98Silverado621

Hi everyone,

I have a 98 Silverado k1500 with the 5.7L vortec...here's the scoop, the truck wouldnt start and i knew the fuel pump i had wasnt exactly a good brand so i bought a fuel pressure gauge to hook up to the fuel rail and give it a look over, as i expected i was only getting 40 psi to the rail.

I started by replacing the fuel pump and filter which usually solves everyone's problem and go figure, 40 psi at the rail.

After that we tore down the intake and replaced the fuel pressure regulator (more difficult than anyone needed to make it) and put it all back together with hopes that was it, and go figure again, 40 psi.

Now i have two questions, one question is when i opened the intake up, there was no vaccum line in the upper intake to even go on the fuel pressure regulator, so is there even supposed to be one?

question two, after replacing everything in the fuel system and im only still getting 40 psi does anything know what else this could even be (and yes i do have spark and my crank pos. sensor has been replaced).

does anyone know?!?!

Thanks everyone look foward to hearing from you.
Ryan

lukemoore646

no there is no vacum hose because the regulator is surrounded by vacum, that said i didn't hear you say you replaced the fuel filter, you did didn't you? also test the voltage at the pump.

JKR1040

Check fuse and/or fuel relay.

98Silverado621

yeah i replaced the filter when i replaced the pump, also the fuel pump relay which was never the issue, the pump always cycled on, but it only got 40psi to the rail, but now here is the update, i went to poor alil gas into the butterfly valve on the throttle body to get it running, so i pull the air intake back and poor, start it and it runs, now i go to put the air intake back over it, and it starts to die, i pull the pipe back away from it, it runs fine again....so just for ****s and gigles i pull the maf and the air temp sensor...and it runs smooth, and now its getting 60 psi to the pump while engine isnt running, and 50 while its running, and it will now start on its own, im not sure exactly whats going on or why the maf would affect fuel pressure while the engine wasnt running...so i have no idea, and also when i first started it when the intake sensors were still hooked up, i could punch the gas and it would bog out, when i unplugged it, i could send it right up to rev limiter just fine, i took it out on the road and it ran smooth till about 4k rpm then sputtered (my guess is bc the MAF was still unplugged)

anyone got any idea?