[thegawd]

98 Sierra RWD, 5.7

the truck wont start immediately, if i prime the pump by turning the key on n off like 15 times it will start on the 2nd try and run strong. it will continue to start and run fine as long as it dosent sit for a few hours. Im assuming with these symptoms and lack of codes and since the truck runs perfectly that the fuel pressure regulator is screwed.

Now I have watched the video below from 1a auto... its a great start to finish video except they dont actually replace it with a new one. The recommend replacing the upper intake gasket as a part of the process... of course, good idea. they didnt really clean anything besides the upper intake gasket surface.

I havent been inside a 350 since i was in high school... when I completely rebuilt one of these engines with a team of my classmates. It was a vortec and brand spanking new... it ran great! hahah anyways I dont really have much experience with the fuel system.

SOOOOO my question(s)...

Can any part of the vacume system cause a fpr problem? I see there is a vacume line running to it... I have some sort of leak on top of the motor... its been bandaided back together and I havent even looked into it.... it dosent seem to cause any problems besides a hiss... Ill take a pic of this line in a bit... I dont think its a vacume line.

what else should be done during this procedure.... Im thinking shave the butterfly valve, clean clean clean whatever may be under the intake. how can this be done properly and with what? Im debating on starting this today but probably wont... waiting for some feed back. HAHA

have a goodd one and Thanks Guys!

Al

 

[kennythewelder]

Have you run a fuel pressure test Al ? How old is your fuel pump? You know these pumps get week as they get old, and the pressure drops, making the truck hard to start. I think mine is just starting to do the same thing. Have you tried putting a little gas in the throttle body, and will it fire rite up then ? I think I am on my forth pump in my truck, and I can see number 5 coming . These pumps just don,t hold up. I don't care what brand you use, they just get week in time and make the truck hard to start. I have never had an issue with the fuel pressure regulator, not to say you can't though. As for changing it, it is inside the intake, so all you need to do is pull the top half of the intake to get at it.

 

[thegawd]

No I havent run a FP test yet, I dont have the tools. The age of the pump is unknown. I might actually be able to put a FPTester together, I have some stuff Ill dig up if need be. Not having any other FP problems I dont think it wold be the pump, no backfires or anything like that. but then again I dont have any experience with fuel pumps, or fuel delivery problems thus far on any of my trucks so I dont know, It could be the pump.

I havent bothered troubleshooting anything yet at all Kenny. Just prime the pump by turning the key so no i havent put any fuel in the intake at all.

 

[kennythewelder]

The first time my pump went out, it just quit. The truck would not run at all. The second time was very hard to figure out. I had no issues at all, ecept the truck was hard to start, but only after it sat over night or longer. Also at wide open throttle it would loose power above 3500 RPMs. I was so fustrared with it, I was about to sale the truck. After a lot of rearch, I got a tester from Auto Zone and ran a fuel pressure test. 52 PSI pre start. Man if you dont have over 60 PSI, these trucks are hard to start. After replacing the pump, all the issues went away. So when you first get in the truck, and you turn on the key, you need about 62 or 63 PSI before you crank the engine. Once it starts, the pressure will drop some, into the 50s.

 

[kennythewelder]

Also it is the impella that wares and looses it close toleraance. This makes less pressure. As long as the electric pump is working, anyway.

 

[Zach Smith]

I'm with ktw all the way here. Also, assuming this is vortec, If you do end up having to pull the intake, shaving the baffle off the throttle plate and shaving the tplate bar is helpful. You can use brake clean or something like perl solvent (stuff for parts cleaners), both work fine, come to think of it...I've used b12 also and had no issues...just don't use (physically) harsh abrasives... Except maybe some emery cloth or soft brush where necessary. You might as well swap injection rack while you are in there...run the upgraded unit...that's about it for that area, unless you wanted to do some emissions deletes...
Edit, almost forgot...if you shave baffle, you need to replug two holes you opened up when rivets came off...they are the outer two, the inner one is metered air.

 

[kennythewelder]

Just cut the curved part off at the throttle plate and leave what is on the throttle plate it self alone (like in the video I posted in the past ) and you will be good on idle. Thats how I did mine.

 

[kennythewelder]

Here is the video. Remember it is all the same mod, 4.3,,5.0,,or 5.7L it doesn't mater.

 

[kennythewelder]

The only brand pump to get is ether AC Delco, or Delphi. Don't get or use anything else, or you will regret it.

 

[kennythewelder]

My wife's nice, has a Burb like yours. They changed there FP a few years ago. I remember that they had to change the whole assembly, and could not change just the fuel pump. IDK if the tank is different or what. The pump by it self is about $65, but the assembly is around $215.
https://www.autopartswarehouse.com/...uel_Pump/1998/LS/8_Cyl_5-dot-7L/ACMU1748.html
Here is the pump for my truck. IDK why, this won't fit the Burb. Check out the max pressure, Its 108
http://www.jegs.com/i/ACDelco/065/EP381/10002/-1