Need Help! 1990 Gmc Sierra Sl

[thapoet1]

Hi everyone,

I'm new to this forum so please bare with me.

OK, I've got a 1990 GMC Sierra SL. I picked it up from an old friend a few weeks ago. Ran good for first week, now I've got issues.

 

First, everything thats been replaced:

Map Sensor, rotor, vacuum lines, fuel pump (is 2 years old), and upgraded fuel pump harness, thermostat, fuel filter, fuel pump relay switch.

As I stated above, I'm getting fuel to the intake, pulled the #1 plug and found good compression, used a screwdriver to check fire from plug wire (got fire)...

I also reset the ECM by disconnecting negative battery terminal for 30 mins.

 

From my own "tinkering, I've found that the truck will start briefly (although very rough idle) and only runs for a few seconds then kills. Also, if I unplug the vac line to the map sensor and plug the line, i can achieve ignition and engine runs very smooth for about 10-15 seconds then abruptly dies and backfires air from the top of carborator assembly.

 

I may have missed some details, so please ask. IF ANYONE can help, please respond.It is not only my work truck, but also my family's only means of transportation at the moment.

 

 

Thanks,

 

MJ

[98 Z71 SLT]

Sounds like it is starved for fuel.

 

Take a small cup, fill it with gasoline. Have somebody start the engine, then with it running, SLOWLY pour the cup of gasoline on the butterflies of the throttle body.

 

If the engine stays running and smooths up a bit, you got a bad fuel pump. Being replaced 2 years ago means nothing.

 

Also...how old is the fuel filter??

[93Sierra]

sounds like not enough fuel pressure,.....can you get a borrow a fuel pressure gauge and test it?

[thapoet1]

i think so. what should the presure be? and what would i replace in order to fix it? the regulator?

thanks for your response.

sounds like not enough fuel pressure,.....can you get a borrow a fuel pressure gauge and test it?

[thapoet1]

the filter is about 2 months old and i here the fuel pump whining for about 3 seconds when the key is turned to the on position.oh, i almost forgot, it also smells like its burning a little rich too...

Sounds like it is starved for fuel.

 

Take a small cup, fill it with gasoline. Have somebody start the engine, then with it running, SLOWLY pour the cup of gasoline on the butterflies of the throttle body.

 

If the engine stays running and smooths up a bit, you got a bad fuel pump. Being replaced 2 years ago means nothing.

 

Also...how old is the fuel filter??