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Old 12-28-2005, 07:50 PM
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vortec fuel regulator bad or good?

I have two vehicles with the same symtoms one a 2000 gmc and the other a 99 gmc. both of these vehicles take extended cranks to start .both fuel pumps turn on with the first ignition start, I have been told that the fuel presure regulator is going bad or is bad ,how do you check them?. The 2000 is an external regulator on the fuel rail. and the 1999 is internal under the intake. anyone know how. thanks gb

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Old 12-28-2005, 08:30 PM
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changed my mind

Last edited by Greg Latvala; 12-28-2005 at 10:35 PM.
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Old 12-28-2005, 08:56 PM
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the 99 version is what's called cfi, and gm has a lot of problems with it. to check your regulator, hook up a pressure guage to the test port on the main fuel line going into the intake. it's the bigger of the two if you're unsure as to which one it is, and the valve will be right on top. when you turn on the key, the fuel pump should come on for 2-3 seconds then stop. this is done to prime the fuel system, and will work the same way on the 2000. the fuel pump will come back on as soon as the computer sees a cranking rpm signal. if you turn on the key and go straight to the start position, the pump will actually continue to run, as the rpm signal will be there before the time runs out for the initial prime. i always turn the key to run, wait a second, then crank.........anyway, what you're looking for on the 1999 is a fuel pressure reading with the engine running of 58-62 psi. trust me on this one, if it's 55 psi, you will have driveability problems. i replace the injectors on these motors almost as often as oil changes, as the poppets get plugged up really easy. don't see the regulators go bad very often though, but those are replaced with the injectors as a package deal at our shop. for the 2000, the test port will again be on the main fuel line, or the larger of the two. i don't remember right off hand what the fuel pressure specs are for that one, but i think they are about 45 psi or so. consult your service manual for that info. pressure is checked the same way with the guage though. again, i have yet to see a regulator on those systems go bad. not to say they don't, but not common. long crank times on these can be contributed to plugged fuel filters and pumps going bad, and these apply to the 99 as well. best thing you can do is check your fuel pressures, make sure your tune-up parts are good, and go from there. if your fuel pressures are low, replace the fuel filter first.....they are alot cheaper than a fuel pump, and alot easier to change. on the 99, if the fuel pressure is good, make sure the maf sensor is clean, and if that doesn't help, i'd have to say it's time for new injectors. there is a process to clean them, but personally, it's a waste of money. typically, we've seen these injectors start to fail after about 60k miles or so, and when driven mostly city miles. vehicles with the cfi systems that are driven alot on the highway tend to have fewer problems. let me know if this helps you out.
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Old 12-29-2005, 08:23 PM
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the spider injectors, on 96+ are called "sfi" . they fire as each cyl needs fuel. there are 6 individual injectors inside the "injector block". they are in the 2 piece, aluminum lower and plastic upper manifolds. the "cpi" spider injectors are in the 93-95 2 piece, both aluminum, 4.3 manifolds. the cpi injector is basically a tbi injector inside a spider housing. it is on all the time. as in, each cyl is getting fuel all the time.

my 97 4.3 has had an idle psi of 52 since day one. i bought it new, and it has always run fine. has 14,500 miles on it now. and well over 300hp
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Old 12-29-2005, 09:24 PM
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he never mentioned if it was a v-6 or v-8. yes, i know the differences between them. those fuel pressure specs i gave were directly from the factory service manual. yes, i know what the systems are and how they work. i work on them wayyyyyyyyy to much. not the best systems gm came up with (spider style that is)............also, the problems i've mentioned are ones that i've experienced first hand. done alot of v-6's too...........injectors in these systems are basically junk. gm has a service bulletin out on them outlining a replacement to a MFI setup, available at dealerships to retro fit vehicles with "spider" type injector systems. the tsb covers basically all versions of it that they produced. i'd have to look up the details to be 100% sure on that though, so that will give me something to do at work tomorrow. i'll post it here tomorrow night.

as far as your 4.3 producing "well over 300 hp" goes, what have you done to it to get it there? it ain't stock or chipped............stock isn't even close, and it would take one hell of alot more than just a chip..........and did you get the motor dynoed for this figure? is that number crankshaft hp, rear wheel hp, or just an estimate? just curious......................
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Old 12-31-2005, 10:04 AM
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i just added the few pics i have on this hard drive, to my gallery.
3600# truck, 13.8 @ 98. and had problems while doing that.
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Old 12-31-2005, 12:07 PM
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i got the tsb as i promised, but i'm not going to post it. i really don't feel like scanning 21 pages to post them here!!! i'll relay any of the info if you like though...............also, the "spider style" systems, as i'll refer to them, were used until 2002 on certain applications. they are very common in vans and cabover trucks equipped with 5.7L (350's) engines. some vehicles have problems with them, some don't. just as i mentioned before though, not the best design in the world, and that's why gm changed it and went to more conventional design. once i get my new car built though, i'll run ya!!!
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Old 12-31-2005, 03:18 PM
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yeah, its a pretty crappy design.

as far as running me. sure, come on down
but remember, if i was looking to be the fastest around. do you really thing i would pick a 4.3 to to it with . mid 12's will be just fine with me.
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Old 12-31-2005, 05:25 PM
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hehehe, faster than my project right now...........i can't push that fast.......hahahahaha................but give it time..............7 seconds here i come!!!! (1/4 mile)
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Old 01-01-2006, 08:05 AM
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lol, well, then we just might have a race. the top of my engine is laying all around my garage.
did you see my pics ?
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Old 01-01-2006, 12:08 PM
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yeah, i did..........nice project...........except you've got a few more pieces than mine.................don't make me add on juice............i'll do it...............i wonder if i can run faster while shooting nitrous? more oxygen ya know..........hahahahhaa
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Old 01-02-2006, 08:55 AM
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ok, the race is on !!! we'll put No2 bottles on our backs. and run(pun intended) heads up. LOL (they need some more/better smillies in here)

btw, i am putting a manifold like this one on my engine.
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