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Help me brainstorm why my 1989 GMC C2500 TBI injectors wont fire

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I thank anyone in advance for the help.

 

Ok, I'll try to fit in as much detail as possible on what I've done so far.  I have a 1989 GMC C2500 that was my old work truck.  It has a 350 with TBI.  It has not been in service for  a number of years however I have been moving it around my yard at least once a month all this time.  When I move it I always drive it around the neighborhood for little bit and generally let it sit and idle for a pretty decent amount of time also.  Last time I drove it was three weeks ago and she ran normal, strong.

 

Went to move it yesterday.  It started up normal, ran for maybe 20 seconds and died.  They way it died sounded to me like an electrical thing, not a lack of fuel.  No sputtering, just instant shut off.

 

If I pour fuel into the throttle body it will run and sound normal for a moment until the fuel is burned.  Doing this it idles normal sounding then starts sputtering until it dies. I can get one good rev that sounds normal before sputtering out.

 

- I first checked all fuses under the dash on drivers side and even put new ones in the slots labeled INJ A-B and IGN.  

- I put in a new fuel pump relay, pass side on engine side firewall and checked the fuel pump fuse that is next to the relay.  

- Fuel filter is not plugged up.  I can blow through it as easy as breathing out.

- With the fuel filter removed I get a very short dribble of fuel from the line with the key in the ON position and then the flow stops.  Turn to the START position and fuel pours out of the line.

- I removed the inbound fuel line from the back of the throttle body, routed into a plastic bottle and turned the key to start twice.  That filled the bottle half way so it seems I'm getting a decent flow to the throttle body. My understanding is this truck requires somewhere around 12psi however it appears the only way to check the pressure is if the truck is running due to the TBI setup.

- Removed the top half of the TBI injector thing, turned the key to start and fuel started filling into the exposed passages but at a rate slower than what I would have expected.  The fuel pressure regulator inside the TBI I think looks OK.  Honestly not sure what it is supposed to look like but, the spring was hard to compress, the little metal piece that pivots on the diaphragm moved freely and the gasket looked ok.  When the fuel pressure regulator is assembled I tried pushing on the opening at the bottom with a screw driver and it didn't seem to move.  Again, I'm not sure how this part works.  

- Touched a 9v battery to the two pins on top of the injectors and can hear them click loud and clear.

- My test light registers voltage to one side of the injector wire plugs with the key in the on position.  I do not own a noid light at this point.

- When trying to start a tiny dribble of fuel comes out the injectors, measured in drops.  Very small amount.

- When I pour fuel into the throttle body and the truck is running the injectors dribble fuel, a hair more then when trying to start but still a dribble measured in drops.

- Tried tapping the injectors while running, no change.

- I found this connector (picture below) not plugged into anything, it looks factory for sure, but looking everywhere I can see and feel for going in both from the top and under the truck I can't find what it is supposed to be plugged into.  It comes out of the wiring harness on the firewall behind the distributor and based on it's short reach and location whatever it is supposed to plug into seems like it should be very close to the distributor.  It is a single female plug of some kind.  I also find it possible but not probable that it would simply pop off its connection all by its self because the plug is not broken and the clip on it looks solid.  

 

So I'm getting fuel to the throttle body in a unknown but decent amount.  I get dribbles from the injectors when trying to start or running but they won't fire normally.  I don't know where to go from here and hope someone might be able to help.  

 

Thank you again, the picture of the plug:

 

IMG_20150819_141516.jpg

 

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its possible the fuel pump has failed............. once they go they just drop pressure and will not supply the required psi that the injectors need to operate properly. happened to my wife while driving 65mph on the highway...........no warning at all.

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Update.

 

Just tested with a noid light and the injectors are receiving a proper signal.  I'm starting to lean towards the fuel pump but that loose wire connection has me concerned.  I'm a cheap bastard and dont want to go through the trouble of dropping the fuel tank and the money for a new pump if that wire is the issue.

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I am with ya, sometimes bitting the bullet and paying a dealership or very good mechanic to do a "diagnosis" (mine charges $95) to get to the problem is worth it.....................

 

Last time I had an issue the diagnosis found a bad $53 part (electronic) ................... I never would have found the problem..............

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I am with ya, sometimes bitting the bullet and paying a dealership or very good mechanic to do a "diagnosis" (mine charges $95) to get to the problem is worth it.....................

 

Last time I had an issue the diagnosis found a bad $53 part (electronic) ................... I never would have found the problem..............

 

Yep. Not only do they have equipment most of us don't have, they may have previous experience with the same issue on the same type vehicle. My Dakota started randomly eating #2 O2 sensors, and I was getting a lot of use out of my various "sonofabitch tools" trying to figure out why. I finally went to a mechanic that does a lot of work on Chrysler products, and he immediately knew the cause. It turns out there is a small pressure switch behind the power steering pump that tends to develop a small slow leak, and when it happens it leaks just enough fluid right into the wiring harness in just the right place to cause random and intermittent shorts to, you guessed it, the #2 O2 sensor. I may never have found that on my own.

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