If the injectors are in fact firing, then you might as well go get a new spider assembly, and make sure to get new O-rings for the fuel lines where they connect to the back of the plenum. Most of the time when they go bad, you can smell gas real strong at the top of the engine, and when you remove the upper part of the plenum you will see a puddle of fuel down in the lower section. When you do this job, make sure to get both upper and lower plenum (intake) gaskets, as they don't come together in one package. Go figure? How I test the system is; I purchase a can of carburetor cleaner, remove the big hose on the air intake, spray about 3-4 seconds into the throat of the intake with the throttle wide open, remove the spray, and hit the starter. If it runs for a second or two, then the problem most definitly is the fuel supply. Then check the rail pressure, and finally make sure the injectors are firing. If all this is correct, then replace the unit, and you will be good to go. A good idea is to have a fire extingusher handy, and a big blanket that you could wet an throw over the entire engine if you had a fire flare up for whatever reason. The blanket works best as it will smother the fire out, and you should have no damage.
Part 2:
What you have is not a carb. It is a throttle body injection that has two injectors that are centered in the top of the throttle body, and all the poppet nozzles does is; directs fuel to the proper cylinder. If you remove one of the nozzles, and you have no fuel at it, but have line pressure, then are the injectors firing? You must check signal to injectors with a noid light to determine if they are in fact getting signal, ground, and reference voltage of .5 volts. The spray test determines if the computer is firing the spark plugs. By removing the connector for the injectors, and hooking a noid light to it, tells you if you have an injector problem. A faulty ground either at the battery, the wire that goes to the body/frame, and the ground strap that goes from the engine to the fire wall must all be clean, and making a good connection, or the engine won't run. I'm sure the end result will be; the spider assembly is bad, and must be replaced. The test you are looking for is outlined in my answer.
Glad to help out, Good Luck!!!

Answer 3

The PCM grounds the injector which sends pressurized fuel down to the poppet nozzles. The PCM gets the trigger for this by crank pulses from the distributor module or the crank sensor depending upon the year you have. If you also have no spark, fix this first as it won't fire the injectors until your ignition system is working.