Starts fine then loads up and wont take fuel - 1989 GMC Sierra

Battery cables ! Do you know what voltage drop testing is ? Starter Voltage Drop

Have a load test done on the battery as the glo-plugs should get very hot very quickly. Diesel engines have to have a high rpm crank speed or they will not start and will leave unburnt fuel in the cylinders ( wet glo- plugs). Every indication is that the battery is flat or is not the right capacity for the car.

When you say the fuel pump relay is good did you test for power to the relay circuit ?

fuel pressure is to be at 35 to 45 psi .and has to be constant, its the only thing that will do it the MAP no it wont, the TPS no ,EGR no, IAC no, you can change fuel filter first, see if that helps other than that its a fuel pump, because it start up fine it a fuel problem, your OBD1 it doesnt store a code,

Low fuel pressure,the fuel pump is failing it cannot give correct amount needed to sustain a load higher than 2000RPM. plus you verified it when you sprayed into the intake.

So you have used the Noid lights to see if the computer is pulsing the Injectors, and you have GOOD Kv on the spartk minimum 25-30 Kv's?

Also it might get gas but how much gas? you need to perform a volume test there is a certain amount of fuel the car needs her minute to sustain demand load variations.

Is it port injection or thortle body? What engine is ? if its port injection your fuel pressure is to low , if its a throtle boty i think 15-18 is minimum to keep the car running, might have a bypassing fuel pump in the tank.

Need more info.

you need to check fuel pressure on fuel rail,you need at least 55psi of fuel pressure to fire up.check fuel pump fuse and relay or any anti theft problems

Change the filter first and see if that helps, if not, have a fuel pressure test done.
Also check all the vacuum lines for bad hoses, all it takes is a pin hole in these damn emissions systems to screw up the whole system.

Well an easy way to see if it is the fuel pump is to when its doing its thing and wont run spay some starting fluid into intake to be sure its the fuel pump..If stays running you know the answer.If problem still persists I give you other scenarios to try to fix the problem...

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_a3369546f8067589

check the timing and the catalytic converter,,,if the converter is clogged it wont run