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Discussion Starter #1
I have a real problem with my sisters 96 S-Blazer 4.3. It will not start till you remove the cover on the air valve and pour 1/4 cup of raw gas onto the closed throttle plate. Then hook up the cover and it fires and runs like a new vehicle. It sets no codes, my reader says no old ones either. This started about a week ago on a once in a while basis. Now it is steady. Once the car sets with engine off and gets cold, it will not start. Untill you repeat the raw gas procedure. Fuel pressure is in spec and a new filter. Local shops can't figure it out either,, but they want to start replacing some very expensive pieces at the customers expense to try to find it. Help! She is driving me NUTS!!! Thanks for any suggestions,, Brother BOB
 

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Check the fuel pump relay. If it is faulty, the fuel pump won't start until the engine builds up oil pressure. Worth a try.
 

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Closely related: there should be a circuit that powers up that realy for a few seconds to allow the pump to work while starting. If it doesn't do it's job, there will be no fuel for starting but it could run fine.
 

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No start cold

When you turn the key on you should have a prime command from the ECM. You should be able to hear the pump run. What does the fuel pressure gauge show when it is cold not running? I would install the fuel pressure gauge on the cold engine and see if it shoots up your pressure when you cycle the key on. It could be bleeding back thru the pump unit over night. Cycle the key several times and see if pressure is developed.
Keep in mind also the 4.3 Vortec is noted for the injector to leak. It's a one piece design under your plenium that some call a spider.
1996 also had a service bulletin out on 4.3 W engines for no start cold in which the key could be left on for about 5 minutes and the vehicle would start. There was no pump signal, but the ECM's analog to digital processor would "warm" the ecm up by the data being read with the key on and it would start. Cure was a updated ECM.:thumbup:
 

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Discussion Starter #5
I get immediate pressure when the key is turned on. I can also hear the pump for about two seconds. I will try the key trick. I may have a different ecm to try. thanks.
 

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An engine coolant temp sensor (ECT) can cause this to happen. It's telling the ECM that the motor is still warmed up when it's not. This won't allow for the richer mixture required for a cold start. It can be faulty and still be within parameters so no code will set. Did the people checking it out access the datastream?
 
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