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I think your 1985 has a throttle body correct? To high a pump pressure can cause this.Is there a fuel pressure regulator on the intake? It may be or gone bad.
Fuel pressure regulator probabaly flooding it when you turn the key forward it primes but the regulator just dumps to much fuel into the cylinders flooding the plugs pull a plug out after you try starting it if it dont start and see if there full of gas
The Vortec engines were notorious for those kind of problems. The problem will be under the upper-intake manifold, and the fuel injector assembly will either have a cracked plastic fuel line running out to one or more of the fuel injectors, or the fuel pressure regulator that is located on the end of the fuel injector assembly is faulty or it has detached from the fuel injector assembly. Either way the lower intake manifold will be flooded with fuel anytime that the fuel pump runs.
There were two types made, the first type had fuel lines that connected to the lower intake manifold, and then from the metal fittings the fuel line turns into plastic and runs inside the lower intake manifold and under the upper-intake manifold where it runs over to the fuel injector assembly, and this type can really flood out an engine when it becomes faulty.
The second type had metal fuel lines running over the upper intake manifold and they connected to the top of the fuel injector assembly, however, under the upper-intake manifold there are still plastic lines to the fuel injectors and also the fuel pressure regulator that could be faulty and cause the engine to severely flood.
The upper-intake manifold is not that difficult to remove, and after you remove the upper-intake manifold then (replace the fuel lines to the fuel injector assembly if it is the second type) turn the ignition to the "Run" position and when the fuel pump runs you should see where the fuel is leaking/spraying from, and it will most likely be a large high pressure leak from a ruptured plastic fuel line.
Let me know if you require any further assistance.
Try spraying starting fluid into the air intake, with the help of someone else starting the car. As they crank over the car, spray the starting fluid into the air intake. Do this for at least 15 seconds. If the car tries to start up the fuel pump has probably gone bad. When turning the key to the on position do you hear the fuel pump humming? If the pump is not humming the fuel pump is probably bad.
yes you should be able to hear the fuel pump run for about 5 seconds once the key is turned to the on pos. check to make sure you have spark. if you do try having someone spray air intake or carb cleaner into intake manifold while you crank. If the truck starts right up for a second (or stays running as you keep spraying) Id say you have a bad fuel pump and id change the sending unit also. (First check the fuel pump fuse and fuel pump relay) GMC and Chevy are nororiously known for having bad fuel pump/sending unit problems. I have prob changed over 60 myself.
When starting any fuel injected vehicle you DO NOT need to press the gas peddle. Once the ignition is turned on the fuel pump energizes and fuel is injected into the intake.
A very common problem on the 99 S10 is a leaky fuel pressure regulator in the intake plenum.What happens is when the truck sits for a few hours or more the regulator leaks all of the fuel in the fuel injection system into the intake air plenum. This does 2 things, 1 it has no fuel pressure when starting and 2 it floods the air intake with raw fuel. Sometimes if you turn the key on wait 3 seconds then turn key off then turn key back on and just turn key to crank starter for a split second and wait 3 seconds.do this 3 times to repressurize fuel system then crank to start(you will hear fuel pump buzz each time you do this.also you may have leaky fuel injectors. Try to crank engine with the gas pedel to the floor. This will tell the computer to stop spraying fuel trhough the injectors and it will start. Joe ASE Master Tech
With the upper plenum removed and spark disabled turn on the key and allow the fuel pump to prime while watching the fuel lines from the back of the intake to the injector. I suspect you lines are leaking. Have seen this before. ALOT.
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