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

MDTAHOE

There is not supposed to be a vac line. The regulator is inside a vac chamber,that's how it gets vac. Also lack of vac would increase pressure not decrease it. It is possible your gauge is not accurate. 40 psi should be enough for the engine at least idle maybe not good but still run some what. If you have fuel and spark it is possible you can not get air out,clogged exhaust. Did it die while driving?

98Silverado621

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?
<!-- / message -->

broknindarkagain

It sounds like you have a bad mass air flow sensor.

The MAF measures how dense the air the air coming into the engine is and regulates your fuel accordingly.

Replace your MAF and you should be set. Unfortunately, it will run you about 130 bucks....its not really a cheap part.

jharrisman

I have somewhat of the same issue but my truck is a 97. I am having a problem starting and so I check my fuel pressure and I was at 60psi. Does that mean I have a bad fuel pressure regulator?
I have spark and I am getting enough fuel to the engine but I am not sure if the pressure regulator is working correctly, even though I changed it a year and a half ago, what do I do?
I can get it to start but it is a hard start and when I press on the gas pedal it sputters and almost dies.

Odball

I have a 1997 Silverado Z71 with the 5.7 vortec the problem I am having is that the engine overloads on fuel when at idle and when stopped at a light in drive. thinking it is the fuel pressure regulator. Am I on the right track for this.

Jeffrey Frechette

mine has same exact problem but only 20psi of pressure and loses pressure immediatly after, will not start, cranks all day no fire unless on ether... replaced tank, pump, screen, filter, FPR. and CPS! lol still no fire and 20psi of pressure

Angel Smoyer

I'm having somewhat same issue except mine was spider injection replaced because of preventive maintenance. To prevent blowing head gasket from broken poppets like I got on 98 black gmc 4.3.
looking at throttle body position sensor and the little sensor right by it on side of throttle body. Also looking at replacing the whole sending unit the fuel pump is in.
As well as the actual connection that plugs into spider injection unit.
Mine is a 96 chevy burb 5.7 vortec so hope this gave you any ideas.
I'm sure n same boat.

Brandon Kiesel

Did you ever discover your issue? I'm getting the same thing on my 97 Yukon.

CJsluck

Try changing the cam sensor or crankshaft sensor. Both those can make your truck stall and run poorly. Also if one goes out it won't start until you do replace em. When mine was going out on my avalanche it ran rough and gas milage was terrible.